libtorrent todo-list

find out what error code is reported when the filesystem does not support hard links.

../src/file.cpp:538

	{
#ifdef TORRENT_WINDOWS

#if TORRENT_USE_WSTRING
#define CreateHardLink_ CreateHardLinkW
		std::wstring n_exist = convert_to_wstring(file);
		std::wstring n_link = convert_to_wstring(link);
#else
#define CreateHardLink_ CreateHardLinkA
		std::string n_exist = convert_to_native(file);
		std::string n_link = convert_to_native(link);
#endif
		BOOL ret = CreateHardLink_(n_link.c_str(), n_exist.c_str(), NULL);
		if (ret)
		{
			ec.clear();
			return;
		}

		// something failed. Does the filesystem not support hard links?
		DWORD error = GetLastError();
		if (error != ERROR_NOT_SUPPORTED || error != ERROR_ACCESS_DENIED)
		{
			// it's possible CreateHardLink will copy the file internally too,
			// if the filesystem does not support it.
			ec.assign(GetLastError(), system_category());
			return;
		}

		// fall back to making a copy

#else

		std::string n_exist = convert_to_native(file);
		std::string n_link = convert_to_native(link);

		// assume posix's link() function exists
		int ret = ::link(n_exist.c_str(), n_link.c_str());

		if (ret == 0)
		{
			ec.clear();
			return;
		}

		// most errors are passed through, except for the ones that indicate that
		// hard links are not supported and require a copy.

instead of having to ask the torrent whether it's in graceful pause mode or not, the peers should keep that state (and the torrent should update them when it enters graceful pause). When a peer enters graceful pause mode, it should cancel all outstanding requests and clear its request queue.

../src/peer_connection.cpp:2962

		// to disk or are in the disk write cache
		if (picker.is_piece_finished(p.piece) && !was_finished)
		{
#if TORRENT_USE_INVARIANT_CHECKS
			check_postcondition post_checker2_(t, false);
#endif
			t->verify_piece(p.piece);
		}

		check_graceful_pause();

		if (is_disconnecting()) return;

		if (request_a_block(*t, *this))
			m_counters.inc_stats_counter(counters::incoming_piece_picks);
		send_block_requests();
	}

	void peer_connection::check_graceful_pause()
	{
		boost::shared_ptr<torrent> t = m_torrent.lock();
		if (!t || !t->graceful_pause()) return;

		if (m_outstanding_bytes > 0) return;

#ifndef TORRENT_DISABLE_LOGGING
		peer_log(peer_log_alert::info, "GRACEFUL_PAUSE", "NO MORE DOWNLOAD");
#endif
		disconnect(errors::torrent_paused, op_bittorrent);
	}

	void peer_connection::on_disk_write_complete(disk_io_job const* j
		, peer_request p, boost::shared_ptr<torrent> t)
	{
		TORRENT_ASSERT(is_single_thread());
		torrent_ref_holder h(t.get(), "async_write");
		if (t) t->dec_refcount("async_write");

#ifndef TORRENT_DISABLE_LOGGING
		peer_log(peer_log_alert::info, "FILE_ASYNC_WRITE_COMPLETE", "ret: %d piece: %d s: %x l: %x e: %s"
			, j->ret, p.piece, p.start, p.length, j->error.ec.message().c_str());
#endif

		m_counters.inc_stats_counter(counters::queued_write_bytes, -p.length);
		m_outstanding_writing_bytes -= p.length;

		TORRENT_ASSERT(m_outstanding_writing_bytes >= 0);

		// flush send buffer at the end of
		// this burst of disk events
//		m_ses.cork_burst(this);

once peers are properly put in graceful pause mode, they can cancel all outstanding requests and this test can be removed.

../src/peer_connection.cpp:3832

		}

		TORRENT_ASSERT(piece >= 0 && piece < m_sent_suggested_pieces.size());

		if (m_sent_suggested_pieces[piece]) return;
		m_sent_suggested_pieces.set_bit(piece);

		write_suggest(piece);
	}

	void peer_connection::send_block_requests()
	{
		TORRENT_ASSERT(is_single_thread());
		INVARIANT_CHECK;

		boost::shared_ptr<torrent> t = m_torrent.lock();
		TORRENT_ASSERT(t);

		if (m_disconnecting) return;

		if (t->graceful_pause()) return;

		// we can't download pieces in these states
		if (t->state() == torrent_status::checking_files
			|| t->state() == torrent_status::checking_resume_data
			|| t->state() == torrent_status::downloading_metadata
			|| t->state() == torrent_status::allocating)
			return;

		if (int(m_download_queue.size()) >= m_desired_queue_size
			|| t->upload_mode()) return;

		bool empty_download_queue = m_download_queue.empty();

		while (!m_request_queue.empty()
			&& (int(m_download_queue.size()) < m_desired_queue_size
				|| m_queued_time_critical > 0))
		{
			pending_block block = m_request_queue.front();

			m_request_queue.erase(m_request_queue.begin());
			if (m_queued_time_critical) --m_queued_time_critical;

			// if we're a seed, we don't have a piece picker
			// so we don't have to worry about invariants getting
			// out of sync with it
			if (!t->has_picker()) continue;

			// this can happen if a block times out, is re-requested and
			// then arrives "unexpectedly"
			if (t->picker().is_finished(block.block)

port map SSL udp socket here

../src/session_impl.cpp:2065

		udp::endpoint ssl_bind_if(m_listen_interface.address(), ssl_port);

		// if ssl port is 0, we don't want to listen on an SSL port
		if (ssl_port != 0)
		{
			m_ssl_udp_socket.bind(ssl_bind_if, ec);
			if (ec)
			{
#ifndef TORRENT_DISABLE_LOGGING
				session_log("SSL: cannot bind to UDP interface \"%s\": %s"
					, print_endpoint(m_listen_interface).c_str(), ec.message().c_str());
#endif
				if (m_alerts.should_post<listen_failed_alert>())
				{
					error_code err;
					m_alerts.emplace_alert<listen_failed_alert>(ssl_bind_if.address().to_string()
						, ssl_port, listen_failed_alert::bind, ec, listen_failed_alert::utp_ssl);
				}
				ec.clear();
			}
		}
#endif // TORRENT_USE_OPENSSL

it would probably make sense to have a separate list of peers that are eligible for optimistic unchoke, similar to the torrents perhaps this could even iterate over the pool allocators of torrent_peer objects. It could probably be done in a single pass and collect the n best candidates

../src/session_impl.cpp:3806

			, torrent_peer const* const r)
		{
			return l->last_optimistically_unchoked
				< r->last_optimistically_unchoked;
		}
	}

	void session_impl::recalculate_optimistic_unchoke_slots()
	{
		INVARIANT_CHECK;

		TORRENT_ASSERT(is_single_thread());
		if (m_stats_counters[counters::num_unchoke_slots] == 0) return;

		std::vector<torrent_peer*> opt_unchoke;

		// collect the currently optimistically unchoked peers here, so we can
		// choke them when we've found new optimistic unchoke candidates.
		std::vector<torrent_peer*> prev_opt_unchoke;

		for (connection_map::iterator i = m_connections.begin()
			, end(m_connections.end()); i != end; ++i)
		{
			peer_connection* p = i->get();
			TORRENT_ASSERT(p);
			torrent_peer* pi = p->peer_info_struct();
			if (!pi) continue;
			if (pi->web_seed) continue;

			if (pi->optimistically_unchoked)
			{
				prev_opt_unchoke.push_back(pi);
			}

			torrent* t = p->associated_torrent().lock().get();
			if (!t) continue;

peers should know whether their torrent is paused or not, instead of having to ask it over and over again

../src/session_impl.cpp:3828

		// choke them when we've found new optimistic unchoke candidates.
		std::vector<torrent_peer*> prev_opt_unchoke;

		for (connection_map::iterator i = m_connections.begin()
			, end(m_connections.end()); i != end; ++i)
		{
			peer_connection* p = i->get();
			TORRENT_ASSERT(p);
			torrent_peer* pi = p->peer_info_struct();
			if (!pi) continue;
			if (pi->web_seed) continue;

			if (pi->optimistically_unchoked)
			{
				prev_opt_unchoke.push_back(pi);
			}

			torrent* t = p->associated_torrent().lock().get();
			if (!t) continue;

			if (t->is_paused()) continue;

			if (!p->is_connecting()
				&& !p->is_disconnecting()
				&& p->is_peer_interested()
				&& t->free_upload_slots()
				&& (p->is_choked() || pi->optimistically_unchoked)
				&& !p->ignore_unchoke_slots()
				&& t->valid_metadata())
			{
				opt_unchoke.push_back(pi);
			}
		}

		// find the peers that has been waiting the longest to be optimistically
		// unchoked

		int num_opt_unchoke = m_settings.get_int(settings_pack::num_optimistic_unchoke_slots);
		int const allowed_unchoke_slots = m_stats_counters[counters::num_unchoke_slots];
		if (num_opt_unchoke == 0) num_opt_unchoke = (std::max)(1, allowed_unchoke_slots / 5);
		if (num_opt_unchoke > int(opt_unchoke.size())) num_opt_unchoke =
			int(opt_unchoke.size());

		// find the n best optimistic unchoke candidates
		std::partial_sort(opt_unchoke.begin()
			, opt_unchoke.begin() + num_opt_unchoke
			, opt_unchoke.end(), &last_optimistic_unchoke_cmp);

#ifndef TORRENT_DISABLE_EXTENSIONS
		if (m_session_extension_features & plugin::optimistic_unchoke_feature)
		{

there should be a pre-calculated list of all peers eligible for unchoking

../src/session_impl.cpp:4105

			if (want_peers_download.empty() && want_peers_finished.empty()) break;
			// if we have gone a whole loop without
			// handing out a single connection, break
			if (steps_since_last_connect > num_torrents + 1) break;
			// maintain the global limit on number of connections
			if (num_connections() >= m_settings.get_int(settings_pack::connections_limit)) break;
		}
	}

	void session_impl::recalculate_unchoke_slots()
	{
		TORRENT_ASSERT(is_single_thread());
		INVARIANT_CHECK;

		time_point now = aux::time_now();
		time_duration unchoke_interval = now - m_last_choke;
		m_last_choke = now;

		// build list of all peers that are
		// unchokable.
		std::vector<peer_connection*> peers;
		for (connection_map::iterator i = m_connections.begin();
			i != m_connections.end();)
		{
			boost::shared_ptr<peer_connection> p = *i;
			TORRENT_ASSERT(p);
			++i;
			torrent* t = p->associated_torrent().lock().get();
			torrent_peer* pi = p->peer_info_struct();

			if (p->ignore_unchoke_slots() || t == 0 || pi == 0
				|| pi->web_seed || t->is_paused())
			{
				p->reset_choke_counters();
				continue;
			}

			if (!p->is_peer_interested()
				|| p->is_disconnecting()
				|| p->is_connecting())
			{
				// this peer is not unchokable. So, if it's unchoked
				// already, make sure to choke it.
				if (p->is_choked())
				{
					p->reset_choke_counters();
					continue;
				}
				if (pi && pi->optimistically_unchoked)
				{
					m_stats_counters.inc_stats_counter(counters::num_peers_up_unchoked_optimistic, -1);

this really needs to be moved to do_async_save_resume_data. flags need to be passed on

../src/torrent.cpp:9611

				alerts().emplace_alert<save_resume_data_failed_alert>(get_handle()
					, m_error);
				return;
			}

			// storage may be NULL during shutdown
			if (!m_storage)
			{
				TORRENT_ASSERT(m_abort);
				alerts().emplace_alert<save_resume_data_failed_alert>(get_handle()
					, boost::asio::error::operation_aborted);
				return;
			}

			boost::shared_ptr<entry> rd(new entry);
			write_resume_data(*rd);
			alerts().emplace_alert<save_resume_data_alert>(rd, get_handle());
			return;
		}

		if ((flags & torrent_handle::flush_disk_cache) && m_storage.get())
			m_ses.disk_thread().async_release_files(m_storage.get());

		m_ses.queue_async_resume_data(shared_from_this());
	}

	bool torrent::do_async_save_resume_data()
	{
		if (!need_loaded())
		{
			alerts().emplace_alert<save_resume_data_failed_alert>(get_handle(), m_error);
			return false;
		}
		// storage may be NULL during shutdown
		if (!m_storage)
		{
			TORRENT_ASSERT(m_abort);
			alerts().emplace_alert<save_resume_data_failed_alert>(get_handle()
				, boost::asio::error::operation_aborted);
			return false;
		}
		inc_refcount("save_resume");
		m_ses.disk_thread().async_save_resume_data(m_storage.get()
			, boost::bind(&torrent::on_save_resume_data, shared_from_this(), _1));
		return true;
	}

	bool torrent::should_check_files() const
	{
		TORRENT_ASSERT(is_single_thread());
		// #error should m_allow_peers really affect checking?

listen_interface is not used. It's meant to bind the broadcast socket. it would probably have to be changed to a vector of interfaces to bind to though, since the broadcast socket opens one socket per local interface by default

../src/upnp.cpp:94

	, portmap_callback_t const& cb, log_callback_t const& lcb
	, bool ignore_nonrouters)
	: m_user_agent(user_agent)
	, m_callback(cb)
	, m_log_callback(lcb)
	, m_retry_count(0)
	, m_io_service(ios)
	, m_resolver(ios)
	, m_socket(udp::endpoint(address_v4::from_string("239.255.255.250"
		, ignore_error), 1900))
	, m_broadcast_timer(ios)
	, m_refresh_timer(ios)
	, m_map_timer(ios)
	, m_disabled(false)
	, m_closing(false)
	, m_ignore_non_routers(ignore_nonrouters)
	, m_last_if_update(min_time())
{
	TORRENT_ASSERT(cb);

	TORRENT_UNUSED(listen_interface);
}

void upnp::start()
{
	error_code ec;
	m_socket.open(boost::bind(&upnp::on_reply, self(), _1, _2, _3)
		, m_refresh_timer.get_io_service(), ec);

	m_mappings.reserve(10);
}

upnp::~upnp()
{
}

void upnp::discover_device()
{
	mutex::scoped_lock l(m_mutex);
	if (m_socket.num_send_sockets() == 0)
		log("No network interfaces to broadcast to", l);

	discover_device_impl(l);
}

void upnp::log(char const* msg, mutex::scoped_lock& l)
{
	l.unlock();
	m_log_callback(msg);
	l.lock();
}

the XORing should be done at full words instead of bytes

../src/kademlia/node_id.cpp:54

#include "libtorrent/kademlia/node_id.hpp"
#include "libtorrent/kademlia/node_entry.hpp"
#include "libtorrent/hasher.hpp"
#include "libtorrent/assert.hpp"
#include "libtorrent/broadcast_socket.hpp" // for is_local et.al
#include "libtorrent/socket_io.hpp" // for hash_address
#include "libtorrent/random.hpp" // for random
#include "libtorrent/hasher.hpp" // for hasher
#include "libtorrent/crc32c.hpp" // for crc32c

namespace libtorrent { namespace dht
{

// returns the distance between the two nodes
// using the kademlia XOR-metric
node_id distance(node_id const& n1, node_id const& n2)
{
	node_id ret;
	node_id::iterator k = ret.begin();
	for (node_id::const_iterator i = n1.begin(), j = n2.begin()
		, end(n1.end()); i != end; ++i, ++j, ++k)
	{
		*k = *i ^ *j;
	}
	return ret;
}

// returns true if: distance(n1, ref) < distance(n2, ref)
bool compare_ref(node_id const& n1, node_id const& n2, node_id const& ref)
{

the XORing should be done at full words instead of bytes

../src/kademlia/node_id.cpp:66

namespace libtorrent { namespace dht
{

// returns the distance between the two nodes
// using the kademlia XOR-metric
node_id distance(node_id const& n1, node_id const& n2)
{
	node_id ret;
	node_id::iterator k = ret.begin();
	for (node_id::const_iterator i = n1.begin(), j = n2.begin()
		, end(n1.end()); i != end; ++i, ++j, ++k)
	{
		*k = *i ^ *j;
	}
	return ret;
}

// returns true if: distance(n1, ref) < distance(n2, ref)
bool compare_ref(node_id const& n1, node_id const& n2, node_id const& ref)
{
	for (node_id::const_iterator i = n1.begin(), j = n2.begin()
		, k = ref.begin(), end(n1.end()); i != end; ++i, ++j, ++k)
	{
		boost::uint8_t lhs = (*i ^ *k);
		boost::uint8_t rhs = (*j ^ *k);
		if (lhs < rhs) return true;
		if (lhs > rhs) return false;
	}
	return false;
}

// returns n in: 2^n <= distance(n1, n2) < 2^(n+1)
// useful for finding out which bucket a node belongs to
int distance_exp(node_id const& n1, node_id const& n2)
{

the xoring should be done at full words and _builtin_clz() could be used as the last step

../src/kademlia/node_id.cpp:82

}

// returns true if: distance(n1, ref) < distance(n2, ref)
bool compare_ref(node_id const& n1, node_id const& n2, node_id const& ref)
{
	for (node_id::const_iterator i = n1.begin(), j = n2.begin()
		, k = ref.begin(), end(n1.end()); i != end; ++i, ++j, ++k)
	{
		boost::uint8_t lhs = (*i ^ *k);
		boost::uint8_t rhs = (*j ^ *k);
		if (lhs < rhs) return true;
		if (lhs > rhs) return false;
	}
	return false;
}

// returns n in: 2^n <= distance(n1, n2) < 2^(n+1)
// useful for finding out which bucket a node belongs to
int distance_exp(node_id const& n1, node_id const& n2)
{
	int byte = node_id::size - 1;
	for (node_id::const_iterator i = n1.begin(), j = n2.begin()
		, end(n1.end()); i != end; ++i, ++j, --byte)
	{
		TORRENT_ASSERT(byte >= 0);
		boost::uint8_t t = *i ^ *j;
		if (t == 0) continue;
		// we have found the first non-zero byte
		// return the bit-number of the first bit
		// that differs
		int const bit = byte * 8;
		for (int b = 7; b >= 0; --b)
			if (t >= (1 << b)) return bit + b;
		return bit;
	}

	return 0;
}

node_id generate_id_impl(address const& ip_, boost::uint32_t r)
{
	boost::uint8_t* ip = 0;

	static const boost::uint8_t v4mask[] = { 0x03, 0x0f, 0x3f, 0xff };
#if TORRENT_USE_IPV6
	static const boost::uint8_t v6mask[] = { 0x01, 0x03, 0x07, 0x0f, 0x1f, 0x3f, 0x7f, 0xff };
#endif
	boost::uint8_t const* mask = 0;
	int num_octets = 0;

	address_v4::bytes_type b4;

the call to compare_ip_cidr here is expensive. peel off some layers of abstraction here to make it quicker. Look at xoring and using _builtin_ctz()

../src/kademlia/routing_table.cpp:698

	// that we have an updated RTT
	j = std::find_if(rb.begin(), rb.end(), boost::bind(&node_entry::id, _1) == e.id);
	if (j != rb.end())
	{
		// a new IP address just claimed this node-ID
		// ignore it
		if (j->addr() != e.addr() || j->port() != e.port())
			return failed_to_add;

		TORRENT_ASSERT(j->id == e.id && j->ep() == e.ep());
		j->timeout_count = 0;
		j->update_rtt(e.rtt);
		e = *j;
		erase_one(m_ips, j->addr().to_v4().to_bytes());
		rb.erase(j);
	}

	if (m_settings.restrict_routing_ips)
	{
		// don't allow multiple entries from IPs very close to each other
		j = std::find_if(b.begin(), b.end(), boost::bind(&compare_ip_cidr, _1, e));
		if (j == b.end())
		{
			j = std::find_if(rb.begin(), rb.end(), boost::bind(&compare_ip_cidr, _1, e));
			if (j == rb.end()) goto ip_ok;
		}

		// we already have a node in this bucket with an IP very
		// close to this one. We know that it's not the same, because
		// it claims a different node-ID. Ignore this to avoid attacks
#ifndef TORRENT_DISABLE_LOGGING
		char hex_id1[41];
		to_hex(e.id.data(), 20, hex_id1);
		char hex_id2[41];
		to_hex(j->id.data(), 20, hex_id2);
		m_log->log(dht_logger::routing_table, "ignoring node: %s %s existing node: %s %s"
			, hex_id1, print_address(e.addr()).c_str()
			, hex_id2, print_address(j->addr()).c_str());
#endif
		return failed_to_add;
	}
ip_ok:

	// can we split the bucket?
	// only nodes that haven't failed can split the bucket, and we can only
	// split the last bucket
	bool const can_split = (boost::next(i) == m_buckets.end()
		&& m_buckets.size() < 159)
		&& e.fail_count() == 0
		&& (i == m_buckets.begin() || boost::prior(i)->live_nodes.size() > 1);

move this into it's own .cpp file

../src/kademlia/rpc_manager.cpp:87

void intrusive_ptr_add_ref(observer const* o)
{
	TORRENT_ASSERT(o != 0);
	TORRENT_ASSERT(o->m_refs < 0xffff);
	++o->m_refs;
}

void intrusive_ptr_release(observer const* o)
{
	TORRENT_ASSERT(o != 0);
	TORRENT_ASSERT(o->m_refs > 0);
	if (--o->m_refs == 0)
	{
		boost::intrusive_ptr<traversal_algorithm> ta = o->algorithm();
		(const_cast<observer*>(o))->~observer();
		ta->free_observer(const_cast<observer*>(o));
	}
}

dht_observer* observer::get_observer() const
{
	return m_algorithm->get_node().observer();
}

void observer::set_target(udp::endpoint const& ep)
{
	m_sent = clock_type::now();

	m_port = ep.port();
#if TORRENT_USE_IPV6
	if (ep.address().is_v6())
	{
		flags |= flag_ipv6_address;
		m_addr.v6 = ep.address().to_v6().to_bytes();
	}
	else
#endif
	{
		flags &= ~flag_ipv6_address;
		m_addr.v4 = ep.address().to_v4().to_bytes();
	}
}

address observer::target_addr() const
{
#if TORRENT_USE_IPV6
	if (flags & flag_ipv6_address)
		return address_v6(m_addr.v6);
	else
#endif

enable this assert and fix remaining causes of it triggering

../include/libtorrent/socks5_stream.hpp:114

		, m_listen(0)
	{}

	void set_version(int v) { m_version = v; }

	void set_command(int c)
	{
		TORRENT_ASSERT(c >= socks5_connect && c <=socks5_udp_associate);
		m_command = c;
	}

	void set_username(std::string const& user
		, std::string const& password)
	{
		m_user = user;
		m_password = password;
	}

	void set_dst_name(std::string const& host)
	{
/*
#if TORRENT_USE_ASSERTS
		error_code ec;
		address::from_string(host, ec);
		// if this assert trips, set_dst_name() is called wth an IP address rather
		// than a hostname. Instead, resolve the IP into an address and pass it to
		// async_connect instead
		TORRENT_ASSERT(ec);
#endif
*/
		m_dst_name = host;
		if (m_dst_name.size() > 255)
			m_dst_name.resize(255);
	}

	void close(error_code& ec)
	{
		m_dst_name.clear();
		proxy_base::close(ec);
	}

#ifndef BOOST_NO_EXCEPTIONS
	void close()
	{
		m_dst_name.clear();
		proxy_base::close();
	}
#endif

factor out the links (as well as update_list() to a separate class that torrent can inherit)

../include/libtorrent/torrent.hpp:1347

		// this was the last time _we_ saw a seed in this swarm
		time_t m_last_seen_complete;

		// this is the time last any of our peers saw a seed
		// in this swarm
		time_t m_swarm_last_seen_complete;

		// keep a copy if the info-hash here, so it can be accessed from multiple
		// threads, and be cheap to access from the client
		sha1_hash m_info_hash;

	public:
		// these are the lists this torrent belongs to. For more
		// details about each list, see session_impl.hpp. Each list
		// represents a group this torrent belongs to and makes it
		// efficient to enumerate only torrents belonging to a specific
		// group. Such as torrents that want peer connections or want
		// to be ticked etc.

		link m_links[aux::session_interface::num_torrent_lists];

	private:

		// m_num_verified = m_verified.count()
		boost::uint32_t m_num_verified;

		// this timestamp is kept in session-time, to
		// make it fit in 16 bits
		boost::uint16_t m_last_saved_resume;

		// if this torrent is running, this was the time
		// when it was started. This is used to have a
		// bias towards keeping seeding torrents that
		// recently was started, to avoid oscillation
		// this is specified at a second granularity
		// in session-time. see session_impl for details.
		// the reference point is stepped forward every 4
		// hours to keep the timestamps fit in 16 bits
		boost::uint16_t m_started;

		// if we're a seed, this is the session time
		// timestamp of when we became one
		boost::uint16_t m_became_seed;

		// if we're finished, this is the session time
		// timestamp of when we finished
		boost::uint16_t m_became_finished;

		// when checking, this is the first piece we have not
		// issued a hash job for

consider replacing all the setters and getters for pause, resume, stop-when-ready, share-mode, upload-mode, super-seeding, apply-ip-filter, resolve-countries, pinned, sequential-download, seed-mode with just set_flags() and clear_flags() using the flags from add_torrent_params. Perhaps those flags should have a more generic name.

../include/libtorrent/torrent_handle.hpp:237

	// 	expensive if done from within a GUI thread that needs to stay
	// 	responsive. Try to avoid quering for information you don't need, and
	// 	try to do it in as few calls as possible. You can get most of the
	// 	interesting information about a torrent from the
	// 	torrent_handle::status() call.
	// 
	// The default constructor will initialize the handle to an invalid state.
	// Which means you cannot perform any operation on it, unless you first
	// assign it a valid handle. If you try to perform any operation on an
	// uninitialized handle, it will throw ``invalid_handle``.
	// 
	// .. warning::
	// 	All operations on a torrent_handle may throw libtorrent_exception
	// 	exception, in case the handle is no longer refering to a torrent.
	// 	There is one exception is_valid() will never throw. Since the torrents
	// 	are processed by a background thread, there is no guarantee that a
	// 	handle will remain valid between two calls.
	// 
	struct TORRENT_EXPORT torrent_handle
	{
		friend class invariant_access;
		friend struct aux::session_impl;
		friend class session;
		friend struct session_handle;
		friend struct feed;
		friend class torrent;
		friend std::size_t hash_value(torrent_handle const& th);

		// constructs a torrent handle that does not refer to a torrent.
		// i.e. is_valid() will return false.
		torrent_handle() {}

		torrent_handle(torrent_handle const& t)
		{ if (!t.m_torrent.expired()) m_torrent = t.m_torrent; }

#if __cplusplus >= 201103L
		torrent_handle& operator=(torrent_handle const&) = default;
#endif

		// flags for add_piece().
		enum flags_t { overwrite_existing = 1 };

		// This function will write ``data`` to the storage as piece ``piece``,
		// as if it had been downloaded from a peer. ``data`` is expected to
		// point to a buffer of as many bytes as the size of the specified piece.
		// The data in the buffer is copied and passed on to the disk IO thread
		// to be written at a later point.
		//
		// By default, data that's already been downloaded is not overwritten by
		// this buffer. If you trust this data to be correct (and pass the piece
		// hash check) you may pass the overwrite_existing flag. This will

unify url_seed and http_seed with just web_seed, using the web_seed_entry.

../include/libtorrent/torrent_handle.hpp:484

		// announce url for the tracker as well as an int ``tier``, which is
		// specifies the order in which this tracker is tried. If you want
		// libtorrent to use another list of trackers for this torrent, you can
		// use ``replace_trackers()`` which takes a list of the same form as the
		// one returned from ``trackers()`` and will replace it. If you want an
		// immediate effect, you have to call force_reannounce(). See
		// announce_entry.
		// 
		// ``add_tracker()`` will look if the specified tracker is already in the
		// set. If it is, it doesn't do anything. If it's not in the current set
		// of trackers, it will insert it in the tier specified in the
		// announce_entry.
		// 
		// The updated set of trackers will be saved in the resume data, and when
		// a torrent is started with resume data, the trackers from the resume
		// data will replace the original ones.
		std::vector<announce_entry> trackers() const;
		void replace_trackers(std::vector<announce_entry> const&) const;
		void add_tracker(announce_entry const&) const;


		// ``add_url_seed()`` adds another url to the torrent's list of url
		// seeds. If the given url already exists in that list, the call has no
		// effect. The torrent will connect to the server and try to download
		// pieces from it, unless it's paused, queued, checking or seeding.
		// ``remove_url_seed()`` removes the given url if it exists already.
		// ``url_seeds()`` return a set of the url seeds currently in this
		// torrent. Note that urls that fails may be removed automatically from
		// the list.
		// 
		// See http-seeding_ for more information.
		void add_url_seed(std::string const& url) const;
		void remove_url_seed(std::string const& url) const;
		std::set<std::string> url_seeds() const;

		// These functions are identical as the ``*_url_seed()`` variants, but
		// they operate on `BEP 17`_ web seeds instead of `BEP 19`_.
		// 
		// See http-seeding_ for more information.
		void add_http_seed(std::string const& url) const;
		void remove_http_seed(std::string const& url) const;
		std::set<std::string> http_seeds() const;

		// add the specified extension to this torrent. The ``ext`` argument is
		// a function that will be called from within libtorrent's context
		// passing in the internal torrent object and the specified userdata
		// pointer. The function is expected to return a shared pointer to
		// a torrent_plugin instance.
		void add_extension(
			boost::function<boost::shared_ptr<torrent_plugin>(torrent_handle const&, void*)> const& ext
			, void* userdata = 0);

if we make this be a disk_buffer_holder instead we would save a copy use allocate_disk_receive_buffer and release_disk_receive_buffer

../include/libtorrent/web_peer_connection.hpp:131

		boost::optional<piece_block_progress> downloading_piece_progress() const TORRENT_OVERRIDE;

		void handle_padfile();

		// this has one entry per http-request
		// (might be more than the bt requests)
		struct file_request_t
		{
			int file_index;
			int length;
			boost::int64_t start;
		};
		std::deque<file_request_t> m_file_requests;

		std::string m_url;

		web_seed_t* m_web;

		// this is used for intermediate storage of pieces to be delivered to the
		// bittorrent engine
		std::vector<char> m_piece;

		// the number of bytes we've forwarded to the incoming_payload() function
		// in the current HTTP response. used to know where in the buffer the
		// next response starts
		int m_received_body;

		// this is the offset inside the current receive
		// buffer where the next chunk header will be.
		// this is updated for each chunk header that's
		// parsed. It does not necessarily point to a valid
		// offset in the receive buffer, if we haven't received
		// it yet. This offset never includes the HTTP header
		int m_chunk_pos;

		// this is the number of bytes we've already received
		// from the next chunk header we're waiting for
		int m_partial_chunk_header;

		// the number of responses we've received so far on
		// this connection
		int m_num_responses;
	};
}

#endif // TORRENT_WEB_PEER_CONNECTION_HPP_INCLUDED

to improve memory locality and scanning performance, turn the routing table into a single vector with boundaries for the nodes instead. Perhaps replacement nodes should be in a separate vector.

../include/libtorrent/kademlia/routing_table.hpp:99

// * Nodes are not marked as being stale, they keep a counter
// 	that tells how many times in a row they have failed. When
// 	a new node is to be inserted, the node that has failed
// 	the most times is replaced. If none of the nodes in the
// 	bucket has failed, then it is put in the replacement
// 	cache (just like in the paper).

namespace impl
{
	template <typename F>
	inline void forwarder(void* userdata, node_entry const& node)
	{
		F* f = reinterpret_cast<F*>(userdata);
		(*f)(node);
	}
}

class TORRENT_EXTRA_EXPORT routing_table : boost::noncopyable
{
public:
	typedef std::vector<routing_table_node> table_t;

	routing_table(node_id const& id, int bucket_size
		, dht_settings const& settings
		, dht_logger* log);

#ifndef TORRENT_NO_DEPRECATE
	void status(session_status& s) const;
#endif

	void status(std::vector<dht_routing_bucket>& s) const;

	void node_failed(node_id const& id, udp::endpoint const& ep);

	// adds an endpoint that will never be added to
	// the routing table
	void add_router_node(udp::endpoint router);

	// iterates over the router nodes added
	typedef std::set<udp::endpoint>::const_iterator router_iterator;
	router_iterator router_begin() const { return m_router_nodes.begin(); }
	router_iterator router_end() const { return m_router_nodes.end(); }

	enum add_node_status_t {
		failed_to_add = 0,
		node_added,
		need_bucket_split
	};
	add_node_status_t add_node_impl(node_entry e);

	bool add_node(node_entry e);

make sure the handlers we pass in are potentially movable!

../include/libtorrent/aux_/allocating_handler.hpp:77

			: used(false)
		{}

		bool used;
#else
		handler_storage() {}
#endif
		boost::aligned_storage<Size> bytes;
	private:
		handler_storage(handler_storage const&);
	};

	// this class is a wrapper for an asio handler object. Its main purpose
	// is to pass along additional parameters to the asio handler allocator
	// function, as well as providing a distinct type for the handler
	// allocator function to overload on
	template <class Handler, std::size_t Size>
	struct allocating_handler
	{

#if !defined BOOST_NO_CXX11_RVALUE_REFERENCES
		allocating_handler(
			Handler&& h, handler_storage<Size>& s)
			: handler(std::move(h))
			, storage(s)
		{}
#endif

		allocating_handler(
			Handler const& h, handler_storage<Size>& s)
			: handler(h)
			, storage(s)
		{}

#if !defined BOOST_NO_CXX11_VARIADIC_TEMPLATES \
		&& !defined BOOST_NO_CXX11_RVALUE_REFERENCES
		template <class... A>
		void operator()(A&&... a) const
		{
			handler(std::forward<A>(a)...);
		}
#else
		template <class A0>
		void operator()(A0 const& a0) const
		{
			handler(a0);
		}

		template <class A0, class A1>
		void operator()(A0 const& a0, A1 const& a1) const
		{

split this test up into smaller test cases

../test/test_dht.cpp:514

		va_end(v);
		m_log.push_back(buf);
	}
	virtual void log_packet(message_direction_t dir, char const* pkt, int len
		, udp::endpoint node) TORRENT_OVERRIDE {}
	virtual bool on_dht_request(char const* query, int query_len
		, dht::msg const& request, entry& response) TORRENT_OVERRIDE { return false; }

	std::vector<std::string> m_log;
};

dht_settings test_settings()
{
	dht_settings sett;
	sett.max_torrents = 4;
	sett.max_dht_items = 4;
	sett.enforce_node_id = false;
	return sett;
}

TORRENT_TEST(dht)
{
	dht_settings sett = test_settings();
	mock_socket s;
	obs observer;
	counters cnt;
	dht::node node(&s, sett, node_id(0), &observer, cnt);

	// DHT should be running on port 48199 now
	bdecode_node response;
	char error_string[200];
	bool ret;

	// ====== ping ======
	udp::endpoint source(address::from_string("10.0.0.1"), 20);
	send_dht_request(node, "ping", source, &response);

	dht::key_desc_t pong_desc[] = {
		{"y", bdecode_node::string_t, 1, 0},
		{"t", bdecode_node::string_t, 2, 0},
		{"r", bdecode_node::dict_t, 0, key_desc_t::parse_children},
			{"id", bdecode_node::string_t, 20, key_desc_t::last_child},
	};

	bdecode_node pong_keys[4];

	fprintf(stderr, "msg: %s\n", print_entry(response).c_str());
	ret = dht::verify_message(response, pong_desc, pong_keys, error_string
		, sizeof(error_string));
	TEST_CHECK(ret);
	if (ret)

split this up into smaller test cases

../test/test_dht.cpp:2141

	TEST_EQUAL(to_hex(std::string(signature, 64))
		, "6834284b6b24c3204eb2fea824d82f88883a3d95e8b4a21b8c0ded553d17d17d"
		"df9a8a7104b1258f30bed3787e6cb896fca78c58f8e03b5f18f14951a87d9a08");

	sha1_hash target_id = item_target_id(test_salt, public_key);
	TEST_EQUAL(to_hex(target_id.to_string()), "411eba73b6f087ca51a3795d9c8c938d365e32c1");
}

TORRENT_TEST(signing_test3)
{
	// test vector 3

	// test content
	std::pair<char const*, int> test_content("12:Hello World!", 15);

	sha1_hash target_id = item_target_id(test_content);
	TEST_EQUAL(to_hex(target_id.to_string()), "e5f96f6f38320f0f33959cb4d3d656452117aadb");
}

TORRENT_TEST(verify_message)
{
	char error_string[200];

	// test verify_message
	static const key_desc_t msg_desc[] = {
		{"A", bdecode_node::string_t, 4, 0},
		{"B", bdecode_node::dict_t, 0, key_desc_t::optional | key_desc_t::parse_children},
			{"B1", bdecode_node::string_t, 0, 0},
			{"B2", bdecode_node::string_t, 0, key_desc_t::last_child},
		{"C", bdecode_node::dict_t, 0, key_desc_t::optional | key_desc_t::parse_children},
			{"C1", bdecode_node::string_t, 0, 0},
			{"C2", bdecode_node::string_t, 0, key_desc_t::last_child},
	};

	bdecode_node msg_keys[7];

	bdecode_node ent;

	error_code ec;
	char const test_msg[] = "d1:A4:test1:Bd2:B15:test22:B25:test3ee";
	bdecode(test_msg, test_msg + sizeof(test_msg)-1, ent, ec);
	fprintf(stderr, "%s\n", print_entry(ent).c_str());

	bool ret = verify_message(ent, msg_desc, msg_keys, error_string
		, sizeof(error_string));
	TEST_CHECK(ret);
	TEST_CHECK(msg_keys[0]);
	if (msg_keys[0]) TEST_EQUAL(msg_keys[0].string_value(), "test");
	TEST_CHECK(msg_keys[1]);
	TEST_CHECK(msg_keys[2]);

split this up into smaller tests (where we print_title)

../test/test_piece_picker.cpp:281

	std::vector<piece_block> picked;
	counters pc;
	p->pick_pieces(string2vec(availability), picked
		, num_blocks, prefer_contiguous_blocks, peer_struct
		, options, suggested_pieces, 20, pc);
	print_pick(picked);
	TEST_CHECK(verify_pick(p, picked));
	return picked;
}

int test_pick(boost::shared_ptr<piece_picker> const& p
	, int options = piece_picker::rarest_first)
{
	const std::vector<int> empty_vector;
	std::vector<piece_block> picked = pick_pieces(p, "*******", 1, 0, 0
		, options, empty_vector);
	if (picked.empty()) return -1;
	return picked[0].piece_index;
}

TORRENT_TEST(piece_picker)
{
	tcp::endpoint endp;
	piece_picker::downloading_piece st;
#if TORRENT_USE_ASSERTS
	tmp0.in_use = true;
	tmp1.in_use = true;
	tmp2.in_use = true;
	tmp3.in_use = true;
	tmp4.in_use = true;
	tmp5.in_use = true;
	tmp6.in_use = true;
	tmp7.in_use = true;
	tmp8.in_use = true;
	tmp9.in_use = true;
	peer_struct.in_use = true;
#endif
	tmp_peer = &tmp1;
	std::vector<piece_block> picked;
	boost::shared_ptr<piece_picker> p;
	const int options = piece_picker::rarest_first;
	std::pair<int, int> dc;
	counters pc;

	print_title("test piece_block");

	TEST_CHECK(piece_block(0, 0) != piece_block(0, 1));
	TEST_CHECK(piece_block(0, 0) != piece_block(1, 0));
	TEST_CHECK(!(piece_block(0, 0) != piece_block(0, 0)));

	TEST_CHECK(!(piece_block(0, 0) == piece_block(0, 1)));

split this test up into smaller parts

../test/test_storage.cpp:485

	boost::shared_ptr<void> dummy;
	boost::shared_ptr<piece_manager> pm = boost::make_shared<piece_manager>(new default_storage(p), dummy, &fs);
	libtorrent::mutex lock;

	bool done = false;
	bdecode_node frd;
	std::vector<std::string> links;
	io.async_check_fastresume(pm.get(), &frd, links
		, boost::bind(&on_check_resume_data, _1, &done));
	io.submit_jobs();
	ios.reset();
	run_until(ios, done);

	io.set_num_threads(0);
}

#ifdef TORRENT_NO_DEPRECATE
#define storage_mode_compact storage_mode_sparse
#endif

void run_test(bool unbuffered)
{
	std::string test_path = current_working_directory();
	std::cerr << "\n=== " << test_path << " ===\n" << std::endl;

	boost::shared_ptr<torrent_info> info;

	buf_ptr piece0 = new_piece(piece_size);
	buf_ptr piece1 = new_piece(piece_size);
	buf_ptr piece2 = new_piece(piece_size);
	buf_ptr piece3 = new_piece(piece_size);

	{
	error_code ec;
	remove_all(combine_path(test_path, "temp_storage"), ec);
	if (ec && ec != boost::system::errc::no_such_file_or_directory)
		std::cerr << "remove_all '" << combine_path(test_path, "temp_storage")
		<< "': " << ec.message() << std::endl;
	file_storage fs;
	fs.add_file("temp_storage/test1.tmp", 17);
	fs.add_file("temp_storage/test2.tmp", 612);
	fs.add_file("temp_storage/test3.tmp", 0);
	fs.add_file("temp_storage/test4.tmp", 0);
	fs.add_file("temp_storage/test5.tmp", 3253);
	fs.add_file("temp_storage/test6.tmp", 841);
	const int last_file_size = 4 * piece_size - fs.total_size();
	fs.add_file("temp_storage/test7.tmp", last_file_size);

	// File layout
	// +-+--+++-------+-------+----------------------------------------------------------------------------------------+
	// |1| 2||| file5 | file6 | file7                                                                                  |

the salt here is allocated on the heap. It would be nice to allocate in in the stack_allocator

../src/alert.cpp:1461

			, operation_names[op]
			, error.value()
			, convert_from_native(error.message()).c_str());
		return msg;
	}

	dht_immutable_item_alert::dht_immutable_item_alert(aux::stack_allocator&
		, sha1_hash const& t, entry const& i)
		: target(t), item(i)
	{}

	std::string dht_immutable_item_alert::message() const
	{
		char msg[1050];
		snprintf(msg, sizeof(msg), "DHT immutable item %s [ %s ]"
			, to_hex(target.to_string()).c_str()
			, item.to_string().c_str());
		return msg;
	}

	dht_mutable_item_alert::dht_mutable_item_alert(aux::stack_allocator&
		, boost::array<char, 32> k
		, boost::array<char, 64> sig
		, boost::uint64_t sequence
		, std::string const& s
		, entry const& i
		, bool a)
		: key(k), signature(sig), seq(sequence), salt(s), item(i), authoritative(a)
	{}

	std::string dht_mutable_item_alert::message() const
	{
		char msg[1050];
		snprintf(msg, sizeof(msg), "DHT mutable item (key=%s salt=%s seq=%" PRId64 " %s) [ %s ]"
			, to_hex(std::string(&key[0], 32)).c_str()
			, salt.c_str()
			, seq
			, authoritative ? "auth" : "non-auth"
			, item.to_string().c_str());
		return msg;
	}

	dht_put_alert::dht_put_alert(aux::stack_allocator&, sha1_hash const& t, int n)
		: target(t)
		, seq(0)
		, num_success(n)
	{}

	dht_put_alert::dht_put_alert(aux::stack_allocator&
		, boost::array<char, 32> key
		, boost::array<char, 64> sig

keep a count of the number of threads waiting. Only if it's > 0 notify them

../src/alert_manager.cpp:90

		return NULL;
	}

	void alert_manager::maybe_notify(alert* a, mutex::scoped_lock& lock)
	{
		if (a->type() == save_resume_data_failed_alert::alert_type
			|| a->type() == save_resume_data_alert::alert_type)
			++m_num_queued_resume;

		if (m_alerts[m_generation].size() == 1)
		{
			lock.unlock();

			// we just posted to an empty queue. If anyone is waiting for
			// alerts, we need to notify them. Also (potentially) call the
			// user supplied m_notify callback to let the client wake up its
			// message loop to poll for alerts.
			if (m_notify) m_notify();

			m_condition.notify_all();
		}
		else
		{
			lock.unlock();
		}

#ifndef TORRENT_DISABLE_EXTENSIONS
		for (ses_extension_list_t::iterator i = m_ses_extensions.begin()
			, end(m_ses_extensions.end()); i != end; ++i)
		{
			(*i)->on_alert(a);
		}
#endif
	}

#ifndef TORRENT_NO_DEPRECATE

	bool alert_manager::maybe_dispatch(alert const& a)
	{
		if (m_dispatch)
		{
			m_dispatch(a.clone());
			return true;
		}
		return false;
	}

#ifdef __GNUC__
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"

turn these return values into enums returns -1: block not in cache -2: out of memory

../src/block_cache.cpp:1723

			{
				TORRENT_PIECE_ASSERT(!p.blocks[k].dirty, &p);
				TORRENT_PIECE_ASSERT(!p.blocks[k].pending, &p);
				TORRENT_PIECE_ASSERT(p.blocks[k].refcount == 0, &p);
			}
			TORRENT_PIECE_ASSERT(p.blocks[k].refcount >= 0, &p);
			num_refcount += p.blocks[k].refcount;
		}
		TORRENT_PIECE_ASSERT(num_blocks == p.num_blocks, &p);
		TORRENT_PIECE_ASSERT(num_pending <= p.refcount, &p);
		TORRENT_PIECE_ASSERT(num_refcount == p.refcount, &p);
		TORRENT_PIECE_ASSERT(num_dirty == p.num_dirty, &p);
	}
	TORRENT_ASSERT(m_read_cache_size == cached_read_blocks);
	TORRENT_ASSERT(m_write_cache_size == cached_write_blocks);
	TORRENT_ASSERT(m_pinned_blocks == num_pinned);
	TORRENT_ASSERT(m_write_cache_size + m_read_cache_size <= in_use());
}
#endif


int block_cache::copy_from_piece(cached_piece_entry* pe, disk_io_job* j
	, bool expect_no_fail)
{
	INVARIANT_CHECK;
	TORRENT_UNUSED(expect_no_fail);

	TORRENT_PIECE_ASSERT(j->buffer.disk_block == 0, pe);
	TORRENT_PIECE_ASSERT(pe->in_use, pe);

	// copy from the cache and update the last use timestamp
	int block = j->d.io.offset / block_size();
	int block_offset = j->d.io.offset & (block_size()-1);
	int buffer_offset = 0;
	int size = j->d.io.buffer_size;
	int blocks_to_read = block_offset > 0 && (size > block_size() - block_offset) ? 2 : 1;
	TORRENT_PIECE_ASSERT(size <= block_size(), pe);
	const int start_block = block;

#if TORRENT_USE_ASSERTS
	int piece_size = j->storage->files()->piece_size(j->piece);
	int blocks_in_piece = (piece_size + block_size() - 1) / block_size();
	TORRENT_PIECE_ASSERT(start_block < blocks_in_piece, pe);
#endif

	// if there's no buffer, we don't have this block in
	// the cache, and we're not currently reading it in either
	// since it's not pending

	if (inc_block_refcount(pe, start_block, ref_reading) == false)
	{

this should probably be moved into string_util.cpp

../src/escape_string.cpp:209

		}
		return false;
	}

	void convert_path_to_posix(std::string& path)
	{
		for (std::string::iterator i = path.begin()
			, end(path.end()); i != end; ++i)
			if (*i == '\\') *i = '/';
	}

#ifdef TORRENT_WINDOWS
	void convert_path_to_windows(std::string& path)
	{
		for (std::string::iterator i = path.begin()
			, end(path.end()); i != end; ++i)
			if (*i == '/') *i = '\\';
	}
#endif

	std::string read_until(char const*& str, char delim, char const* end)
	{
		TORRENT_ASSERT(str <= end);

		std::string ret;
		while (str != end && *str != delim)
		{
			ret += *str;
			++str;
		}
		// skip the delimiter as well
		while (str != end && *str == delim) ++str;
		return ret;
	}

	std::string maybe_url_encode(std::string const& url)
	{
		std::string protocol, host, auth, path;
		int port;
		error_code ec;
		boost::tie(protocol, auth, host, port, path) = parse_url_components(url, ec);
		if (ec) return url;
		
		// first figure out if this url contains unencoded characters
		if (!need_encoding(path.c_str(), path.size()))
			return url;

		char msg[TORRENT_MAX_PATH*4];
		snprintf(msg, sizeof(msg), "%s://%s%s%s%s%s%s", protocol.c_str(), auth.c_str()
			, auth.empty()?"":"@", host.c_str()
			, port == -1 ? "" : ":"

test this on a FAT volume to see what error we get!

../src/file.cpp:567

		}

		// fall back to making a copy

#else

		std::string n_exist = convert_to_native(file);
		std::string n_link = convert_to_native(link);

		// assume posix's link() function exists
		int ret = ::link(n_exist.c_str(), n_link.c_str());

		if (ret == 0)
		{
			ec.clear();
			return;
		}

		// most errors are passed through, except for the ones that indicate that
		// hard links are not supported and require a copy.
		if (errno != EMLINK || errno != EXDEV)
		{
			// some error happened, report up to the caller
			ec.assign(errno, system_category());
			return;
		}

		// fall back to making a copy

#endif

		// if we get here, we should copy the file
		copy_file(file, link, ec);
	}

	bool is_directory(std::string const& f, error_code& ec)
	{
		ec.clear();
		error_code e;
		file_status s;
		stat_file(f, &s, e);
		if (!e && s.mode & file_status::directory) return true;
		ec = e;
		return false;
	}

	void recursive_copy(std::string const& old_path, std::string const& new_path, error_code& ec)
	{
		TORRENT_ASSERT(!ec);
		if (is_directory(old_path, ec))
		{

returning a bool here is redundant. Instead this function should return the peer_entry

../src/http_tracker_connection.cpp:379

		}
		else
		{
			std::list<address> ip_list;
			if (m_tracker_connection)
			{
				error_code ignore;
				std::vector<tcp::endpoint> const& epts = m_tracker_connection->endpoints();
				for (std::vector<tcp::endpoint>::const_iterator i = epts.begin()
					, end(epts.end()); i != end; ++i)
				{
					ip_list.push_back(i->address());
				}
			}

			cb->tracker_response(tracker_req(), m_tracker_ip, ip_list, resp);
		}
		close();
	}

	bool extract_peer_info(bdecode_node const& info, peer_entry& ret, error_code& ec)
	{
		// extract peer id (if any)
		if (info.type() != bdecode_node::dict_t)
		{
			ec.assign(errors::invalid_peer_dict, get_libtorrent_category());
			return false;
		}
		bdecode_node i = info.dict_find_string("peer id");
		if (i && i.string_length() == 20)
		{
			std::copy(i.string_ptr(), i.string_ptr()+20, ret.pid.begin());
		}
		else
		{
			// if there's no peer_id, just initialize it to a bunch of zeroes
			std::fill_n(ret.pid.begin(), 20, 0);
		}

		// extract ip
		i = info.dict_find_string("ip");
		if (i == 0)
		{
			ec.assign(errors::invalid_tracker_response, get_libtorrent_category());
			return false;
		}
		ret.hostname = i.string_value();

		// extract port
		i = info.dict_find_int("port");
		if (i == 0)

peer_connection and tracker_connection should probably be flags

../src/instantiate_connection.cpp:43

move this function into libtorrent::aux namespace

../src/instantiate_connection.cpp:44

LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.

*/

#include "libtorrent/socket.hpp"
#include "libtorrent/session_settings.hpp"
#include "libtorrent/socket_type.hpp"
#include "libtorrent/utp_socket_manager.hpp"
#include "libtorrent/instantiate_connection.hpp"
#include <boost/shared_ptr.hpp>
#include <stdexcept>

namespace libtorrent
{
	bool instantiate_connection(io_service& ios
		, aux::proxy_settings const& ps, socket_type& s
		, void* ssl_context
		, utp_socket_manager* sm
		, bool peer_connection
		, bool tracker_connection)
	{
#ifndef TORRENT_USE_OPENSSL
		TORRENT_UNUSED(ssl_context);
#endif

		if (sm)
		{
			utp_stream* str;
#ifdef TORRENT_USE_OPENSSL
			if (ssl_context)
			{
				s.instantiate<ssl_stream<utp_stream> >(ios, ssl_context);
				str = &s.get<ssl_stream<utp_stream> >()->next_layer();
			}
			else
#endif
			{
				s.instantiate<utp_stream>(ios);
				str = s.get<utp_stream>();
			}
			str->set_impl(sm->new_utp_socket(str));
		}
#if TORRENT_USE_I2P
		else if (ps.type == settings_pack::i2p_proxy)
		{

this should probably be based on time instead of number of request messages. For a very high throughput connection, 300 may be a legitimate number of requests to have in flight when getting choked

../src/peer_connection.cpp:2382

				, "piece: %d s: %d l: %d invalid request"
				, r.piece , r.start , r.length);
#endif

			write_reject_request(r);
			++m_num_invalid_requests;

			if (t->alerts().should_post<invalid_request_alert>())
			{
				// msvc 12 appears to deduce the rvalue reference template
				// incorrectly for bool temporaries. So, create a dummy instance
				bool peer_interested = bool(m_peer_interested);
				t->alerts().emplace_alert<invalid_request_alert>(
					t->get_handle(), m_remote, m_peer_id, r
					, t->has_piece_passed(r.piece), peer_interested, false);
			}

			// every ten invalid request, remind the peer that it's choked
			if (!m_peer_interested && m_num_invalid_requests % 10 == 0 && m_choked)
			{
				if (m_num_invalid_requests > 300 && !m_peer_choked
					&& can_disconnect(error_code(errors::too_many_requests_when_choked
						, get_libtorrent_category())))
				{
					disconnect(errors::too_many_requests_when_choked, op_bittorrent, 2);
					return;
				}
#ifndef TORRENT_DISABLE_LOGGING
				peer_log(peer_log_alert::outgoing_message, "CHOKE");
#endif
				write_choke();
			}

			return;
		}

		// if we have choked the client
		// ignore the request
		const int blocks_per_piece = static_cast<int>(
			(t->torrent_file().piece_length() + t->block_size() - 1) / t->block_size());

		// disconnect peers that downloads more than foo times an allowed
		// fast piece
		if (m_choked && fast_idx != -1 && m_accept_fast_piece_cnt[fast_idx] >= 3 * blocks_per_piece
			&& can_disconnect(error_code(errors::too_many_requests_when_choked, get_libtorrent_category())))
		{
			disconnect(errors::too_many_requests_when_choked, op_bittorrent, 2);
			return;
		}

		if (m_choked && fast_idx == -1)

since we throw away the queue entry once we issue the disk job, this may happen. Instead, we should keep the queue entry around, mark it as having been requested from disk and once the disk job comes back, discard it if it has been cancelled. Maybe even be able to cancel disk jobs?

../src/peer_connection.cpp:3116

		std::vector<peer_request>::iterator i
			= std::find(m_requests.begin(), m_requests.end(), r);

		if (i != m_requests.end())
		{
			m_counters.inc_stats_counter(counters::cancelled_piece_requests);
			m_requests.erase(i);

			if (m_requests.empty())
				m_counters.inc_stats_counter(counters::num_peers_up_requests, -1);

#ifndef TORRENT_DISABLE_LOGGING
			peer_log(peer_log_alert::outgoing_message, "REJECT_PIECE", "piece: %d s: %x l: %x cancelled"
				, r.piece , r.start , r.length);
#endif
			write_reject_request(r);
		}
		else
		{
#ifndef TORRENT_DISABLE_LOGGING
			peer_log(peer_log_alert::info, "INVALID_CANCEL", "got cancel not in the queue");
#endif
		}
	}

	// -----------------------------
	// --------- DHT PORT ----------
	// -----------------------------

	void peer_connection::incoming_dht_port(int listen_port)
	{
		TORRENT_ASSERT(is_single_thread());
		INVARIANT_CHECK;

#ifndef TORRENT_DISABLE_LOGGING
		peer_log(peer_log_alert::incoming_message, "DHT_PORT", "p: %d", listen_port);
#endif
#ifndef TORRENT_DISABLE_DHT
		m_ses.add_dht_node(udp::endpoint(
			m_remote.address(), listen_port));
#else
		TORRENT_UNUSED(listen_port);
#endif
	}

	// -----------------------------
	// --------- HAVE ALL ----------
	// -----------------------------

	void peer_connection::incoming_have_all()

use a deadline_timer for timeouts. Don't rely on second_tick()! Hook this up to connect timeout as well. This would improve performance because of less work in second_tick(), and might let use remove ticking entirely eventually

../src/peer_connection.cpp:4791

				connect_timeout += 20;
#endif

			if (d > seconds(connect_timeout)
				&& can_disconnect(error_code(errors::timed_out, get_libtorrent_category())))
			{
#ifndef TORRENT_DISABLE_LOGGING
				peer_log(peer_log_alert::info, "CONNECT_FAILED", "waited %d seconds"
					, int(total_seconds(d)));
#endif
				connect_failed(errors::timed_out);
				return;
			}
		}

		// if we can't read, it means we're blocked on the rate-limiter
		// or the disk, not the peer itself. In this case, don't blame
		// the peer and disconnect it
		bool may_timeout = (m_channel_state[download_channel] & peer_info::bw_network) != 0;

		if (may_timeout && d > seconds(timeout()) && !m_connecting && m_reading_bytes == 0
			&& can_disconnect(error_code(errors::timed_out_inactivity, get_libtorrent_category())))
		{
#ifndef TORRENT_DISABLE_LOGGING
			peer_log(peer_log_alert::info, "LAST_ACTIVITY", "%d seconds ago"
				, int(total_seconds(d)));
#endif
			disconnect(errors::timed_out_inactivity, op_bittorrent);
			return;
		}

		// do not stall waiting for a handshake
		int timeout = m_settings.get_int (settings_pack::handshake_timeout);
#if TORRENT_USE_I2P
		timeout *= is_i2p(*m_socket) ? 4 : 1;
#endif
		if (may_timeout
			&& !m_connecting
			&& in_handshake()
			&& d > seconds(timeout))
		{
#ifndef TORRENT_DISABLE_LOGGING
			peer_log(peer_log_alert::info, "NO_HANDSHAKE", "waited %d seconds"
				, int(total_seconds(d)));
#endif
			disconnect(errors::timed_out_no_handshake, op_bittorrent);
			return;
		}

		// disconnect peers that we unchoked, but
		// they didn't send a request within 60 seconds.

it would be nice if there was a way to iterate over these torrent_peer objects in the order they are allocated in the pool instead. It would probably be more efficient

../src/peer_list.cpp:495

		, int session_time, torrent_state* state)
	{
		TORRENT_ASSERT(is_single_thread());
		INVARIANT_CHECK;

		const int candidate_count = 10;
		peers.reserve(candidate_count);

		int erase_candidate = -1;

		if (m_finished != state->is_finished)
			recalculate_connect_candidates(state);

		external_ip const& external = *state->ip;
		int external_port = state->port;

		if (m_round_robin >= int(m_peers.size())) m_round_robin = 0;

		int max_peerlist_size = state->max_peerlist_size;

		for (int iterations = (std::min)(int(m_peers.size()), 300);
			iterations > 0; --iterations)
		{
			++state->loop_counter;

			if (m_round_robin >= int(m_peers.size())) m_round_robin = 0;

			torrent_peer& pe = *m_peers[m_round_robin];
			TORRENT_ASSERT(pe.in_use);
			int current = m_round_robin;

			// if the number of peers is growing large
			// we need to start weeding.

			if (int(m_peers.size()) >= max_peerlist_size * 0.95
				&& max_peerlist_size > 0)
			{
				if (is_erase_candidate(pe)
					&& (erase_candidate == -1
						|| !compare_peer_erase(*m_peers[erase_candidate], pe)))
				{
					if (should_erase_immediately(pe))
					{
						if (erase_candidate > current) --erase_candidate;
						erase_peer(m_peers.begin() + current, state);
						continue;
					}
					else
					{
						erase_candidate = current;
					}

make the 2048 limit configurable

../src/piece_picker.cpp:1982

	// returned block picks.
	boost::uint32_t piece_picker::pick_pieces(bitfield const& pieces
		, std::vector<piece_block>& interesting_blocks, int num_blocks
		, int prefer_contiguous_blocks, torrent_peer* peer
		, int options, std::vector<int> const& suggested_pieces
		, int num_peers
		, counters& pc
		) const
	{
		TORRENT_ASSERT(peer == 0 || peer->in_use);
		boost::uint32_t ret = 0;

		// prevent the number of partial pieces to grow indefinitely
		// make this scale by the number of peers we have. For large
		// scale clients, we would have more peers, and allow a higher
		// threshold for the number of partials
		// deduct pad files because they case partial pieces which are OK
		// the second condition is to make sure we cap the number of partial
		// _bytes_. The larger the pieces are, the fewer partial pieces we want.
		// 2048 corresponds to 32 MiB
		const int num_partials = int(m_downloads[piece_pos::piece_downloading].size())
			- m_num_pad_files;
		if (num_partials > num_peers * 3 / 2
			|| num_partials * m_blocks_per_piece > 2048)
		{
			// if we have too many partial pieces, prioritize completing
			// them. In order for this to have an affect, also disable
			// prefer whole pieces (otherwise partial pieces would be de-prioritized)
			options |= prioritize_partials;
			prefer_contiguous_blocks = 0;

			ret |= picker_log_alert::partial_ratio;
		}

		if (prefer_contiguous_blocks) ret |= picker_log_alert::prefer_contiguous;

		// only one of rarest_first and sequential can be set.
		TORRENT_ASSERT(((options & rarest_first) ? 1 : 0)
			+ ((options & sequential) ? 1 : 0) <= 1);
#ifdef TORRENT_EXPENSIVE_INVARIANT_CHECKS
		TORRENT_PIECE_PICKER_INVARIANT_CHECK;
#endif
		TORRENT_ASSERT(num_blocks > 0);
		TORRENT_ASSERT(pieces.size() == m_piece_map.size());

		TORRENT_ASSERT(!m_priority_boundries.empty() || m_dirty);

		// this will be filled with blocks that we should not request
		// unless we can't find num_blocks among the other ones.
		std::vector<piece_block> backup_blocks;
		std::vector<piece_block> backup_blocks2;

the first_block returned here is the largest free range, not the first-fit range, which would be better

../src/piece_picker.cpp:2614

			, end(m_block_info.end()); i != end; ++i)
		{
			TORRENT_ASSERT(i->peer == 0 || static_cast<torrent_peer*>(i->peer)->in_use);
		}
	}
#endif

	void piece_picker::clear_peer(torrent_peer* peer)
	{
		for (std::vector<block_info>::iterator i = m_block_info.begin()
			, end(m_block_info.end()); i != end; ++i)
		{
			if (i->peer == peer) i->peer = 0;
		}
	}

	// the first bool is true if this is the only peer that has requested and downloaded
	// blocks from this piece.
	// the second bool is true if this is the only active peer that is requesting
	// and downloading blocks from this piece. Active means having a connection.
	boost::tuple<bool, bool, int, int> piece_picker::requested_from(
		piece_picker::downloading_piece const& p
		, int num_blocks_in_piece, torrent_peer* peer) const
	{
		bool exclusive = true;
		bool exclusive_active = true;
		int contiguous_blocks = 0;
		int max_contiguous = 0;
		int first_block = 0;
		block_info const* binfo = blocks_for_piece(p);
		for (int j = 0; j < num_blocks_in_piece; ++j)
		{
			piece_picker::block_info const& info = binfo[j];
			TORRENT_ASSERT(info.peer == 0 || static_cast<torrent_peer*>(info.peer)->in_use);
			TORRENT_ASSERT(info.piece_index == p.index);
			if (info.state == piece_picker::block_info::state_none)
			{
				++contiguous_blocks;
				continue;
			}
			if (contiguous_blocks > max_contiguous)
			{
				max_contiguous = contiguous_blocks;
				first_block = j - contiguous_blocks;
			}
			contiguous_blocks = 0;
			if (info.peer != peer)
			{
				exclusive = false;
				if (info.state == piece_picker::block_info::state_requested
					&& info.peer != 0)

it would be nice if this could be folded into lock_piece() the main distinction is that this also maintains the m_num_passed counter and the passed_hash_check member Is there ever a case where we call write filed without also locking the piece? Perhaps write_failed() should imply locking it.

../src/piece_picker.cpp:3395

		int state = m_piece_map[piece].download_queue();
		if (state == piece_pos::piece_open) return;
		std::vector<downloading_piece>::iterator i = find_dl_piece(state, piece);
		if (i == m_downloads[state].end()) return;

		TORRENT_ASSERT(i->passed_hash_check == false);
		if (i->passed_hash_check)
		{
			// it's not clear why this would happen,
			// but it seems reasonable to not break the
			// accounting over it.
			i->passed_hash_check = false;
			TORRENT_ASSERT(m_num_passed > 0);
			--m_num_passed;
		}

		// prevent this piece from being picked until it's restored
		i->locked = true;
	}

	void piece_picker::write_failed(piece_block block)
	{
		TORRENT_PIECE_PICKER_INVARIANT_CHECK;

#if TORRENT_USE_INVARIANT_CHECKS
		check_piece_state();
#endif

#ifdef TORRENT_PICKER_LOG
		std::cerr << "[" << this << "] " << "write_failed( {" << block.piece_index << ", " << block.block_index << "} )" << std::endl;
#endif

		int state = m_piece_map[block.piece_index].download_queue();
		if (state == piece_pos::piece_open) return;
		std::vector<downloading_piece>::iterator i = find_dl_piece(state, block.piece_index);
		if (i == m_downloads[state].end()) return;

		block_info* binfo = blocks_for_piece(*i);
		block_info& info = binfo[block.block_index];
		TORRENT_ASSERT(&info >= &m_block_info[0]);
		TORRENT_ASSERT(&info < &m_block_info[0] + m_block_info.size());
		TORRENT_ASSERT(info.piece_index == block.piece_index);
		TORRENT_ASSERT(info.state == block_info::state_writing);
		TORRENT_ASSERT(info.num_peers == 0);

		TORRENT_ASSERT(i->writing > 0);
		TORRENT_ASSERT(info.state == block_info::state_writing);

		if (info.state == block_info::state_finished) return;
		if (info.state == block_info::state_writing) --i->writing;

is there a reason not to move all of this into init()? and just post it to the io_service?

../src/session_impl.cpp:463

		m_posting_torrent_updates = false;
#endif
		m_udp_socket.set_rate_limit(m_settings.get_int(settings_pack::dht_upload_rate_limit));

		m_udp_socket.subscribe(&m_utp_socket_manager);
		m_udp_socket.subscribe(this);
		m_udp_socket.subscribe(&m_tracker_manager);

#ifdef TORRENT_USE_OPENSSL
		m_ssl_udp_socket.subscribe(&m_ssl_utp_socket_manager);
		m_ssl_udp_socket.subscribe(this);
#endif

		error_code ec;
		m_listen_interface = tcp::endpoint(address_v4::any(), 0);
		TORRENT_ASSERT_VAL(!ec, ec);
	}

	// This function is called by the creating thread, not in the message loop's
	// / io_service thread.
	void session_impl::start_session(settings_pack const& pack)
	{
		if (pack.has_val(settings_pack::alert_mask))
		{
			m_alerts.set_alert_mask(pack.get_int(settings_pack::alert_mask));
		}

#ifndef TORRENT_DISABLE_LOGGING
		session_log("start session");
#endif

		error_code ec;
#ifdef TORRENT_USE_OPENSSL
		m_ssl_ctx.set_verify_mode(boost::asio::ssl::context::verify_none, ec);
#if BOOST_VERSION >= 104700
#if OPENSSL_VERSION_NUMBER >= 0x90812f
		aux::openssl_set_tlsext_servername_callback(m_ssl_ctx.native_handle()
			, servername_callback);
		aux::openssl_set_tlsext_servername_arg(m_ssl_ctx.native_handle(), this);
#endif // OPENSSL_VERSION_NUMBER
#endif // BOOST_VERSION
#endif

#ifndef TORRENT_DISABLE_DHT
		m_next_dht_torrent = m_torrents.begin();
#endif
		m_next_lsd_torrent = m_torrents.begin();
		m_tcp_mapping[0] = -1;
		m_tcp_mapping[1] = -1;
		m_udp_mapping[0] = -1;
		m_udp_mapping[1] = -1;

the udp socket(s) should be using the same generic mechanism and not be restricted to a single one we should open a one listen socket for each entry in the listen_interfaces list

../src/session_impl.cpp:1946

				}
#endif // TORRENT_USE_OPENSSL
			}
#endif // TORRENT_USE_IPV6

			// set our main IPv4 and IPv6 interfaces
			// used to send to the tracker
			std::vector<ip_interface> ifs = enum_net_interfaces(m_io_service, ec);
			for (std::vector<ip_interface>::const_iterator i = ifs.begin()
					, end(ifs.end()); i != end; ++i)
			{
				address const& addr = i->interface_address;
				if (addr.is_v6() && !is_local(addr) && !is_loopback(addr))
					m_ipv6_interface = tcp::endpoint(addr, m_listen_interface.port());
				else if (addr.is_v4() && !is_local(addr) && !is_loopback(addr))
					m_ipv4_interface = tcp::endpoint(addr, m_listen_interface.port());
			}
		}
		else
		{
			for (int i = 0; i < m_listen_interfaces.size(); ++i)
			{
				std::string const& device = m_listen_interfaces[i].first;
				int port = m_listen_interfaces[i].second;

				int num_device_fails = 0;

#if TORRENT_USE_IPV6
				const int first_family = 0;
#else
				const int first_family = 1;
#endif
				boost::asio::ip::tcp protocol[]
					= { boost::asio::ip::tcp::v6(), boost::asio::ip::tcp::v4() };

				for (int address_family = first_family; address_family < 2; ++address_family)
				{
					error_code err;
					address test_family = address::from_string(device.c_str(), err);
					if (!err
						&& test_family.is_v4() != address_family
						&& !is_any(test_family))
						continue;

					listen_socket_t s = setup_listener(device, protocol[address_family]
						, port, flags, ec);

					if (ec == error_code(boost::system::errc::no_such_device, generic_category()))
					{
						++num_device_fails;
						continue;

use bind_to_device in udp_socket

../src/session_impl.cpp:2049

				m_listen_interface.port(m_listen_interface.port() + 1);
				--listen_port_retries;
				goto retry;
			}
			if (m_alerts.should_post<listen_failed_alert>())
				m_alerts.emplace_alert<listen_failed_alert>(
					m_listen_interface.address().to_string()
					, m_listen_interface.port()
					, listen_failed_alert::bind
					, ec, listen_failed_alert::tcp);
			return;
		}

#ifdef TORRENT_USE_OPENSSL
		int ssl_port = m_settings.get_int(settings_pack::ssl_listen);
		udp::endpoint ssl_bind_if(m_listen_interface.address(), ssl_port);

		// if ssl port is 0, we don't want to listen on an SSL port
		if (ssl_port != 0)
		{
			m_ssl_udp_socket.bind(ssl_bind_if, ec);
			if (ec)
			{
#ifndef TORRENT_DISABLE_LOGGING
				session_log("SSL: cannot bind to UDP interface \"%s\": %s"
					, print_endpoint(m_listen_interface).c_str(), ec.message().c_str());
#endif
				if (m_alerts.should_post<listen_failed_alert>())
				{
					error_code err;
					m_alerts.emplace_alert<listen_failed_alert>(ssl_bind_if.address().to_string()
						, ssl_port, listen_failed_alert::bind, ec, listen_failed_alert::utp_ssl);
				}
				ec.clear();
			}

use bind_to_device in udp_socket

../src/session_impl.cpp:2069

		if (ssl_port != 0)
		{
			m_ssl_udp_socket.bind(ssl_bind_if, ec);
			if (ec)
			{
#ifndef TORRENT_DISABLE_LOGGING
				session_log("SSL: cannot bind to UDP interface \"%s\": %s"
					, print_endpoint(m_listen_interface).c_str(), ec.message().c_str());
#endif
				if (m_alerts.should_post<listen_failed_alert>())
				{
					error_code err;
					m_alerts.emplace_alert<listen_failed_alert>(ssl_bind_if.address().to_string()
						, ssl_port, listen_failed_alert::bind, ec, listen_failed_alert::utp_ssl);
				}
				ec.clear();
			}
		}
#endif // TORRENT_USE_OPENSSL

		m_udp_socket.bind(udp::endpoint(m_listen_interface.address()
			, m_listen_interface.port()), ec);
		if (ec)
		{
#ifndef TORRENT_DISABLE_LOGGING
			session_log("cannot bind to UDP interface \"%s\": %s"
				, print_endpoint(m_listen_interface).c_str(), ec.message().c_str());
#endif
			if (listen_port_retries > 0)
			{
				m_listen_interface.port(m_listen_interface.port() + 1);
				--listen_port_retries;
				goto retry;
			}
			if (m_alerts.should_post<listen_failed_alert>())
			{
				error_code err;
				m_alerts.emplace_alert<listen_failed_alert>(m_listen_interface.address().to_string()
					, m_listen_interface.port()
					, listen_failed_alert::bind
					, ec, listen_failed_alert::udp);
			}
			return;
		}
		else
		{
			m_external_udp_port = m_udp_socket.local_port();
			maybe_update_udp_mapping(0, m_listen_interface.port(), m_listen_interface.port());
			maybe_update_udp_mapping(1, m_listen_interface.port(), m_listen_interface.port());
		}

make a list for torrents that want to be announced on the DHT so we don't have to loop over all torrents, just to find the ones that want to announce

../src/session_impl.cpp:3576

		if (!m_dht_torrents.empty())
		{
			boost::shared_ptr<torrent> t;
			do
			{
				t = m_dht_torrents.front().lock();
				m_dht_torrents.pop_front();
			} while (!t && !m_dht_torrents.empty());

			if (t)
			{
				t->dht_announce();
				return;
			}
		}
		if (m_torrents.empty()) return;

		if (m_next_dht_torrent == m_torrents.end())
			m_next_dht_torrent = m_torrents.begin();
		m_next_dht_torrent->second->dht_announce();
		++m_next_dht_torrent;
		if (m_next_dht_torrent == m_torrents.end())
			m_next_dht_torrent = m_torrents.begin();
	}
#endif

	void session_impl::on_lsd_announce(error_code const& e)
	{
#if defined TORRENT_ASIO_DEBUGGING
		complete_async("session_impl::on_lsd_announce");
#endif
		m_stats_counters.inc_stats_counter(counters::on_lsd_counter);
		TORRENT_ASSERT(is_single_thread());
		if (e) return;

		if (m_abort) return;

#if defined TORRENT_ASIO_DEBUGGING
		add_outstanding_async("session_impl::on_lsd_announce");
#endif
		// announce on local network every 5 minutes
		int delay = (std::max)(m_settings.get_int(settings_pack::local_service_announce_interval)
			/ (std::max)(int(m_torrents.size()), 1), 1);
		error_code ec;
		m_lsd_announce_timer.expires_from_now(seconds(delay), ec);
		m_lsd_announce_timer.async_wait(
			bind(&session_impl::on_lsd_announce, this, _1));

		if (m_torrents.empty()) return;

		if (m_next_lsd_torrent == m_torrents.end())

this should be factored into the udp socket, so we only have the code once

../src/session_impl.cpp:6057

	{
		return upload_rate_limit(m_local_peer_class);
	}

	int session_impl::local_download_rate_limit() const
	{
		return download_rate_limit(m_local_peer_class);
	}

	int session_impl::upload_rate_limit() const
	{
		return upload_rate_limit(m_global_class);
	}

	int session_impl::download_rate_limit() const
	{
		return download_rate_limit(m_global_class);
	}
#endif

	void session_impl::update_peer_tos()
	{
		error_code ec;

#if TORRENT_USE_IPV6 && defined IPV6_TCLASS
		if (m_udp_socket.local_endpoint(ec).address().is_v6())
			m_udp_socket.set_option(traffic_class(m_settings.get_int(settings_pack::peer_tos)), ec);
		else
#endif
			m_udp_socket.set_option(type_of_service(m_settings.get_int(settings_pack::peer_tos)), ec);

#ifdef TORRENT_USE_OPENSSL
#if TORRENT_USE_IPV6 && defined IPV6_TCLASS
		if (m_ssl_udp_socket.local_endpoint(ec).address().is_v6())
			m_ssl_udp_socket.set_option(traffic_class(m_settings.get_int(settings_pack::peer_tos)), ec);
		else
#endif
			m_ssl_udp_socket.set_option(type_of_service(m_settings.get_int(settings_pack::peer_tos)), ec);
#endif

#ifndef TORRENT_DISABLE_LOGGING
		session_log(">>> SET_TOS [ udp_socket tos: %x e: %s ]"
			, m_settings.get_int(settings_pack::peer_tos)
			, ec.message().c_str());
#endif
	}

	void session_impl::update_user_agent()
	{
		// replace all occurances of '\n' with ' '.
		std::string agent = m_settings.get_str(settings_pack::user_agent);

perhaps DHT logging should be disabled by TORRENT_DISABLE_LOGGING too

../src/session_impl.cpp:6761

	void session_impl::get_peers(sha1_hash const& ih)
	{
		if (!m_alerts.should_post<dht_get_peers_alert>()) return;
		m_alerts.emplace_alert<dht_get_peers_alert>(ih);
	}

	void session_impl::announce(sha1_hash const& ih, address const& addr
		, int port)
	{
		if (!m_alerts.should_post<dht_announce_alert>()) return;
		m_alerts.emplace_alert<dht_announce_alert>(addr, port, ih);
	}

	void session_impl::outgoing_get_peers(sha1_hash const& target
		, sha1_hash const& sent_target, udp::endpoint const& ep)
	{
		if (!m_alerts.should_post<dht_outgoing_get_peers_alert>()) return;
		m_alerts.emplace_alert<dht_outgoing_get_peers_alert>(target, sent_target, ep);
	}

	TORRENT_FORMAT(3,4)
	void session_impl::log(libtorrent::dht::dht_logger::module_t m, char const* fmt, ...)
	{
		if (!m_alerts.should_post<dht_log_alert>()) return;

		va_list v;
		va_start(v, fmt);
		char buf[1024];
		vsnprintf(buf, sizeof(buf), fmt, v);
		va_end(v);
		m_alerts.emplace_alert<dht_log_alert>(static_cast<dht_log_alert::dht_module_t>(m), buf);
	}

	void session_impl::log_packet(message_direction_t dir, char const* pkt, int len
		, udp::endpoint node)
	{
		if (!m_alerts.should_post<dht_pkt_alert>()) return;

		dht_pkt_alert::direction_t d = dir == dht_logger::incoming_message
			? dht_pkt_alert::incoming : dht_pkt_alert::outgoing;

		m_alerts.emplace_alert<dht_pkt_alert>(pkt, len, d, node);
	}

	bool session_impl::on_dht_request(char const* query, int query_len
		, dht::msg const& request, entry& response)
	{
#ifndef TORRENT_DISABLE_EXTENSIONS
		if (query_len > max_dht_query_length) return false;

		for (m_extension_dht_queries_t::iterator i = m_extension_dht_queries.begin();

we probably need to do this unconditionally in this function. Even if the resume data file appears stale, we need to create these hard links, right?

../src/storage.cpp:1069

			{
				ec.ec = errors::mismatching_file_size;
				ec.file = i;
				ec.operation = storage_error::none;
				return false;
			}

			if (settings().get_bool(settings_pack::ignore_resume_timestamps)) continue;

			// allow some slack, because of FAT volumes
			if (expected_time != 0 &&
				(file_time > expected_time + 5 * 60 || file_time < expected_time - 5))
			{
				ec.ec = errors::mismatching_file_timestamp;
				ec.file = i;
				ec.operation = storage_error::stat;
				return false;
			}
		}

#ifndef TORRENT_DISABLE_MUTABLE_TORRENTS
		if (links)
		{
			// if this is a mutable torrent, and we need to pick up some files
			// from other torrents, do that now. Note that there is an inherent
			// race condition here. We checked if the files existed on a different
			// thread a while ago. These files may no longer exist or may have been
			// moved. If so, we just fail. The user is responsible to not touch
			// other torrents until a new mutable torrent has been completely
			// added.
			int idx = 0;
			for (std::vector<std::string>::const_iterator i = links->begin();
				i != links->end(); ++i, ++idx)
			{
				if (i->empty()) continue;

				error_code err;
				std::string file_path = fs.file_path(idx, m_save_path);
				hard_link(*i, file_path, err);

				// if the file already exists, that's not an error

is this risky? The upper layer will assume we have the whole file. Perhaps we should verify that at least the size of the file is correct

../src/storage.cpp:1093

		if (links)
		{
			// if this is a mutable torrent, and we need to pick up some files
			// from other torrents, do that now. Note that there is an inherent
			// race condition here. We checked if the files existed on a different
			// thread a while ago. These files may no longer exist or may have been
			// moved. If so, we just fail. The user is responsible to not touch
			// other torrents until a new mutable torrent has been completely
			// added.
			int idx = 0;
			for (std::vector<std::string>::const_iterator i = links->begin();
				i != links->end(); ++i, ++idx)
			{
				if (i->empty()) continue;

				error_code err;
				std::string file_path = fs.file_path(idx, m_save_path);
				hard_link(*i, file_path, err);

				// if the file already exists, that's not an error
				if (!err || err == boost::system::errc::file_exists)
					continue;

				ec.ec = err;
				ec.file = idx;
				ec.operation = storage_error::hard_link;
				return false;
			}
		}
#endif // TORRENT_DISABLE_MUTABLE_TORRENTS

		return true;
	}

	int default_storage::move_storage(std::string const& sp, int flags, storage_error& ec)
	{
		int ret = piece_manager::no_error;
		std::string save_path = complete(sp);

		// check to see if any of the files exist
		error_code e;
		file_storage const& f = files();

		file_status s;
		if (flags == fail_if_exist)
		{
			stat_file(save_path, &s, e);
			if (e != boost::system::errc::no_such_file_or_directory)
			{
				// the directory exists, check all the files
				for (int i = 0; i < f.num_files(); ++i)

post alert

../src/torrent.cpp:681

		if (new_gauge_state == m_current_gauge_state) return;

		if (m_current_gauge_state != no_gauge_state)
			inc_stats_counter(m_current_gauge_state + counters::num_checking_torrents, -1);
		if (new_gauge_state != no_gauge_state)
			inc_stats_counter(new_gauge_state + counters::num_checking_torrents, 1);

		m_current_gauge_state = new_gauge_state;
	}

	void torrent::leave_seed_mode(bool skip_checking)
	{
		if (!m_seed_mode) return;

		if (!skip_checking)
		{
			// this means the user promised we had all the
			// files, but it turned out we didn't. This is
			// an error.


#ifndef TORRENT_DISABLE_LOGGING
			debug_log("*** FAILED SEED MODE, rechecking");
#endif
		}

#ifndef TORRENT_DISABLE_LOGGING
		debug_log("*** LEAVING SEED MODE (%s)"
			, skip_checking ? "as seed" : "as non-seed");
#endif
		m_seed_mode = false;
		// seed is false if we turned out not
		// to be a seed after all
		if (!skip_checking)
		{
			m_have_all = false;
			set_state(torrent_status::downloading);
			force_recheck();
		}
		m_num_verified = 0;
		m_verified.clear();
		m_verifying.clear();

		set_need_save_resume();
	}

	void torrent::verified(int piece)
	{
		TORRENT_ASSERT(piece < int(m_verified.size()));
		TORRENT_ASSERT(piece >= 0);
		TORRENT_ASSERT(m_verified.get_bit(piece) == false);

add a unit test where we don't have metadata, connect to a peer that sends a bitfield that's too large, then we get the metadata

../src/torrent.cpp:1907

			{
				read_resume_data(m_resume_data->node);
			}
		}

#if TORRENT_USE_ASSERTS
		m_resume_data_loaded = true;
#endif

		construct_storage();

		if (m_share_mode && valid_metadata())
		{
			// in share mode, all pieces have their priorities initialized to 0
			m_file_priority.clear();
			m_file_priority.resize(m_torrent_file->num_files(), 0);
		}

		// it's important to initialize the peers early, because this is what will
		// fix up their have-bitmasks to have the correct size
		if (!m_connections_initialized)
		{
			m_connections_initialized = true;
			// all peer connections have to initialize themselves now that the metadata
			// is available
			// copy the peer list since peers may disconnect and invalidate
			// m_connections as we initialize them
			std::vector<peer_connection*> peers = m_connections;
			for (torrent::peer_iterator i = peers.begin();
				i != peers.end(); ++i)
			{
				peer_connection* pc = *i;
				if (pc->is_disconnecting()) continue;
				pc->on_metadata_impl();
				if (pc->is_disconnecting()) continue;
				pc->init();
			}
		}

		// if we've already loaded file priorities, don't load piece priorities,
		// they will interfere.
		if (!m_seed_mode && m_resume_data && m_file_priority.empty())
		{
			bdecode_node piece_priority = m_resume_data->node
				.dict_find_string("piece_priority");

			if (piece_priority && piece_priority.string_length()
				== m_torrent_file->num_pieces())
			{
				char const* p = piece_priority.string_ptr();
				for (int i = 0; i < piece_priority.string_length(); ++i)

abort lookups this torrent has made via the session host resolver interface

../src/torrent.cpp:4941

		// files belonging to the torrents
		disconnect_all(errors::torrent_aborted, op_bittorrent);

		// post a message to the main thread to destruct
		// the torrent object from there
		if (m_storage.get())
		{
			inc_refcount("release_files");
			m_ses.disk_thread().async_stop_torrent(m_storage.get()
				, boost::bind(&torrent::on_cache_flushed, shared_from_this(), _1));
		}
		else
		{
			TORRENT_ASSERT(m_abort);
			if (alerts().should_post<cache_flushed_alert>())
				alerts().emplace_alert<cache_flushed_alert>(get_handle());
		}

		m_storage.reset();


		if (!m_apply_ip_filter)
		{
			inc_stats_counter(counters::non_filter_torrents, -1);
			m_apply_ip_filter = true;
		}

		m_allow_peers = false;
		m_auto_managed = false;
		update_state_list();
		for (int i = 0; i < aux::session_interface::num_torrent_lists; ++i)
		{
			if (!m_links[i].in_list()) continue;
			m_links[i].unlink(m_ses.torrent_list(i), i);
		}
		// don't re-add this torrent to the state-update list
		m_state_subscription = false;
	}

	void torrent::super_seeding(bool on)
	{
		if (on == m_super_seeding) return;

		m_super_seeding = on;
		set_need_save_resume();

		if (m_super_seeding) return;

		// disable super seeding for all peers
		for (peer_iterator i = begin(); i != end(); ++i)
		{

if peer is a really good peer, maybe we shouldn't disconnect it perhaps this logic should be disabled if we have too many idle peers (with some definition of idle)

../src/torrent.cpp:8127

#ifndef TORRENT_DISABLE_LOGGING
		debug_log("incoming peer (%d)", int(m_connections.size()));
#endif

#ifdef TORRENT_DEBUG
		error_code ec;
		TORRENT_ASSERT(p->remote() == p->get_socket()->remote_endpoint(ec) || ec);
#endif

		TORRENT_ASSERT(p->peer_info_struct() != NULL);

		// we need to do this after we've added the peer to the peer_list
		// since that's when the peer is assigned its peer_info object,
		// which holds the rank
		if (maybe_replace_peer)
		{
			// now, find the lowest rank peer and disconnect that
			// if it's lower rank than the incoming connection
			peer_connection* peer = find_lowest_ranking_peer();

			if (peer && peer->peer_rank() < p->peer_rank())
			{
#ifndef TORRENT_DISABLE_LOGGING
				debug_log("CLOSING CONNECTION \"%s\" peer list full (low peer rank) "
					"connections: %d limit: %d"
					, print_endpoint(peer->remote()).c_str()
					, int(m_connections.size())
					, m_max_connections);
#endif
				peer->disconnect(errors::too_many_connections, op_bittorrent);
				p->peer_disconnected_other();
			}
			else
			{
#ifndef TORRENT_DISABLE_LOGGING
				debug_log("CLOSING CONNECTION \"%s\" peer list full (low peer rank) "
					"connections: %d limit: %d"
					, print_endpoint(p->remote()).c_str()
					, int(m_connections.size())
					, m_max_connections);
#endif
				p->disconnect(errors::too_many_connections, op_bittorrent);
				// we have to do this here because from the peer's point of
				// it wasn't really attached to the torrent, but we do need
				// to let peer_list know we're removing it
				remove_peer(p);
				return false;
			}
		}

#if TORRENT_USE_INVARIANT_CHECKS

some of these arguments could probably be moved to the tracker request itself. like the ip_filter and settings

../src/tracker_manager.cpp:200

			, interval == 0 ? min_interval : interval);
		close();
	}

	void tracker_connection::sent_bytes(int bytes)
	{
		m_man.sent_bytes(bytes);
	}

	void tracker_connection::received_bytes(int bytes)
	{
		m_man.received_bytes(bytes);
	}

	void tracker_connection::close()
	{
		cancel();
		m_man.remove_request(this);
	}

	tracker_manager::tracker_manager(class udp_socket& sock
		, counters& stats_counters
		, resolver_interface& resolver
		, aux::session_settings const& sett
#if !defined TORRENT_DISABLE_LOGGING || TORRENT_USE_ASSERTS
		, aux::session_logger& ses
#endif
		)
		: m_udp_socket(sock)
		, m_host_resolver(resolver)
		, m_settings(sett)
		, m_stats_counters(stats_counters)
#if !defined TORRENT_DISABLE_LOGGING || TORRENT_USE_ASSERTS
		, m_ses(ses)
#endif
		, m_abort(false)
	{}

	tracker_manager::~tracker_manager()
	{
		TORRENT_ASSERT(m_abort);
		abort_all_requests(true);
	}

	void tracker_manager::sent_bytes(int bytes)
	{
		TORRENT_ASSERT(m_ses.is_single_thread());
		m_stats_counters.inc_stats_counter(counters::sent_tracker_bytes, bytes);
	}

	void tracker_manager::received_bytes(int bytes)

the udp_socket should really just be a single socket, and the session should support having more than one, just like with TCP sockets for now, just make bind failures non-fatal

../src/udp_socket.cpp:810

	{
		m_ipv4_sock.open(udp::v4(), ec);
		if (ec) return;

		// this is best-effort. ignore errors
		error_code err;
#ifdef TORRENT_WINDOWS
		m_ipv4_sock.set_option(exclusive_address_use(true), err);
#endif
		m_ipv4_sock.set_option(boost::asio::socket_base::reuse_address(true), err);

		m_ipv4_sock.bind(ep, ec);
		if (ec) return;
		udp::socket::non_blocking_io ioc(true);
		m_ipv4_sock.io_control(ioc, ec);
		if (ec) return;
		setup_read(&m_ipv4_sock);
	}

#if TORRENT_USE_IPV6
	if (supports_ipv6() && (ep.address().is_v6() || is_any(ep.address())))
	{
		udp::endpoint ep6 = ep;
		if (is_any(ep.address())) ep6.address(address_v6::any());
		m_ipv6_sock.open(udp::v6(), ec);
		if (ec) return;

		// this is best-effort. ignore errors
		error_code err;
#ifdef TORRENT_WINDOWS
		m_ipv6_sock.set_option(exclusive_address_use(true), err);
#endif
		m_ipv6_sock.set_option(boost::asio::socket_base::reuse_address(true), err);
		m_ipv6_sock.set_option(boost::asio::ip::v6_only(true), err);

		m_ipv6_sock.bind(ep6, ec);
		if (ec != error_code(boost::system::errc::address_not_available
			, boost::system::generic_category()))
		{
			if (ec) return;
			udp::socket::non_blocking_io ioc(true);
			m_ipv6_sock.io_control(ioc, ec);
			if (ec) return;
			setup_read(&m_ipv6_sock);
		}
		else
		{
			ec.clear();
		}
	}
#endif

support authentication here. tracker_req().auth

../src/udp_tracker_connection.cpp:83

		udp_tracker_connection::m_connection_cache;

	mutex udp_tracker_connection::m_cache_mutex;

	udp_tracker_connection::udp_tracker_connection(
		io_service& ios
		, tracker_manager& man
		, tracker_request const& req
		, boost::weak_ptr<request_callback> c)
		: tracker_connection(man, req, ios, c)
		, m_transaction_id(0)
		, m_attempts(0)
		, m_state(action_error)
		, m_abort(false)
	{
		update_transaction_id();
	}

	void udp_tracker_connection::start()
	{
		std::string hostname;
		std::string protocol;
		int port;
		error_code ec;

		using boost::tuples::ignore;
		boost::tie(protocol, ignore, hostname, port, ignore)
			= parse_url_components(tracker_req().url, ec);
		if (port == -1) port = protocol == "http" ? 80 : 443;

		if (ec)
		{
			tracker_connection::fail(ec);
			return;
		}
		
		aux::session_settings const& settings = m_man.settings();

		if (settings.get_bool(settings_pack::proxy_hostnames)
			&& (settings.get_int(settings_pack::proxy_type) == settings_pack::socks5
				|| settings.get_int(settings_pack::proxy_type) == settings_pack::socks5_pw))
		{
			m_hostname = hostname;
			m_target.port(port);
			start_announce();
		}
		else
		{
#if defined TORRENT_ASIO_DEBUGGING
			add_outstanding_async("udp_tracker_connection::name_lookup");
#endif

if we were to initialize m_metadata_size lazily instead, we would probably be more efficient initialize m_metadata_size

../src/ut_metadata.cpp:123

				metadata();
		}

		bool need_loaded()
		{ return m_torrent.need_loaded(); }

		virtual void on_unload() TORRENT_OVERRIDE
		{
			m_metadata.reset();
		}

		virtual void on_load() TORRENT_OVERRIDE
		{
			// initialize m_metadata_size
			TORRENT_ASSERT(m_torrent.is_loaded());
			metadata();
		}

		virtual void on_files_checked() TORRENT_OVERRIDE
		{
			metadata();
		}

		virtual boost::shared_ptr<peer_plugin> new_connection(
			peer_connection_handle const& pc) TORRENT_OVERRIDE;

		int get_metadata_size() const
		{
			TORRENT_ASSERT(m_metadata_size > 0);
			return m_metadata_size;
		}

		buffer::const_interval metadata() const
		{
			if (!m_torrent.need_loaded()) return buffer::const_interval(NULL, NULL);
			TORRENT_ASSERT(m_torrent.valid_metadata());
			if (!m_metadata)
			{
				m_metadata = m_torrent.torrent_file().metadata();
				m_metadata_size = m_torrent.torrent_file().metadata_size();
				TORRENT_ASSERT(hasher(m_metadata.get(), m_metadata_size).final()
					== m_torrent.torrent_file().info_hash());
			}
			return buffer::const_interval(m_metadata.get(), m_metadata.get()
				+ m_metadata_size);
		}

		bool received_metadata(ut_metadata_peer_plugin& source
			, char const* buf, int size, int piece, int total_size);

		// returns a piece of the metadata that

we may want to take ec into account here. possibly close connections quicker

../src/utp_socket_manager.cpp:235

			error_code err;
			m_interfaces = enum_net_interfaces(m_sock.get_io_service(), err);
			if (err) return socket_ep;
		}

		for (std::vector<ip_interface>::iterator i = m_interfaces.begin()
			, end(m_interfaces.end()); i != end; ++i)
		{
			if (i->interface_address.is_v4() != remote.is_v4())
				continue;

			if (strcmp(best->name, i->name) == 0)
				return tcp::endpoint(i->interface_address, socket_ep.port());
		}
		return socket_ep;
	}

	bool utp_socket_manager::incoming_packet(error_code const& ec, udp::endpoint const& ep
			, char const* p, int size)
	{
		TORRENT_UNUSED(ec);
//		UTP_LOGV("incoming packet size:%d\n", size);

		if (size < int(sizeof(utp_header))) return false;

		utp_header const* ph = reinterpret_cast<utp_header const*>(p);

//		UTP_LOGV("incoming packet version:%d\n", int(ph->get_version()));

		if (ph->get_version() != 1) return false;

		const time_point receive_time = clock_type::now();

		// parse out connection ID and look for existing
		// connections. If found, forward to the utp_stream.
		boost::uint16_t id = ph->connection_id;

		// first test to see if it's the same socket as last time
		// in most cases it is
		if (m_last_socket
			&& utp_match(m_last_socket, ep, id))
		{
			return utp_incoming_packet(m_last_socket, p, size, ep, receive_time);
		}

		std::pair<socket_map_t::iterator, socket_map_t::iterator> r =
			m_utp_sockets.equal_range(id);

		for (; r.first != r.second; ++r.first)
		{
			if (!utp_match(r.first->second, ep, id)) continue;

it would be nice if not everything would have to be public here

../src/utp_stream.cpp:389

	void incoming(boost::uint8_t const* buf, int size, packet* p, time_point now);
	void do_ledbat(int acked_bytes, int delay, int in_flight);
	int packet_timeout() const;
	bool test_socket_state();
	void maybe_trigger_receive_callback();
	void maybe_trigger_send_callback();
	bool cancel_handlers(error_code const& ec, bool kill);
	bool consume_incoming_data(
		utp_header const* ph, boost::uint8_t const* ptr, int payload_size, time_point now);
	void update_mtu_limits();
	void experienced_loss(int seq_nr);

	void set_state(int s);

private:

	// non-copyable
	utp_socket_impl(utp_socket_impl const&);
	utp_socket_impl const& operator=(utp_socket_impl const&);

public:

	void check_receive_buffers() const;

#if TORRENT_USE_INVARIANT_CHECKS
	void check_invariant() const;
#endif

	utp_socket_manager* m_sm;

	// userdata pointer passed along
	// with any callback. This is initialized to 0
	// then set to point to the utp_stream when
	// hooked up, and then reset to 0 once the utp_stream
	// detaches. This is used to know whether or not
	// the socket impl is still attached to a utp_stream
	// object. When it isn't, we'll never be able to
	// signal anything back to the client, and in case
	// of errors, we just have to delete ourselves
	// i.e. transition to the UTP_STATE_DELETED state
	void* m_userdata;

	// This is a platform-independent replacement
	// for the regular iovec type in posix. Since
	// it's not used in any system call, we might as
	// well define our own type instead of wrapping
	// the system's type.
	struct iovec_t
	{
		iovec_t(void* b, size_t l): buf(b), len(l) {}
		void* buf;

do we really need a special case here? wouldn't the multi-file case handle single file torrents correctly too?

../src/web_peer_connection.cpp:328

			incoming_piece_fragment(m_piece.size());
			m_web->restart_request.piece = -1;
		}

#if 0
			std::cerr << this << " REQ: p: " << pr.piece << " " << pr.start << std::endl;
#endif
		size -= pr.length;
	}

	int proxy_type = m_settings.get_int(settings_pack::proxy_type);
	bool using_proxy = (proxy_type == settings_pack::http
		|| proxy_type == settings_pack::http_pw) && !m_ssl;

	// the number of pad files that have been "requested". In case we _only_
	// request padfiles, we can't rely on handling them in the on_receive()
	// callback (because we won't receive anything), instead we have to post a
	// pretend read callback where we can deliver the zeroes for the partfile
	int num_pad_files = 0;

	if (single_file_request)
	{
		file_request_t file_req;
		file_req.file_index = 0;
		file_req.start = boost::int64_t(req.piece) * info.piece_length()
			+ req.start;
		file_req.length = req.length;

		request += "GET ";
		// do not encode single file paths, they are
		// assumed to be encoded in the torrent file
		request += using_proxy ? m_url : m_path;
		request += " HTTP/1.1\r\n";
		add_headers(request, m_settings, using_proxy);
		request += "\r\nRange: bytes=";
		request += to_string(file_req.start).elems;
		request += "-";
		request += to_string(file_req.start + file_req.length - 1).elems;
		request += "\r\n\r\n";
		m_first_request = false;

		m_file_requests.push_back(file_req);
	}
	else
	{
		if (!t->need_loaded())
		{
			disconnect(errors::torrent_aborted, op_bittorrent);
			return;
		}

just make this peer not have the pieces associated with the file we just requested. Only when it doesn't have any of the file do the following

../src/web_peer_connection.cpp:550

	peer_connection::received_invalid_data(index, single_peer);

	// if we don't think we have any of the files, allow banning the web seed
	if (num_have_pieces() == 0) return true;

	// don't disconnect, we won't request anything from this file again
	return false;
}

void web_peer_connection::on_receive_padfile()
{
	handle_padfile();
}

void web_peer_connection::handle_error(int bytes_left)
{
	boost::shared_ptr<torrent> t = associated_torrent().lock();
	TORRENT_ASSERT(t);

	int retry_time = atoi(m_parser.header("retry-after").c_str());
	if (retry_time <= 0) retry_time = m_settings.get_int(settings_pack::urlseed_wait_retry);
	// temporarily unavailable, retry later
	t->retry_web_seed(this, retry_time);
	std::string error_msg = to_string(m_parser.status_code()).elems
		+ (" " + m_parser.message());
	if (t->alerts().should_post<url_seed_alert>())
	{
		t->alerts().emplace_alert<url_seed_alert>(t->get_handle(), m_url
			, error_msg);
	}
	received_bytes(0, bytes_left);
	disconnect(error_code(m_parser.status_code(), get_http_category()), op_bittorrent, 1);
	return;
}

void web_peer_connection::handle_redirect(int bytes_left)
{
	// this means we got a redirection request
	// look for the location header
	std::string location = m_parser.header("location");
	received_bytes(0, bytes_left);

	boost::shared_ptr<torrent> t = associated_torrent().lock();
	TORRENT_ASSERT(t);

	if (location.empty())
	{
		// we should not try this server again.
		t->remove_web_seed(this, errors::missing_location, op_bittorrent, 2);
		m_web = NULL;

create a mapping of file-index to redirection URLs. Use that to form URLs instead. Support to reconnect to a new server without destructing this peer_connection

../src/web_peer_connection.cpp:603

		m_web = NULL;
		TORRENT_ASSERT(is_disconnecting());
		return;
	}

	bool single_file_request = false;
	if (!m_path.empty() && m_path[m_path.size() - 1] != '/')
		single_file_request = true;

	// add the redirected url and remove the current one
	if (!single_file_request)
	{
		TORRENT_ASSERT(!m_file_requests.empty());
		int const file_index = m_file_requests.front().file_index;

		if (!t->need_loaded())
		{
			disconnect(errors::torrent_aborted, op_bittorrent);
			return;
		}
		torrent_info const& info = t->torrent_file();
		std::string path = info.orig_files().file_path(file_index);
#ifdef TORRENT_WINDOWS
		convert_path_to_posix(path);
#endif
		path = escape_path(path.c_str(), path.length());
		size_t i = location.rfind(path);
		if (i == std::string::npos)
		{
			t->remove_web_seed(this, errors::invalid_redirection, op_bittorrent, 2);
			m_web = NULL;
			TORRENT_ASSERT(is_disconnecting());
			return;
		}
		location.resize(i);
	}
	else
	{
		location = resolve_redirect_location(m_url, location);
	}

#ifndef TORRENT_DISABLE_LOGGING
	peer_log(peer_log_alert::info, "LOCATION", "%s", location.c_str());
#endif
	t->add_web_seed(location, web_seed_entry::url_seed, m_external_auth, m_extra_headers);
	t->remove_web_seed(this, errors::redirecting, op_bittorrent, 2);
	m_web = NULL;
	TORRENT_ASSERT(is_disconnecting());
	return;
}

make this configurable in dht_settings

../src/kademlia/dht_storage.cpp:110

	// this is a group. It contains a set of group members
	struct torrent_entry
	{
		std::string name;
		std::set<peer_entry> peers;
	};

#ifndef TORRENT_NO_DEPRECATE
	struct count_peers
	{
		int* count;
		count_peers(int* c): count(c) {}
		void operator()(std::pair<libtorrent::sha1_hash
			, torrent_entry> const& t)
		{
			*count += t.second.peers.size();
		}
	};
#endif

	enum { announce_interval = 30 };

	struct dht_immutable_item
	{
		dht_immutable_item() : value(0), num_announcers(0), size(0) {}
		// malloced space for the actual value
		char* value;
		// this counts the number of IPs we have seen
		// announcing this item, this is used to determine
		// popularity if we reach the limit of items to store
		bloom_filter<128> ips;
		// the last time we heard about this
		time_point last_seen;
		// number of IPs in the bloom filter
		int num_announcers;
		// size of malloced space pointed to by value
		int size;
	};

	struct ed25519_public_key { char bytes[item_pk_len]; };

	struct dht_mutable_item : dht_immutable_item
	{
		char sig[item_sig_len];
		boost::int64_t seq;
		ed25519_public_key key;
		char* salt;
		int salt_size;
	};

	void touch_item(dht_immutable_item* f, address const& address)

it would be nice to have a bias towards node-id prefixes that are missing in the bucket

../src/kademlia/node.cpp:656

	// this shouldn't happen
	TORRENT_ASSERT(m_id != ne->id);
	if (ne->id == m_id) return;

	int bucket = 159 - distance_exp(m_id, ne->id);
	TORRENT_ASSERT(bucket < 160);
	send_single_refresh(ne->ep(), bucket, ne->id);
}

void node::send_single_refresh(udp::endpoint const& ep, int bucket
	, node_id const& id)
{
	TORRENT_ASSERT(id != m_id);
	void* ptr = m_rpc.allocate_observer();
	if (ptr == 0) return;

	TORRENT_ASSERT(bucket >= 0);
	TORRENT_ASSERT(bucket <= 159);

	// generate a random node_id within the given bucket
	node_id mask = generate_prefix_mask(bucket + 1);
	node_id target = generate_secret_id() & ~mask;
	target |= m_id & mask;

	// create a dummy traversal_algorithm
	// this is unfortunately necessary for the observer
	// to free itself from the pool when it's being released
	boost::intrusive_ptr<traversal_algorithm> algo(
		new traversal_algorithm(*this, (node_id::min)()));
	observer_ptr o(new (ptr) ping_observer(algo, ep, id));
#if defined TORRENT_DEBUG || defined TORRENT_RELEASE_ASSERTS
	o->m_in_constructor = false;
#endif
	entry e;
	e["y"] = "q";
	entry& a = e["a"];

	if (m_table.is_full(bucket))
	{
		// current bucket is full, just ping it.
		e["q"] = "ping";
		m_counters.inc_stats_counter(counters::dht_ping_out);
	}
	else
	{
		// use get_peers instead of find_node. We'll get nodes in the response
		// either way.
		e["q"] = "get_peers";
		a["info_hash"] = target.to_string();
		m_counters.inc_stats_counter(counters::dht_get_peers_out);
	}

use the non deprecated function instead of this one

../src/kademlia/node.cpp:734

	for (std::set<traversal_algorithm*>::iterator i = m_running_requests.begin()
		, end(m_running_requests.end()); i != end; ++i)
	{
		requests.push_back(dht_lookup());
		dht_lookup& lookup = requests.back();
		(*i)->status(lookup);
	}
}

void node::update_stats_counters(counters& c) const
{
	const dht_storage_counters& dht_cnt = m_storage->counters();
	c.set_value(counters::dht_torrents, dht_cnt.torrents);
	c.set_value(counters::dht_peers, dht_cnt.peers);
	c.set_value(counters::dht_immutable_data, dht_cnt.immutable_data);
	c.set_value(counters::dht_mutable_data, dht_cnt.mutable_data);
}

#ifndef TORRENT_NO_DEPRECATE
void node::status(session_status& s)
{
	mutex_t::scoped_lock l(m_mutex);

	m_table.status(s);
	s.dht_torrents = int(m_storage->num_torrents());
	s.active_requests.clear();
	s.dht_total_allocations = m_rpc.num_allocated_observers();
	for (std::set<traversal_algorithm*>::iterator i = m_running_requests.begin()
		, end(m_running_requests.end()); i != end; ++i)
	{
		s.active_requests.push_back(dht_lookup());
		dht_lookup& lookup = s.active_requests.back();
		(*i)->status(lookup);
	}
}
#endif

void node::lookup_peers(sha1_hash const& info_hash, entry& reply
	, bool noseed, bool scrape) const
{
	if (m_observer)
		m_observer->get_peers(info_hash);

	m_storage->get_peers(info_hash, noseed, scrape, reply);
}

void TORRENT_EXTRA_EXPORT write_nodes_entry(entry& r, nodes_t const& nodes)
{
	entry& n = r["nodes"];
	std::back_insert_iterator<std::string> out(n.string());

find_node should write directly to the response entry

../src/kademlia/node.cpp:893

				, int(reply["values"].list().size()));
		}
#endif
	}
	else if (query_len == 9 && memcmp(query, "find_node", 9) == 0)
	{
		key_desc_t msg_desc[] = {
			{"target", bdecode_node::string_t, 20, 0},
		};

		bdecode_node msg_keys[1];
		if (!verify_message(arg_ent, msg_desc, msg_keys, error_string, sizeof(error_string)))
		{
			incoming_error(e, error_string);
			return;
		}

		m_counters.inc_stats_counter(counters::dht_find_node_in);
		sha1_hash target(msg_keys[0].string_ptr());

		nodes_t n;
		m_table.find_node(target, n, 0);
		write_nodes_entry(reply, n);
	}
	else if (query_len == 13 && memcmp(query, "announce_peer", 13) == 0)
	{
		key_desc_t msg_desc[] = {
			{"info_hash", bdecode_node::string_t, 20, 0},
			{"port", bdecode_node::int_t, 0, 0},
			{"token", bdecode_node::string_t, 0, 0},
			{"n", bdecode_node::string_t, 0, key_desc_t::optional},
			{"seed", bdecode_node::int_t, 0, key_desc_t::optional},
			{"implied_port", bdecode_node::int_t, 0, key_desc_t::optional},
		};

		bdecode_node msg_keys[6];
		if (!verify_message(arg_ent, msg_desc, msg_keys, error_string, sizeof(error_string)))
		{
			m_counters.inc_stats_counter(counters::dht_invalid_announce);
			incoming_error(e, error_string);
			return;
		}

		int port = int(msg_keys[1].int_value());

		// is the announcer asking to ignore the explicit
		// listen port and instead use the source port of the packet?
		if (msg_keys[5] && msg_keys[5].int_value() != 0)
			port = m.addr.port();

		if (port < 0 || port >= 65536)

use the non deprecated function instead of this one

../src/kademlia/routing_table.cpp:132

	static const int size_exceptions[] = {16, 8, 4, 2};
	if (bucket < int(sizeof(size_exceptions)/sizeof(size_exceptions[0])))
		return m_bucket_size * size_exceptions[bucket];
	return m_bucket_size;
}

void routing_table::status(std::vector<dht_routing_bucket>& s) const
{
	for (table_t::const_iterator i = m_buckets.begin()
		, end(m_buckets.end()); i != end; ++i)
	{
		dht_routing_bucket b;
		b.num_nodes = i->live_nodes.size();
		b.num_replacements = i->replacements.size();
		s.push_back(b);
	}
}

#ifndef TORRENT_NO_DEPRECATE
void routing_table::status(session_status& s) const
{
	int ignore;
	boost::tie(s.dht_nodes, s.dht_node_cache, ignore) = size();
	s.dht_global_nodes = num_global_nodes();

	for (table_t::const_iterator i = m_buckets.begin()
		, end(m_buckets.end()); i != end; ++i)
	{
		dht_routing_bucket b;
		b.num_nodes = i->live_nodes.size();
		b.num_replacements = i->replacements.size();
#ifndef TORRENT_NO_DEPRECATE
		b.last_active = 0;
#endif
		s.dht_routing_table.push_back(b);
	}
}
#endif

boost::tuple<int, int, int> routing_table::size() const
{
	int nodes = 0;
	int replacements = 0;
	int confirmed = 0;
	for (table_t::const_iterator i = m_buckets.begin()
		, end(m_buckets.end()); i != end; ++i)
	{
		nodes += i->live_nodes.size();
		for (bucket_t::const_iterator k = i->live_nodes.begin()
			, end2(i->live_nodes.end()); k != end2; ++k)

move the lowest priority nodes to the replacement bucket

../src/kademlia/routing_table.cpp:991

	bucket_t& rb = m_buckets[bucket_index].replacements;

	// move any node whose (160 - distane_exp(m_id, id)) >= (i - m_buckets.begin())
	// to the new bucket
	int const new_bucket_size = bucket_limit(bucket_index + 1);
	for (bucket_t::iterator j = b.begin(); j != b.end();)
	{
		int const d = distance_exp(m_id, j->id);
		if (d >= 159 - bucket_index)
		{
			++j;
			continue;
		}
		// this entry belongs in the new bucket
		new_bucket.push_back(*j);
		j = b.erase(j);
	}

	if (b.size() > bucket_size_limit)
	{
		for (bucket_t::iterator i = b.begin() + bucket_size_limit
			, end(b.end()); i != end; ++i)
		{
			rb.push_back(*i);
		}

		b.resize(bucket_size_limit);
	}

	// split the replacement bucket as well. If the live bucket
	// is not full anymore, also move the replacement entries
	// into the main bucket
	for (bucket_t::iterator j = rb.begin(); j != rb.end();)
	{
		if (distance_exp(m_id, j->id) >= 159 - bucket_index)
		{
			if (int(b.size()) >= bucket_size_limit)
			{
				++j;
				continue;
			}
			b.push_back(*j);
		}
		else
		{
			// this entry belongs in the new bucket
			if (int(new_bucket.size()) < new_bucket_size)
				new_bucket.push_back(*j);
			else
				new_replacement_bucket.push_back(*j);
		}

should the alert baseclass have this object instead?

../include/libtorrent/alert_types.hpp:1416

	{
		// internal
		portmap_log_alert(aux::stack_allocator& alloc, int t, const char* m);

		TORRENT_DEFINE_ALERT(portmap_log_alert, 52)

		static const int static_category = alert::port_mapping_log_notification;
		virtual std::string message() const TORRENT_OVERRIDE;

		int map_type;

#ifndef TORRENT_NO_DEPRECATE
		std::string msg;
#endif

		// the message associated with this log line
		char const* log_message() const;

	private:

		aux::stack_allocator const& m_alloc;

		int m_log_idx;
	};

#endif

	// This alert is generated when a fastresume file has been passed to
	// add_torrent() but the files on disk did not match the fastresume file.
	// The error_code explains the reason why the resume file was rejected.
	struct TORRENT_EXPORT fastresume_rejected_alert TORRENT_FINAL : torrent_alert
	{
		// internal
		fastresume_rejected_alert(aux::stack_allocator& alloc
			, torrent_handle const& h
			, error_code const& ec
			, std::string const& file
			, char const* op);

		TORRENT_DEFINE_ALERT(fastresume_rejected_alert, 53)

		static const int static_category = alert::status_notification
			| alert::error_notification;
		virtual std::string message() const TORRENT_OVERRIDE;

		error_code error;

#ifndef TORRENT_NO_DEPRECATE
		// If the error happend to a specific file, ``file`` is the path to it.
		std::string file;
#endif

instead of using a dummy function to cause link errors when incompatible build configurations are used, make the namespace name depend on the configuration, and have a using declaration in the headers to pull it into libtorrent.

../include/libtorrent/build_config.hpp:40

AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.

*/

#ifndef TORRENT_BUILD_CONFIG_HPP_INCLUDED
#define TORRENT_BUILD_CONFIG_HPP_INCLUDED

#include "libtorrent/config.hpp"
#include <boost/preprocessor/cat.hpp>
#include <boost/preprocessor/stringize.hpp>

#if TORRENT_USE_IPV6
#define TORRENT_CFG_IPV6 ipv6_
#else
#define TORRENT_CFG_IPV6 noipv6_
#endif

#ifdef TORRENT_NO_DEPRECATE
#define TORRENT_CFG_DEPR nodeprecate_
#else
#define TORRENT_CFG_DEPR deprecated_
#endif

#define TORRENT_CFG \
	BOOST_PP_CAT(TORRENT_CFG_IPV6, \
	TORRENT_CFG_DEPR)

#define TORRENT_CFG_STRING BOOST_PP_STRINGIZE(TORRENT_CFG)

#endif

this could be done more efficiently by just looking up the interface with the given name, maybe even with if_nametoindex()

../include/libtorrent/enum_net.hpp:151

			// providing 0.0.0.0 as the device, turn it into "::"
			if (ip == address_v4::any() && protocol == boost::asio::ip::tcp::v6())
				ip = address_v6::any();
#endif
			bind_ep.address(ip);
			// it appears to be an IP. Just bind to that address
			sock.bind(bind_ep, ec);
			return bind_ep.address();
		}

		ec.clear();

#ifdef SO_BINDTODEVICE
		// try to use SO_BINDTODEVICE here, if that exists. If it fails,
		// fall back to the mechanism we have below
		sock.set_option(bind_to_device_opt(device_name), ec);
		if (ec)
#endif
		{
			ec.clear();
			std::vector<ip_interface> ifs = enum_net_interfaces(ios, ec);
			if (ec) return bind_ep.address();

			bool found = false;

			for (int i = 0; i < int(ifs.size()); ++i)
			{
				// we're looking for a specific interface, and its address
				// (which must be of the same family as the address we're
				// connecting to)
				if (strcmp(ifs[i].name, device_name) != 0) continue;
				if (ifs[i].interface_address.is_v4() != (protocol == boost::asio::ip::tcp::v4()))
					continue;

				bind_ep.address(ifs[i].interface_address);
				found = true;
				break;
			}

			if (!found)
			{
				ec = error_code(boost::system::errc::no_such_device, generic_category());
				return bind_ep.address();
			}
		}
		sock.bind(bind_ep, ec);
		return bind_ep.address();
	}

	// returns true if the given device exists
	TORRENT_EXTRA_EXPORT bool has_interface(char const* name, io_service& ios

add emplace_back() version

../include/libtorrent/heterogeneous_queue.hpp:56

#include <vector>

#include <boost/cstdint.hpp>
#include <boost/utility/enable_if.hpp>
#include <boost/type_traits/is_base_of.hpp>

#include "libtorrent/assert.hpp"

namespace libtorrent {

	template <class T>
	struct heterogeneous_queue
	{
		heterogeneous_queue()
			: m_storage(NULL)
			, m_capacity(0)
			, m_size(0)
			, m_num_items(0)
		{}

		template <class U>
		typename boost::enable_if<boost::is_base_of<T, U> >::type
		push_back(U const& a)
		{
			// the size of the type rounded up to pointer alignment
			const int object_size = (sizeof(U) + sizeof(*m_storage) - 1)
				/ sizeof(*m_storage);

			// +1 for the length prefix
			if (m_size + object_size + header_size > m_capacity)
				grow_capacity(object_size);

			uintptr_t* ptr = m_storage + m_size;

			// length prefix
			header_t* hdr = reinterpret_cast<header_t*>(ptr);
			hdr->len = object_size;
			hdr->move = &move<U>;
			ptr += header_size;

			// construct in-place
			new (ptr) U(a);

			// if we constructed the object without throwing any exception
			// update counters to indicate the new item is in there
			++m_num_items;
			m_size += header_size + object_size;
		}

		void get_pointers(std::vector<T*>& out)
		{

rename this target queue size

../include/libtorrent/peer_connection.hpp:1116

		// the number of bytes send to the disk-io
		// thread that hasn't yet been completely written.
		int m_outstanding_writing_bytes;

		// max transfer rates seen on this peer
		int m_download_rate_peak;
		int m_upload_rate_peak;

		// when using the BitTyrant choker, this is our
		// estimated reciprocation rate. i.e. the rate
		// we need to send to this peer for it to unchoke
		// us
		int m_est_reciprocation_rate;

		// stop sending data after this many bytes, INT_MAX = inf
		int m_send_barrier;

		// the number of request we should queue up
		// at the remote end.
		boost::uint16_t m_desired_queue_size;

#ifndef TORRENT_NO_DEPRECATE
#ifndef TORRENT_DISABLE_RESOLVE_COUNTRIES
		// in case the session settings is set
		// to resolve countries, this is set to
		// the two character country code this
		// peer resides in.
		char m_country[2];
#endif
#endif // TORRENT_NO_DEPRECATE

		// if set to non-zero, this peer will always prefer
		// to request entire n pieces, rather than blocks.
		// where n is the value of this variable.
		// if it is 0, the download rate limit setting
		// will be used to determine if whole pieces
		// are preferred.
		boost::uint8_t m_prefer_contiguous_blocks;

		// this is the number of times this peer has had
		// a request rejected because of a disk I/O failure.
		// once this reaches a certain threshold, the
		// peer is disconnected in order to avoid infinite
		// loops of consistent failures
		boost::uint8_t m_disk_read_failures;

		// this is used in seed mode whenever we trigger a hash check
		// for a piece, before we read it. It's used to throttle
		// the hash checks to just a few per peer at a time.
		boost::uint8_t m_outstanding_piece_verification:3;

having 8 priority levels is probably excessive. It should probably be changed to 3 levels + dont-download

../include/libtorrent/piece_picker.hpp:594

			// the number of peers that has this piece
			// (availability)
#ifdef TORRENT_OPTIMIZE_MEMORY_USAGE
			boost::uint32_t peer_count : 9;
#else
			boost::uint32_t peer_count : 16;
#endif

			// one of the enums from state_t. This indicates whether this piece
			// is currently being downloaded or not, and what state it's in if
			// it is. Specifically, as an optimization, pieces that have all blocks
			// requested from them are separated out into separate lists to make
			// lookups quicker. The main oddity is that whether a downloading piece
			// has only been requested from peers that are reverse, that's
			// recorded as piece_downloading_reverse, which really means the same
			// as piece_downloading, it just saves space to also indicate that it
			// has a bit lower priority. The reverse bit is only relevant if the
			// state is piece_downloadin.
			boost::uint32_t download_state : 3;


			// is 0 if the piece is filtered (not to be downloaded)
			// 1 is low priority
			// 2 is low priority
			// 3 is mid priority
			// 4 is default priority
			// 5 is mid priority
			// 6 is high priority
			// 7 is high priority
			boost::uint32_t piece_priority : 3;

			// index in to the piece_info vector
#ifdef TORRENT_OPTIMIZE_MEMORY_USAGE
			boost::uint32_t index : 17;
#else
			boost::uint32_t index;
#endif

#ifdef TORRENT_DEBUG_REFCOUNTS
			// all the peers that have this piece
			std::set<const torrent_peer*> have_peers;
#endif

			enum
			{
				// index is set to this to indicate that we have the
				// piece. There is no entry for the piece in the
				// buckets if this is the case.
#ifdef TORRENT_OPTIMIZE_MEMORY_USAGE
				we_have_index = 0x3ffff,
#else

use the resolver interface that has a built-in cache

../include/libtorrent/proxy_base.hpp:260

		return m_sock.lowest_layer();
	}

	next_layer_type& next_layer()
	{
		return m_sock;
	}

	bool is_open() const { return m_sock.is_open(); }

protected:

	bool handle_error(error_code const& e, boost::shared_ptr<handler_type> const& h);

	tcp::socket m_sock;
	std::string m_hostname;
	int m_port;

	endpoint_type m_remote_endpoint;

	tcp::resolver m_resolver;
};

}

#endif

the ip filter should probably be saved here too

../include/libtorrent/session_handle.hpp:78

	class port_filter;
	class alert;

#ifndef TORRENT_NO_DEPRECATE
	struct session_status;
#endif

	typedef boost::function<void(sha1_hash const&, std::vector<char>&
		, error_code&)> user_load_function_t;

	struct TORRENT_EXPORT session_handle
	{
		session_handle() : m_impl(NULL) {}

		session_handle(aux::session_impl* impl)
			: m_impl(impl)
		{}

		bool is_valid() const { return m_impl != NULL; }


		// flags that determines which aspects of the session should be
		// saved when calling save_state().
		enum save_state_flags_t
		{
			// saves settings (i.e. the session_settings)
			save_settings =     0x001,

			// saves dht_settings
			save_dht_settings = 0x002,

			// saves dht state such as nodes and node-id, possibly accelerating
			// joining the DHT if provided at next session startup.
			save_dht_state =    0x004,

			// save pe_settings
			save_encryption_settings = 0x020,

			// internal
			save_as_map =       0x040

#ifndef TORRENT_NO_DEPRECATE
			,
			// saves RSS feeds
			save_feeds =        0x080,
			save_proxy =        0x008,
			save_i2p_proxy =    0x010,
			save_dht_proxy = save_proxy,
			save_peer_proxy = save_proxy,
			save_web_proxy = save_proxy,
			save_tracker_proxy = save_proxy

add async_connect() that takes a hostname and port as well

../include/libtorrent/socks5_stream.hpp:144

*/
		m_dst_name = host;
		if (m_dst_name.size() > 255)
			m_dst_name.resize(255);
	}

	void close(error_code& ec)
	{
		m_dst_name.clear();
		proxy_base::close(ec);
	}

#ifndef BOOST_NO_EXCEPTIONS
	void close()
	{
		m_dst_name.clear();
		proxy_base::close();
	}
#endif

	template <class Handler>
	void async_connect(endpoint_type const& endpoint, Handler const& handler)
	{
		// make sure we don't try to connect to INADDR_ANY. binding is fine,
		// and using a hostname is fine on SOCKS version 5.
		TORRENT_ASSERT(m_command == socks5_bind
			|| endpoint.address() != address()
			|| (!m_dst_name.empty() && m_version == 5));

		m_remote_endpoint = endpoint;

		// the connect is split up in the following steps:
		// 1. resolve name of proxy server
		// 2. connect to proxy server
		// 3. if version == 5:
		//   3.1 send SOCKS5 authentication method message
		//   3.2 read SOCKS5 authentication response
		//   3.3 send username+password
		// 4. send SOCKS command message

		// to avoid unnecessary copying of the handler,
		// store it in a shaed_ptr
		boost::shared_ptr<handler_type> h(new handler_type(handler));

#if defined TORRENT_ASIO_DEBUGGING
		add_outstanding_async("socks5_stream::name_lookup");
#endif
		tcp::resolver::query q(m_hostname, to_string(m_port).elems);
		m_resolver.async_resolve(q, boost::bind(
			&socks5_stream::name_lookup, this, _1, _2, h));
	}

this class probably doesn't need to have virtual functions.

../include/libtorrent/tracker_manager.hpp:290

		int m_completion_timeout;

		typedef mutex mutex_t;
		mutable mutex_t m_mutex;

		// used for timeouts
		// this is set when the request has been sent
		time_point m_start_time;

		// this is set every time something is received
		time_point m_read_time;

		// the asio async operation
		deadline_timer m_timeout;

		int m_read_timeout;

		bool m_abort;
	};

	struct TORRENT_EXTRA_EXPORT tracker_connection
		: timeout_handler
	{
		tracker_connection(tracker_manager& man
			, tracker_request const& req
			, io_service& ios
			, boost::weak_ptr<request_callback> r);

		void update_transaction_id(boost::shared_ptr<udp_tracker_connection> c
			, boost::uint64_t tid);

		boost::shared_ptr<request_callback> requester() const;
		virtual ~tracker_connection() {}

		tracker_request const& tracker_req() const { return m_req; }

		void fail(error_code const& ec, int code = -1, char const* msg = ""
			, int interval = 0, int min_interval = 0);
		virtual void start() = 0;
		virtual void close();
		address const& bind_interface() const { return m_req.bind_ip; }
		void sent_bytes(int bytes);
		void received_bytes(int bytes);
		virtual bool on_receive(error_code const&, udp::endpoint const&
			, char const* /* buf */, int /* size */) { return false; }
		virtual bool on_receive_hostname(error_code const&
			, char const* /* hostname */
			, char const* /* buf */, int /* size */) { return false; }

		boost::shared_ptr<tracker_connection> shared_from_this()
		{

the throttling of saving resume data could probably be factored out into a separate class

../include/libtorrent/aux_/session_impl.hpp:1163

			// each second tick the timer takes a little
			// bit longer than one second to trigger. The
			// extra time it took is accumulated into this
			// counter. Every time it exceeds 1000, torrents
			// will tick their timers 2 seconds instead of one.
			// this keeps the timers more accurate over time
			// as a kind of "leap second" to adjust for the
			// accumulated error
			boost::uint16_t m_tick_residual;

#ifndef TORRENT_DISABLE_LOGGING
			virtual void session_log(char const* fmt, ...) const TORRENT_OVERRIDE TORRENT_FORMAT(2,3);
			virtual void session_vlog(char const* fmt, va_list& va) const TORRENT_OVERRIDE TORRENT_FORMAT(2,0);

			// this list of tracker loggers serves as tracker_callbacks when
			// shutting down. This list is just here to keep them alive during
			// whe shutting down process
			std::list<boost::shared_ptr<tracker_logger> > m_tracker_loggers;
#endif

			virtual void queue_async_resume_data(boost::shared_ptr<torrent> const& t) TORRENT_OVERRIDE;
			virtual void done_async_resume() TORRENT_OVERRIDE;
			void async_resume_dispatched();

			// state for keeping track of external IPs
			external_ip m_external_ip;

#ifndef TORRENT_DISABLE_EXTENSIONS
			// this is a list to allow extensions to potentially remove themselves.
			typedef std::list<boost::shared_ptr<plugin> > ses_extension_list_t;
			ses_extension_list_t m_ses_extensions;

			// the union of all session extensions' implemented_features(). This is
			// used to exclude callbacks to the session extensions.
			boost::uint32_t m_session_extension_features;

			// std::string could be used for the query names if only all common
			// implementations used SSO *glares at gcc*
			struct extension_dht_query
			{
				boost::uint8_t query_len;
				boost::array<char, max_dht_query_length> query;
				dht_extension_handler_t handler;
			};
			typedef std::vector<extension_dht_query> m_extension_dht_queries_t;
			m_extension_dht_queries_t m_extension_dht_queries;
#endif

			// if this function is set, it indicates that torrents are allowed
			// to be unloaded. If it isn't, torrents will never be unloaded
			user_load_function_t m_user_load_torrent;

the IP voting mechanism should be factored out to its own class, not part of the session

../include/libtorrent/aux_/session_interface.hpp:137

#if TORRENT_USE_ASSERTS
		virtual bool is_single_thread() const = 0;
		virtual bool has_peer(peer_connection const* p) const = 0;
		virtual bool any_torrent_has_peer(peer_connection const* p) const = 0;
		virtual bool is_posting_torrent_updates() const = 0;
#endif
	protected:
		~session_logger() {}
	};
#endif // TORRENT_DISABLE_LOGGING || TORRENT_USE_ASSERTS

	// TOOD: 2 make this interface a lot smaller. It could be split up into
	// several smaller interfaces. Each subsystem could then limit the size
	// of the mock object to test it.
	struct TORRENT_EXTRA_EXPORT session_interface
		: buffer_allocator_interface
#if !defined TORRENT_DISABLE_LOGGING || TORRENT_USE_ASSERTS
		, session_logger
#endif
	{
		enum
		{
			source_dht = 1,
			source_peer = 2,
			source_tracker = 4,
			source_router = 8
		};

		virtual void set_external_address(address const& ip
			, int source_type, address const& source) = 0;
		virtual external_ip const& external_address() const = 0;

		virtual disk_interface& disk_thread() = 0;

		virtual alert_manager& alerts() = 0;

		virtual torrent_peer_allocator_interface* get_peer_allocator() = 0;
		virtual io_service& get_io_service() = 0;
		virtual resolver_interface& get_resolver() = 0;

		typedef boost::function<void(error_code const&, std::vector<address> const&)>
			callback_t;

remove this. There's already get_resolver()

../include/libtorrent/aux_/session_interface.hpp:162

			source_peer = 2,
			source_tracker = 4,
			source_router = 8
		};

		virtual void set_external_address(address const& ip
			, int source_type, address const& source) = 0;
		virtual external_ip const& external_address() const = 0;

		virtual disk_interface& disk_thread() = 0;

		virtual alert_manager& alerts() = 0;

		virtual torrent_peer_allocator_interface* get_peer_allocator() = 0;
		virtual io_service& get_io_service() = 0;
		virtual resolver_interface& get_resolver() = 0;

		typedef boost::function<void(error_code const&, std::vector<address> const&)>
			callback_t;

		virtual void async_resolve(std::string const& host, int flags
			, callback_t const& h) = 0;

		virtual bool has_connection(peer_connection* p) const = 0;
		virtual void insert_peer(boost::shared_ptr<peer_connection> const& c) = 0;

		virtual void queue_async_resume_data(boost::shared_ptr<torrent> const& t) = 0;
		virtual void done_async_resume() = 0;
		virtual void evict_torrent(torrent* t) = 0;

		virtual void remove_torrent(torrent_handle const& h, int options = 0) = 0;
		virtual void remove_torrent_impl(boost::shared_ptr<torrent> tptr, int options) = 0;

		// port filter
		virtual port_filter const& get_port_filter() const = 0;
		virtual void ban_ip(address addr) = 0;

		virtual boost::int64_t session_time() const = 0;

		virtual bool is_paused() const = 0;
		virtual bool is_aborted() const = 0;
		virtual int num_uploads() const = 0;
		virtual bool preemptive_unchoke() const = 0;
		virtual void trigger_optimistic_unchoke() = 0;
		virtual void trigger_unchoke() = 0;

		virtual boost::weak_ptr<torrent> find_torrent(sha1_hash const& info_hash) const = 0;
		virtual boost::weak_ptr<torrent> find_disconnect_candidate_torrent() const = 0;
		virtual boost::shared_ptr<torrent> delay_load_torrent(sha1_hash const& info_hash
			, peer_connection* pc) = 0;
		virtual void insert_torrent(sha1_hash const& ih, boost::shared_ptr<torrent> const& t

factor out the thread pool for socket jobs into a separate class used to (potentially) issue socket write calls onto multiple threads

../include/libtorrent/aux_/session_interface.hpp:217

		virtual int num_torrents() const = 0;

		virtual peer_id const& get_peer_id() const = 0;

		// cork a peer and schedule a delayed uncork
		// does nothing if the peer is already corked
		virtual void cork_burst(peer_connection* p) = 0;

		virtual void close_connection(peer_connection* p, error_code const& ec) = 0;
		virtual int num_connections() const = 0;

		virtual char* allocate_buffer() = 0;
		virtual void free_buffer(char* buf) = 0;
		virtual int send_buffer_size() const = 0;

		virtual void deferred_submit_jobs() = 0;

		virtual boost::uint16_t listen_port() const = 0;
		virtual boost::uint16_t ssl_listen_port() const = 0;

		virtual void post_socket_job(socket_job& j) = 0;

		// load the specified torrent. also evict one torrent, except
		// for the one specified, if we are at the limit of loaded torrents
		virtual bool load_torrent(torrent* t) = 0;

		// bump the specified torrent to make it the most recently used one
		// in the torrent LRU (i.e. the least likely to get unloaded)
		virtual void bump_torrent(torrent* t, bool back = true) = 0;

		// ask for which interface and port to bind outgoing peer connections on
		virtual tcp::endpoint bind_outgoing_socket(socket_type& s, address const&
			remote_address, error_code& ec) const = 0;
		virtual bool verify_bound_address(address const& addr, bool utp
			, error_code& ec) = 0;

#ifndef TORRENT_DISABLE_MUTABLE_TORRENTS
		virtual std::vector<boost::shared_ptr<torrent> > find_collection(
			std::string const& collection) const = 0;
#endif

it would be nice to have the number of threads be set dynamically

../src/disk_io_thread.cpp:218

		TORRENT_ASSERT(m_magic == 0x1337);
#if TORRENT_USE_ASSERTS
		m_magic = 0xdead;
#endif
	}

	void disk_io_thread::abort(bool wait)
	{
		m_abort = true;
		if (m_num_threads == 0)
		{
			abort_jobs();
		}
		else
		{
			set_num_threads(0, wait);
		}
	}

	void disk_io_thread::set_num_threads(int i, bool wait)
	{
		TORRENT_ASSERT(m_magic == 0x1337);
		if (i == m_num_threads) return;

		if (i > m_num_threads)
		{
			while (m_num_threads < i)
			{
				int thread_id = (++m_num_threads) - 1;
				thread_type_t type = generic_thread;

				// this keeps the io_service::run() call blocked from returning.
				// When shutting down, it's possible that the event queue is drained
				// before the disk_io_thread has posted its last callback. When this
				// happens, the io_service will have a pending callback from the
				// disk_io_thread, but the event loop is not running. this means
				// that the event is destructed after the disk_io_thread. If the
				// event refers to a disk buffer it will try to free it, but the
				// buffer pool won't exist anymore, and crash. This prevents that.
				boost::shared_ptr<io_service::work> work =
					boost::make_shared<io_service::work>(boost::ref(m_ios));

				// the magic number 3 is also used in add_job()
				// every 4:th thread is a hasher thread
				if ((thread_id & 0x3) == 3) type = hasher_thread;
				m_threads.push_back(boost::shared_ptr<thread>(
					new thread(boost::bind(&disk_io_thread::thread_fun, this
						, thread_id, type, work))));
			}
		}

in chunked encoding mode, this assert won't hold. the chunk headers should be subtracted from the receive_buffer_size

../src/http_seed_connection.cpp:129

	boost::optional<piece_block_progress>
	http_seed_connection::downloading_piece_progress() const
	{
		if (m_requests.empty())
			return boost::optional<piece_block_progress>();

		boost::shared_ptr<torrent> t = associated_torrent().lock();
		TORRENT_ASSERT(t);

		piece_block_progress ret;

		peer_request const& pr = m_requests.front();
		ret.piece_index = pr.piece;
		if (!m_parser.header_finished())
		{
			ret.bytes_downloaded = 0;
		}
		else
		{
			int receive_buffer_size = m_recv_buffer.get().left() - m_parser.body_start();
			TORRENT_ASSERT_VAL(receive_buffer_size <= t->block_size(), receive_buffer_size);
			ret.bytes_downloaded = t->block_size() - receive_buffer_size;
		}
		// this is used to make sure that the block_index stays within
		// bounds. If the entire piece is downloaded, the block_index
		// would otherwise point to one past the end
		int correction = ret.bytes_downloaded ? -1 : 0;
		ret.block_index = (pr.start + ret.bytes_downloaded + correction) / t->block_size();
		ret.full_block_bytes = t->block_size();
		const int last_piece = t->torrent_file().num_pieces() - 1;
		if (ret.piece_index == last_piece && ret.block_index
			== t->torrent_file().piece_size(last_piece) / t->block_size())
			ret.full_block_bytes = t->torrent_file().piece_size(last_piece) % t->block_size();
		return ret;
	}

	void http_seed_connection::write_request(peer_request const& r)
	{
		INVARIANT_CHECK;

		boost::shared_ptr<torrent> t = associated_torrent().lock();
		TORRENT_ASSERT(t);

		TORRENT_ASSERT(t->valid_metadata());
		// http_seeds don't support requesting more than one piece
		// at a time
		TORRENT_ASSERT(r.length <= t->torrent_file().piece_size(r.piece));

		std::string request;
		request.reserve(400);

report the proper address of the router as the source IP of this understanding of our external address, instead of the empty address

../src/session_impl.cpp:5449

	void session_impl::on_port_mapping(int mapping, address const& ip, int port
		, error_code const& ec, int map_transport)
	{
		TORRENT_ASSERT(is_single_thread());

		TORRENT_ASSERT(map_transport >= 0 && map_transport <= 1);

		if (mapping == m_udp_mapping[map_transport] && port != 0)
		{
			m_external_udp_port = port;
			if (m_alerts.should_post<portmap_alert>())
				m_alerts.emplace_alert<portmap_alert>(mapping, port
					, map_transport);
			return;
		}

		if (mapping == m_tcp_mapping[map_transport] && port != 0)
		{
			if (ip != address())
			{
				set_external_address(ip, source_router, address());
			}

			if (!m_listen_sockets.empty()) {
				m_listen_sockets.front().external_address = ip;
				m_listen_sockets.front().external_port = port;
			}
			if (m_alerts.should_post<portmap_alert>())
				m_alerts.emplace_alert<portmap_alert>(mapping, port
					, map_transport);
			return;
		}

		if (ec)
		{
			if (m_alerts.should_post<portmap_error_alert>())
				m_alerts.emplace_alert<portmap_error_alert>(mapping
					, map_transport, ec);
		}
		else
		{
			if (m_alerts.should_post<portmap_alert>())
				m_alerts.emplace_alert<portmap_alert>(mapping, port
					, map_transport);
		}
	}

#ifndef TORRENT_NO_DEPRECATE
	session_status session_impl::status() const
	{
//		INVARIANT_CHECK;

make this depend on the error and on the filesystem the files are being downloaded to. If the error is no_space_left_on_device and the filesystem doesn't support sparse files, only zero the priorities of the pieces that are at the tails of all files, leaving everything up to the highest written piece in each file

../src/torrent.cpp:1240

		// notify the user of the error
		if (alerts().should_post<file_error_alert>())
			alerts().emplace_alert<file_error_alert>(j->error.ec
				, resolve_filename(j->error.file), j->error.operation_str(), get_handle());

		// if a write operation failed, and future writes are likely to
		// fail, while reads may succeed, just set the torrent to upload mode
		// if we make an incorrect assumption here, it's not the end of the
		// world, if we ever issue a read request and it fails as well, we
		// won't get in here and we'll actually end up pausing the torrent
		if (j->action == disk_io_job::write
			&& (j->error.ec == boost::system::errc::read_only_file_system
			|| j->error.ec == boost::system::errc::permission_denied
			|| j->error.ec == boost::system::errc::operation_not_permitted
			|| j->error.ec == boost::system::errc::no_space_on_device
			|| j->error.ec == boost::system::errc::file_too_large))
		{
			// if we failed to write, stop downloading and just
			// keep seeding.
			set_upload_mode(true);
			return;
		}

		// put the torrent in an error-state
		set_error(j->error.ec, j->error.file);

		// if the error appears to be more serious than a full disk, just pause the torrent
		pause();
	}

	void torrent::on_piece_fail_sync(disk_io_job const* j, piece_block b)
	{
		TORRENT_UNUSED(j);
		TORRENT_UNUSED(b);

		update_gauge();
		// some peers that previously was no longer interesting may
		// now have become interesting, since we lack this one piece now.
		for (peer_iterator i = begin(); i != end();)
		{
			peer_connection* p = *i;
			// update_interest may disconnect the peer and
			// invalidate the iterator
			++i;
			// no need to do anything with peers that
			// already are interested. Gaining a piece may
			// only make uninteresting peers interesting again.
			if (p->is_interesting()) continue;
			p->update_interest();
			if (!m_abort)

save the send_stats state instead of throwing them away it may pose an issue when downgrading though

../src/torrent.cpp:7227

					for (int k = 0; k < bits; ++k)
						v |= (info[j*8+k].state == piece_picker::block_info::state_finished)
						? (1 << k) : 0;
					bitmask.append(1, v);
					TORRENT_ASSERT(bits == 8 || j == num_bitmask_bytes - 1);
				}
				piece_struct["bitmask"] = bitmask;
				// push the struct onto the unfinished-piece list
				up.push_back(piece_struct);
			}
		}

		// save trackers
		entry::list_type& tr_list = ret["trackers"].list();
		tr_list.push_back(entry::list_type());
		int tier = 0;
		for (std::vector<announce_entry>::const_iterator i = m_trackers.begin()
			, end(m_trackers.end()); i != end; ++i)
		{
			// don't save trackers we can't trust
			if (i->send_stats == false) continue;
			if (i->tier == tier)
			{
				tr_list.back().list().push_back(i->url);
			}
			else
			{
				tr_list.push_back(entry::list_t);
				tr_list.back().list().push_back(i->url);
				tier = i->tier;
			}
		}

		// save web seeds
		if (!m_web_seeds.empty())
		{
			entry::list_type& url_list = ret["url-list"].list();
			entry::list_type& httpseed_list = ret["httpseeds"].list();
			for (std::list<web_seed_t>::const_iterator i = m_web_seeds.begin()
				, end(m_web_seeds.end()); i != end; ++i)
			{
				if (i->removed) continue;
				if (i->type == web_seed_entry::url_seed)
					url_list.push_back(i->url);
				else if (i->type == web_seed_entry::http_seed)
					httpseed_list.push_back(i->url);
			}
		}

		// write have bitmask
		// the pieces string has one byte per piece. Each

should disconnect all peers that have the pieces we have not just seeds. It would be pretty expensive to check all pieces for all peers though

../src/torrent.cpp:8471

		set_state(torrent_status::finished);
		set_queue_position(-1);

		m_became_finished = m_ses.session_time();

		// we have to call completed() before we start
		// disconnecting peers, since there's an assert
		// to make sure we're cleared the piece picker
		if (is_seed()) completed();

		send_upload_only();
		state_updated();

		if (m_completed_time == 0)
			m_completed_time = time(0);

		// disconnect all seeds
		if (settings().get_bool(settings_pack::close_redundant_connections))
		{
			std::vector<peer_connection*> seeds;
			for (peer_iterator i = m_connections.begin();
				i != m_connections.end(); ++i)
			{
				peer_connection* p = *i;
				TORRENT_ASSERT(p->associated_torrent().lock().get() == this);
				if (p->upload_only())
				{
#ifndef TORRENT_DISABLE_LOGGING
					p->peer_log(peer_log_alert::info, "SEED", "CLOSING CONNECTION");
#endif
					seeds.push_back(p);
				}
			}
			std::for_each(seeds.begin(), seeds.end()
				, boost::bind(&peer_connection::disconnect, _1, errors::torrent_finished
				, op_bittorrent, 0));
		}

		if (m_abort) return;

		update_want_peers();

		if (m_storage)
		{
			// we need to keep the object alive during this operation
			inc_refcount("release_files");
			m_ses.disk_thread().async_release_files(m_storage.get()
				, boost::bind(&torrent::on_cache_flushed, shared_from_this(), _1));
		}

instead, have one instance per possible subnet, global IPv4, global IPv6, loopback, 192.168.x.x, 10.x.x.x, etc.

../include/libtorrent/ip_voter.hpp:124

		// away all the votes and started from scratch, in case
		// our IP has changed
		time_point m_last_rotate;
	};

	// this keeps track of multiple external IPs (for now, just IPv6 and IPv4, but
	// it could be extended to deal with loopback and local network addresses as well)
	struct TORRENT_EXTRA_EXPORT external_ip
	{
		// returns true if a different IP is the top vote now
		// i.e. we changed our idea of what our external IP is
		bool cast_vote(address const& ip, int source_type, address const& source);

		// the external IP as it would be observed from `ip`
		address external_address(address const& ip) const;

	private:

		// for now, assume one external IPv4 and one external IPv6 address
		// 0 = IPv4 1 = IPv6
		ip_voter m_vote_group[2];
	};

}

#endif

test try_evict_blocks

../test/test_block_cache.cpp:469

test evicting volatile pieces, to see them be removed

../test/test_block_cache.cpp:470

test evicting dirty pieces

../test/test_block_cache.cpp:471

test free_piece

../test/test_block_cache.cpp:472

test abort_dirty

../test/test_block_cache.cpp:473

test unaligned reads

../test/test_block_cache.cpp:474

	// it's supposed to be a cache hit
	TEST_CHECK(ret >= 0);
	// return the reference to the buffer we just read
	RETURN_BUFFER;

	tailqueue<disk_io_job> jobs;
	bc.clear(jobs);
}

TORRENT_TEST(block_cache)
{
	test_write();
	test_flush();
	test_insert();
	test_evict();
	test_arc_promote();
	test_arc_unghost();
	test_iovec();
	test_unaligned_read();

}

test size()

../test/test_bloom_filter.cpp:130

test clear()

../test/test_bloom_filter.cpp:131

	TEST_EQUAL(memcmp(bits_out.c_str(), bits, 4), 0);

	sha1_hash k( "\x01\x00\x02\x00                ");
	TEST_CHECK(!filter.find(k));
	filter.set(k);
	TEST_CHECK(filter.find(k));

	boost::uint8_t compare[4] = { 0x16, 0xff, 0x55, 0xaa};

	bits_out = filter.to_string();
	TEST_EQUAL(memcmp(compare, bits_out.c_str(), 4), 0);
}

TORRENT_TEST(bloom_filter)
{
	test_set_and_get();
	test_set_bits();
	test_count_zeroes();
	test_to_from_string();

}

ideally the mock_socket would contain this queue of packets, to make tests independent

../test/test_dht.cpp:103

		carry = sum > 255;
	}
}

void node_push_back(void* userdata, libtorrent::dht::node_entry const& n)
{
	using namespace libtorrent::dht;
	std::vector<node_entry>* nv = (std::vector<node_entry>*)userdata;
	nv->push_back(n);
}

static void nop(void* userdata, libtorrent::dht::node_entry const& n) {}

std::list<std::pair<udp::endpoint, entry> > g_sent_packets;

struct mock_socket : udp_socket_interface
{
	bool has_quota() { return true; }
	bool send_packet(entry& msg, udp::endpoint const& ep, int flags)
	{
		g_sent_packets.push_back(std::make_pair(ep, msg));
		return true;
	}
};

sha1_hash generate_next()
{
	sha1_hash ret;
	for (int i = 0; i < 20; ++i) ret[i] = rand() & 0xff;
	return ret;
}

boost::array<char, 64> generate_key()
{
	boost::array<char, 64> ret;
	for (int i = 0; i < 64; ++i) ret[i] = rand() & 0xff;
	return ret;
}

static const std::string no;

std::list<std::pair<udp::endpoint, entry> >::iterator
find_packet(udp::endpoint ep)
{
	return std::find_if(g_sent_packets.begin(), g_sent_packets.end()
		, boost::bind(&std::pair<udp::endpoint, entry>::first, _1) == ep);
}

void lazy_from_entry(entry const& e, bdecode_node& l)
{
	error_code ec;

check to make sure the "best" items are stored

../test/test_dht.cpp:420

		key_desc_t desc[] =
		{
			{ "r", bdecode_node::dict_t, 0, key_desc_t::parse_children },
				{ "v", bdecode_node::dict_t, 0, 0},
				{ "id", bdecode_node::string_t, 20, key_desc_t::last_child},
			{ "y", bdecode_node::string_t, 1, 0},
		};

		bdecode_node parsed[4];
		char error_string[200];

		int ret = verify_message(response, desc, parsed, error_string
			, sizeof(error_string));
		if (ret)
		{
			items_num.insert(items_num.begin(), j);
		}
	}

	TEST_EQUAL(items_num.size(), 4);
}

int sum_distance_exp(int s, node_entry const& e, node_id const& ref)
{
	return s + distance_exp(e.id, ref);
}

std::vector<tcp::endpoint> g_got_peers;

void get_peers_cb(std::vector<tcp::endpoint> const& peers)
{
	g_got_peers.insert(g_got_peers.end(), peers.begin(), peers.end());
}

std::vector<dht::item> g_got_items;
dht::item g_put_item;
int g_put_count;

void get_mutable_item_cb(dht::item const& i, bool a)
{
	if (!a) return;
	if (!i.empty())
		g_got_items.push_back(i);
}

void put_mutable_item_data_cb(dht::item& i)
{
	if (!i.empty())
		g_got_items.push_back(i);

test obfuscated_get_peers

../test/test_dht.cpp:513

test sending invalid requests (out of bound piece index, offsets and sizes)

../test/test_fast_extension.cpp:880

	sha1_hash ih;
	boost::shared_ptr<lt::session> ses;
	io_service ios;
	tcp::socket s(ios);
	setup_peer(s, ih, ses);

	char recv_buffer[1000];
	do_handshake(s, ih, recv_buffer);
	print_session_log(*ses);
	send_have_none(s);

	peer_request req;
	req.piece = 124134235;
	req.start = 0;
	req.length = 0x4000;
	send_request(s, req);
}

#endif // TORRENT_DISABLE_EXTENSIONS

test the update function too

../test/test_file_progress.cpp:109

	for (int idx = 0; idx < fs.num_pieces(); ++idx)
	{
		piece_picker picker;
		picker.init(4, fs.total_size() % 4, fs.num_pieces());
		picker.we_have(idx);

		std::vector<boost::int64_t> vec;
		aux::file_progress fp;

		fp.init(picker, fs);
		fp.export_progress(vec);

		boost::uint64_t sum = 0;
		for (int i = 0; i < int(vec.size()); ++i)
			sum += vec[i];

		TEST_EQUAL(int(sum), fs.piece_size(idx));
	}
}

test file_storage::optimize

../test/test_file_storage.cpp:214

test map_block

../test/test_file_storage.cpp:215

test piece_size(int piece)

../test/test_file_storage.cpp:216

test file_index_at_offset

../test/test_file_storage.cpp:217

test file attributes

../test/test_file_storage.cpp:218

test symlinks

../test/test_file_storage.cpp:219

test pad_files

../test/test_file_storage.cpp:220

test reorder_file (make sure internal_file_entry::swap() is used)

../test/test_file_storage.cpp:221

	TEST_EQUAL(rq.start, 298);
	TEST_EQUAL(rq.length, 841);
}

TORRENT_TEST(file_path_hash)
{
	// test file_path_hash and path_hash. Make sure we can detect a path
	// whose name collides with
	file_storage fs;
	fs.set_piece_length(512);
	fs.add_file(combine_path("temp_storage", "Foo"), 17);
	fs.add_file(combine_path("temp_storage", "foo"), 612);

	fprintf(stderr, "path: %s\n", fs.file_path(0).c_str());
	fprintf(stderr, "file: %s\n", fs.file_path(1).c_str());
	boost::uint32_t file_hash0 = fs.file_path_hash(0, "a");
	boost::uint32_t file_hash1 = fs.file_path_hash(1, "a");
	TEST_EQUAL(file_hash0, file_hash1);
}

test erasing peers

../test/test_peer_list.cpp:939

test update_peer_port with allow_multiple_connections_per_ip and without

../test/test_peer_list.cpp:940

test add i2p peers

../test/test_peer_list.cpp:941

test allow_i2p_mixed

../test/test_peer_list.cpp:942

test insert_peer failing with all error conditions

../test/test_peer_list.cpp:943

test IPv6

../test/test_peer_list.cpp:944

test connect_to_peer() failing

../test/test_peer_list.cpp:945

test connection_closed

../test/test_peer_list.cpp:946

connect candidates recalculation when incrementing failcount

../test/test_peer_list.cpp:947

	torrent_peer* peer4 = add_peer(p, st, ep("10.0.0.4", 8080));
	TEST_CHECK(peer4);
	TEST_EQUAL(p.num_peers(), 4);
	torrent_peer* peer5 = add_peer(p, st, ep("10.0.0.5", 8080));
	TEST_CHECK(peer5);
	TEST_EQUAL(p.num_peers(), 5);
	torrent_peer* peer6 = p.add_peer(ep("10.0.0.6", 8080), 0, 0, &st);
	TEST_CHECK(peer6 == NULL);
	TEST_EQUAL(p.num_peers(), 5);

	// one of the connection should have been removed
	TEST_EQUAL(has_peer(p, ep("10.0.0.1", 8080))
		+ has_peer(p, ep("10.0.0.2", 8080))
		+ has_peer(p, ep("10.0.0.3", 8080))
		+ has_peer(p, ep("10.0.0.4", 8080))
		+ has_peer(p, ep("10.0.0.5", 8080))
		+ has_peer(p, ep("10.0.0.6", 8080))
		, 5);
}

test files with different piece size (negative test)

../test/test_resolve_links.cpp:80

	{ "test2", "test1_pad_files", 0},
	{ "test3", "test1_pad_files", 0},
	{ "test2", "test1_single", 0},

	// these are all padded. The first small file will accidentally also
	// match, even though it's not tail padded, the following file is identical
	{ "test2_pad_files", "test1_pad_files", 2},
	{ "test3_pad_files", "test1_pad_files", 2},
	{ "test3_pad_files", "test2_pad_files", 2},
	{ "test1_pad_files", "test2_pad_files", 2},
	{ "test1_pad_files", "test3_pad_files", 2},
	{ "test2_pad_files", "test3_pad_files", 2},

	// one might expect this to work, but since the tail of the single file
	// torrent is not padded, the last piece hash won't match
	{ "test1_pad_files", "test1_single", 0},

	// if it's padded on the other hand, it will work
	{ "test1_pad_files", "test1_single_padded", 1},

};

it would be nice to test resolving of more than just 2 files as well. like 3 single file torrents merged into one, resolving all 3 files.

../test/test_resolve_links.cpp:83

	{ "test2", "test1_single", 0},

	// these are all padded. The first small file will accidentally also
	// match, even though it's not tail padded, the following file is identical
	{ "test2_pad_files", "test1_pad_files", 2},
	{ "test3_pad_files", "test1_pad_files", 2},
	{ "test3_pad_files", "test2_pad_files", 2},
	{ "test1_pad_files", "test2_pad_files", 2},
	{ "test1_pad_files", "test3_pad_files", 2},
	{ "test2_pad_files", "test3_pad_files", 2},

	// one might expect this to work, but since the tail of the single file
	// torrent is not padded, the last piece hash won't match
	{ "test1_pad_files", "test1_single", 0},

	// if it's padded on the other hand, it will work
	{ "test1_pad_files", "test1_single_padded", 1},

};


TORRENT_TEST(resolve_links)
{

#ifndef TORRENT_DISABLE_MUTABLE_TORRENTS
	std::string path = combine_path(parent_path(current_working_directory())
		, "mutable_test_torrents");

	for (int i = 0; i < int(sizeof(test_torrents)/sizeof(test_torrents[0])); ++i)
	{
		test_torrent_t const& e = test_torrents[i];

		std::string p = combine_path(path, e.filename1) + ".torrent";
		fprintf(stderr, "loading %s\n", p.c_str());
		boost::shared_ptr<torrent_info> ti1 = boost::make_shared<torrent_info>(p);

		p = combine_path(path, e.filename2) + ".torrent";
		fprintf(stderr, "loading %s\n", p.c_str());
		boost::shared_ptr<torrent_info> ti2 = boost::make_shared<torrent_info>(p);

		fprintf(stderr, "resolving\n");
		resolve_links l(ti1);
		l.match(ti2, ".");

		std::vector<resolve_links::link_t> const& links = l.get_links();

		int num_matches = std::count_if(links.begin(), links.end()
			, boost::bind(&resolve_links::link_t::ti, _1));

		// some debug output in case the test fails
		if (num_matches > e.expected_matches)

test what happens when loading a resume file with both piece priorities and file priorities (file prio should take presedence)

../test/test_resume.cpp:232

		fprintf(stderr, "%s\n", ra->resume_data->to_string().c_str());
		entry::string_type prios = (*ra->resume_data)["piece_priority"].string();
		TEST_EQUAL(int(prios.size()), ti->num_pieces());
		TEST_EQUAL(prios[0], '\0');
		TEST_EQUAL(prios[1], '\x04');
		TEST_EQUAL(prios[ti->num_pieces()-1], '\0');

		bencode(std::back_inserter(p.resume_data), *ra->resume_data);
	}

	ses.remove_torrent(h);

	// now, make sure the piece priorities are loaded correctly
	h = ses.add_torrent(p);

	TEST_EQUAL(h.piece_priority(0), 0);
	TEST_EQUAL(h.piece_priority(1), 4);
	TEST_EQUAL(h.piece_priority(ti->num_pieces()-1), 0);
}

make sure a resume file only ever contain file priorities OR piece priorities. Never both.

../test/test_resume.cpp:235

		entry::string_type prios = (*ra->resume_data)["piece_priority"].string();
		TEST_EQUAL(int(prios.size()), ti->num_pieces());
		TEST_EQUAL(prios[0], '\0');
		TEST_EQUAL(prios[1], '\x04');
		TEST_EQUAL(prios[ti->num_pieces()-1], '\0');

		bencode(std::back_inserter(p.resume_data), *ra->resume_data);
	}

	ses.remove_torrent(h);

	// now, make sure the piece priorities are loaded correctly
	h = ses.add_torrent(p);

	TEST_EQUAL(h.piece_priority(0), 0);
	TEST_EQUAL(h.piece_priority(1), 4);
	TEST_EQUAL(h.piece_priority(ti->num_pieces()-1), 0);
}

generally save

../test/test_resume.cpp:238

		TEST_EQUAL(int(prios.size()), ti->num_pieces());
		TEST_EQUAL(prios[0], '\0');
		TEST_EQUAL(prios[1], '\x04');
		TEST_EQUAL(prios[ti->num_pieces()-1], '\0');

		bencode(std::back_inserter(p.resume_data), *ra->resume_data);
	}

	ses.remove_torrent(h);

	// now, make sure the piece priorities are loaded correctly
	h = ses.add_torrent(p);

	TEST_EQUAL(h.piece_priority(0), 0);
	TEST_EQUAL(h.piece_priority(1), 4);
	TEST_EQUAL(h.piece_priority(ti->num_pieces()-1), 0);
}




TORRENT_TEST(file_priorities_default)
{
	lt::session ses;
	std::vector<int> file_priorities = test_resume_flags(ses, 0, "", "").file_priorities();

	TEST_EQUAL(file_priorities.size(), 3);
	TEST_EQUAL(file_priorities[0], 4);
	TEST_EQUAL(file_priorities[1], 4);
	TEST_EQUAL(file_priorities[2], 4);
}

TORRENT_TEST(file_priorities_resume_seed_mode)
{
	// in share mode file priorities should always be 0
	lt::session ses;
	std::vector<int> file_priorities = test_resume_flags(ses,
		add_torrent_params::flag_share_mode, "", "123").file_priorities();

	TEST_EQUAL(file_priorities.size(), 3);
	TEST_EQUAL(file_priorities[0], 0);
	TEST_EQUAL(file_priorities[1], 0);
	TEST_EQUAL(file_priorities[2], 0);
}

TORRENT_TEST(file_priorities_seed_mode)
{
	// in share mode file priorities should always be 0
	lt::session ses;
	std::vector<int> file_priorities = test_resume_flags(ses,
		add_torrent_params::flag_share_mode, "123", "").file_priorities();

test all other resume flags here too. This would require returning more than just the torrent_status from test_resume_flags. Also http seeds and trackers for instance

../test/test_resume.cpp:695

	lt::session ses;
	// resume data overrides the paused flag
	torrent_status s = test_resume_flags(ses, add_torrent_params::flag_paused).status();
	default_tests(s);
#ifdef TORRENT_WINDOWS
	TEST_EQUAL(s.save_path, "c:\\add_torrent_params save_path");
#else
	TEST_EQUAL(s.save_path, "/add_torrent_params save_path");
#endif
	TEST_EQUAL(s.sequential_download, false);
	TEST_EQUAL(s.paused, false);
	TEST_EQUAL(s.auto_managed, false);
	TEST_EQUAL(s.seed_mode, false);
	TEST_EQUAL(s.super_seeding, false);
	TEST_EQUAL(s.share_mode, false);
	TEST_EQUAL(s.upload_mode, false);
	TEST_EQUAL(s.ip_filter_applies, false);
	TEST_EQUAL(s.connections_limit, 1345);
	TEST_EQUAL(s.uploads_limit, 1346);

}

TORRENT_TEST(url_seed_resume_data)
{
	// merge url seeds with resume data
	fprintf(stderr, "flags: merge_resume_http_seeds\n");
	lt::session ses;
	torrent_handle h = test_resume_flags(ses,
		add_torrent_params::flag_merge_resume_http_seeds);
	std::set<std::string> us = h.url_seeds();
	std::set<std::string> ws = h.http_seeds();

	TEST_EQUAL(us.size(), 3);
	TEST_EQUAL(std::count(us.begin(), us.end()
		, "http://add_torrent_params_url_seed.com"), 1);
	TEST_EQUAL(std::count(us.begin(), us.end()
		, "http://torrent_file_url_seed.com/"), 1);
	TEST_EQUAL(std::count(us.begin(), us.end()
		, "http://resume_data_url_seed.com/"), 1);

	TEST_EQUAL(ws.size(), 1);
	TEST_EQUAL(std::count(ws.begin(), ws.end()
		, "http://resume_data_http_seed.com"), 1);
}

TORRENT_TEST(resume_override_torrent)
{
	// resume data overrides the .torrent_file
	fprintf(stderr, "flags: no merge_resume_http_seed\n");
	lt::session ses;
	torrent_handle h = test_resume_flags(ses,

load_pack_from_dict

../test/test_settings_pack.cpp:140

	TEST_EQUAL(pack.get_bool(settings_pack::send_redundant_have), true);

	pack.clear();

	TEST_EQUAL(pack.has_val(settings_pack::send_redundant_have), false);
	TEST_EQUAL(pack.has_val(settings_pack::user_agent), false);
	TEST_EQUAL(pack.has_val(settings_pack::lazy_bitfields), false);
}

TORRENT_TEST(duplicates)
{
	settings_pack p;
	p.set_str(settings_pack::peer_fingerprint, "abc");
	p.set_str(settings_pack::peer_fingerprint, "cde");
	p.set_str(settings_pack::peer_fingerprint, "efg");
	p.set_str(settings_pack::peer_fingerprint, "hij");

	TEST_EQUAL(p.get_str(settings_pack::peer_fingerprint), "hij");
}

test using a signed certificate with the wrong info-hash in DN

../test/test_ssl.cpp:394

	// in verifying peers
	ctx.set_verify_mode(context::verify_none, ec);
	if (ec)
	{
		fprintf(stderr, "Failed to set SSL verify mode: %s\n"
			, ec.message().c_str());
		TEST_CHECK(!ec);
		return false;
	}

	std::string certificate = combine_path("..", combine_path("ssl", "peer_certificate.pem"));
	std::string private_key = combine_path("..", combine_path("ssl", "peer_private_key.pem"));
	std::string dh_params = combine_path("..", combine_path("ssl", "dhparams.pem"));

	if (flags & invalid_certificate)
	{
		certificate = combine_path("..", combine_path("ssl", "invalid_peer_certificate.pem"));
		private_key = combine_path("..", combine_path("ssl", "invalid_peer_private_key.pem"));
	}


	if (flags & (valid_certificate | invalid_certificate))
	{
		fprintf(stderr, "set_password_callback\n");
		ctx.set_password_callback(boost::bind(&password_callback, _1, _2, "test"), ec);
		if (ec)
		{
			fprintf(stderr, "Failed to set certificate password callback: %s\n"
				, ec.message().c_str());
			TEST_CHECK(!ec);
			return false;
		}
		fprintf(stderr, "use_certificate_file \"%s\"\n", certificate.c_str());
		ctx.use_certificate_file(certificate, context::pem, ec);
		if (ec)
		{
			fprintf(stderr, "Failed to set certificate file: %s\n"
				, ec.message().c_str());
			TEST_CHECK(!ec);
			return false;
		}
		fprintf(stderr, "use_private_key_file \"%s\"\n", private_key.c_str());
		ctx.use_private_key_file(private_key, context::pem, ec);
		if (ec)
		{
			fprintf(stderr, "Failed to set private key: %s\n"
				, ec.message().c_str());
			TEST_CHECK(!ec);
			return false;
		}
		fprintf(stderr, "use_tmp_dh_file \"%s\"\n", dh_params.c_str());

also test using a hash that refers to a valid torrent but that differs from the SNI hash

../test/test_ssl.cpp:492

	print_alerts(ses1, "ses1", true, true, true, &on_alert);
	if (ec)
	{
		fprintf(stderr, "Failed SSL handshake: %s\n"
			, ec.message().c_str());
		return false;
	}

	char handshake[] = "\x13" "BitTorrent protocol\0\0\0\0\0\0\0\x04"
		"                    " // space for info-hash
		"aaaaaaaaaaaaaaaaaaaa" // peer-id
		"\0\0\0\x01\x02"; // interested

	// fill in the info-hash
	if (flags & valid_bittorrent_hash)
	{
		std::memcpy(handshake + 28, &t->info_hash()[0], 20);
	}
	else
	{
		std::generate(handshake + 28, handshake + 48, &rand);
	}

	// fill in the peer-id
	std::generate(handshake + 48, handshake + 68, &rand);

	fprintf(stderr, "bittorrent handshake\n");
	boost::asio::write(ssl_sock, boost::asio::buffer(handshake, (sizeof(handshake) - 1)), ec);
	print_alerts(ses1, "ses1", true, true, true, &on_alert);
	if (ec)
	{
		fprintf(stderr, "failed to write bittorrent handshake: %s\n"
			, ec.message().c_str());
		return false;
	}

	char buf[68];
	fprintf(stderr, "read bittorrent handshake\n");
	boost::asio::read(ssl_sock, boost::asio::buffer(buf, sizeof(buf)), ec);
	print_alerts(ses1, "ses1", true, true, true, &on_alert);
	if (ec)
	{
		fprintf(stderr, "failed to read bittorrent handshake: %s\n"
			, ec.message().c_str());
		return false;
	}

	if (memcmp(buf, "\x13" "BitTorrent protocol", 20) != 0)
	{
		fprintf(stderr, "invalid bittorrent handshake\n");
		return false;

test the case where we have > 120 samples (and have the base delay actually be updated)

../test/test_timestamp_history.cpp:54

test the case where a sample is lower than the history entry but not lower than the base

../test/test_timestamp_history.cpp:55

#include "libtorrent/timestamp_history.hpp"

TORRENT_TEST(timestamp_history)
{
	using namespace libtorrent;

	timestamp_history h;
	TEST_EQUAL(h.add_sample(0x32, false), 0);
	TEST_EQUAL(h.base(), 0x32);
	TEST_EQUAL(h.add_sample(0x33, false), 0x1);
	TEST_EQUAL(h.base(), 0x32);
	TEST_EQUAL(h.add_sample(0x3433, false), 0x3401);
	TEST_EQUAL(h.base(), 0x32);
	TEST_EQUAL(h.add_sample(0x30, false), 0);
	TEST_EQUAL(h.base(), 0x30);

	// test that wrapping of the timestamp is properly handled
	h.add_sample(0xfffffff3, false);
	TEST_EQUAL(h.base(), 0xfffffff3);

}

wait for an alert rather than just waiting 10 seconds. This is kind of silly

../test/test_torrent.cpp:135

			TEST_EQUAL(int(h.file_priorities().size()), info->num_files());
			TEST_EQUAL(h.file_priorities()[0], 0);
			if (info->num_files() > 1)
				TEST_EQUAL(h.file_priorities()[1], 0);
			if (info->num_files() > 2)
				TEST_EQUAL(h.file_priorities()[2], 1);
		}
	}

	if (info->num_pieces() > 0)
	{
		h.piece_priority(0, 1);
		st = h.status();
		TEST_CHECK(st.pieces.size() > 0 && st.pieces[0] == false);
		std::vector<char> piece(info->piece_length());
		for (int i = 0; i < int(piece.size()); ++i)
			piece[i] = (i % 26) + 'A';
		h.add_piece(0, &piece[0]);

		// wait until the piece is done writing and hashing
		test_sleep(2000);
		st = h.status();
		TEST_CHECK(st.pieces.size() > 0 && st.pieces[0] == true);

		std::cout << "reading piece 0" << std::endl;
		h.read_piece(0);
		alert const* a = wait_for_alert(ses, read_piece_alert::alert_type, "read_piece");
		TEST_CHECK(a);
		read_piece_alert const* rpa = alert_cast<read_piece_alert>(a);
		TEST_CHECK(rpa);
		if (rpa)
		{
			std::cout << "SUCCEEDED!" << std::endl;
			TEST_CHECK(memcmp(&piece[0], rpa->buffer.get(), piece.size()) == 0);
			TEST_CHECK(rpa->size == info->piece_size(0));
			TEST_CHECK(rpa->piece == 0);
			TEST_CHECK(hasher(&piece[0], piece.size()).final() == info->hash_for_piece(0));
		}
	}
}

TORRENT_TEST(long_names)
{
	entry info;
	info["pieces"] = "aaaaaaaaaaaaaaaaaaaa";
	info["name"] = "slightly shorter name, it's kind of sad that people started the trend of incorrectly encoding the regular name field and then adding another one with correct encoding";
	info["name.utf-8"] = "this is a long ass name in order to try to make make_magnet_uri overflow and hopefully crash. Although, by the time you read this that particular bug should have been fixed";
	info["piece length"] = 16 * 1024;
	info["length"] = 3245;
	entry torrent;
	torrent["info"] = info;

test remap_files

../test/test_torrent_info.cpp:156

merkle torrents. specifically torrent_info::add_merkle_nodes and torrent with "root hash"

../test/test_torrent_info.cpp:157

torrent with 'p' (padfile) attribute

../test/test_torrent_info.cpp:158

torrent with 'h' (hidden) attribute

../test/test_torrent_info.cpp:159

torrent with 'x' (executable) attribute

../test/test_torrent_info.cpp:160

torrent with 'l' (symlink) attribute

../test/test_torrent_info.cpp:161

creating a merkle torrent (torrent_info::build_merkle_list)

../test/test_torrent_info.cpp:162

torrent with multiple trackers in multiple tiers, making sure we shuffle them (how do you test shuffling?, load it multiple times and make sure it's in different order at least once)

../test/test_torrent_info.cpp:163

torrents with a missing name

../test/test_torrent_info.cpp:164

torrents with a zero-length name

../test/test_torrent_info.cpp:165

torrents with a merkle tree and add_merkle_nodes

../test/test_torrent_info.cpp:166

torrent with a non-dictionary info-section

../test/test_torrent_info.cpp:167

torrents with DHT nodes

../test/test_torrent_info.cpp:168

torrent with url-list as a single string

../test/test_torrent_info.cpp:169

torrent with http seed as a single string

../test/test_torrent_info.cpp:170

torrent with a comment

../test/test_torrent_info.cpp:171

torrent with an SSL cert

../test/test_torrent_info.cpp:172

torrent with attributes (executable and hidden)

../test/test_torrent_info.cpp:173

torrent_info::add_tracker

../test/test_torrent_info.cpp:174

torrent_info::unload

../test/test_torrent_info.cpp:175

torrent_info constructor that takes an invalid bencoded buffer

../test/test_torrent_info.cpp:176

verify_encoding with a string that triggers character replacement

../test/test_torrent_info.cpp:177

test_failing_torrent_t test_error_torrents[] =
{
	{ "missing_piece_len.torrent", errors::torrent_missing_piece_length },
	{ "invalid_piece_len.torrent", errors::torrent_missing_piece_length },
	{ "negative_piece_len.torrent", errors::torrent_missing_piece_length },
	{ "no_name.torrent", errors::torrent_missing_name },
	{ "invalid_name.torrent", errors::torrent_missing_name },
	{ "invalid_info.torrent", errors::torrent_missing_info },
	{ "string.torrent", errors::torrent_is_no_dict },
	{ "negative_size.torrent", errors::torrent_invalid_length },
	{ "negative_file_size.torrent", errors::torrent_invalid_length },
	{ "invalid_path_list.torrent", errors::torrent_missing_name},
	{ "missing_path_list.torrent", errors::torrent_missing_name },
	{ "invalid_pieces.torrent", errors::torrent_missing_pieces },
	{ "unaligned_pieces.torrent", errors::torrent_invalid_hashes },
	{ "invalid_root_hash.torrent", errors::torrent_invalid_hashes },
	{ "invalid_root_hash2.torrent", errors::torrent_missing_pieces },
	{ "invalid_file_size.torrent", errors::torrent_invalid_length },
};


TORRENT_TEST(add_url_seed)
{
	torrent_info ti(sha1_hash("                   "));
	TEST_EQUAL(ti.web_seeds().size(), 0);

	ti.add_url_seed("http://test.com");

	TEST_EQUAL(ti.web_seeds().size(), 1);
	web_seed_entry we = ti.web_seeds()[0];
	TEST_EQUAL(we.type, web_seed_entry::url_seed);
	TEST_EQUAL(we.url, "http://test.com");
}

TORRENT_TEST(add_http_seed)
{
	torrent_info ti(sha1_hash("                   "));
	TEST_EQUAL(ti.web_seeds().size(), 0);

	ti.add_http_seed("http://test.com");

	TEST_EQUAL(ti.web_seeds().size(), 1);
	web_seed_entry we = ti.web_seeds()[0];
	TEST_EQUAL(we.type, web_seed_entry::http_seed);
	TEST_EQUAL(we.url, "http://test.com");
}

TORRENT_TEST(set_web_seeds)
{
	torrent_info ti(sha1_hash("                   "));
	TEST_EQUAL(ti.web_seeds().size(), 0);

test scrape requests

../test/test_tracker.cpp:53

test parse peers6

../test/test_tracker.cpp:54

test parse tracker-id

../test/test_tracker.cpp:55

test parse failure-reason

../test/test_tracker.cpp:56

test all failure paths, including invalid bencoding not a dictionary no files entry in scrape response no info-hash entry in scrape response malformed peers in peer list of dictionaries uneven number of bytes in peers and peers6 string responses

../test/test_tracker.cpp:57

#include "test.hpp"
#include "setup_transfer.hpp"
#include "udp_tracker.hpp"
#include "settings.hpp"
#include "libtorrent/alert.hpp"
#include "libtorrent/peer_info.hpp" // for peer_list_entry
#include "libtorrent/broadcast_socket.hpp" // for supports_ipv6
#include "libtorrent/alert_types.hpp"
#include "libtorrent/session.hpp"
#include "libtorrent/error_code.hpp"
#include "libtorrent/tracker_manager.hpp"
#include "libtorrent/http_tracker_connection.hpp" // for parse_tracker_response
#include "libtorrent/torrent_info.hpp"
#include "libtorrent/announce_entry.hpp"

#include <fstream>

using namespace libtorrent;
namespace lt = libtorrent;


TORRENT_TEST(parse_hostname_peers)
{
	char const response[] = "d5:peersld7:peer id20:aaaaaaaaaaaaaaaaaaaa2:ip13:test_hostname4:porti1000eed7:peer id20:bbbbabaababababababa2:ip12:another_host4:porti1001eeee";
	error_code ec;
	tracker_response resp = parse_tracker_response(response, sizeof(response) - 1
		, ec, false, sha1_hash());

	TEST_EQUAL(ec, error_code());
	TEST_EQUAL(resp.peers.size(), 2);
	if (resp.peers.size() == 2)
	{
		peer_entry const& e0 = resp.peers[0];
		peer_entry const& e1 = resp.peers[1];
		TEST_EQUAL(e0.hostname, "test_hostname");
		TEST_EQUAL(e0.port, 1000);
		TEST_EQUAL(e0.pid, peer_id("aaaaaaaaaaaaaaaaaaaa"));

		TEST_EQUAL(e1.hostname, "another_host");
		TEST_EQUAL(e1.port, 1001);
		TEST_EQUAL(e1.pid, peer_id("bbbbabaababababababa"));
	}
}

TORRENT_TEST(parse_peers4)
{
	char const response[] = "d5:peers12:\x01\x02\x03\x04\x30\x10"
		"\x09\x08\x07\x06\x20\x10" "e";
	error_code ec;
	tracker_response resp = parse_tracker_response(response, sizeof(response) - 1
		, ec, false, sha1_hash());

these settings_pack tests belong in their own test

../test/test_transfer.cpp:215

	pack.set_int(settings_pack::min_reconnect_time, 0);
	pack.set_int(settings_pack::stop_tracker_timeout, 1);
	pack.set_bool(settings_pack::announce_to_all_trackers, true);
	pack.set_bool(settings_pack::announce_to_all_tiers, true);

	// make sure we announce to both http and udp trackers
	pack.set_bool(settings_pack::prefer_udp_trackers, false);
	pack.set_bool(settings_pack::enable_outgoing_utp, false);
	pack.set_bool(settings_pack::enable_incoming_utp, false);
	pack.set_bool(settings_pack::enable_lsd, false);
	pack.set_bool(settings_pack::enable_natpmp, false);
	pack.set_bool(settings_pack::enable_upnp, false);
	pack.set_bool(settings_pack::enable_dht, false);
	pack.set_int(settings_pack::alert_mask, mask);

	pack.set_int(settings_pack::out_enc_policy, settings_pack::pe_disabled);
	pack.set_int(settings_pack::in_enc_policy, settings_pack::pe_disabled);

	pack.set_bool(settings_pack::allow_multiple_connections_per_ip, false);

	pack.set_int(settings_pack::unchoke_slots_limit, 0);
	ses1.apply_settings(pack);
	TEST_CHECK(ses1.get_settings().get_int(settings_pack::unchoke_slots_limit) == 0);

	pack.set_int(settings_pack::unchoke_slots_limit, -1);
	ses1.apply_settings(pack);
	TEST_CHECK(ses1.get_settings().get_int(settings_pack::unchoke_slots_limit) == -1);

	pack.set_int(settings_pack::unchoke_slots_limit, 8);
	ses1.apply_settings(pack);
	TEST_CHECK(ses1.get_settings().get_int(settings_pack::unchoke_slots_limit) == 8);

	ses2.apply_settings(pack);

	torrent_handle tor1;
	torrent_handle tor2;

	create_directory("tmp1_transfer", ec);
	std::ofstream file("tmp1_transfer/temporary");
	boost::shared_ptr<torrent_info> t = ::create_torrent(&file, "temporary", 16 * 1024, 13, false);
	file.close();

	TEST_CHECK(exists(combine_path("tmp1_transfer", "temporary")));

	add_torrent_params addp(&test_storage_constructor);
	addp.flags &= ~add_torrent_params::flag_paused;
	addp.flags &= ~add_torrent_params::flag_auto_managed;

	add_torrent_params params;
	params.storage_mode = storage_mode;
	params.flags &= ~add_torrent_params::flag_paused;

factor out the disk-full test into its own unit test

../test/test_transfer.cpp:294

		print_alerts(ses1, "ses1", true, true, true, &on_alert);
		print_alerts(ses2, "ses2", true, true, true, &on_alert);

		if (i % 10 == 0)
		{
			print_ses_rate(i / 10.f, &st1, &st2);
		}

		if (!test_move_storage && st2.progress > 0.25f)
		{
			test_move_storage = true;
			tor1.move_storage("tmp1_transfer_moved");
			tor2.move_storage("tmp2_transfer_moved");
			std::cerr << "moving storage" << std::endl;
		}

		// wait 10 loops before we restart the torrent. This lets
		// us catch all events that failed (and would put the torrent
		// back into upload mode) before we restart it.

		if (test_disk_full && st2.upload_mode && ++upload_mode_timer > 10)
		{
			test_disk_full = false;
			((test_storage*)tor2.get_storage_impl())->set_limit(16 * 1024 * 1024);

			// if we reset the upload mode too soon, there may be more disk
			// jobs failing right after, putting us back in upload mode. So,
			// give the disk some time to fail all disk jobs before resetting
			// upload mode to false
			test_sleep(500);

			// then we need to drain the alert queue, so the peer_disconnects
			// counter doesn't get incremented by old alerts
			print_alerts(ses1, "ses1", true, true, true, &on_alert);
			print_alerts(ses2, "ses2", true, true, true, &on_alert);

			lt::error_code err = tor2.status().errc;
			fprintf(stderr, "error: \"%s\"\n", err.message().c_str());
			TEST_CHECK(!err);
			tor2.set_upload_mode(false);

			// at this point we probably disconnected the seed
			// so we need to reconnect as well
			fprintf(stderr, "%s: reconnecting peer\n", time_now_string());
			error_code ec;
			tor2.connect_peer(tcp::endpoint(address::from_string("127.0.0.1", ec)
				, ses1.listen_port()));

			TEST_CHECK(tor2.status().is_finished == false);
			fprintf(stderr, "disconnects: %d\n", peer_disconnects);
			TEST_CHECK(peer_disconnects >= 2);

store the log and verify that some key messages are there

../test/test_upnp.cpp:108

		"USN:uuid:000f-66d6-7296000099dc::upnp:rootdevice\r\n"
		"Location: http://127.0.0.1:%d/upnp.xml\r\n"
		"Server: Custom/1.0 UPnP/1.0 Proc/Ver\r\n"
		"EXT:\r\n"
		"Cache-Control:max-age=180\r\n"
		"DATE: Fri, 02 Jan 1970 08:10:38 GMT\r\n\r\n";

	TORRENT_ASSERT(g_port != 0);
	char buf[sizeof(msg) + 30];
	int len = snprintf(buf, sizeof(buf), msg, g_port);

	error_code ec;
	sock->send(buf, len, ec);

	if (ec) std::cerr << "*** error sending " << ec.message() << std::endl;
}

void log_callback(char const* err)
{
	std::cerr << "UPnP: " << err << std::endl;
}

struct callback_info
{
	int mapping;
	int port;
	error_code ec;
	bool operator==(callback_info const& e)
	{ return mapping == e.mapping && port == e.port && !ec == !e.ec; }
};

std::list<callback_info> callbacks;

void callback(int mapping, address const& ip, int port, error_code const& err)
{
	callback_info info = {mapping, port, err};
	callbacks.push_back(info);
	std::cerr << "mapping: " << mapping << ", port: " << port << ", IP: " << ip
		<< ", error: \"" << err.message() << "\"\n";
}

void run_upnp_test(char const* root_filename, char const* router_model, char const* control_name, int igd_version)
{
	libtorrent::io_service ios;

	g_port = start_web_server();

	std::vector<char> buf;
	error_code ec;
	load_file(root_filename, buf, ec);
	buf.push_back(0);

it's somewhat expensive to iterate over this linked list. Presumably because of the random access of memory. It would be nice if pieces with no evictable blocks weren't in this list

../src/block_cache.cpp:987

	}
	else if (m_last_cache_op == ghost_hit_lru1)
	{
		// when we insert new items or move things from L1 to L2
		// evict blocks from L2
		lru_list[1] = &m_lru[cached_piece_entry::read_lru2];
		lru_list[2] = &m_lru[cached_piece_entry::read_lru1];
	}
	else
	{
		// when we get cache hits in L2 evict from L1
		lru_list[1] = &m_lru[cached_piece_entry::read_lru1];
		lru_list[2] = &m_lru[cached_piece_entry::read_lru2];
	}

	// end refers to which end of the ARC cache we're evicting
	// from. The LFU or the LRU end
	for (int end = 0; num > 0 && end < 3; ++end)
	{
		// iterate over all blocks in order of last being used (oldest first) and
		for (list_iterator<cached_piece_entry> i = lru_list[end]->iterate(); i.get() && num > 0;)
		{
			cached_piece_entry* pe = reinterpret_cast<cached_piece_entry*>(i.get());
			TORRENT_PIECE_ASSERT(pe->in_use, pe);
			i.next();

			if (pe == ignore)
				continue;

			if (pe->ok_to_evict())
			{
#ifdef TORRENT_DEBUG
				for (int j = 0; j < pe->blocks_in_piece; ++j)
					TORRENT_PIECE_ASSERT(pe->blocks[j].buf == 0, pe);
#endif
				TORRENT_PIECE_ASSERT(pe->refcount == 0, pe);
				move_to_ghost(pe);
				continue;
			}

			TORRENT_PIECE_ASSERT(pe->num_dirty == 0, pe);

			// all blocks are pinned in this piece, skip it
			if (pe->num_blocks <= pe->pinned) continue;

			// go through the blocks and evict the ones that are not dirty and not
			// referenced
			for (int j = 0; j < pe->blocks_in_piece && num > 0; ++j)
			{
				cached_block_entry& b = pe->blocks[j];

this should probably only be done every n:th time

../src/block_cache.cpp:1051

			}

			if (pe->ok_to_evict())
			{
#ifdef TORRENT_DEBUG
				for (int j = 0; j < pe->blocks_in_piece; ++j)
					TORRENT_PIECE_ASSERT(pe->blocks[j].buf == 0, pe);
#endif
				move_to_ghost(pe);
			}
		}
	}

	// if we can't evict enough blocks from the read cache, also look at write
	// cache pieces for blocks that have already been written to disk and can be
	// evicted the first pass, we only evict blocks that have been hashed, the
	// second pass we flush anything this is potentially a very expensive
	// operation, since we're likely to have iterate every single block in the
	// cache, and we might not get to evict anything.

	if (num > 0 && m_read_cache_size > m_pinned_blocks)
	{
		for (int pass = 0; pass < 2 && num > 0; ++pass)
		{
			for (list_iterator<cached_piece_entry> i = m_lru[cached_piece_entry::write_lru].iterate(); i.get() && num > 0;)
			{
				cached_piece_entry* pe = reinterpret_cast<cached_piece_entry*>(i.get());
				TORRENT_PIECE_ASSERT(pe->in_use, pe);

				i.next();

				if (pe == ignore)
					continue;

				if (pe->ok_to_evict())
				{
#ifdef TORRENT_DEBUG
					for (int j = 0; j < pe->blocks_in_piece; ++j)
						TORRENT_PIECE_ASSERT(pe->blocks[j].buf == 0, pe);
#endif
					TORRENT_PIECE_ASSERT(pe->refcount == 0, pe);
					erase_piece(pe);
					continue;
				}

				// all blocks in this piece are dirty
				if (pe->num_dirty == pe->num_blocks)
					continue;

				int end = pe->blocks_in_piece;

create a holder for refcounts that automatically decrement

../src/block_cache.cpp:1810

	}

	j->buffer.disk_block = allocate_buffer("send buffer");
	if (j->buffer.disk_block == 0) return -2;

	while (size > 0)
	{
		TORRENT_PIECE_ASSERT(pe->blocks[block].buf, pe);
		int to_copy = (std::min)(block_size()
			- block_offset, size);
		std::memcpy(j->buffer.disk_block + buffer_offset
			, pe->blocks[block].buf + block_offset
			, to_copy);
		size -= to_copy;
		block_offset = 0;
		buffer_offset += to_copy;
		++block;
	}
	// we incremented the refcount for both of these blocks.
	// now decrement it.
	dec_block_refcount(pe, start_block, ref_reading);
	if (blocks_to_read == 2) dec_block_refcount(pe, start_block + 1, ref_reading);
	return j->d.io.buffer_size;
}

void block_cache::reclaim_block(block_cache_reference const& ref)
{
	cached_piece_entry* pe = find_piece(ref);
	TORRENT_ASSERT(pe);
	if (pe == NULL) return;

	TORRENT_PIECE_ASSERT(pe->in_use, pe);

	TORRENT_PIECE_ASSERT(pe->blocks[ref.block].buf, pe);
	dec_block_refcount(pe, ref.block, block_cache::ref_reading);

	TORRENT_PIECE_ASSERT(m_send_buffer_blocks > 0, pe);
	--m_send_buffer_blocks;

	maybe_free_piece(pe);
}

bool block_cache::maybe_free_piece(cached_piece_entry* pe)
{
	if (!pe->ok_to_evict()
		|| !pe->marked_for_deletion
		|| !pe->jobs.empty())
		return false;

	DLOG(stderr, "[%p] block_cache maybe_free_piece "
		"piece: %d refcount: %d marked_for_deletion: %d\n"

this could be optimized using knuth morris pratt

../src/bt_peer_connection.cpp:691

		}

		m_rc4->set_incoming_key(&remote_key[0], 20);
		m_rc4->set_outgoing_key(&local_key[0], 20);

#ifndef TORRENT_DISABLE_LOGGING
		peer_log(peer_log_alert::info, "ENCRYPTION", "computed RC4 keys");
#endif
	}

	int bt_peer_connection::get_syncoffset(char const* src, int src_size,
		char const* target, int target_size) const
	{
		TORRENT_ASSERT(target_size >= src_size);
		TORRENT_ASSERT(src_size > 0);
		TORRENT_ASSERT(src);
		TORRENT_ASSERT(target);

		int traverse_limit = target_size - src_size;

		for (int i = 0; i < traverse_limit; ++i)
		{
			char const* target_ptr = target + i;
			if (std::equal(src, src+src_size, target_ptr))
				return i;
		}

		// Partial sync
//		for (int i = 0; i < target_size; ++i)
//		{
//			// first is iterator in src[] at which mismatch occurs
//			// second is iterator in target[] at which mismatch occurs
//			std::pair<const char*, const char*> ret;
//			int src_sync_size;
//			if (i > traverse_limit) // partial sync test
//			{
//				ret = std::mismatch(src, src + src_size - (i - traverse_limit), &target[i]);
//				src_sync_size = ret.first - src;
//				if (src_sync_size == (src_size - (i - traverse_limit)))
//					return i;
//			}
//			else // complete sync test
//			{
//				ret = std::mismatch(src, src + src_size, &target[i]);
//				src_sync_size = ret.first - src;
//				if (src_sync_size == src_size)
//					return i;
//			}
//		}

		// no complete sync

if we're finished, send upload_only message

../src/bt_peer_connection.cpp:2261

		}
		peer_log(peer_log_alert::outgoing_message, "BITFIELD"
			, "%s", bitfield_string.c_str());
#endif
		m_sent_bitfield = true;

		send_buffer(reinterpret_cast<char const*>(msg), packet_size);

		stats_counters().inc_stats_counter(counters::num_outgoing_bitfield);

		if (num_lazy_pieces > 0)
		{
			for (int i = 0; i < num_lazy_pieces; ++i)
			{
#ifndef TORRENT_DISABLE_LOGGING
				peer_log(peer_log_alert::outgoing_message, "HAVE"
					, "piece: %d", lazy_pieces[i]);
#endif
				write_have(lazy_pieces[i]);
			}
		}

		if (m_supports_fast)
			send_allowed_set();
	}

#ifndef TORRENT_DISABLE_EXTENSIONS
	void bt_peer_connection::write_extensions()
	{
		INVARIANT_CHECK;

		TORRENT_ASSERT(m_supports_extensions);
		TORRENT_ASSERT(m_sent_handshake);

		entry handshake;
		entry::dictionary_type& m = handshake["m"].dict();

		// if we're using a proxy, our listen port won't be useful
		// anyway.
		if (!m_settings.get_bool(settings_pack::force_proxy) && is_outgoing())
			handshake["p"] = m_ses.listen_port();

		// only send the port in case we bade the connection
		// on incoming connections the other end already knows
		// our listen port
		if (!m_settings.get_bool(settings_pack::anonymous_mode))
		{
			handshake["v"] = m_settings.get_str(settings_pack::handshake_client_version).empty()
				? m_settings.get_str(settings_pack::user_agent)
				: m_settings.get_str(settings_pack::handshake_client_version);
		}

optimize this using partial_sort or something. We don't need to sort the entire list

../src/choker.cpp:336

			return upload_slots;
		}

		// ==== rate-based ====
		//
		// The rate based unchoker looks at our upload rate to peers, and find
		// a balance between number of upload slots and the rate we achieve. The
		// intention is to not spread upload bandwidth too thin, but also to not
		// unchoke few enough peers to not be able to saturate the up-link.
		// this is done by traversing the peers sorted by our upload rate to
		// them in decreasing rates. For each peer we increase our threshold
		// by 1 kB/s. The first peer we get to to whom we upload slower than
		// the threshold, we stop and that's the number of unchoke slots we have.
		if (sett.get_int(settings_pack::choking_algorithm)
			== settings_pack::rate_based_choker)
		{
			// first reset the number of unchoke slots, because we'll calculate
			// it purely based on the current state of our peers.
			upload_slots = 0;

make the comparison function a free function and move it into this cpp file

../src/choker.cpp:339

		}

		// ==== rate-based ====
		//
		// The rate based unchoker looks at our upload rate to peers, and find
		// a balance between number of upload slots and the rate we achieve. The
		// intention is to not spread upload bandwidth too thin, but also to not
		// unchoke few enough peers to not be able to saturate the up-link.
		// this is done by traversing the peers sorted by our upload rate to
		// them in decreasing rates. For each peer we increase our threshold
		// by 1 kB/s. The first peer we get to to whom we upload slower than
		// the threshold, we stop and that's the number of unchoke slots we have.
		if (sett.get_int(settings_pack::choking_algorithm)
			== settings_pack::rate_based_choker)
		{
			// first reset the number of unchoke slots, because we'll calculate
			// it purely based on the current state of our peers.
			upload_slots = 0;


			std::sort(peers.begin(), peers.end()
				, boost::bind(&upload_rate_compare, _1, _2));

make configurable

../src/choker.cpp:344

		//
		// The rate based unchoker looks at our upload rate to peers, and find
		// a balance between number of upload slots and the rate we achieve. The
		// intention is to not spread upload bandwidth too thin, but also to not
		// unchoke few enough peers to not be able to saturate the up-link.
		// this is done by traversing the peers sorted by our upload rate to
		// them in decreasing rates. For each peer we increase our threshold
		// by 1 kB/s. The first peer we get to to whom we upload slower than
		// the threshold, we stop and that's the number of unchoke slots we have.
		if (sett.get_int(settings_pack::choking_algorithm)
			== settings_pack::rate_based_choker)
		{
			// first reset the number of unchoke slots, because we'll calculate
			// it purely based on the current state of our peers.
			upload_slots = 0;


			std::sort(peers.begin(), peers.end()
				, boost::bind(&upload_rate_compare, _1, _2));

			int rate_threshold = 1024;

			for (std::vector<peer_connection*>::const_iterator i = peers.begin()
				, end(peers.end()); i != end; ++i)
			{
				peer_connection const& p = **i;
				int rate = int(p.uploaded_in_last_round()
					* 1000 / total_milliseconds(unchoke_interval));

				if (rate < rate_threshold) break;

				++upload_slots;

make configurable

../src/choker.cpp:358

			// it purely based on the current state of our peers.
			upload_slots = 0;


			std::sort(peers.begin(), peers.end()
				, boost::bind(&upload_rate_compare, _1, _2));

			int rate_threshold = 1024;

			for (std::vector<peer_connection*>::const_iterator i = peers.begin()
				, end(peers.end()); i != end; ++i)
			{
				peer_connection const& p = **i;
				int rate = int(p.uploaded_in_last_round()
					* 1000 / total_milliseconds(unchoke_interval));

				if (rate < rate_threshold) break;

				++upload_slots;

				rate_threshold += 1024;
			}
			++upload_slots;
		}

		// sorts the peers that are eligible for unchoke by download rate and
		// secondary by total upload. The reason for this is, if all torrents are
		// being seeded, the download rate will be 0, and the peers we have sent
		// the least to should be unchoked

		// we use partial sort here, because we only care about the top
		// upload_slots peers.

		if (sett.get_int(settings_pack::seed_choking_algorithm)
			== settings_pack::round_robin)
		{
			int pieces = sett.get_int(settings_pack::seeding_piece_quota);

			std::partial_sort(peers.begin(), peers.begin()
				+ (std::min)(upload_slots, int(peers.size())), peers.end()
				, boost::bind(&unchoke_compare_rr, _1, _2, pieces));
		}
		else if (sett.get_int(settings_pack::seed_choking_algorithm)
			== settings_pack::fastest_upload)
		{
			std::partial_sort(peers.begin(), peers.begin()
				+ (std::min)(upload_slots, int(peers.size())), peers.end()
				, boost::bind(&unchoke_compare_fastest_upload, _1, _2));
		}
		else if (sett.get_int(settings_pack::seed_choking_algorithm)
			== settings_pack::anti_leech)

this should probably be optional

../src/create_torrent.cpp:287

		counters cnt;
		disk_io_thread disk_thread(ios, cnt, 0);
		disk_thread.set_num_threads(1);

		storage_params params;
		params.files = &t.files();
		params.mapped_files = NULL;
		params.path = path;
		params.pool = &disk_thread.files();
		params.mode = storage_mode_sparse;

		storage_interface* storage_impl = default_storage_constructor(params);

		boost::shared_ptr<piece_manager> storage = boost::make_shared<piece_manager>(
			storage_impl, dummy, const_cast<file_storage*>(&t.files()));

		settings_pack sett;
		sett.set_int(settings_pack::cache_size, 0);
		sett.set_int(settings_pack::hashing_threads, 2);

		alert_manager dummy2(0, 0);
		disk_thread.set_settings(&sett, dummy2);

		int piece_counter = 0;
		int completed_piece = 0;
		int piece_read_ahead = 15 * 1024 * 1024 / t.piece_length();
		if (piece_read_ahead < 1) piece_read_ahead = 1;

		for (int i = 0; i < piece_read_ahead; ++i)
		{
			disk_thread.async_hash(storage.get(), i, disk_io_job::sequential_access
				, boost::bind(&on_hash, _1, &t, storage, &disk_thread
				, &piece_counter, &completed_piece, &f, &ec), NULL);
			++piece_counter;
			if (piece_counter >= t.num_pieces()) break;
		}
		disk_thread.submit_jobs();
		ios.run(ec);
	}

	create_torrent::~create_torrent() {}

	create_torrent::create_torrent(file_storage& fs, int piece_size
		, int pad_file_limit, int flags, int alignment)
		: m_files(fs)
		, m_creation_date(time(0))
		, m_multifile(fs.num_files() > 1)
		, m_private(false)
		, m_merkle_torrent((flags & merkle) != 0)
		, m_include_mtime((flags & modification_time) != 0)
		, m_include_symlinks((flags & symlinks) != 0)

perhaps we should sort the buffers here?

../src/disk_buffer_pool.cpp:322

		mutex::scoped_lock l(m_pool_mutex);
		for (int i = 0; i < iov_len; ++i)
		{
			iov[i].iov_base = allocate_buffer_impl(l, "pending read");
			iov[i].iov_len = block_size();
			if (iov[i].iov_base == NULL)
			{
				// uh oh. We failed to allocate the buffer!
				// we need to roll back and free all the buffers
				// we've already allocated
				for (int j = 0; j < i; ++j)
					free_buffer_impl(static_cast<char*>(iov[j].iov_base), l);
				return -1;
			}
		}
		return 0;
	}

	void disk_buffer_pool::free_iovec(file::iovec_t* iov, int iov_len)
	{
		mutex::scoped_lock l(m_pool_mutex);
		for (int i = 0; i < iov_len; ++i)
			free_buffer_impl(static_cast<char*>(iov[i].iov_base), l);
		check_buffer_level(l);
	}

	char* disk_buffer_pool::allocate_buffer_impl(mutex::scoped_lock& l
		, char const*)
	{
		TORRENT_ASSERT(m_settings_set);
		TORRENT_ASSERT(m_magic == 0x1337);
		TORRENT_ASSERT(l.locked());
		TORRENT_UNUSED(l);

		char* ret;
#if TORRENT_HAVE_MMAP
		if (m_cache_pool)
		{
			if (m_free_list.size() <= (m_max_use - m_low_watermark)
				/ 2 && !m_exceeded_max_size)
			{
				m_exceeded_max_size = true;
				m_trigger_cache_trim();
			}
			if (m_free_list.empty()) return 0;
			boost::uint64_t slot_index = m_free_list.back();
			m_free_list.pop_back();
			ret = m_cache_pool + (slot_index * 0x4000);
			TORRENT_ASSERT(is_disk_buffer(ret, l));
		}
		else

it would be nice to optimize this by having the cache pieces also ordered by

../src/disk_io_thread.cpp:883

			// from disk_io_thread::do_delete, which is a fence job and should
			// have any other jobs active, i.e. there should not be any references
			// keeping pieces or blocks alive
			if ((flags & flush_delete_cache) && (flags & flush_expect_clear))
			{
				boost::unordered_set<cached_piece_entry*> const& storage_pieces = storage->cached_pieces();
				for (boost::unordered_set<cached_piece_entry*>::const_iterator i = storage_pieces.begin()
					, end(storage_pieces.end()); i != end; ++i)
				{
					cached_piece_entry* pe = m_disk_cache.find_piece(storage, (*i)->piece);
					TORRENT_PIECE_ASSERT(pe->num_dirty == 0, pe);
				}
			}
#endif
		}
		else
		{
			std::pair<block_cache::iterator, block_cache::iterator> range = m_disk_cache.all_pieces();
			while (range.first != range.second)
			{
				if ((flags & (flush_read_cache | flush_delete_cache)) == 0)
				{
					// if we're not flushing the read cache, and not deleting the
					// cache, skip pieces with no dirty blocks, i.e. read cache
					// pieces
					while (range.first->num_dirty == 0)
					{
						++range.first;
						if (range.first == range.second) return;
					}
				}
				cached_piece_entry* pe = const_cast<cached_piece_entry*>(&*range.first);
				flush_piece(pe, flags, completed_jobs, l);
				range = m_disk_cache.all_pieces();
			}
		}
	}

	// this is called if we're exceeding (or about to exceed) the cache
	// size limit. This means we should not restrict ourselves to contiguous
	// blocks of write cache line size, but try to flush all old blocks
	// this is why we pass in 1 as cont_block to the flushing functions
	void disk_io_thread::try_flush_write_blocks(int num, jobqueue_t& completed_jobs
		, mutex::scoped_lock& l)
	{
		DLOG("try_flush_write_blocks: %d\n", num);

		list_iterator<cached_piece_entry> range = m_disk_cache.write_lru_pieces();
		std::vector<std::pair<piece_manager*, int> > pieces;
		pieces.reserve(m_disk_cache.num_write_lru_pieces());

instead of doing a lookup each time through the loop, save cached_piece_entry pointers with piece_refcount incremented to pin them

../src/disk_io_thread.cpp:926

	// this is why we pass in 1 as cont_block to the flushing functions
	void disk_io_thread::try_flush_write_blocks(int num, jobqueue_t& completed_jobs
		, mutex::scoped_lock& l)
	{
		DLOG("try_flush_write_blocks: %d\n", num);

		list_iterator<cached_piece_entry> range = m_disk_cache.write_lru_pieces();
		std::vector<std::pair<piece_manager*, int> > pieces;
		pieces.reserve(m_disk_cache.num_write_lru_pieces());

		for (list_iterator<cached_piece_entry> p = range; p.get() && num > 0; p.next())
		{
			cached_piece_entry* e = p.get();
			if (e->num_dirty == 0) continue;
			pieces.push_back(std::make_pair(e->storage.get(), int(e->piece)));
		}

		for (std::vector<std::pair<piece_manager*, int> >::iterator i = pieces.begin()
			, end(pieces.end()); i != end; ++i)
		{
			cached_piece_entry* pe = m_disk_cache.find_piece(i->first, i->second);
			if (pe == NULL) continue;

			// another thread may flush this piece while we're looping and
			// evict it into a read piece and then also evict it to ghost
			if (pe->cache_state != cached_piece_entry::write_lru) continue;

#if TORRENT_USE_ASSERTS
			pe->piece_log.push_back(piece_log_t(piece_log_t::try_flush_write_blocks, -1));
#endif
			++pe->piece_refcount;
			kick_hasher(pe, l);
			num -= try_flush_hashed(pe, 1, completed_jobs, l);
			--pe->piece_refcount;
		}

		// when the write cache is under high pressure, it is likely
		// counter productive to actually do this, since a piece may
		// not have had its flush_hashed job run on it
		// so only do it if no other thread is currently flushing

		if (num == 0 || m_stats_counters[counters::num_writing_threads] > 0) return;

		// if we still need to flush blocks, start over and flush
		// everything in LRU order (degrade to lru cache eviction)
		for (std::vector<std::pair<piece_manager*, int> >::iterator i = pieces.begin()
			, end(pieces.end()); i != end; ++i)
		{
			cached_piece_entry* pe = m_disk_cache.find_piece(i->first, i->second);
			if (pe == NULL) continue;
			if (pe->num_dirty == 0) continue;

instead of doing this. pass in the settings to each storage_interface call. Each disk thread could hold its most recent understanding of the settings in a shared_ptr, and update it every time it wakes up from a job. That way each access to the settings won't require a mutex to be held.

../src/disk_io_thread.cpp:1105

	{
		INVARIANT_CHECK;
		TORRENT_ASSERT(j->next == 0);
		TORRENT_ASSERT((j->flags & disk_io_job::in_progress) || !j->storage);

		mutex::scoped_lock l(m_cache_mutex);

		check_cache_level(l, completed_jobs);

		DLOG("perform_job job: %s ( %s%s) piece: %d offset: %d outstanding: %d\n"
			, job_action_name[j->action]
			, (j->flags & disk_io_job::fence) ? "fence ": ""
			, (j->flags & disk_io_job::force_copy) ? "force_copy ": ""
			, j->piece, j->d.io.offset
			, j->storage ? j->storage->num_outstanding_jobs() : -1);

		l.unlock();

		boost::shared_ptr<piece_manager> storage = j->storage;

		if (storage && storage->get_storage_impl()->m_settings == 0)
			storage->get_storage_impl()->m_settings = &m_settings;

		TORRENT_ASSERT(j->action < sizeof(job_functions)/sizeof(job_functions[0]));

		time_point start_time = clock_type::now();

		m_stats_counters.inc_stats_counter(counters::num_running_disk_jobs, 1);

		// call disk function
		int ret = (this->*(job_functions[j->action]))(j, completed_jobs);

		// note that -2 erros are OK
		TORRENT_ASSERT(ret != -1 || (j->error.ec && j->error.operation != 0));

		m_stats_counters.inc_stats_counter(counters::num_running_disk_jobs, -1);

		if (ret == retry_job)
		{
			mutex::scoped_lock l2(m_job_mutex);
			// to avoid busy looping here, give up
			// our quanta in case there aren't any other
			// jobs to run in between

a potentially more efficient solution would be to have a special queue for retry jobs, that's only ever run when a job completes, in any thread. It would only work if counters::num_running_disk_jobs > 0

../src/disk_io_thread.cpp:1133

		time_point start_time = clock_type::now();

		m_stats_counters.inc_stats_counter(counters::num_running_disk_jobs, 1);

		// call disk function
		int ret = (this->*(job_functions[j->action]))(j, completed_jobs);

		// note that -2 erros are OK
		TORRENT_ASSERT(ret != -1 || (j->error.ec && j->error.operation != 0));

		m_stats_counters.inc_stats_counter(counters::num_running_disk_jobs, -1);

		if (ret == retry_job)
		{
			mutex::scoped_lock l2(m_job_mutex);
			// to avoid busy looping here, give up
			// our quanta in case there aren't any other
			// jobs to run in between


			TORRENT_ASSERT((j->flags & disk_io_job::in_progress) || !j->storage);

			bool need_sleep = m_queued_jobs.empty();
			m_queued_jobs.push_back(j);
			l2.unlock();
			if (need_sleep) sleep(0);
			return;
		}

#if TORRENT_USE_ASSERTS

it should clear the hash state even when there's an error, right?

../src/disk_io_thread.cpp:1147

		m_stats_counters.inc_stats_counter(counters::num_running_disk_jobs, -1);

		if (ret == retry_job)
		{
			mutex::scoped_lock l2(m_job_mutex);
			// to avoid busy looping here, give up
			// our quanta in case there aren't any other
			// jobs to run in between


			TORRENT_ASSERT((j->flags & disk_io_job::in_progress) || !j->storage);

			bool need_sleep = m_queued_jobs.empty();
			m_queued_jobs.push_back(j);
			l2.unlock();
			if (need_sleep) sleep(0);
			return;
		}

#if TORRENT_USE_ASSERTS
		if (j->action == disk_io_job::hash && !j->error.ec)
		{
			// a hash job should never return without clearing pe->hash
			l.lock();
			cached_piece_entry* pe = m_disk_cache.find_piece(j);
			if (pe != NULL)
			{
				TORRENT_PIECE_ASSERT(pe->hash == NULL, pe);
			}
			l.unlock();
		}
#endif

		if (ret == defer_handler) return;

		j->ret = ret;

		time_point now = clock_type::now();
		m_job_time.add_sample(total_microseconds(now - start_time));
		completed_jobs.push_back(j);
	}

	int disk_io_thread::do_uncached_read(disk_io_job* j)
	{
		j->buffer.disk_block = m_disk_cache.allocate_buffer("send buffer");
		if (j->buffer.disk_block == 0)
		{
			j->error.ec = error::no_memory;
			j->error.operation = storage_error::alloc_cache_piece;
			return -1;
		}

maybe the tailqueue_iterator should contain a pointer-pointer instead and have an unlink function

../src/disk_io_thread.cpp:1848

		j->callback = handler;

		add_fence_job(storage, j);
	}

	void disk_io_thread::async_delete_files(piece_manager* storage
		, boost::function<void(disk_io_job const*)> const& handler)
	{
#ifdef TORRENT_DEBUG
		// the caller must increment the torrent refcount before
		// issuing an async disk request
		storage->assert_torrent_refcount();
#endif

		// remove cache blocks belonging to this torrent
		jobqueue_t completed_jobs;

		// remove outstanding jobs belonging to this torrent
		mutex::scoped_lock l2(m_job_mutex);

		disk_io_job* qj = m_queued_jobs.get_all();
		jobqueue_t to_abort;

		while (qj)
		{
			disk_io_job* next = qj->next;
#if TORRENT_USE_ASSERTS
			qj->next = NULL;
#endif
			if (qj->storage.get() == storage)
				to_abort.push_back(qj);
			else
				m_queued_jobs.push_back(qj);
			qj = next;
		}
		l2.unlock();

		mutex::scoped_lock l(m_cache_mutex);
		flush_cache(storage, flush_delete_cache, completed_jobs, l);
		l.unlock();

		disk_io_job* j = allocate_job(disk_io_job::delete_files);
		j->storage = storage->shared_from_this();
		j->callback = handler;
		add_fence_job(storage, j);

		fail_jobs_impl(storage_error(boost::asio::error::operation_aborted)
			, to_abort, completed_jobs);

		if (completed_jobs.size())
			add_completed_jobs(completed_jobs);

this is potentially very expensive. One way to solve it would be to have a fence for just this one piece.

../src/disk_io_thread.cpp:2113

	}

	void disk_io_thread::async_clear_piece(piece_manager* storage, int index
		, boost::function<void(disk_io_job const*)> const& handler)
	{
#ifdef TORRENT_DEBUG
		// the caller must increment the torrent refcount before
		// issuing an async disk request
		storage->assert_torrent_refcount();
#endif

		disk_io_job* j = allocate_job(disk_io_job::clear_piece);
		j->storage = storage->shared_from_this();
		j->piece = index;
		j->callback = handler;

		// regular jobs are not guaranteed to be executed in-order
		// since clear piece must guarantee that all write jobs that
		// have been issued finish before the clear piece job completes

		add_fence_job(storage, j);
	}

	void disk_io_thread::clear_piece(piece_manager* storage, int index)
	{
		mutex::scoped_lock l(m_cache_mutex);

		cached_piece_entry* pe = m_disk_cache.find_piece(storage, index);
		if (pe == 0) return;
		TORRENT_PIECE_ASSERT(pe->hashing == false, pe);
		pe->hashing_done = 0;
		delete pe->hash;
		pe->hash = NULL;

		// evict_piece returns true if the piece was in fact
		// evicted. A piece may fail to be evicted if there
		// are still outstanding operations on it, which should
		// never be the case when this function is used
		// in fact, no jobs should really be hung on this piece
		// at this point
		jobqueue_t jobs;
		bool ok = m_disk_cache.evict_piece(pe, jobs);
		TORRENT_PIECE_ASSERT(ok, pe);
		TORRENT_UNUSED(ok);
		fail_jobs(storage_error(boost::asio::error::operation_aborted), jobs);
	}

	void disk_io_thread::kick_hasher(cached_piece_entry* pe, mutex::scoped_lock& l)
	{
		if (!pe->hash) return;
		if (pe->hashing) return;

we should probably just hang the job on the piece and make sure the hasher gets kicked

../src/disk_io_thread.cpp:2375

		if (pe == NULL)
		{
			int cache_state = (j->flags & disk_io_job::volatile_read)
				? cached_piece_entry::volatile_read_lru
				: cached_piece_entry::read_lru1;
			pe = m_disk_cache.allocate_piece(j, cache_state);
		}
		if (pe == NULL)
		{
			j->error.ec = error::no_memory;
			j->error.operation = storage_error::alloc_cache_piece;
			return -1;
		}

		if (pe->hashing)
		{
			TORRENT_PIECE_ASSERT(pe->hash, pe);
			// another thread is hashing this piece right now
			// try again in a little bit
			DLOG("do_hash: retry\n");
			return retry_job;
		}

		pe->hashing = 1;

		TORRENT_PIECE_ASSERT(pe->cache_state <= cached_piece_entry::read_lru1
			|| pe->cache_state == cached_piece_entry::read_lru2, pe);
		++pe->piece_refcount;

		if (pe->hash == NULL)
		{
			pe->hashing_done = 0;
			pe->hash = new partial_hash;
		}
		partial_hash* ph = pe->hash;

		int block_size = m_disk_cache.block_size();
		int blocks_in_piece = (piece_size + block_size - 1) / block_size;
		
		// keep track of which blocks we have locked by incrementing
		// their refcounts. This is used to decrement only these blocks
		// later.
		int* locked_blocks = TORRENT_ALLOCA(int, blocks_in_piece);
		memset(locked_blocks, 0, blocks_in_piece * sizeof(int));
		int num_locked_blocks = 0;

		// increment the refcounts of all
		// blocks up front, and then hash them without holding the lock
		TORRENT_PIECE_ASSERT(ph->offset % block_size == 0, pe);
		for (int i = ph->offset / block_size; i < blocks_in_piece; ++i)
		{

introduce a holder class that automatically increments and decrements the piece_refcount

../src/disk_io_thread.cpp:2442

		{
			file::iovec_t iov;
			iov.iov_len = (std::min)(block_size, piece_size - ph->offset);

			if (next_locked_block < num_locked_blocks
				&& locked_blocks[next_locked_block] == i)
			{
				++next_locked_block;
				TORRENT_PIECE_ASSERT(pe->blocks[i].buf, pe);
				TORRENT_PIECE_ASSERT(ph->offset == i * block_size, pe);
				ph->offset += iov.iov_len;
				ph->h.update(pe->blocks[i].buf, iov.iov_len);
			}
			else
			{
				iov.iov_base = m_disk_cache.allocate_buffer("hashing");

				if (iov.iov_base == NULL)
				{
					l.lock();

					// decrement the refcounts of the blocks we just hashed
					for (int k = 0; k < num_locked_blocks; ++k)
						m_disk_cache.dec_block_refcount(pe, locked_blocks[k], block_cache::ref_hashing);

					--pe->piece_refcount;
					pe->hashing = false;
					delete pe->hash;
					pe->hash = NULL;

					m_disk_cache.maybe_free_piece(pe);

					j->error.ec = errors::no_memory;
					j->error.operation = storage_error::alloc_cache_piece;
					return -1;
				}

				DLOG("do_hash: reading (piece: %d block: %d)\n", int(pe->piece), i);

				time_point start_time = clock_type::now();

				TORRENT_PIECE_ASSERT(ph->offset == i * block_size, pe);
				ret = j->storage->get_storage_impl()->readv(&iov, 1, j->piece
						, ph->offset, file_flags, j->error);

				if (ret < 0)
				{
					TORRENT_ASSERT(j->error.ec && j->error.operation != 0);
					m_disk_cache.free_buffer(static_cast<char*>(iov.iov_base));
					l.lock();
					break;

it would be nice to not have to lock the mutex every turn through this loop

../src/disk_io_thread.cpp:2692

			j->error.ec = error::no_memory;
			j->error.operation = storage_error::alloc_cache_piece;
			return -1;
		}

#if TORRENT_USE_ASSERTS
		pe->piece_log.push_back(piece_log_t(j->action));
#endif
		TORRENT_PIECE_ASSERT(pe->cache_state <= cached_piece_entry::read_lru1
			|| pe->cache_state == cached_piece_entry::read_lru2, pe);
		++pe->piece_refcount;

		int block_size = m_disk_cache.block_size();
		int piece_size = j->storage->files()->piece_size(j->piece);
		int blocks_in_piece = (piece_size + block_size - 1) / block_size;
		
		file::iovec_t iov;
		int ret = 0;
		int offset = 0;

		for (int i = 0; i < blocks_in_piece; ++i)
		{
			iov.iov_len = (std::min)(block_size, piece_size - offset);

			// is the block already in the cache?
			if (pe->blocks[i].buf) continue;
			l.unlock();

			iov.iov_base = m_disk_cache.allocate_buffer("read cache");

			if (iov.iov_base == NULL)
			{
				//#error introduce a holder class that automatically increments and decrements the piece_refcount
				--pe->piece_refcount;
				m_disk_cache.maybe_free_piece(pe);
				j->error.ec = errors::no_memory;
				j->error.operation = storage_error::alloc_cache_piece;
				return -1;
			}

			DLOG("do_cache_piece: reading (piece: %d block: %d)\n"
				, int(pe->piece), i);

			time_point start_time = clock_type::now();

			ret = j->storage->get_storage_impl()->readv(&iov, 1, j->piece
				, offset, file_flags, j->error);

			if (ret < 0)
			{
				l.lock();

it would be nice to not depend on alert_manager here

../src/file_progress.cpp:137

	{
		if (m_file_progress.empty())
			return;

		const int piece_size = fs.piece_length();
		boost::int64_t off = boost::int64_t(index) * piece_size;
		int file_index = fs.file_index_at_offset(off);
		int size = fs.piece_size(index);
		for (; size > 0; ++file_index)
		{
			boost::int64_t file_offset = off - fs.file_offset(file_index);
			TORRENT_ASSERT(file_index != fs.num_files());
			TORRENT_ASSERT(file_offset <= fs.file_size(file_index));
			int add = (std::min)(fs.file_size(file_index)
				- file_offset, boost::int64_t(size));
			m_file_progress[file_index] += add;

			TORRENT_ASSERT(m_file_progress[file_index]
					<= fs.file_size(file_index));

			if (m_file_progress[file_index] >= fs.file_size(file_index) && alerts)
			{
				if (!fs.pad_file_at(file_index))
				{
					if (alerts->should_post<file_completed_alert>())
					{
						// this file just completed, post alert
						alerts->emplace_alert<file_completed_alert>(h, file_index);
					}
				}
			}
			size -= add;
			off += add;
			TORRENT_ASSERT(size >= 0);
		}
	}

#if TORRENT_USE_INVARIANT_CHECKS
	void file_progress::check_invariant(file_storage const& fs) const
	{
		if (!m_file_progress.empty())
		{
			for (std::vector<boost::uint64_t>::const_iterator i = m_file_progress.begin()
				, end(m_file_progress.end()); i != end; ++i)
			{
				int index = i - m_file_progress.begin();
				TORRENT_ASSERT(*i <= fs.file_size(index));
			}
		}
	}
#endif

support this somehow

../src/http_tracker_connection.cpp:186

			{
				if (tracker_req().i2pconn->local_endpoint().empty())
				{
					fail(error_code(errors::no_i2p_endpoint), -1, "Waiting for i2p acceptor from SAM bridge", 5);
					return;
				}
				else
				{
					url += "&ip=" + tracker_req ().i2pconn->local_endpoint () + ".i2p";
				}
			}
			else
#endif
			if (!settings.get_bool(settings_pack::anonymous_mode))
			{
				std::string announce_ip = settings.get_str(settings_pack::announce_ip);
				if (!announce_ip.empty())
				{
					url += "&ip=" + escape_string(announce_ip.c_str(), announce_ip.size());
				}
/*				else if (settings.get_bool(settings_pack::announce_double_nat)
					&& is_local(m_ses.listen_address()))
				{
					// only use the global external listen address here
					// if it turned out to be on a local network
					// since otherwise the tracker should use our
					// source IP to determine our origin
					url += "&ip=" + print_address(m_ses.listen_address());
				}
*/
			}
		}

		m_tracker_connection.reset(new http_connection(get_io_service(), m_man.host_resolver()
			, boost::bind(&http_tracker_connection::on_response, shared_from_this(), _1, _2, _3, _4)
			, true, settings.get_int(settings_pack::max_http_recv_buffer_size)
			, boost::bind(&http_tracker_connection::on_connect, shared_from_this(), _1)
			, boost::bind(&http_tracker_connection::on_filter, shared_from_this(), _1, _2)
#ifdef TORRENT_USE_OPENSSL
			, tracker_req().ssl_ctx
#endif
			));

		int timeout = tracker_req().event==tracker_request::stopped
			?settings.get_int(settings_pack::stop_tracker_timeout)
			:settings.get_int(settings_pack::tracker_completion_timeout);

		// when sending stopped requests, prefer the cached DNS entry
		// to avoid being blocked for slow or failing responses. Chances
		// are that we're shutting down, and this should be a best-effort
		// attempt. It's not worth stalling shutdown.

this is not safe. The torrent could be unloaded while we're still sending the metadata

../src/metadata_transfer.cpp:365

					= req_to_offset(req, int(m_tp.metadata().left()));

				char msg[15];
				char* ptr = msg;

#ifndef TORRENT_DISABLE_LOGGING
				m_pc.peer_log(peer_log_alert::outgoing_message, "METADATA"
					, "start: %d total_size: %d offset: %d data_size: %d"
					, req.first, req.second, offset.first, offset.second);
#endif
				// yes, we have metadata, send it
				detail::write_uint32(11 + offset.second, ptr);
				detail::write_uint8(bt_peer_connection::msg_extended, ptr);
				detail::write_uint8(m_message_index, ptr);
				// means 'data packet'
				detail::write_uint8(1, ptr);
				detail::write_uint32(int(m_tp.metadata().left()), ptr);
				detail::write_uint32(offset.first, ptr);
				m_pc.send_buffer(msg, sizeof(msg));

				char const* metadata = m_tp.metadata().begin;
				m_pc.append_const_send_buffer(metadata + offset.first, offset.second);
			}
			else
			{
#ifndef TORRENT_DISABLE_LOGGING
				m_pc.peer_log(peer_log_alert::outgoing_message, "METADATA"
					, "don't have metadata");
#endif
				char msg[4+3];
				char* ptr = msg;

				// we don't have the metadata, reply with
				// don't have-message
				detail::write_uint32(1 + 2, ptr);
				detail::write_uint8(bt_peer_connection::msg_extended, ptr);
				detail::write_uint8(m_message_index, ptr);
				// means 'have no data'
				detail::write_uint8(2, ptr);
				m_pc.send_buffer(msg, sizeof(msg));
			}
			m_pc.setup_send();
		}

		virtual bool on_extended(int length
			, int msg, buffer::const_interval body) TORRENT_OVERRIDE
		{
			if (msg != 14) return false;
			if (m_message_index == 0) return false;

			if (length > 500 * 1024)

use compare_less_wrap for this comparison as well

../src/packet_buffer.cpp:180

		void** new_storage = static_cast<void**>(malloc(sizeof(void*) * new_size));
#ifndef BOOST_NO_EXCEPTIONS
		if (new_storage == NULL) throw std::bad_alloc();
#endif

		for (index_type i = 0; i < new_size; ++i)
			new_storage[i] = 0;

		for (index_type i = m_first; i < (m_first + m_capacity); ++i)
			new_storage[i & (new_size - 1)] = m_storage[i & (m_capacity - 1)];

		free(m_storage);

		m_storage = new_storage;
		m_capacity = new_size;
	}

	void* packet_buffer_impl::remove(index_type idx)
	{
		INVARIANT_CHECK;
		if (idx >= m_first + m_capacity)
			return 0;

		if (compare_less_wrap(idx, m_first, 0xffff))
			return 0;

		const int mask = (m_capacity - 1);
		void* old_value = m_storage[idx & mask];
		m_storage[idx & mask] = 0;

		if (old_value)
		{
			--m_size;
			if (m_size == 0) m_last = m_first;
		}

		if (idx == m_first && m_size != 0)
		{
			++m_first;
			for (boost::uint32_t i = 0; i < m_capacity; ++i, ++m_first)
				if (m_storage[m_first & mask]) break;
			m_first &= 0xffff;
		}

		if (((idx + 1) & 0xffff) == m_last && m_size != 0)
		{
			--m_last;
			for (boost::uint32_t i = 0; i < m_capacity; ++i, --m_last)
				if (m_storage[m_last & mask]) break;
			++m_last;
			m_last &= 0xffff;

what do we do if someone is currently reading from the disk from this piece? does it matter? Since we won't actively erase the data from disk, but it may be overwritten soon, it's probably not that big of a deal

../src/part_file.cpp:252

		if (((mode & file::rw_mask) != file::read_only)
			&& ec == boost::system::errc::no_such_file_or_directory)
		{
			// this means the directory the file is in doesn't exist.
			// so create it
			ec.clear();
			create_directories(m_path, ec);

			if (ec) return;
			m_file.open(fn, mode, ec);
		}
	}

	void part_file::free_piece(int piece)
	{
		mutex::scoped_lock l(m_mutex);

		boost::unordered_map<int, int>::iterator i = m_piece_map.find(piece);
		if (i == m_piece_map.end()) return;


		m_free_slots.push_back(i->second);
		m_piece_map.erase(i);
		m_dirty_metadata = true;
	}

	void part_file::move_partfile(std::string const& path, error_code& ec)
	{
		mutex::scoped_lock l(m_mutex);

		flush_metadata_impl(ec);
		if (ec) return;

		m_file.close();

		if (!m_piece_map.empty())
		{
			std::string old_path = combine_path(m_path, m_name);
			std::string new_path = combine_path(path, m_name);

			rename(old_path, new_path, ec);
			if (ec == boost::system::errc::no_such_file_or_directory)
				ec.clear();

			if (ec)
			{
				copy_file(old_path, new_path, ec);
				if (ec) return;
				remove(old_path, ec);
			}
		}

instead of rebuilding the whole file header and flushing it, update the slot entries as we go

../src/part_file.cpp:353

				if (block_to_copy == m_piece_size)
				{
					m_free_slots.push_back(i->second);
					m_piece_map.erase(i);
					m_dirty_metadata = true;
				}
			}
			file_offset += block_to_copy;
			piece_offset = 0;
			size -= block_to_copy;
		}
	}

	void part_file::flush_metadata(error_code& ec)
	{
		mutex::scoped_lock l(m_mutex);

		flush_metadata_impl(ec);
	}

	void part_file::flush_metadata_impl(error_code& ec)
	{
		// do we need to flush the metadata?
		if (m_dirty_metadata == false) return;

		if (m_piece_map.empty())
		{
			m_file.close();

			// if we don't have any pieces left in the
			// part file, remove it
			std::string p = combine_path(m_path, m_name);
			remove(p, ec);

			if (ec == boost::system::errc::no_such_file_or_directory)
				ec.clear();
			return;
		}

		open_file(file::read_write, ec);
		if (ec) return;

		boost::scoped_array<boost::uint32_t> header(new boost::uint32_t[m_header_size]);

		using namespace libtorrent::detail;

		char* ptr = reinterpret_cast<char*>(header.get());

		write_uint32(m_max_pieces, ptr);
		write_uint32(m_piece_size, ptr);

it would be neat to be able to print this straight into the alert's stack allocator

../src/peer_connection.cpp:524

	}

#ifndef TORRENT_DISABLE_LOGGING
	void peer_connection::peer_log(peer_log_alert::direction_t direction
		, char const* event) const
	{
		peer_log(direction, event, "");
	}

	TORRENT_FORMAT(4,5)
	void peer_connection::peer_log(peer_log_alert::direction_t direction
		, char const* event, char const* fmt, ...) const
	{
		TORRENT_ASSERT(is_single_thread());

		if (!m_ses.alerts().should_post<peer_log_alert>()) return;

		va_list v;
		va_start(v, fmt);

		char buf[512];
		vsnprintf(buf, sizeof(buf), fmt, v);
		va_end(v);

		torrent_handle h;
		boost::shared_ptr<torrent> t = m_torrent.lock();
		if (t) h = t->get_handle();

		m_ses.alerts().emplace_alert<peer_log_alert>(
			h, m_remote, m_peer_id, direction, event, buf);
	}
#endif

#ifndef TORRENT_DISABLE_EXTENSIONS
	void peer_connection::add_extension(boost::shared_ptr<peer_plugin> ext)
	{
		TORRENT_ASSERT(is_single_thread());
		m_extensions.push_back(ext);
	}

	peer_plugin const* peer_connection::find_plugin(char const* type)
	{
		TORRENT_ASSERT(is_single_thread());
		for (extension_list_t::iterator i = m_extensions.begin()
			, end(m_extensions.end()); i != end; ++i)
		{
			if (strcmp((*i)->type(), type) == 0) return (*i).get();
		}
		return 0;
	}
#endif

this should be the global download rate

../src/peer_connection.cpp:1031

		int rate = 0;

		// if we haven't received any data recently, the current download rate
		// is not representative
		if (aux::time_now() - m_last_piece > seconds(30) && m_download_rate_peak > 0)
		{
			rate = m_download_rate_peak;
		}
		else if (aux::time_now() - m_last_unchoked < seconds(5)
			&& m_statistics.total_payload_upload() < 2 * 0x4000)
		{
			// if we're have only been unchoked for a short period of time,
			// we don't know what rate we can get from this peer. Instead of assuming
			// the lowest possible rate, assume the average.

			int peers_with_requests = stats_counters()[counters::num_peers_down_requests];
			// avoid division by 0
			if (peers_with_requests == 0) peers_with_requests = 1;

			rate = t->statistics().transfer_rate(stat::download_payload) / peers_with_requests;
		}
		else
		{
			// current download rate in bytes per seconds
			rate = m_statistics.transfer_rate(stat::download_payload);
		}

		// avoid division by zero
		if (rate < 50) rate = 50;

		// average of current rate and peak
//		rate = (rate + m_download_rate_peak) / 2;

		return milliseconds((m_outstanding_bytes + extra_bytes
			+ m_queued_time_critical * t->block_size() * 1000) / rate);
	}

	void peer_connection::add_stat(boost::int64_t downloaded, boost::int64_t uploaded)
	{
		TORRENT_ASSERT(is_single_thread());
		m_statistics.add_stat(downloaded, uploaded);
	}

	void peer_connection::received_bytes(int bytes_payload, int bytes_protocol)
	{
		TORRENT_ASSERT(is_single_thread());
		m_statistics.received_bytes(bytes_payload, bytes_protocol);
		if (m_ignore_stats) return;
		boost::shared_ptr<torrent> t = m_torrent.lock();
		if (!t) return;

sort the allowed fast set in priority order

../src/peer_connection.cpp:3364

		// if the peer has the piece and we want
		// to download it, request it
		if (int(m_have_piece.size()) > index
			&& m_have_piece[index]
			&& !t->has_piece_passed(index)
			&& t->valid_metadata()
			&& t->has_picker()
			&& t->picker().piece_priority(index) > 0)
		{
			t->peer_is_interesting(*this);
		}
	}

	std::vector<int> const& peer_connection::allowed_fast()
	{
		TORRENT_ASSERT(is_single_thread());
		boost::shared_ptr<torrent> t = m_torrent.lock();
		TORRENT_ASSERT(t);

		return m_allowed_fast;
	}

	bool peer_connection::can_request_time_critical() const
	{
		TORRENT_ASSERT(is_single_thread());
		if (has_peer_choked() || !is_interesting()) return false;
		if (int(m_download_queue.size()) + int(m_request_queue.size())
			> m_desired_queue_size * 2) return false;
		if (on_parole()) return false;
		if (m_disconnecting) return false;
		boost::shared_ptr<torrent> t = m_torrent.lock();
		TORRENT_ASSERT(t);
		if (t->upload_mode()) return false;

		// ignore snubbed peers, since they're not likely to return pieces in a
		// timely manner anyway
		if (m_snubbed) return false;
		return true;
	}

	bool peer_connection::make_time_critical(piece_block const& block)
	{
		TORRENT_ASSERT(is_single_thread());
		std::vector<pending_block>::iterator rit = std::find_if(m_request_queue.begin()
			, m_request_queue.end(), has_block(block));
		if (rit == m_request_queue.end()) return false;
#if TORRENT_USE_ASSERTS
		boost::shared_ptr<torrent> t = m_torrent.lock();
		TORRENT_ASSERT(t);
		TORRENT_ASSERT(t->has_picker());

The stats checks can not be honored when authenticated encryption is in use because we may have encrypted data which we cannot authenticate yet

../src/peer_connection.cpp:6176

#ifndef TORRENT_DISABLE_LOGGING
			peer_log(peer_log_alert::incoming, "READ"
				, "%d bytes", int(bytes_transferred));
#endif
			// correct the dl quota usage, if not all of the buffer was actually read
			TORRENT_ASSERT(int(bytes_transferred) <= m_quota[download_channel]);
			m_quota[download_channel] -= bytes_transferred;

			if (m_disconnecting)
			{
				trancieve_ip_packet(bytes_in_loop, m_remote.address().is_v6());
				return;
			}

			TORRENT_ASSERT(bytes_transferred > 0);
			m_recv_buffer.received(bytes_transferred);

			int bytes = bytes_transferred;
			int sub_transferred = 0;
			do {
#if 0
				boost::int64_t cur_payload_dl = m_statistics.last_payload_downloaded();
				boost::int64_t cur_protocol_dl = m_statistics.last_protocol_downloaded();
#endif
				sub_transferred = m_recv_buffer.advance_pos(bytes);
				on_receive(error, sub_transferred);
				bytes -= sub_transferred;
				TORRENT_ASSERT(sub_transferred > 0);

#if 0
				TORRENT_ASSERT(m_statistics.last_payload_downloaded() - cur_payload_dl >= 0);
				TORRENT_ASSERT(m_statistics.last_protocol_downloaded() - cur_protocol_dl >= 0);
				boost::int64_t stats_diff = m_statistics.last_payload_downloaded() - cur_payload_dl +
					m_statistics.last_protocol_downloaded() - cur_protocol_dl;
				TORRENT_ASSERT(stats_diff == int(sub_transferred));
#endif
				if (m_disconnecting) return;

			} while (bytes > 0 && sub_transferred > 0);

			m_recv_buffer.normalize();

			TORRENT_ASSERT(m_recv_buffer.pos_at_end());
			TORRENT_ASSERT(m_recv_buffer.packet_size() > 0);

			if (m_peer_choked)
			{
				m_recv_buffer.clamp_size();
			}

			if (num_loops > read_loops) break;

this could probably be optimized by incrementally calling partial_sort to sort one more element in the list. Because chances are that we'll just need a single piece, and once we've picked from it we're done. Sorting the rest of the list in that case is a waste of time.

../src/piece_picker.cpp:2061

				pc.inc_stats_counter(counters::piece_picker_partial_loops);

				// in time critical mode, only pick high priority pieces
				if ((options & time_critical_mode)
					&& piece_priority(i->index) != priority_levels - 1)
					continue;

				if (!is_piece_free(i->index, pieces)) continue;

				TORRENT_ASSERT(m_piece_map[i->index].download_queue()
					== piece_pos::piece_downloading);

				ordered_partials[num_ordered_partials++] = &*i;
			}

			// now, sort the list.
			if (options & rarest_first)
			{
				ret |= picker_log_alert::rarest_first_partials;

				std::sort(ordered_partials, ordered_partials + num_ordered_partials
					, boost::bind(&piece_picker::partial_compare_rarest_first, this
						, _1, _2));
			}

			for (int i = 0; i < num_ordered_partials; ++i)
			{
				ret |= picker_log_alert::prioritize_partials;

				num_blocks = add_blocks_downloading(*ordered_partials[i], pieces
					, interesting_blocks, backup_blocks, backup_blocks2
					, num_blocks, prefer_contiguous_blocks, peer, options);
				if (num_blocks <= 0) return ret;
				if (int(backup_blocks.size()) >= num_blocks
					&& int(backup_blocks2.size()) >= num_blocks)
					break;
			}

			num_blocks = append_blocks(interesting_blocks, backup_blocks
				, num_blocks);
			if (num_blocks <= 0) return ret;

			num_blocks = append_blocks(interesting_blocks, backup_blocks2
				, num_blocks);
			if (num_blocks <= 0) return ret;
		}

		if (!suggested_pieces.empty())
		{
			for (std::vector<int>::const_iterator i = suggested_pieces.begin();
				i != suggested_pieces.end(); ++i)

when expanding pieces for cache stripe reasons, the !downloading condition doesn't make much sense

../src/piece_picker.cpp:2584

		TORRENT_ASSERT(index < int(m_piece_map.size()) || m_piece_map.empty());
		if (index + 1 == int(m_piece_map.size()))
			return m_blocks_in_last_piece;
		else
			return m_blocks_per_piece;
	}

	bool piece_picker::is_piece_free(int piece, bitfield const& bitmask) const
	{
		TORRENT_ASSERT(piece >= 0 && piece < int(m_piece_map.size()));
		return bitmask[piece]
			&& !m_piece_map[piece].have()
			&& !m_piece_map[piece].filtered();
	}

	bool piece_picker::can_pick(int piece, bitfield const& bitmask) const
	{
		TORRENT_ASSERT(piece >= 0 && piece < int(m_piece_map.size()));
		return bitmask[piece]
			&& !m_piece_map[piece].have()
			&& !m_piece_map[piece].downloading()
			&& !m_piece_map[piece].filtered();
	}

#if TORRENT_USE_INVARIANT_CHECKS
	void piece_picker::check_peers()
	{
		for (std::vector<block_info>::iterator i = m_block_info.begin()
			, end(m_block_info.end()); i != end; ++i)
		{
			TORRENT_ASSERT(i->peer == 0 || static_cast<torrent_peer*>(i->peer)->in_use);
		}
	}
#endif

	void piece_picker::clear_peer(torrent_peer* peer)
	{
		for (std::vector<block_info>::iterator i = m_block_info.begin()
			, end(m_block_info.end()); i != end; ++i)
		{
			if (i->peer == peer) i->peer = 0;
		}
	}

	// the first bool is true if this is the only peer that has requested and downloaded
	// blocks from this piece.
	// the second bool is true if this is the only active peer that is requesting
	// and downloading blocks from this piece. Active means having a connection.

there's no rule here to make uTP connections not have the global or local rate limits apply to it. This used to be the default.

../src/session_impl.cpp:523

		m_global_class = m_classes.new_peer_class("global");
		m_tcp_peer_class = m_classes.new_peer_class("tcp");
		m_local_peer_class = m_classes.new_peer_class("local");
		// local peers are always unchoked
		m_classes.at(m_local_peer_class)->ignore_unchoke_slots = true;
		// local peers are allowed to exceed the normal connection
		// limit by 50%
		m_classes.at(m_local_peer_class)->connection_limit_factor = 150;

		TORRENT_ASSERT(m_global_class == session::global_peer_class_id);
		TORRENT_ASSERT(m_tcp_peer_class == session::tcp_peer_class_id);
		TORRENT_ASSERT(m_local_peer_class == session::local_peer_class_id);

		init_peer_class_filter(true);

		// TCP, SSL/TCP and I2P connections should be assigned the TCP peer class
		m_peer_class_type_filter.add(peer_class_type_filter::tcp_socket, m_tcp_peer_class);
		m_peer_class_type_filter.add(peer_class_type_filter::ssl_tcp_socket, m_tcp_peer_class);
		m_peer_class_type_filter.add(peer_class_type_filter::i2p_socket, m_tcp_peer_class);


#ifndef TORRENT_DISABLE_LOGGING

		session_log("config: %s version: %s revision: %s"
			, TORRENT_CFG_STRING
			, LIBTORRENT_VERSION
			, LIBTORRENT_REVISION);

#endif // TORRENT_DISABLE_LOGGING

		// ---- auto-cap max connections ----
		int max_files = max_open_files();
		// deduct some margin for epoll/kqueue, log files,
		// futexes, shared objects etc.
		// 80% of the available file descriptors should go to connections
		m_settings.set_int(settings_pack::connections_limit, (std::min)(
			m_settings.get_int(settings_pack::connections_limit)
			, (std::max)(5, (max_files - 20) * 8 / 10)));
		// 20% goes towards regular files (see disk_io_thread)
#ifndef TORRENT_DISABLE_LOGGING
		session_log("   max connections: %d", m_settings.get_int(settings_pack::connections_limit));
		session_log("   max files: %d", max_files);

		session_log(" generated peer ID: %s", m_peer_id.to_string().c_str());
#endif

		boost::shared_ptr<settings_pack> copy = boost::make_shared<settings_pack>(pack);
		m_io_service.post(boost::bind(&session_impl::init, this, copy));
	}

	void session_impl::init(boost::shared_ptr<settings_pack> pack)

it would be nice to reserve() these vectors up front

../src/session_impl.cpp:1625

			bandwidth_channel* ch = &p->channel[peer_connection::download_channel];
			if (use_quota_overhead(ch, amount_down))
				ret |= 1 << peer_connection::download_channel;
			ch = &p->channel[peer_connection::upload_channel];
			if (use_quota_overhead(ch, amount_up))
				ret |= 1 << peer_connection::upload_channel;
		}
		return ret;
	}

	// session_impl is responsible for deleting 'pack'
	void session_impl::apply_settings_pack(boost::shared_ptr<settings_pack> pack)
	{
		apply_settings_pack_impl(*pack);
	}

	settings_pack session_impl::get_settings() const
	{
		settings_pack ret;
		for (int i = settings_pack::string_type_base;
			i < settings_pack::max_string_setting_internal; ++i)
		{
			ret.set_str(i, m_settings.get_str(i));
		}
		for (int i = settings_pack::int_type_base;
			i < settings_pack::max_int_setting_internal; ++i)
		{
			ret.set_int(i, m_settings.get_int(i));
		}
		for (int i = settings_pack::bool_type_base;
			i < settings_pack::max_bool_setting_internal; ++i)
		{
			ret.set_bool(i, m_settings.get_bool(i));
		}
		return ret;
	}

	void session_impl::apply_settings_pack_impl(settings_pack const& pack)
	{
		bool reopen_listen_port =
			(pack.has_val(settings_pack::ssl_listen)
				&& pack.get_int(settings_pack::ssl_listen)
					!= m_settings.get_int(settings_pack::ssl_listen))
			|| (pack.has_val(settings_pack::listen_interfaces)
				&& pack.get_str(settings_pack::listen_interfaces)
					!= m_settings.get_str(settings_pack::listen_interfaces));

		apply_pack(&pack, m_settings, this);
		m_disk_thread.set_settings(&pack, m_alerts);

instead of having a special case for this, just make the default listen interfaces be "0.0.0.0:6881,[::]:6881" and use the generic path. That would even allow for not listening at all.

../src/session_impl.cpp:1862

		error_code ec;

		int listen_port_retries = m_settings.get_int(settings_pack::max_retry_port_bind);

retry:

		// close the open listen sockets
		// close the listen sockets
		for (std::list<listen_socket_t>::iterator i = m_listen_sockets.begin()
			, end(m_listen_sockets.end()); i != end; ++i)
			i->sock->close(ec);
		m_listen_sockets.clear();
		m_stats_counters.set_value(counters::has_incoming_connections, 0);
		ec.clear();

		if (m_abort) return;

		m_ipv6_interface = tcp::endpoint();
		m_ipv4_interface = tcp::endpoint();

		if (m_listen_interfaces.empty())
		{
			// this means we should open two listen sockets
			// one for IPv4 and one for IPv6
			listen_socket_t s = setup_listener("0.0.0.0", boost::asio::ip::tcp::v4()
				, m_listen_interface.port()
				, flags, ec);

			if (!ec && s.sock)
			{
				// update the listen_interface member with the
				// actual port we ended up listening on, so that the other
				// sockets can be bound to the same one
				m_listen_interface.port(s.external_port);

				TORRENT_ASSERT(!m_abort);
				m_listen_sockets.push_back(s);
			}

#ifdef TORRENT_USE_OPENSSL
			if (m_settings.get_int(settings_pack::ssl_listen))
			{
				s = setup_listener("0.0.0.0", boost::asio::ip::tcp::v4()
					, m_settings.get_int(settings_pack::ssl_listen)
					, flags | open_ssl_socket, ec);

				if (!ec && s.sock)
				{
					TORRENT_ASSERT(!m_abort);
					m_listen_sockets.push_back(s);
				}

should this function take a shared_ptr instead?

../src/session_impl.cpp:2794

#if defined TORRENT_ASIO_DEBUGGING
		complete_async("session_impl::on_socks_accept");
#endif
		m_socks_listen_socket.reset();
		if (e == boost::asio::error::operation_aborted) return;
		if (e)
		{
			if (m_alerts.should_post<listen_failed_alert>())
				m_alerts.emplace_alert<listen_failed_alert>("socks5"
					, -1, listen_failed_alert::accept, e
					, listen_failed_alert::socks5);
			return;
		}
		open_new_incoming_socks_connection();
		incoming_connection(s);
	}

	// if cancel_with_cq is set, the peer connection is
	// currently expected to be scheduled for a connection
	// with the connection queue, and should be cancelled
	void session_impl::close_connection(peer_connection* p
		, error_code const& ec)
	{
		TORRENT_ASSERT(is_single_thread());
		boost::shared_ptr<peer_connection> sp(p->self());

		// someone else is holding a reference, it's important that
		// it's destructed from the network thread. Make sure the
		// last reference is held by the network thread.
		if (!sp.unique())
			m_undead_peers.push_back(sp);

// too expensive
//		INVARIANT_CHECK;

#ifdef TORRENT_DEBUG
//		for (aux::session_impl::torrent_map::const_iterator i = m_torrents.begin()
//			, end(m_torrents.end()); i != end; ++i)
//			TORRENT_ASSERT(!i->second->has_peer((peer_connection*)p));
#endif

#ifndef TORRENT_DISABLE_LOGGING
		session_log(" CLOSING CONNECTION %s : %s"
			, print_endpoint(p->remote()).c_str(), ec.message().c_str());
#else
		TORRENT_UNUSED(ec);
#endif

		TORRENT_ASSERT(p->is_disconnecting());

		TORRENT_ASSERT(sp.use_count() > 0);

have a separate list for these connections, instead of having to loop through all of them

../src/session_impl.cpp:3162

		if (m_auto_manage_time_scaler < 0)
		{
			INVARIANT_CHECK;
			m_auto_manage_time_scaler = settings().get_int(settings_pack::auto_manage_interval);
			recalculate_auto_managed_torrents();
		}

		// --------------------------------------------------------------
		// check for incoming connections that might have timed out
		// --------------------------------------------------------------

		for (connection_map::iterator i = m_connections.begin();
			i != m_connections.end();)
		{
			peer_connection* p = (*i).get();
			++i;
			// ignore connections that already have a torrent, since they
			// are ticked through the torrents' second_tick
			if (!p->associated_torrent().expired()) continue;

			int timeout = m_settings.get_int(settings_pack::handshake_timeout);
#if TORRENT_USE_I2P
			timeout *= is_i2p(*p->get_socket()) ? 4 : 1;
#endif
			if (m_last_tick - p->connected_time () > seconds(timeout))
				p->disconnect(errors::timed_out, op_bittorrent);
		}

		// --------------------------------------------------------------
		// second_tick every torrent (that wants it)
		// --------------------------------------------------------------

#if TORRENT_DEBUG_STREAMING > 0
		printf("\033[2J\033[0;0H");
#endif

		std::vector<torrent*>& want_tick = m_torrent_lists[torrent_want_tick];
		for (int i = 0; i < int(want_tick.size()); ++i)
		{
			torrent& t = *want_tick[i];
			TORRENT_ASSERT(t.want_tick());
			TORRENT_ASSERT(!t.is_aborted());

			t.second_tick(tick_interval_ms);

			// if the call to second_tick caused the torrent
			// to no longer want to be ticked (i.e. it was
			// removed from the list) we need to back up the counter
			// to not miss the torrent after it
			if (!t.want_tick()) --i;
		}

this should apply to all bandwidth channels

../src/session_impl.cpp:3195

#if TORRENT_DEBUG_STREAMING > 0
		printf("\033[2J\033[0;0H");
#endif

		std::vector<torrent*>& want_tick = m_torrent_lists[torrent_want_tick];
		for (int i = 0; i < int(want_tick.size()); ++i)
		{
			torrent& t = *want_tick[i];
			TORRENT_ASSERT(t.want_tick());
			TORRENT_ASSERT(!t.is_aborted());

			t.second_tick(tick_interval_ms);

			// if the call to second_tick caused the torrent
			// to no longer want to be ticked (i.e. it was
			// removed from the list) we need to back up the counter
			// to not miss the torrent after it
			if (!t.want_tick()) --i;
		}

		if (m_settings.get_bool(settings_pack::rate_limit_ip_overhead))
		{
			int up_limit = upload_rate_limit(m_global_class);
			int down_limit = download_rate_limit(m_global_class);

			if (down_limit > 0
				&& m_stat.download_ip_overhead() >= down_limit
				&& m_alerts.should_post<performance_alert>())
			{
				m_alerts.emplace_alert<performance_alert>(torrent_handle()
					, performance_alert::download_limit_too_low);
			}

			if (up_limit > 0
				&& m_stat.upload_ip_overhead() >= up_limit
				&& m_alerts.should_post<performance_alert>())
			{
				m_alerts.emplace_alert<performance_alert>(torrent_handle()
					, performance_alert::upload_limit_too_low);
			}
		}

		m_peak_up_rate = (std::max)(m_stat.upload_rate(), m_peak_up_rate);
		m_peak_down_rate = (std::max)(m_stat.download_rate(), m_peak_down_rate);

		m_stat.second_tick(tick_interval_ms);

		// --------------------------------------------------------------
		// scrape paused torrents that are auto managed
		// (unless the session is paused)
		// --------------------------------------------------------------

use a lower limit than m_settings.connections_limit to allocate the to 10% or so of connection slots for incoming connections

../src/session_impl.cpp:3989

		// robin fashion, so that every torrent is equally likely to connect to a
		// peer

		// boost connections are connections made by torrent connection
		// boost, which are done immediately on a tracker response. These
		// connections needs to be deducted from this second
		if (m_boost_connections > 0)
		{
			if (m_boost_connections > max_connections)
			{
				m_boost_connections -= max_connections;
				max_connections = 0;
			}
			else
			{
				max_connections -= m_boost_connections;
				m_boost_connections = 0;
			}
		}

		int limit = m_settings.get_int(settings_pack::connections_limit)
			- num_connections();

		// this logic is here to smooth out the number of new connection
		// attempts over time, to prevent connecting a large number of
		// sockets, wait 10 seconds, and then try again
		if (m_settings.get_bool(settings_pack::smooth_connects) && max_connections > (limit+1) / 2)
			max_connections = (limit+1) / 2;

		std::vector<torrent*>& want_peers_download = m_torrent_lists[torrent_want_peers_download];
		std::vector<torrent*>& want_peers_finished = m_torrent_lists[torrent_want_peers_finished];

		// if no torrent want any peers, just return
		if (want_peers_download.empty() && want_peers_finished.empty()) return;

		// if we don't have any connection attempt quota, return
		if (max_connections <= 0) return;

		INVARIANT_CHECK;

		int steps_since_last_connect = 0;
		int num_torrents = int(want_peers_finished.size() + want_peers_download.size());
		for (;;)
		{
			if (m_next_downloading_connect_torrent >= int(want_peers_download.size()))
				m_next_downloading_connect_torrent = 0;

			if (m_next_finished_connect_torrent >= int(want_peers_finished.size()))
				m_next_finished_connect_torrent = 0;

			torrent* t = NULL;

post a message to have this happen immediately instead of waiting for the next tick

../src/session_impl.cpp:4141

				continue;
			}

			if (!p->is_peer_interested()
				|| p->is_disconnecting()
				|| p->is_connecting())
			{
				// this peer is not unchokable. So, if it's unchoked
				// already, make sure to choke it.
				if (p->is_choked())
				{
					p->reset_choke_counters();
					continue;
				}
				if (pi && pi->optimistically_unchoked)
				{
					m_stats_counters.inc_stats_counter(counters::num_peers_up_unchoked_optimistic, -1);
					pi->optimistically_unchoked = false;
					// force a new optimistic unchoke
					m_optimistic_unchoke_time_scaler = 0;
				}
				t->choke_peer(*p);
				p->reset_choke_counters();
				continue;
			}

			peers.push_back(p.get());
		}

		// the unchoker wants an estimate of our upload rate capacity
		// (used by bittyrant)
		int max_upload_rate = upload_rate_limit(m_global_class);
		if (m_settings.get_int(settings_pack::choking_algorithm)
			== settings_pack::bittyrant_choker
			&& max_upload_rate == 0)
		{
			// we don't know at what rate we can upload. If we have a
			// measurement of the peak, use that + 10kB/s, otherwise
			// assume 20 kB/s
			max_upload_rate = (std::max)(20000, m_peak_up_rate + 10000);
			if (m_alerts.should_post<performance_alert>())
				m_alerts.emplace_alert<performance_alert>(torrent_handle()
					, performance_alert::bittyrant_with_no_uplimit);
		}

		int const allowed_upload_slots = unchoke_sort(peers, max_upload_rate
			, unchoke_interval, m_settings);
		m_stats_counters.set_value(counters::num_unchoke_slots
			, allowed_upload_slots);

#ifndef TORRENT_DISABLE_LOGGING

it might be a nice feature here to limit the number of torrents to send in a single update. By just posting the first n torrents, they would nicely be round-robined because the torrent lists are always pushed back. Perhaps the status_update_alert could even have a fixed array of n entries rather than a vector, to further improve memory locality.

../src/session_impl.cpp:4525

			t->status(&*i, flags);
		}
	}

	void session_impl::post_torrent_updates(boost::uint32_t flags)
	{
		INVARIANT_CHECK;

		TORRENT_ASSERT(is_single_thread());

		std::vector<torrent*>& state_updates
			= m_torrent_lists[aux::session_impl::torrent_state_updates];

#if TORRENT_USE_ASSERTS
		m_posting_torrent_updates = true;
#endif

		std::vector<torrent_status> status;
		status.reserve(state_updates.size());

		for (std::vector<torrent*>::iterator i = state_updates.begin()
			, end(state_updates.end()); i != end; ++i)
		{
			torrent* t = *i;
			TORRENT_ASSERT(t->m_links[aux::session_impl::torrent_state_updates].in_list());
			status.push_back(torrent_status());
			// querying accurate download counters may require
			// the torrent to be loaded. Loading a torrent, and evicting another
			// one will lead to calling state_updated(), which screws with
			// this list while we're working on it, and break things
			t->status(&status.back(), flags);
			t->clear_in_state_update();
		}
		state_updates.clear();

#if TORRENT_USE_ASSERTS
		m_posting_torrent_updates = false;
#endif

		m_alerts.emplace_alert<state_update_alert>(status);
	}

	void session_impl::post_session_stats()
	{
		m_disk_thread.update_stats_counters(m_stats_counters);

#ifndef TORRENT_DISABLE_DHT
		if (m_dht)
			m_dht->update_stats_counters(m_stats_counters);
#endif

this logic could probably be less spaghetti looking by being moved to a function with early exits

../src/session_impl.cpp:4738

		}

		// figure out the info hash of the torrent
		sha1_hash const* ih = 0;
		sha1_hash tmp;
		if (params.ti) ih = &params.ti->info_hash();
		else if (!params.url.empty())
		{
			// in order to avoid info-hash collisions, for
			// torrents where we don't have an info-hash, but
			// just a URL, set the temporary info-hash to the
			// hash of the URL. This will be changed once we
			// have the actual .torrent file
			tmp = hasher(&params.url[0], params.url.size()).final();
			ih = &tmp;
		}
		else ih = &params.info_hash;

		// we don't have a torrent file. If the user provided
		// resume data, there may be some metadata in there
		if ((!params.ti || !params.ti->is_valid())
			&& !params.resume_data.empty())
		{
			int pos;
			error_code err;
			bdecode_node root;
			bdecode_node info;
#ifndef TORRENT_DISABLE_LOGGING
			session_log("adding magnet link with resume data");
#endif
			if (bdecode(&params.resume_data[0], &params.resume_data[0]
					+ params.resume_data.size(), root, err, &pos) == 0
				&& root.type() == bdecode_node::dict_t
				&& (info = root.dict_find_dict("info")))
			{
#ifndef TORRENT_DISABLE_LOGGING
				session_log("found metadata in resume data");
#endif
				// verify the info-hash of the metadata stored in the resume file matches
				// the torrent we're loading

				std::pair<char const*, int> buf = info.data_section();
				sha1_hash resume_ih = hasher(buf.first, buf.second).final();

				// if url is set, the info_hash is not actually the info-hash of the
				// torrent, but the hash of the URL, until we have the full torrent
				// only require the info-hash to match if we actually passed in one
				if (resume_ih == params.info_hash
					|| !params.url.empty()
					|| params.info_hash.is_all_zeros())
				{

perhaps this function should not exist when logging is disabled

../src/session_impl.cpp:5414

		TORRENT_ASSERT(is_single_thread());

		INVARIANT_CHECK;

		boost::shared_ptr<torrent> t = find_torrent(ih).lock();
		if (!t) return;
		// don't add peers from lsd to private torrents
		if (t->torrent_file().priv() || (t->torrent_file().is_i2p()
			&& !m_settings.get_bool(settings_pack::allow_i2p_mixed))) return;

#ifndef TORRENT_DISABLE_LOGGING
		session_log("added peer from local discovery: %s", print_endpoint(peer).c_str());
#endif
		t->add_peer(peer, peer_info::lsd);
		t->do_connect_boost();

		if (m_alerts.should_post<lsd_peer_alert>())
			m_alerts.emplace_alert<lsd_peer_alert>(t->get_handle(), peer);
	}

	void session_impl::on_port_map_log(
		char const* msg, int map_transport)
	{
#ifndef TORRENT_DISABLE_LOGGING
		TORRENT_ASSERT(map_transport >= 0 && map_transport <= 1);
		// log message
		if (m_alerts.should_post<portmap_log_alert>())
			m_alerts.emplace_alert<portmap_log_alert>(map_transport, msg);
#else
		TORRENT_UNUSED(msg);
		TORRENT_UNUSED(map_transport);
#endif
	}

	void session_impl::on_port_mapping(int mapping, address const& ip, int port
		, error_code const& ec, int map_transport)
	{
		TORRENT_ASSERT(is_single_thread());

		TORRENT_ASSERT(map_transport >= 0 && map_transport <= 1);

		if (mapping == m_udp_mapping[map_transport] && port != 0)
		{
			m_external_udp_port = port;
			if (m_alerts.should_post<portmap_alert>())
				m_alerts.emplace_alert<portmap_alert>(mapping, port
					, map_transport);
			return;
		}

		if (mapping == m_tcp_mapping[map_transport] && port != 0)

make this more generic to not just work if files have been renamed, but also if they have been merged into a single file for instance maybe use the same format as .torrent files and reuse some code from torrent_info

../src/storage.cpp:895

				else
				{
					ec.ec = error;
					ec.file = i;
					ec.operation = storage_error::stat;
					m_stat_cache.set_error(i);
				}
			}

			fl.push_back(entry(entry::list_t));
			entry::list_type& p = fl.back().list();
			p.push_back(entry(file_size));
			p.push_back(entry(file_time));
		}
	}

	bool default_storage::verify_resume_data(bdecode_node const& rd
		, std::vector<std::string> const* links
		, storage_error& ec)
	{
		bdecode_node mapped_files = rd.dict_find_list("mapped_files");
		if (mapped_files && mapped_files.list_size() == m_files.num_files())
		{
			m_mapped_files.reset(new file_storage(m_files));
			for (int i = 0; i < m_files.num_files(); ++i)
			{
				std::string new_filename = mapped_files.list_string_value_at(i);
				if (new_filename.empty()) continue;
				m_mapped_files->rename_file(i, new_filename);
			}
		}

		bdecode_node file_priority = rd.dict_find_list("file_priority");
		if (file_priority && file_priority.list_size()
			== files().num_files())
		{
			m_file_priority.resize(file_priority.list_size());
			for (int i = 0; i < file_priority.list_size(); ++i)
				m_file_priority[i] = boost::uint8_t(file_priority.list_int_value_at(i, 1));
		}

		bdecode_node file_sizes_ent = rd.dict_find_list("file sizes");
		if (file_sizes_ent == 0)
		{
			ec.ec = errors::missing_file_sizes;
			ec.file = -1;
			ec.operation = storage_error::check_resume;
			return false;
		}

		if (file_sizes_ent.list_size() == 0)

if everything moves OK, except for the partfile we currently won't update the save path, which breaks things. it would probably make more sense to give up on the partfile

../src/storage.cpp:1234

					if (ec)
					{
						ec.file = i->second;
						ec.operation = storage_error::copy;
					}
					else
					{
						// ignore errors when removing
						error_code ignore;
						remove_all(old_path, ignore);
					}
					break;
				}
			}
		}

		if (!ec)
		{
			if (m_part_file)
			{
				m_part_file->move_partfile(save_path, ec.ec);
				if (ec)
				{
					ec.file = -1;
					ec.operation = storage_error::partfile_move;
					return piece_manager::fatal_disk_error;
				}
			}

			m_save_path = save_path;
		}
		return ret;
	}

	int default_storage::readv(file::iovec_t const* bufs, int num_bufs
		, int piece, int offset, int flags, storage_error& ec)
	{
		read_fileop op(*this, flags);

#ifdef TORRENT_SIMULATE_SLOW_READ
		boost::thread::sleep(boost::get_system_time()
			+ boost::posix_time::milliseconds(1000));
#endif
		return readwritev(files(), bufs, piece, offset, num_bufs, op, ec);
	}

	int default_storage::writev(file::iovec_t const* bufs, int num_bufs
		, int piece, int offset, int flags, storage_error& ec)
	{
		write_fileop op(*this, flags);
		return readwritev(files(), bufs, piece, offset, num_bufs, op, ec);

warning C4146: unary minus operator applied to unsigned type, result still unsigned

../src/string_util.cpp:60

#include <boost/tuple/tuple.hpp>

#include <cstdlib> // for malloc
#include <cstring> // for memmov/strcpy/strlen

#include "libtorrent/aux_/disable_warnings_pop.hpp"

namespace libtorrent
{

	// lexical_cast's result depends on the locale. We need
	// a well defined result
	boost::array<char, 4 + std::numeric_limits<boost::int64_t>::digits10>
		to_string(boost::int64_t n)
	{
		boost::array<char, 4 + std::numeric_limits<boost::int64_t>::digits10> ret;
		char *p = &ret.back();
		*p = '\0';
		boost::uint64_t un = n;
		if (n < 0)  un = -un;
		do {
			*--p = '0' + un % 10;
			un /= 10;
		} while (un);
		if (n < 0) *--p = '-';
		std::memmove(&ret[0], p, &ret.back() - p + 1);
		return ret;
	}

	bool is_alpha(char c)
	{
		return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z');
	}

	bool is_print(char c)
	{
		return c >= 32 && c < 127;
	}

	bool is_space(char c)
	{
		static const char* ws = " \t\n\r\f\v";
		return strchr(ws, c) != 0;
	}

	char to_lower(char c)
	{
		return (c >= 'A' && c <= 'Z') ? c - 'A' + 'a' : c;
	}

factor out cache_status to its own header

../src/torrent.cpp:101

#include "libtorrent/extensions.hpp"
#include "libtorrent/aux_/session_interface.hpp"
#include "libtorrent/instantiate_connection.hpp"
#include "libtorrent/assert.hpp"
#include "libtorrent/broadcast_socket.hpp"
#include "libtorrent/kademlia/dht_tracker.hpp"
#include "libtorrent/peer_info.hpp"
#include "libtorrent/http_connection.hpp"
#include "libtorrent/random.hpp"
#include "libtorrent/peer_class.hpp" // for peer_class
#include "libtorrent/socket_io.hpp" // for read_*_endpoint
#include "libtorrent/ip_filter.hpp"
#include "libtorrent/request_blocks.hpp"
#include "libtorrent/performance_counters.hpp" // for counters
#include "libtorrent/resolver_interface.hpp"
#include "libtorrent/alloca.hpp"
#include "libtorrent/resolve_links.hpp"
#include "libtorrent/aux_/file_progress.hpp"
#include "libtorrent/alert_manager.hpp"
#include "libtorrent/disk_interface.hpp"
#include "libtorrent/disk_io_thread.hpp" // for cache_status

#ifndef TORRENT_DISABLE_LOGGING
#include "libtorrent/aux_/session_impl.hpp" // for tracker_logger
#endif

using namespace libtorrent;
using boost::tuples::tuple;
using boost::tuples::get;
using boost::tuples::make_tuple;

namespace libtorrent
{
	namespace {

	int root2(int x)
	{
		int ret = 0;
		x >>= 1;
		while (x > 0)
		{
			// if this assert triggers, the block size
			// is not an even 2 exponent!
			TORRENT_ASSERT(x == 1 || (x & 1) == 0);
			++ret;
			x >>= 1;
		}
		return ret;
	}

	} // anonymous namespace

if the existing torrent doesn't have metadata, insert the metadata we just downloaded into it.

../src/torrent.cpp:468

		m_torrent_file = tf;

		// now, we might already have this torrent in the session.
		boost::shared_ptr<torrent> t = m_ses.find_torrent(m_torrent_file->info_hash()).lock();
		if (t)
		{
			if (!m_uuid.empty() && t->uuid().empty())
				t->set_uuid(m_uuid);
			if (!m_url.empty() && t->url().empty())
				t->set_url(m_url);
			if (!m_source_feed_url.empty() && t->source_feed_url().empty())
				t->set_source_feed_url(m_source_feed_url);

			// insert this torrent in the uuid index
			if (!m_uuid.empty() || !m_url.empty())
			{
				m_ses.insert_uuid_torrent(m_uuid.empty() ? m_url : m_uuid, t);
			}


			set_error(error_code(errors::duplicate_torrent, get_libtorrent_category()), error_file_url);
			abort();
			return;
		}

		m_ses.insert_torrent(m_torrent_file->info_hash(), me, m_uuid);

		TORRENT_ASSERT(num_torrents == int(m_ses.m_torrents.size()));

		// if the user added any trackers while downloading the
		// .torrent file, merge them into the new tracker list
		std::vector<announce_entry> new_trackers = m_torrent_file->trackers();
		for (std::vector<announce_entry>::iterator i = m_trackers.begin()
			, end(m_trackers.end()); i != end; ++i)
		{
			// if we already have this tracker, ignore it
			if (std::find_if(new_trackers.begin(), new_trackers.end()
				, boost::bind(&announce_entry::url, _1) == i->url) != new_trackers.end())
				continue;

			// insert the tracker ordered by tier
			new_trackers.insert(std::find_if(new_trackers.begin(), new_trackers.end()
				, boost::bind(&announce_entry::tier, _1) >= i->tier), *i);
		}
		m_trackers.swap(new_trackers);

#if !defined(TORRENT_DISABLE_ENCRYPTION) && !defined(TORRENT_DISABLE_EXTENSIONS)
		hasher h;
		h.update("req2", 4);
		h.update((char*)&m_torrent_file->info_hash()[0], 20);

if the existing torrent doesn't have metadata, insert the metadata we just downloaded into it.

../src/torrent.cpp:580

		m_torrent_file = tf;
		m_info_hash = tf->info_hash();

		// now, we might already have this torrent in the session.
		boost::shared_ptr<torrent> t = m_ses.find_torrent(m_torrent_file->info_hash()).lock();
		if (t)
		{
			if (!m_uuid.empty() && t->uuid().empty())
				t->set_uuid(m_uuid);
			if (!m_url.empty() && t->url().empty())
				t->set_url(m_url);
			if (!m_source_feed_url.empty() && t->source_feed_url().empty())
				t->set_source_feed_url(m_source_feed_url);

			// insert this torrent in the uuid index
			if (!m_uuid.empty() || !m_url.empty())
			{
				m_ses.insert_uuid_torrent(m_uuid.empty() ? m_url : m_uuid, t);
			}


			set_error(error_code(errors::duplicate_torrent, get_libtorrent_category()), torrent_status::error_file_url);
			abort();
			return;
		}

		m_ses.insert_torrent(m_torrent_file->info_hash(), me, m_uuid);

		// if the user added any trackers while downloading the
		// .torrent file, merge them into the new tracker list
		std::vector<announce_entry> new_trackers = m_torrent_file->trackers();
		for (std::vector<announce_entry>::iterator i = m_trackers.begin()
			, end(m_trackers.end()); i != end; ++i)
		{
			// if we already have this tracker, ignore it
			if (std::find_if(new_trackers.begin(), new_trackers.end()
				, boost::bind(&announce_entry::url, _1) == i->url) != new_trackers.end())
				continue;

			// insert the tracker ordered by tier
			new_trackers.insert(std::find_if(new_trackers.begin(), new_trackers.end()
				, boost::bind(&announce_entry::tier, _1) >= i->tier), *i);
		}
		m_trackers.swap(new_trackers);

		// add the web seeds from the .torrent file
		std::vector<web_seed_entry> const& web_seeds = m_torrent_file->web_seeds();
		m_web_seeds.insert(m_web_seeds.end(), web_seeds.begin(), web_seeds.end());

#if !defined(TORRENT_DISABLE_ENCRYPTION) && !defined(TORRENT_DISABLE_EXTENSIONS)
		hasher h;

is verify_peer_cert called once per certificate in the chain, and this function just tells us which depth we're at right now? If so, the comment makes sense. any certificate that isn't the leaf (i.e. the one presented by the peer) should be accepted automatically, given preverified is true. The leaf certificate need to be verified to make sure its DN matches the info-hash

../src/torrent.cpp:1562

			if (pp) p->add_extension(pp);
		}

		// if files are checked for this torrent, call the extension
		// to let it initialize itself
		if (m_connections_initialized)
			tp->on_files_checked();
	}

#endif

#ifdef TORRENT_USE_OPENSSL

#if BOOST_VERSION >= 104700
	bool torrent::verify_peer_cert(bool preverified, boost::asio::ssl::verify_context& ctx)
	{
		// if the cert wasn't signed by the correct CA, fail the verification
		if (!preverified) return false;

		// we're only interested in checking the certificate at the end of the chain.
		int depth = X509_STORE_CTX_get_error_depth(ctx.native_handle());
		if (depth > 0) return true;

		X509* cert = X509_STORE_CTX_get_current_cert(ctx.native_handle());

		// Go through the alternate names in the certificate looking for matching DNS entries
		GENERAL_NAMES* gens = static_cast<GENERAL_NAMES*>(
			X509_get_ext_d2i(cert, NID_subject_alt_name, 0, 0));

#ifndef TORRENT_DISABLE_LOGGING
		std::string names;
		bool match = false;
#endif
		for (int i = 0; i < aux::openssl_num_general_names(gens); ++i)
		{
			GENERAL_NAME* gen = aux::openssl_general_name_value(gens, i);
			if (gen->type != GEN_DNS) continue;
			ASN1_IA5STRING* domain = gen->d.dNSName;
			if (domain->type != V_ASN1_IA5STRING || !domain->data || !domain->length) continue;
			const char* torrent_name = reinterpret_cast<const char*>(domain->data);
			std::size_t name_length = domain->length;

#ifndef TORRENT_DISABLE_LOGGING
			if (i > 1) names += " | n: ";
			names.append(torrent_name, name_length);
#endif
			if (strncmp(torrent_name, "*", name_length) == 0
				|| strncmp(torrent_name, m_torrent_file->name().c_str(), name_length) == 0)
			{
#ifndef TORRENT_DISABLE_LOGGING
				match = true;

instead of creating the picker up front here, maybe this whole section should move to need_picker()

../src/torrent.cpp:1984

			m_have_all = true;
			m_ses.get_io_service().post(boost::bind(&torrent::files_checked, shared_from_this()));
			m_resume_data.reset();
			update_gauge();
			update_state_list();
			return;
		}

		set_state(torrent_status::checking_resume_data);

		int num_pad_files = 0;
		TORRENT_ASSERT(block_size() > 0);
		file_storage const& fs = m_torrent_file->files();
		for (int i = 0; i < fs.num_files(); ++i)
		{
			if (fs.pad_file_at(i)) ++num_pad_files;

			if (!fs.pad_file_at(i) || fs.file_size(i) == 0) continue;
			m_padding += boost::uint32_t(fs.file_size(i));

			need_picker();

			peer_request pr = m_torrent_file->map_file(i, 0, fs.file_size(i));
			int off = pr.start & (block_size()-1);
			if (off != 0) { pr.length -= block_size() - off; pr.start += block_size() - off; }
			TORRENT_ASSERT((pr.start & (block_size()-1)) == 0);

			int block = block_size();
			int blocks_per_piece = m_torrent_file->piece_length() / block;
			piece_block pb(pr.piece, pr.start / block);
			for (; pr.length >= block; pr.length -= block, ++pb.block_index)
			{
				if (int(pb.block_index) == blocks_per_piece) { pb.block_index = 0; ++pb.piece_index; }
				m_picker->mark_as_finished(pb, 0);
			}
			// ugly edge case where padfiles are not used they way they're
			// supposed to be. i.e. added back-to back or at the end
			if (int(pb.block_index) == blocks_per_piece) { pb.block_index = 0; ++pb.piece_index; }
			if (pr.length > 0 && ((i+1 != fs.num_files() && fs.pad_file_at(i+1))
				|| i + 1 == fs.num_files()))
			{
				m_picker->mark_as_finished(pb, 0);
			}
		}

		if (m_padding > 0)
		{
			// if we marked an entire piece as finished, we actually
			// need to consider it finished

			std::vector<piece_picker::downloading_piece> dq

this could be optimized by looking up which files are complete and just look at those

../src/torrent.cpp:2058

		if (!need_loaded()) return;

		if (num_pad_files > 0)
			m_picker->set_num_pad_files(num_pad_files);

		std::vector<std::string> links;
#ifndef TORRENT_DISABLE_MUTABLE_TORRENTS
		if (!m_torrent_file->similar_torrents().empty()
			|| !m_torrent_file->collections().empty())
		{
			resolve_links res(m_torrent_file);

			std::vector<sha1_hash> s = m_torrent_file->similar_torrents();
			for (std::vector<sha1_hash>::iterator i = s.begin(), end(s.end());
				i != end; ++i)
			{
				boost::shared_ptr<torrent> t = m_ses.find_torrent(*i).lock();
				if (!t) continue;

				// Only attempt to reuse files from torrents that are seeding.
				if (!t->is_seed()) continue;

				res.match(t->get_torrent_copy(), t->save_path());
			}
			std::vector<std::string> c = m_torrent_file->collections();
			for (std::vector<std::string>::iterator i = c.begin(), end(c.end());
				i != end; ++i)
			{
				std::vector<boost::shared_ptr<torrent> > ts = m_ses.find_collection(*i);

				for (std::vector<boost::shared_ptr<torrent> >::iterator k = ts.begin()
					, end2(ts.end()); k != end2; ++k)
				{
					// Only attempt to reuse files from torrents that are seeding.

this could be optimized by looking up which files are complete and just look at those

../src/torrent.cpp:2074

				i != end; ++i)
			{
				boost::shared_ptr<torrent> t = m_ses.find_torrent(*i).lock();
				if (!t) continue;

				// Only attempt to reuse files from torrents that are seeding.
				if (!t->is_seed()) continue;

				res.match(t->get_torrent_copy(), t->save_path());
			}
			std::vector<std::string> c = m_torrent_file->collections();
			for (std::vector<std::string>::iterator i = c.begin(), end(c.end());
				i != end; ++i)
			{
				std::vector<boost::shared_ptr<torrent> > ts = m_ses.find_collection(*i);

				for (std::vector<boost::shared_ptr<torrent> >::iterator k = ts.begin()
					, end2(ts.end()); k != end2; ++k)
				{
					// Only attempt to reuse files from torrents that are seeding.
					if (!(*k)->is_seed()) continue;

					res.match((*k)->get_torrent_copy(), (*k)->save_path());
				}
			}

			std::vector<resolve_links::link_t> const& l = res.get_links();
			if (!l.empty())
			{
				for (std::vector<resolve_links::link_t>::const_iterator i = l.begin()
					, end(l.end()); i != end; ++i)
				{
					if (!i->ti) continue;

					torrent_info const& ti = *i->ti;
					std::string const& save_path = i->save_path;
					links.push_back(combine_path(save_path
						, ti.files().file_path(i->file_idx)));
				}
			}
		}
#endif // TORRENT_DISABLE_MUTABLE_TORRENTS

		inc_refcount("check_fastresume");
		// async_check_fastresume will gut links
		m_ses.disk_thread().async_check_fastresume(
			m_storage.get(), m_resume_data ? &m_resume_data->node : NULL
			, links, boost::bind(&torrent::on_resume_data_checked
			, shared_from_this(), _1));
#ifndef TORRENT_DISABLE_LOGGING
		debug_log("init, async_check_fastresume");

there may be peer extensions relying on the torrent extension still being alive. Only do this if there are no peers. And when the last peer is disconnected, if the torrent is unloaded, clear the extensions m_extensions.clear();

../src/torrent.cpp:2240

		// pinned torrents are not allowed to be swapped out
		TORRENT_ASSERT(!m_pinned);

		m_should_be_loaded = false;

		// make sure it's not unloaded in the middle of some operation that uses it
		if (m_refcount > 0) return;

		// call on_unload() on extensions
#ifndef TORRENT_DISABLE_EXTENSIONS
		for (extension_list_t::iterator i = m_extensions.begin()
			, end(m_extensions.end()); i != end; ++i)
		{
			TORRENT_TRY {
				(*i)->on_unload();
			} TORRENT_CATCH (std::exception&) {}
		}

		// also remove extensions and re-instantiate them when the torrent is loaded again
		// they end up using a significant amount of memory
#endif

		// someone else holds a reference to the torrent_info
		// make the torrent release its reference to it,
		// after making a copy and then unloading that version
		// as soon as the user is done with its copy of torrent_info
		// it will be freed, and we'll have the unloaded version left
		if (!m_torrent_file.unique())
			m_torrent_file = boost::make_shared<torrent_info>(*m_torrent_file);

		m_torrent_file->unload();
		inc_stats_counter(counters::num_loaded_torrents, -1);

		m_storage.reset();

		state_updated();
	}

	bt_peer_connection* torrent::find_introducer(tcp::endpoint const& ep) const
	{
#ifndef TORRENT_DISABLE_EXTENSIONS
		for (const_peer_iterator i = m_connections.begin(); i != m_connections.end(); ++i)
		{
			if ((*i)->type() != peer_connection::bittorrent_connection) continue;
			bt_peer_connection* p = static_cast<bt_peer_connection*>(*i);
			if (!p->supports_holepunch()) continue;
			peer_plugin const* pp = p->find_plugin("ut_pex");
			if (!pp) continue;
			if (was_introduced_by(pp, ep)) return p;
		}
#else

this pattern is repeated in a few places. Factor this into a function and generalize the concept of a torrent having a dedicated listen port

../src/torrent.cpp:2932

		// if the files haven't been checked yet, we're
		// not ready for peers. Except, if we don't have metadata,
		// we need peers to download from
		if (!m_files_checked && valid_metadata()) return;

		if (!m_announce_to_lsd) return;

		// private torrents are never announced on LSD
		if (m_torrent_file->is_valid() && m_torrent_file->priv()) return;

		// i2p torrents are also never announced on LSD
		// unless we allow mixed swarms
		if (m_torrent_file->is_valid()
			&& (torrent_file().is_i2p() && !settings().get_bool(settings_pack::allow_i2p_mixed)))
			return;

		if (is_paused()) return;

		if (!m_ses.has_lsd()) return;

#ifdef TORRENT_USE_OPENSSL
		int port = is_ssl_torrent() ? m_ses.ssl_listen_port() : m_ses.listen_port();
#else
		int port = m_ses.listen_port();
#endif

		// announce with the local discovery service
		m_ses.announce_lsd(m_torrent_file->info_hash(), port
			, settings().get_bool(settings_pack::broadcast_lsd) && m_lsd_seq == 0);
		++m_lsd_seq;
	}

#ifndef TORRENT_DISABLE_DHT

	void torrent::dht_announce()
	{
		TORRENT_ASSERT(is_single_thread());
		if (!m_ses.dht())
		{
#ifndef TORRENT_DISABLE_LOGGING
			debug_log("DHT: no dht initialized");
#endif
			return;
		}
		if (!should_announce_dht())
		{
#ifndef TORRENT_DISABLE_LOGGING
			if (!m_ses.announce_dht())
				debug_log("DHT: no listen sockets");

			if (m_torrent_file->is_valid() && !m_files_checked)

add one peer per IP the hostname resolves to

../src/torrent.cpp:3779

#endif

	void torrent::on_peer_name_lookup(error_code const& e
		, std::vector<address> const& host_list, int port)
	{
		TORRENT_ASSERT(is_single_thread());

		INVARIANT_CHECK;

#if defined TORRENT_ASIO_DEBUGGING
		complete_async("torrent::on_peer_name_lookup");
#endif

#ifndef TORRENT_DISABLE_LOGGING
		if (e)
			debug_log("peer name lookup error: %s", e.message().c_str());
#endif

		if (e || host_list.empty() || m_ses.is_aborted()) return;

		tcp::endpoint host(host_list.front(), port);

		if (m_ip_filter && m_ip_filter->access(host.address()) & ip_filter::blocked)
		{
#ifndef TORRENT_DISABLE_LOGGING
			error_code ec;
			debug_log("blocked ip from tracker: %s", host.address().to_string(ec).c_str());
#endif
			if (m_ses.alerts().should_post<peer_blocked_alert>())
				m_ses.alerts().emplace_alert<peer_blocked_alert>(get_handle()
					, host.address(), peer_blocked_alert::ip_filter);
			return;
		}

		if (add_peer(host, peer_info::tracker))
			state_updated();
		update_want_peers();
	}

	boost::int64_t torrent::bytes_left() const
	{
		// if we don't have the metadata yet, we
		// cannot tell how big the torrent is.
		if (!valid_metadata()) return -1;
		return m_torrent_file->total_size()
			- quantized_bytes_done();
	}

	boost::int64_t torrent::quantized_bytes_done() const
	{
//		INVARIANT_CHECK;

update suggest_piece?

../src/torrent.cpp:4719

		if (has_picker())
		{
			torrent_peer* pp = peer->peer_info_struct();
			m_picker->inc_refcount_all(pp);
		}
#ifdef TORRENT_DEBUG
		else
		{
			TORRENT_ASSERT(is_seed() || !m_have_all);
		}
#endif
	}

	void torrent::peer_lost(bitfield const& bits, peer_connection const* peer)
	{
		if (has_picker())
		{
			TORRENT_ASSERT(bits.size() == torrent_file().num_pieces());
			torrent_peer* pp = peer->peer_info_struct();
			m_picker->dec_refcount(bits, pp);
		}
#ifdef TORRENT_DEBUG
		else
		{
			TORRENT_ASSERT(is_seed() || !m_have_all);
		}
#endif
	}

	void torrent::peer_lost(int index, peer_connection const* peer)
	{
		if (m_picker.get())
		{
			torrent_peer* pp = peer->peer_info_struct();
			m_picker->dec_refcount(index, pp);
			update_suggest_piece(index, -1);
		}
#ifdef TORRENT_DEBUG
		else
		{
			TORRENT_ASSERT(is_seed() || !m_have_all);
		}
#endif
	}

	void torrent::add_suggest_piece(int index)
	{
		// it would be nice if we would keep track of piece
		// availability even when we're a seed, for
		// the suggest piece feature
		if (!has_picker()) return;

really, we should just keep the picker around in this case to maintain the availability counters

../src/torrent.cpp:4863

		pieces.reserve(cs.pieces.size());

		// sort in ascending order, to get most recently used first
		std::sort(cs.pieces.begin(), cs.pieces.end()
			, boost::bind(&cached_piece_info::last_use, _1)
			> boost::bind(&cached_piece_info::last_use, _2));

		for (std::vector<cached_piece_info>::iterator i = cs.pieces.begin()
			, end(cs.pieces.end()); i != end; ++i)
		{
			TORRENT_ASSERT(i->storage == m_storage.get());
			if (!has_piece_passed(i->piece)) continue;
			suggest_piece_t p;
			p.piece_index = i->piece;
			if (has_picker())
			{
				p.num_peers = m_picker->get_availability(i->piece);
			}
			else
			{
				p.num_peers = 0;
				for (const_peer_iterator j = m_connections.begin()
					, end2(m_connections.end()); j != end2; ++j)
				{
					peer_connection* peer = *j;
					if (peer->has_piece(p.piece_index)) ++p.num_peers;
				}
			}
			pieces.push_back(p);
		}

		// sort by rarity (stable, to maintain sort
		// by last use)
		std::stable_sort(pieces.begin(), pieces.end());

		// only suggest half of the pieces
		pieces.resize(pieces.size() / 2);

		// send new suggests to peers
		// the peers will filter out pieces we've
		// already suggested to them
		for (std::vector<suggest_piece_t>::iterator i = pieces.begin()
			, end(pieces.end()); i != end; ++i)
		{
			for (peer_iterator p = m_connections.begin();
				p != m_connections.end(); ++p)
				(*p)->send_suggest(i->piece_index);
		}
	}

	void torrent::abort()

make this more generic to not just work if files have been renamed, but also if they have been merged into a single file for instance maybe use the same format as .torrent files and reuse some code from torrent_info The mapped_files needs to be read both in the network thread and in the disk thread, since they both have their own mapped files structures which are kept in sync

../src/torrent.cpp:6926

			{
				m_save_path = p;
#ifndef TORRENT_DISABLE_LOGGING
				debug_log("loaded resume data: save-path: %s", m_save_path.c_str());
#endif
			}
		}

		m_url = rd.dict_find_string_value("url");
		m_uuid = rd.dict_find_string_value("uuid");
		m_source_feed_url = rd.dict_find_string_value("feed");

		if (!m_uuid.empty() || !m_url.empty())
		{
			boost::shared_ptr<torrent> me(shared_from_this());

			// insert this torrent in the uuid index
			m_ses.insert_uuid_torrent(m_uuid.empty() ? m_url : m_uuid, me);
		}

		bdecode_node mapped_files = rd.dict_find_list("mapped_files");
		if (mapped_files && mapped_files.list_size() == m_torrent_file->num_files())
		{
			for (int i = 0; i < m_torrent_file->num_files(); ++i)
			{
				std::string new_filename = mapped_files.list_string_value_at(i);
				if (new_filename.empty()) continue;
				m_torrent_file->rename_file(i, new_filename);
			}
		}

		m_added_time = rd.dict_find_int_value("added_time", m_added_time);
		m_completed_time = rd.dict_find_int_value("completed_time", m_completed_time);
		if (m_completed_time != 0 && m_completed_time < m_added_time)
			m_completed_time = m_added_time;

		// load file priorities except if the add_torrent_param file was set to
		// override resume data
		if (!m_override_resume_data || m_file_priority.empty())
		{
			bdecode_node file_priority = rd.dict_find_list("file_priority");
			if (file_priority)
			{
				const int num_files = (std::min)(file_priority.list_size()
					, m_torrent_file->num_files());
				m_file_priority.resize(num_files, 4);
				for (int i = 0; i < num_files; ++i)
				{
					m_file_priority[i] = file_priority.list_int_value_at(i, 1);
					// this is suspicious, leave seed mode
					if (m_file_priority[i] == 0) m_seed_mode = false;

if this is a merkle torrent and we can't restore the tree, we need to wipe all the bits in the have array, but not necessarily we might want to do a full check to see if we have all the pieces. This is low priority since almost no one uses merkle torrents

../src/torrent.cpp:7059

				add_web_seed(url, web_seed_entry::http_seed);
			}
		}

		if (m_torrent_file->is_merkle_torrent())
		{
			bdecode_node mt = rd.dict_find_string("merkle tree");
			if (mt)
			{
				std::vector<sha1_hash> tree;
				tree.resize(m_torrent_file->merkle_tree().size());
				std::memcpy(&tree[0], mt.string_ptr()
					, (std::min)(mt.string_length(), int(tree.size()) * 20));
				if (mt.string_length() < int(tree.size()) * 20)
					std::memset(&tree[0] + mt.string_length() / 20, 0
						, tree.size() - mt.string_length() / 20);
				m_torrent_file->set_merkle_tree(tree);
			}
			else
			{
				TORRENT_ASSERT(false);
			}
		}

		// updating some of the torrent state may have set need_save_resume_data.
		// clear it here since we've just restored the resume data we already
		// have. Nothing has changed from that state yet.
		m_need_save_resume_data = false;

		if (m_seed_mode)
		{
			// some sanity checking. Maybe we shouldn't be in seed mode anymore
			bdecode_node pieces = rd.dict_find("pieces");
			if (pieces && pieces.type() == bdecode_node::string_t
				&& int(pieces.string_length()) == m_torrent_file->num_pieces())
			{
				char const* pieces_str = pieces.string_ptr();
				for (int i = 0, end(pieces.string_length()); i < end; ++i)
				{
					// being in seed mode and missing a piece is not compatible.
					// Leave seed mode if that happens
					if ((pieces_str[i] & 1)) continue;
					m_seed_mode = false;
					break;
				}
			}

			bdecode_node piece_priority = rd.dict_find_string("piece_priority");
			if (piece_priority && piece_priority.string_length()
				== m_torrent_file->num_pieces())
			{

make this more generic to not just work if files have been renamed, but also if they have been merged into a single file for instance. using file_base

../src/torrent.cpp:7303

			if (!has_picker())
			{
				std::memset(&pieces[0], m_have_all, pieces.size());
			}
			else if (has_picker())
			{
				for (int i = 0, end(pieces.size()); i < end; ++i)
					pieces[i] = m_picker->have_piece(i) ? 1 : 0;
			}

			if (m_seed_mode)
			{
				TORRENT_ASSERT(m_verified.size() == pieces.size());
				TORRENT_ASSERT(m_verifying.size() == pieces.size());
				for (int i = 0, end(pieces.size()); i < end; ++i)
					pieces[i] |= m_verified[i] ? 2 : 0;
			}
		}

		// write renamed files
		if (&m_torrent_file->files() != &m_torrent_file->orig_files()
			&& m_torrent_file->files().num_files() == m_torrent_file->orig_files().num_files())
		{
			entry::list_type& fl = ret["mapped_files"].list();
			file_storage const& fs = m_torrent_file->files();
			for (int i = 0; i < fs.num_files(); ++i)
			{
				fl.push_back(fs.file_path(i));
			}
		}

		// write local peers

		std::back_insert_iterator<entry::string_type> peers(ret["peers"].string());
		std::back_insert_iterator<entry::string_type> banned_peers(ret["banned_peers"].string());
#if TORRENT_USE_IPV6
		std::back_insert_iterator<entry::string_type> peers6(ret["peers6"].string());
		std::back_insert_iterator<entry::string_type> banned_peers6(ret["banned_peers6"].string());
#endif

		int num_saved_peers = 0;

		std::vector<torrent_peer const*> deferred_peers;

		if (m_peer_list)
		{
			for (peer_list::const_iterator i = m_peer_list->begin_peer()
				, end(m_peer_list->end_peer()); i != end; ++i)
			{
				error_code ec;
				torrent_peer const* p = *i;

add a flag to ignore stats, and only care about resume data for content. For unchanged files, don't trigger a load of the metadata just to save an empty resume data file

../src/torrent.cpp:9559

		if (m_complete != 0xffffff) seeds = m_complete;
		else seeds = m_peer_list ? m_peer_list->num_seeds() : 0;

		if (m_incomplete != 0xffffff) downloaders = m_incomplete;
		else downloaders = m_peer_list ? m_peer_list->num_peers() - m_peer_list->num_seeds() : 0;

		if (seeds == 0)
		{
			ret |= no_seeds;
			ret |= downloaders & prio_mask;
		}
		else
		{
			ret |= ((1 + downloaders) * scale / seeds) & prio_mask;
		}

		return ret;
	}

	// this is an async operation triggered by the client
	void torrent::save_resume_data(int flags)
	{
		TORRENT_ASSERT(is_single_thread());
		INVARIANT_CHECK;

		if (!valid_metadata())
		{
			alerts().emplace_alert<save_resume_data_failed_alert>(get_handle()
				, errors::no_metadata);
			return;
		}

		if ((flags & torrent_handle::only_if_modified) && !m_need_save_resume_data)
		{
			alerts().emplace_alert<save_resume_data_failed_alert>(get_handle()
				, errors::resume_data_not_modified);
			return;
		}

		m_need_save_resume_data = false;
		m_last_saved_resume = m_ses.session_time();
		m_save_resume_flags = boost::uint8_t(flags);
		state_updated();

		if (m_state == torrent_status::checking_files
			|| m_state == torrent_status::checking_resume_data)
		{
			if (!need_loaded())
			{
				alerts().emplace_alert<save_resume_data_failed_alert>(get_handle()
					, m_error);

instead of resorting the whole list, insert the peers directly into the right place

../src/torrent.cpp:11186

				printf("timed out [average-piece-time: %d ms ]\n"
					, m_average_piece_time);
#endif
			}

			// pick all blocks for this piece. the peers list is kept up to date
			// and sorted. when we issue a request to a peer, its download queue
			// time will increase and it may need to be bumped in the peers list,
			// since it's ordered by download queue time
			pick_time_critical_block(peers, ignore_peers
				, peers_with_requests
				, pi, &*i, m_picker.get()
				, blocks_in_piece, timed_out);

			// put back the peers we ignored into the peer list for the next piece
			if (!ignore_peers.empty())
			{
				peers.insert(peers.begin(), ignore_peers.begin(), ignore_peers.end());
				ignore_peers.clear();

				std::sort(peers.begin(), peers.end()
					, boost::bind(&peer_connection::download_queue_time, _1, 16*1024)
					< boost::bind(&peer_connection::download_queue_time, _2, 16*1024));
			}

			// if this peer's download time exceeds 2 seconds, we're done.
			// We don't want to build unreasonably long request queues
			if (!peers.empty() && peers[0]->download_queue_time() > milliseconds(2000))
				break;
		}

		// commit all the time critical requests
		for (std::set<peer_connection*>::iterator i = peers_with_requests.begin()
			, end(peers_with_requests.end()); i != end; ++i)
		{
			(*i)->send_block_requests();
		}
	}

	std::set<std::string> torrent::web_seeds(web_seed_entry::type_t type) const
	{
		TORRENT_ASSERT(is_single_thread());
		std::set<std::string> ret;
		for (std::list<web_seed_t>::const_iterator i = m_web_seeds.begin()
			, end(m_web_seeds.end()); i != end; ++i)
		{
			if (i->peer_info.banned) continue;
			if (i->removed) continue;
			if (i->type != type) continue;
			ret.insert(i->url);
		}

how do we deal with our external address changing?

../src/torrent_peer.cpp:188

		, is_v6_addr(false)
#endif
#if TORRENT_USE_I2P
		, is_i2p_addr(false)
#endif
		, on_parole(false)
		, banned(false)
		, supports_utp(true) // assume peers support utp
		, confirmed_supports_utp(false)
		, supports_holepunch(false)
		, web_seed(false)
#if TORRENT_USE_ASSERTS
		, in_use(false)
#endif
	{
		TORRENT_ASSERT((src & 0xff) == src);
	}

	boost::uint32_t torrent_peer::rank(external_ip const& external, int external_port) const
	{
		if (peer_rank == 0)
			peer_rank = peer_priority(
				tcp::endpoint(external.external_address(this->address()), external_port)
				, tcp::endpoint(this->address(), this->port));
		return peer_rank;
	}

#ifndef TORRENT_DISABLE_LOGGING
	std::string torrent_peer::to_string() const
	{
#if TORRENT_USE_I2P
		if (is_i2p_addr) return dest();
#endif // TORRENT_USE_I2P
		error_code ec;
		return address().to_string(ec);
	}
#endif

	boost::uint64_t torrent_peer::total_download() const
	{
		if (connection != 0)
		{
			TORRENT_ASSERT(prev_amount_download == 0);
			return connection->statistics().total_payload_download();
		}
		else
		{
			return boost::uint64_t(prev_amount_download) << 10;
		}
	}

it would be nice to detect this on posix systems also

../src/udp_socket.cpp:320

		else
#endif
		{
			if (m_restart_v4) {
				--m_restart_v4;
				setup_read(s);
			}
		}
		return;
	}
	if (m_abort) return;

	CHECK_MAGIC;

	for (;;)
	{
		error_code err;
		udp::endpoint ep;
		size_t bytes_transferred = s->receive_from(boost::asio::buffer(m_buf, m_buf_size), ep, 0, err);

#ifdef TORRENT_WINDOWS
		if ((err == error_code(ERROR_MORE_DATA, system_category())
			|| err == error_code(WSAEMSGSIZE, system_category()))
			&& m_buf_size < 65536)
		{
			// if this function fails to allocate memory, m_buf_size
			// is set to 0. In that case, don't issue the async_read().
			set_buf_size(m_buf_size * 2);
			if (m_buf_size == 0) return;
			continue;
		}
#endif

		if (err == boost::asio::error::would_block || err == boost::asio::error::try_again) break;
		on_read_impl(ep, err, bytes_transferred);

		// found on iOS, socket will be disconnected when app goes backgroud. try to reopen it.
		if (err == boost::asio::error::not_connected || err == boost::asio::error::bad_descriptor)
		{
			ep = s->local_endpoint(err);
			if (!err) {
				bind(ep, err);
			}
			return;
		}
	}
	call_drained_handler();
	setup_read(s);
}

void udp_socket::call_handler(error_code const& ec, udp::endpoint const& ep, char const* buf, int size)

use the system resolver_interface here

../src/udp_socket.cpp:869

void udp_socket::set_proxy_settings(aux::proxy_settings const& ps)
{
	CHECK_MAGIC;
	TORRENT_ASSERT(is_single_thread());

	error_code ec;
	m_socks5_sock.close(ec);
	m_tunnel_packets = false;

	m_proxy_settings = ps;

	if (m_abort) return;

	if (ps.type == settings_pack::socks5
		|| ps.type == settings_pack::socks5_pw)
	{
		m_queue_packets = true;
		// connect to socks5 server and open up the UDP tunnel

		tcp::resolver::query q(ps.hostname, to_string(ps.port).elems);
		++m_outstanding_ops;
#if TORRENT_USE_ASSERTS
		++m_outstanding_resolve;
#endif
#if defined TORRENT_ASIO_DEBUGGING
		add_outstanding_async("udp_socket::on_name_lookup");
#endif
		m_resolver.async_resolve(q, boost::bind(
			&udp_socket::on_name_lookup, this, _1, _2));
	}
}

void udp_socket::on_name_lookup(error_code const& e, tcp::resolver::iterator i)
{
#if defined TORRENT_ASIO_DEBUGGING
	complete_async("udp_socket::on_name_lookup");
#endif
#if TORRENT_USE_ASSERTS
	TORRENT_ASSERT(m_outstanding_resolve > 0);
	--m_outstanding_resolve;
#endif

	TORRENT_ASSERT(m_outstanding_ops > 0);
	--m_outstanding_ops;
	TORRENT_ASSERT(m_outstanding_ops == m_outstanding_connect
		+ m_outstanding_timeout
		+ m_outstanding_resolve
		+ m_outstanding_socks);

	if (m_abort) return;

we really need to increment the refcounter on the torrent while this buffer is still in the peer's send buffer

../src/ut_metadata.cpp:320

				if (!m_tp.need_loaded()) return;
				metadata = m_tp.metadata().begin + offset;
				metadata_piece_size = (std::min)(
					int(m_tp.get_metadata_size() - offset), 16 * 1024);
				TORRENT_ASSERT(metadata_piece_size > 0);
				TORRENT_ASSERT(offset >= 0);
				TORRENT_ASSERT(offset + metadata_piece_size <= int(m_tp.get_metadata_size()));
			}

			char msg[200];
			char* header = msg;
			char* p = &msg[6];
			int len = bencode(p, e);
			int total_size = 2 + len + metadata_piece_size;
			namespace io = detail;
			io::write_uint32(total_size, header);
			io::write_uint8(bt_peer_connection::msg_extended, header);
			io::write_uint8(m_message_index, header);

			m_pc.send_buffer(msg, len + 6);
			if (metadata_piece_size) m_pc.append_const_send_buffer(
				metadata, metadata_piece_size);

			m_pc.stats_counters().inc_stats_counter(counters::num_outgoing_extended);
			m_pc.stats_counters().inc_stats_counter(counters::num_outgoing_metadata);
		}

		virtual bool on_extended(int length
			, int extended_msg, buffer::const_interval body) TORRENT_OVERRIDE
		{
			if (extended_msg != 2) return false;
			if (m_message_index == 0) return false;

			if (length > 17 * 1024)
			{
#ifndef TORRENT_DISABLE_LOGGING
				m_pc.peer_log(peer_log_alert::incoming_message, "UT_METADATA"
					, "packet too big %d", length);
#endif
				m_pc.disconnect(errors::invalid_metadata_message, op_bittorrent, 2);
				return true;
			}

			if (!m_pc.packet_finished()) return true;

			int len;
			entry msg = bdecode(body.begin, body.end, len);
			if (msg.type() != entry::dictionary_t)
			{
#ifndef TORRENT_DISABLE_LOGGING
				m_pc.peer_log(peer_log_alert::incoming_message, "UT_METADATA"

this loop is not very efficient. It could be fixed by having a separate list of sequence numbers that need resending

../src/utp_stream.cpp:1761

};

// sends a packet, pulls data from the write buffer (if there's any)
// if ack is true, we need to send a packet regardless of if there's
// any data. Returns true if we could send more data (i.e. call
// send_pkt() again)
// returns true if there is more space for payload in our
// congestion window, false if there is no more space.
bool utp_socket_impl::send_pkt(int flags)
{
#ifdef TORRENT_EXPENSIVE_INVARIANT_CHECKS
	INVARIANT_CHECK;
#endif

	bool force = (flags & pkt_ack) || (flags & pkt_fin);

//	TORRENT_ASSERT(m_state != UTP_STATE_FIN_SENT || (flags & pkt_ack));

	// first see if we need to resend any packets

	for (int i = (m_acked_seq_nr + 1) & ACK_MASK; i != m_seq_nr; i = (i + 1) & ACK_MASK)
	{
		packet* p = m_outbuf.at(i);
		if (!p) continue;
		if (!p->need_resend) continue;
		if (!resend_packet(p))
		{
			// we couldn't resend the packet. It probably doesn't
			// fit in our cwnd. If force is set, we need to continue
			// to send our packet anyway, if we don't have force set,
			// we might as well return
			if (!force) return false;
			// resend_packet might have failed
			if (m_state == UTP_STATE_ERROR_WAIT || m_state == UTP_STATE_DELETE) return false;
			break;
		}

		// don't fast-resend this packet
		if (m_fast_resend_seq_nr == i)
			m_fast_resend_seq_nr = (m_fast_resend_seq_nr + 1) & ACK_MASK;
	}

	int sack = 0;
	if (m_inbuf.size())
	{
		// the SACK bitfield should ideally fit all
		// the pieces we have successfully received
		sack = (m_inbuf.span() + 7) / 8;
		if (sack > 32) sack = 32;
	}

introduce a web-seed default class which has a low download priority

../src/web_connection_base.cpp:81

		peer_connection_args const& pack
		, web_seed_t& web)
		: peer_connection(pack)
		, m_first_request(true)
		, m_ssl(false)
		, m_external_auth(web.auth)
		, m_extra_headers(web.extra_headers)
		, m_parser(http_parser::dont_parse_chunks)
		, m_body_start(0)
	{
		TORRENT_ASSERT(&web.peer_info == pack.peerinfo);
		// when going through a proxy, we don't necessarily have an endpoint here,
		// since the proxy might be resolving the hostname, not us
		TORRENT_ASSERT(web.endpoints.empty() || web.endpoints.front() == pack.endp);

		INVARIANT_CHECK;

		TORRENT_ASSERT(is_outgoing());

		// we only want left-over bandwidth

		std::string protocol;
		error_code ec;
		boost::tie(protocol, m_basic_auth, m_host, m_port, m_path)
			= parse_url_components(web.url, ec);
		TORRENT_ASSERT(!ec);

		if (m_port == -1 && protocol == "http")
			m_port = 80;

#ifdef TORRENT_USE_OPENSSL
		if (protocol == "https")
		{
			m_ssl = true;
			if (m_port == -1) m_port = 443;
		}
#endif

		if (!m_basic_auth.empty())
			m_basic_auth = base64encode(m_basic_auth);

		m_server_string = "URL seed @ ";
		m_server_string += m_host;
	}

	int web_connection_base::timeout() const
	{
		// since this is a web seed, change the timeout
		// according to the settings.
		return m_settings.get_int(settings_pack::urlseed_timeout);
	}

c++11 use a lambda here instead

../src/kademlia/dht_storage.cpp:426

			return true;
		}

		void put_mutable_item(sha1_hash const& target
			, char const* buf, int size
			, char const* sig
			, boost::int64_t seq
			, char const* pk
			, char const* salt, int salt_size
			, address const& addr) TORRENT_OVERRIDE
		{
			dht_mutable_table_t::iterator i = m_mutable_table.find(target);
			if (i == m_mutable_table.end())
			{
				// this is the case where we don't have an item in this slot
				// make sure we don't add too many items
				if (int(m_mutable_table.size()) >= m_settings.max_dht_items)
				{
					// delete the least important one (i.e. the one
					// the fewest peers are announcing)
					dht_mutable_table_t::iterator j = std::min_element(m_mutable_table.begin()
						, m_mutable_table.end()
						, boost::bind(&dht_immutable_item::num_announcers
							, boost::bind(&dht_mutable_table_t::value_type::second, _1))
						< boost::bind(&dht_immutable_item::num_announcers
							, boost::bind(&dht_mutable_table_t::value_type::second, _2)));
					TORRENT_ASSERT(j != m_mutable_table.end());
					free(j->second.value);
					free(j->second.salt);
					m_mutable_table.erase(j);
					m_counters.mutable_data -= 1;
				}
				dht_mutable_item to_add;
				to_add.value = static_cast<char*>(malloc(size));
				to_add.size = size;
				to_add.seq = seq;
				to_add.salt = NULL;
				to_add.salt_size = 0;
				if (salt_size > 0)
				{
					to_add.salt = static_cast<char*>(malloc(salt_size));
					to_add.salt_size = salt_size;
					memcpy(to_add.salt, salt, salt_size);
				}
				memcpy(to_add.sig, sig, sizeof(to_add.sig));
				memcpy(to_add.value, buf, size);
				memcpy(&to_add.key, pk, sizeof(to_add.key));

				boost::tie(i, boost::tuples::ignore) = m_mutable_table.insert(
					std::make_pair(target, to_add));
				m_counters.mutable_data += 1;

in the future, this function should update all the dht related counter. For now, it just update the storage related ones.

../src/kademlia/node.cpp:721

	return d;
}

void node::status(std::vector<dht_routing_bucket>& table
	, std::vector<dht_lookup>& requests)
{
	mutex_t::scoped_lock l(m_mutex);

	m_table.status(table);

	for (std::set<traversal_algorithm*>::iterator i = m_running_requests.begin()
		, end(m_running_requests.end()); i != end; ++i)
	{
		requests.push_back(dht_lookup());
		dht_lookup& lookup = requests.back();
		(*i)->status(lookup);
	}
}

void node::update_stats_counters(counters& c) const
{
	const dht_storage_counters& dht_cnt = m_storage->counters();
	c.set_value(counters::dht_torrents, dht_cnt.torrents);
	c.set_value(counters::dht_peers, dht_cnt.peers);
	c.set_value(counters::dht_immutable_data, dht_cnt.immutable_data);
	c.set_value(counters::dht_mutable_data, dht_cnt.mutable_data);
}

#ifndef TORRENT_NO_DEPRECATE

what if o is not an isntance of put_data_observer? This need to be redesigned for better type saftey.

../src/kademlia/put_data.cpp:97

{
	m_done = true;

#ifndef TORRENT_DISABLE_LOGGING
	get_node().observer()->log(dht_logger::traversal, "[%p] %s DONE, response %d, timeout %d"
		, static_cast<void*>(this), name(), m_responses, m_timeouts);
#endif

	m_put_callback(m_data, m_responses);
	traversal_algorithm::done();
}

bool put_data::invoke(observer_ptr o)
{
	if (m_done)
	{
		m_invoke_count = -1;
		return false;
	}

	put_data_observer* po = static_cast<put_data_observer*>(o.get());

	entry e;
	e["y"] = "q";
	e["q"] = "put";
	entry& a = e["a"];
	a["v"] = m_data.value();
	a["token"] = po->m_token;
	if (m_data.is_mutable())
	{
		a["k"] = std::string(m_data.pk().data(), item_pk_len);
		a["seq"] = m_data.seq();
		a["sig"] = std::string(m_data.sig().data(), item_sig_len);
		if (!m_data.salt().empty())
		{
			a["salt"] = m_data.salt();
		}
	}

	return m_node.m_rpc.invoke(e, o->target_ep(), o);
}

} } // namespace libtorrent::dht

include the number of peers received from this tracker, at last announce

../include/libtorrent/announce_entry.hpp:97

		// if this tracker failed the last time it was contacted
		// this error code specifies what error occurred
		error_code last_error;

		// returns the number of seconds to the next announce on this tracker.
		// ``min_announce_in()`` returns the number of seconds until we are
		// allowed to force another tracker update with this tracker.
		// 
		// If the last time this tracker was contacted failed, ``last_error`` is
		// the error code describing what error occurred.
		int next_announce_in() const;
		int min_announce_in() const;

		// the time of next tracker announce
		time_point next_announce;

		// no announces before this time
		time_point min_announce;


		// these are either -1 or the scrape information this tracker last
		// responded with. *incomplete* is the current number of downloaders in
		// the swarm, *complete* is the current number of seeds in the swarm and
		// *downloaded* is the cumulative number of completed downloads of this
		// torrent, since the beginning of time (from this tracker's point of
		// view).

		// if this tracker has returned scrape data, these fields are filled in
		// with valid numbers. Otherwise they are set to -1. the number of
		// current downloaders
		int scrape_incomplete;
		int scrape_complete;
		int scrape_downloaded;

		// the tier this tracker belongs to
		boost::uint8_t tier;

		// the max number of failures to announce to this tracker in
		// a row, before this tracker is not used anymore. 0 means unlimited
		boost::uint8_t fail_limit;

		// the number of times in a row we have failed to announce to this
		// tracker.
		boost::uint8_t fails:7;

		// true while we're waiting for a response from the tracker.
		bool updating:1;

		// flags for the source bitmask, each indicating where
		// we heard about this tracker

make this 32 bits and to count seconds since the block cache was created

../include/libtorrent/block_cache.hpp:223

		bool operator==(cached_piece_entry const& rhs) const
		{ return storage.get() == rhs.storage.get() && piece == rhs.piece; }

		// if this is set, we'll be calculating the hash
		// for this piece. This member stores the interim
		// state while we're calculating the hash.
		partial_hash* hash;

		// set to a unique identifier of a peer that last
		// requested from this piece.
		void* last_requester;

		// the pointers to the block data. If this is a ghost
		// cache entry, there won't be any data here
		boost::shared_array<cached_block_entry> blocks;

		// the last time a block was written to this piece
		// plus the minimum amount of time the block is guaranteed
		// to stay in the cache
		time_point expire;

		boost::uint64_t piece:22;

		// the number of dirty blocks in this piece
		boost::uint64_t num_dirty:14;

		// the number of blocks in the cache for this piece
		boost::uint64_t num_blocks:14;

		// the total number of blocks in this piece (and the number
		// of elements in the blocks array)
		boost::uint64_t blocks_in_piece:14;

		// ---- 64 bit boundary ----

		// while we have an outstanding async hash operation
		// working on this piece, 'hashing' is set to 1
		// When the operation returns, this is set to 0.
		boost::uint32_t hashing:1;

		// if we've completed at least one hash job on this
		// piece, and returned it. This is set to one
		boost::uint32_t hashing_done:1;

		// if this is true, whenever refcount hits 0,
		// this piece should be deleted
		boost::uint32_t marked_for_deletion:1;

		// this is set to true once we flush blocks past
		// the hash cursor. Once this happens, there's

Make this count Unicode characters instead of bytes on windows

../include/libtorrent/config.hpp:362

#pragma message ( "unknown OS, assuming BSD" )
#else
#warning "unknown OS, assuming BSD"
#endif

#define TORRENT_BSD
#endif

#if defined __GNUC__ && !(defined TORRENT_USE_OSATOMIC \
	|| defined TORRENT_USE_INTERLOCKED_ATOMIC \
	|| defined TORRENT_USE_BEOS_ATOMIC \
	|| defined TORRENT_USE_SOLARIS_ATOMIC)
// atomic operations in GCC were introduced in 4.1.1
# if (__GNUC__ >= 4 && __GNUC_MINOR__ >= 1 && __GNUC_PATCHLEVEL__ >= 1) || __GNUC__ > 4
#  define TORRENT_USE_GCC_ATOMIC 1
# endif
#endif

// on windows, NAME_MAX refers to Unicode characters
// on linux it refers to bytes (utf-8 encoded)

// windows
#if defined FILENAME_MAX
#define TORRENT_MAX_PATH FILENAME_MAX

// beos
#elif defined B_PATH_NAME_LENGTH
#define TORRENT_MAX_PATH B_PATH_NAME_LENGTH

// solaris
#elif defined MAXPATH
#define TORRENT_MAX_PATH MAXPATH

// none of the above
#else
// this is the maximum number of characters in a
// path element / filename on windows and also on many filesystems commonly used
// on linux
#define TORRENT_MAX_PATH 255

#ifdef _MSC_VER
#pragma message ( "unknown platform, assuming the longest path is 255" )
#else
#warning "unknown platform, assuming the longest path is 255"
#endif

#endif

#define TORRENT_UNUSED(x) (void)(x)

#if (defined _MSC_VER && _MSC_VER < 1900) && !defined TORRENT_MINGW

try to remove the observers, only using the async_allocate handlers

../include/libtorrent/disk_buffer_pool.hpp:137

		// number of bytes per block. The BitTorrent
		// protocol defines the block size to 16 KiB.
		const int m_block_size;

		// number of disk buffers currently allocated
		int m_in_use;

		// cache size limit
		int m_max_use;

		// if we have exceeded the limit, we won't start
		// allowing allocations again until we drop below
		// this low watermark
		int m_low_watermark;

		// if we exceed the max number of buffers, we start
		// adding up callbacks to this queue. Once the number
		// of buffers in use drops below the low watermark,
		// we start calling these functions back
		std::vector<boost::shared_ptr<disk_observer> > m_observers;

		// these handlers are executed when a new buffer is available
		std::vector<handler_t> m_handlers;

		// callback used to tell the cache it needs to free up some blocks
		boost::function<void()> m_trigger_cache_trim;

		// set to true to throttle more allocations
		bool m_exceeded_max_size;

		// this is the main thread io_service. Callbacks are
		// posted on this in order to have them execute in
		// the main thread.
		io_service& m_ios;

	private:

		void check_buffer_level(mutex::scoped_lock& l);

		mutable mutex m_pool_mutex;

		int m_cache_buffer_chunk_size;
		bool m_lock_disk_cache;

#if TORRENT_HAVE_MMAP
		// the file descriptor of the cache mmap file
		int m_cache_fd;
		// the pointer to the block of virtual address space
		// making up the mmapped cache space
		char* m_cache_pool;

move this into a separate header file, TU pair

../include/libtorrent/file.hpp:173

	TORRENT_EXTRA_EXPORT std::string parent_path(std::string const& f);
	TORRENT_EXTRA_EXPORT bool has_parent_path(std::string const& f);
	TORRENT_EXTRA_EXPORT char const* filename_cstr(char const* f);

	// internal used by create_torrent.hpp
	TORRENT_EXTRA_EXPORT std::string filename(std::string const& f);
	TORRENT_EXTRA_EXPORT std::string combine_path(std::string const& lhs
		, std::string const& rhs);
	TORRENT_EXTRA_EXPORT void append_path(std::string& branch
		, std::string const& leaf);
	TORRENT_EXTRA_EXPORT void append_path(std::string& branch
		, char const* str, int len);
	// internal used by create_torrent.hpp
	TORRENT_EXTRA_EXPORT std::string complete(std::string const& f);
	TORRENT_EXTRA_EXPORT bool is_complete(std::string const& f);
	TORRENT_EXTRA_EXPORT std::string current_working_directory();
#if TORRENT_USE_UNC_PATHS
	TORRENT_EXTRA_EXPORT std::string canonicalize_path(std::string const& f);
#endif

	class TORRENT_EXTRA_EXPORT directory : public boost::noncopyable
	{
	public:
		directory(std::string const& path, error_code& ec);
		~directory();
		void next(error_code& ec);
		std::string file() const;
		boost::uint64_t inode() const;
		bool done() const { return m_done; }
	private:
#ifdef TORRENT_WINDOWS
		HANDLE m_handle;
		int m_inode;
#if TORRENT_USE_WSTRING
		WIN32_FIND_DATAW m_fd;
#else
		WIN32_FIND_DATAA m_fd;
#endif
#else
		DIR* m_handle;
		// the dirent struct contains a zero-sized
		// array at the end, it will end up referring
		// to the m_name field
		struct dirent m_dirent;
		char m_name[TORRENT_MAX_PATH + 1]; // +1 to make room for null
#endif
		bool m_done;
	};

	struct file;

if this throws, should we do anything?

../include/libtorrent/heterogeneous_queue.hpp:184

			- 1) / sizeof(uintptr_t);

		void grow_capacity(int size)
		{
			int amount_to_grow = (std::max)(size + header_size
				, (std::max)(m_capacity * 3 / 2, 128));

			uintptr_t* new_storage = new uintptr_t[m_capacity + amount_to_grow];

			uintptr_t* src = m_storage;
			uintptr_t* dst = new_storage;
			uintptr_t const* const end = m_storage + m_size;
			while (src < end)
			{
				header_t* src_hdr = reinterpret_cast<header_t*>(src);
				header_t* dst_hdr = reinterpret_cast<header_t*>(dst);
				*dst_hdr = *src_hdr;
				src += header_size;
				dst += header_size;
				TORRENT_ASSERT(src + src_hdr->len <= end);
				src_hdr->move(dst, src);
				src += src_hdr->len;
				dst += src_hdr->len;
			}

			delete[] m_storage;
			m_storage = new_storage;
			m_capacity += amount_to_grow;
		}

		template <class U>
		static void move(uintptr_t* dst, uintptr_t* src)
		{
			U* rhs = reinterpret_cast<U*>(src);
#if __cplusplus >= 201103L
			new (dst) U(std::move(*rhs));
#else
			new (dst) U(*rhs);
#endif
			rhs->~U();
		}

		uintptr_t* m_storage;
		// number of uintptr_t's allocated under m_storage
		int m_capacity;
		// the number of uintptr_t's used under m_storage
		int m_size;
		// the number of objects allocated under m_storage
		int m_num_items;
	};
}

hide these declarations when deprecaated functions are disabled, and expose them internally in a header under aux_.

../include/libtorrent/identify_client.hpp:50

*/

#ifndef TORRENT_IDENTIFY_CLIENT_HPP_INCLUDED
#define TORRENT_IDENTIFY_CLIENT_HPP_INCLUDED

#include "libtorrent/config.hpp"

#include "libtorrent/aux_/disable_warnings_push.hpp"

#include <boost/optional.hpp>

#include "libtorrent/aux_/disable_warnings_pop.hpp"

#include "libtorrent/peer_id.hpp"
#include "libtorrent/fingerprint.hpp"

namespace libtorrent
{


	// these functions don't really need to be public. This mechanism of
	// advertising client software and version is also out-dated.

	// This function can can be used to extract a string describing a client
	// version from its peer-id. It will recognize most clients that have this
	// kind of identification in the peer-id.
	TORRENT_DEPRECATED_EXPORT TORRENT_DEPRECATED
	std::string identify_client(const peer_id& p);

	// Returns an optional fingerprint if any can be identified from the peer
	// id. This can be used to automate the identification of clients. It will
	// not be able to identify peers with non- standard encodings. Only Azureus
	// style, Shadow's style and Mainline style.
	TORRENT_DEPRECATED_EXPORT TORRENT_DEPRECATED
	boost::optional<fingerprint>
		client_fingerprint(peer_id const& p);

}

#endif // TORRENT_IDENTIFY_CLIENT_HPP_INCLUDED

make this a raw pointer (to save size in the first cache line) and make the constructor take a raw pointer. torrent objects should always outlive their peers

../include/libtorrent/peer_connection.hpp:209

			, m_connecting(!t.expired())
			, m_endgame_mode(false)
			, m_snubbed(false)
			, m_interesting(false)
			, m_choked(true)
			, m_corked(false)
			, m_ignore_stats(false)
		{}

	protected:

		// the pieces the other end have
		bitfield m_have_piece;

		// this is the torrent this connection is
		// associated with. If the connection is an
		// incoming connection, this is set to zero
		// until the info_hash is received. Then it's
		// set to the torrent it belongs to.

		boost::weak_ptr<torrent> m_torrent;

	public:

		// a back reference to the session
		// the peer belongs to.
		aux::session_interface& m_ses;

		// settings that apply to this peer
		aux::session_settings const& m_settings;

	protected:

		// this is true if this connection has been added
		// to the list of connections that will be closed.
		bool m_disconnecting:1;

		// this is true until this socket has become
		// writable for the first time (i.e. the
		// connection completed). While connecting
		// the timeout will not be triggered. This is
		// because windows XP SP2 may delay connection
		// attempts, which means that the connection
		// may not even have been attempted when the
		// time out is reached.
		bool m_connecting:1;

		// this is set to true if the last time we tried to
		// pick a piece to download, we could only find
		// blocks that were already requested from other
		// peers. In this case, we should not try to pick

factor this out into its own class with a virtual interface torrent and session should implement this interface

../include/libtorrent/peer_connection.hpp:1044

		// the local endpoint for this peer, i.e. our address
		// and our port. If this is set for outgoing connections
		// before the connection completes, it means we want to
		// force the connection to be bound to the specified interface.
		// if it ends up being bound to a different local IP, the connection
		// is closed.
		tcp::endpoint m_local;

		// remote peer's id
		peer_id m_peer_id;

		// the bandwidth channels, upload and download
		// keeps track of the current quotas
		bandwidth_channel m_bandwidth_channel[num_channels];

	protected:
		// statistics about upload and download speeds
		// and total amount of uploads and downloads for
		// this peer
		stat m_statistics;

		// the number of outstanding bytes expected
		// to be received by extensions
		int m_extension_outstanding_bytes;

		// the number of time critical requests
		// queued up in the m_request_queue that
		// soon will be committed to the download
		// queue. This is included in download_queue_time()
		// so that it can be used while adding more
		// requests and take the previous requests
		// into account without submitting it all
		// immediately
		int m_queued_time_critical;

		// the number of bytes we are currently reading
		// from disk, that will be added to the send
		// buffer as soon as they complete
		int m_reading_bytes;

		// options used for the piece picker. These flags will
		// be augmented with flags controlled by other settings
		// like sequential download etc. These are here to
		// let plugins control flags that should always be set
		int m_picker_options;

		// the number of invalid piece-requests
		// we have got from this peer. If the request
		// queue gets empty, and there have been
		// invalid requests, we can assume the

make this interface smaller!

../include/libtorrent/peer_connection_interface.hpp:47

CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.

*/

#ifndef TORRENT_PEER_CONNECTION_INTERFACE_HPP
#define TORRENT_PEER_CONNECTION_INTERFACE_HPP

#include "libtorrent/socket.hpp"
#include "libtorrent/error_code.hpp"
#include "libtorrent/alert_types.hpp"
#include "libtorrent/operations.hpp" // for operation_t enum

namespace libtorrent
{
	struct torrent_peer;
	class stat;
	struct peer_info;

	struct TORRENT_EXTRA_EXPORT peer_connection_interface
	{
		virtual tcp::endpoint const& remote() const = 0;
		virtual tcp::endpoint local_endpoint() const = 0;
		virtual void disconnect(error_code const& ec
			, operation_t op, int error = 0) = 0;
		virtual peer_id const& pid() const = 0;
		virtual void set_holepunch_mode() = 0;
		virtual torrent_peer* peer_info_struct() const = 0;
		virtual void set_peer_info(torrent_peer* pi) = 0;
		virtual bool is_outgoing() const = 0;
		virtual void add_stat(boost::int64_t downloaded, boost::int64_t uploaded) = 0;
		virtual bool fast_reconnect() const = 0;
		virtual bool is_choked() const = 0;
		virtual bool failed() const = 0;
		virtual stat const& statistics() const = 0;
		virtual void get_peer_info(peer_info& p) const = 0;
#ifndef TORRENT_DISABLE_LOGGING
		virtual void peer_log(peer_log_alert::direction_t direction
			, char const* event, char const* fmt = "", ...) const TORRENT_FORMAT(4,5) = 0;
#endif
	protected:
		~peer_connection_interface() {}
	};
}

#endif

should keepalives be in here too? how about dont-have, share-mode, upload-only

../include/libtorrent/performance_counters.hpp:139

			// a connect candidate
			connection_attempt_loops,
			// successful incoming connections (not rejected for any reason)
			incoming_connections,

			// counts events where the network
			// thread wakes up
			on_read_counter,
			on_write_counter,
			on_tick_counter,
			on_lsd_counter,
			on_lsd_peer_counter,
			on_udp_counter,
			on_accept_counter,
			on_disk_queue_counter,
			on_disk_counter,

			torrent_evicted_counter,

			// bittorrent message counters
			num_incoming_choke,
			num_incoming_unchoke,
			num_incoming_interested,
			num_incoming_not_interested,
			num_incoming_have,
			num_incoming_bitfield,
			num_incoming_request,
			num_incoming_piece,
			num_incoming_cancel,
			num_incoming_dht_port,
			num_incoming_suggest,
			num_incoming_have_all,
			num_incoming_have_none,
			num_incoming_reject,
			num_incoming_allowed_fast,
			num_incoming_ext_handshake,
			num_incoming_pex,
			num_incoming_metadata,
			num_incoming_extended,

			num_outgoing_choke,
			num_outgoing_unchoke,
			num_outgoing_interested,
			num_outgoing_not_interested,
			num_outgoing_have,
			num_outgoing_bitfield,
			num_outgoing_request,
			num_outgoing_piece,
			num_outgoing_cancel,
			num_outgoing_dht_port,
			num_outgoing_suggest,

some space could be saved here by making gauges 32 bits

../include/libtorrent/performance_counters.hpp:450

restore these to regular integers. Instead have one copy of the counters per thread and collect them at convenient synchronization points

../include/libtorrent/performance_counters.hpp:451

			num_utp_deleted,

			num_counters,
			num_gauges_counters = num_counters - num_stats_counters
		};

		counters();

		counters(counters const&);
		counters& operator=(counters const&);

		// returns the new value
		boost::int64_t inc_stats_counter(int c, boost::int64_t value = 1);
		boost::int64_t operator[](int i) const;

		void set_value(int c, boost::int64_t value);
		void blend_stats_counter(int c, boost::int64_t value, int ratio);

	private:

#if BOOST_ATOMIC_LLONG_LOCK_FREE == 2
		boost::atomic<boost::int64_t> m_stats_counter[num_counters];
#else
		// if the atomic type is't lock-free, use a single lock instead, for
		// the whole array
		mutable mutex m_mutex;
		boost::int64_t m_stats_counter[num_counters];
#endif
	};
}

#endif

should this be allocated lazily?

../include/libtorrent/piece_picker.hpp:756

		std::vector<downloading_piece>::const_iterator find_dl_piece(int queue, int index) const;
		std::vector<downloading_piece>::iterator find_dl_piece(int queue, int index);

		// returns an iterator to the downloading piece, whichever
		// download list it may live in now
		std::vector<downloading_piece>::iterator update_piece_state(
			std::vector<downloading_piece>::iterator dp);

	private:

		// the following vectors are mutable because they sometimes may
		// be updated lazily, triggered by const functions

		// this maps indices to number of peers that has this piece and
		// index into the m_piece_info vectors.
		// piece_pos::we_have_index means that we have the piece, so it
		// doesn't exist in the piece_info buckets
		// pieces with the filtered flag set doesn't have entries in
		// the m_piece_info buckets either
		mutable std::vector<piece_pos> m_piece_map;

		// the number of seeds. These are not added to
		// the availability counters of the pieces
		int m_seeds;

		// the number of pieces that have passed the hash check
		int m_num_passed;

		// this vector contains all piece indices that are pickable
		// sorted by priority. Pieces are in random random order
		// among pieces with the same priority
		mutable std::vector<int> m_pieces;

		// these are indices to the priority boundries inside
		// the m_pieces vector. priority 0 always start at
		// 0, priority 1 starts at m_priority_boundries[0] etc.
		mutable std::vector<int> m_priority_boundries;

		// each piece that's currently being downloaded has an entry in this list
		// with block allocations. i.e. it says wich parts of the piece that is
		// being downloaded. This list is ordered by piece index to make lookups
		// efficient there are as many buckets as there are piece states. See
		// piece_pos::state_t. The only download state that does not have a
		// corresponding downloading_piece vector is piece_open and
		// piece_downloading_reverse (the latter uses the same as
		// piece_downloading).
		std::vector<downloading_piece> m_downloads[piece_pos::num_download_categories];

		// this holds the information of the blocks in partially downloaded
		// pieces. the downloading_piece::info index point into this vector for

it would be nice to remember the bind port and bind once we know where the proxy is m_sock.bind(endpoint, ec);

../include/libtorrent/proxy_base.hpp:174

	void bind(endpoint_type const& /* endpoint */)
	{
//		m_sock.bind(endpoint);
	}
#endif

	error_code cancel(error_code& ec)
	{
		return m_sock.cancel(ec);
	}

	void bind(endpoint_type const& /* endpoint */, error_code& /* ec */)
	{
		// the reason why we ignore binds here is because we don't
		// (necessarily) yet know what address family the proxy
		// will resolve to, and binding to the wrong one would
		// break our connection attempt later. The caller here
		// doesn't necessarily know that we're proxying, so this
		// bind address is based on the final endpoint, not the
		// proxy.
	}

#ifndef BOOST_NO_EXCEPTIONS
	void open(protocol_type const&)
	{
//		m_sock.open(p);
	}
#endif

	void open(protocol_type const&, error_code&)
	{
		// we need to ignore this for the same reason as stated
		// for ignoring bind()
//		m_sock.open(p, ec);
	}

#ifndef BOOST_NO_EXCEPTIONS
	void close()
	{
		m_remote_endpoint = endpoint_type();
		m_sock.close();
		m_resolver.cancel();
	}
#endif

	void close(error_code& ec)
	{
		m_remote_endpoint = endpoint_type();
		m_sock.close(ec);
		m_resolver.cancel();
	}

Detect when the start of the next crpyto packet is aligned with the start of piece data and the crpyto packet is at least as large as the piece data. With a little extra work we could receive directly into a disk buffer in that case.

../include/libtorrent/receive_buffer.hpp:258

	void cut(int size, int packet_size, int offset = 0);

	void crypto_cut(int size, int packet_size)
	{
		TORRENT_ASSERT(m_recv_pos != INT_MAX);
		m_connection_buffer.cut(size, m_recv_pos + packet_size, m_recv_pos);
	}

	void reset(int packet_size);
	void crypto_reset(int packet_size);

	void set_soft_packet_size(int size);

	int advance_pos(int bytes);

	buffer::const_interval get() const;

	bool can_recv_contiguous(int /*size*/) const
	{
		return m_recv_pos == INT_MAX;
	}

	void mutable_buffers(std::vector<boost::asio::mutable_buffer>& vec
		, std::size_t bytes_transfered);

private:
	// explicitly disallow assignment, to silence msvc warning
	crypto_receive_buffer& operator=(crypto_receive_buffer const&);

	int m_recv_pos;
	int m_packet_size;
	int m_soft_packet_size;
	receive_buffer& m_connection_buffer;
};
#endif // TORRENT_DISABLE_ENCRYPTION

} // namespace libtorrent

#endif // #ifndef TORRENT_RECEIVE_BUFFER_HPP_INCLUDED

add get_peer_class_type_filter() as well

../include/libtorrent/session_handle.hpp:682

		//
		// The ``peer_class`` argument cannot be greater than 31. The bitmasks
		// representing peer classes in the ``peer_class_filter`` are 32 bits.
		//
		// For more information, see peer-classes_.
		void set_peer_class_filter(ip_filter const& f);

		// Sets and gets the *peer class type filter*. This is controls automatic
		// peer class assignments to peers based on what kind of socket it is.
		//
		// It does not only support assigning peer classes, it also supports
		// removing peer classes based on socket type.
		//
		// The order of these rules being applied are:
		//
		// 1. peer-class IP filter
		// 2. peer-class type filter, removing classes
		// 3. peer-class type filter, adding classes
		//
		// For more information, see peer-classes_.
		void set_peer_class_type_filter(peer_class_type_filter const& f);

		// Creates a new peer class (see peer-classes_) with the given name. The
		// returned integer is the new peer class' identifier. Peer classes may
		// have the same name, so each invocation of this function creates a new
		// class and returns a unique identifier.
		//
		// Identifiers are assigned from low numbers to higher. So if you plan on
		// using certain peer classes in a call to `set_peer_class_filter()`_,
		// make sure to create those early on, to get low identifiers.
		//
		// For more information on peer classes, see peer-classes_.
		int create_peer_class(char const* name);

		// This call dereferences the reference count of the specified peer
		// class. When creating a peer class it's automatically referenced by 1.
		// If you want to recycle a peer class, you may call this function. You
		// may only call this function **once** per peer class you create.
		// Calling it more than once for the same class will lead to memory
		// corruption.
		//
		// Since peer classes are reference counted, this function will not
		// remove the peer class if it's still assigned to torrents or peers. It
		// will however remove it once the last peer and torrent drops their
		// references to it.
		//
		// There is no need to call this function for custom peer classes. All
		// peer classes will be properly destructed when the session object
		// destructs.
		//
		// For more information on peer classes, see peer-classes_.

deprecate this ``max_rejects`` is the number of piece requests we will reject in a row while a peer is choked before the peer is considered abusive and is disconnected.

../include/libtorrent/settings_pack.hpp:1094

			// this is the minimum allowed announce interval for a tracker. This
			// is specified in seconds and is used as a sanity check on what is
			// returned from a tracker. It mitigates hammering misconfigured
			// trackers.
			min_announce_interval,

			// this is the number of seconds a torrent is considered active after
			// it was started, regardless of upload and download speed. This is so
			// that newly started torrents are not considered inactive until they
			// have a fair chance to start downloading.
			auto_manage_startup,

			// ``seeding_piece_quota`` is the number of pieces to send to a peer,
			// when seeding, before rotating in another peer to the unchoke set.
			// It defaults to 3 pieces, which means that when seeding, any peer
			// we've sent more than this number of pieces to will be unchoked in
			// favour of a choked peer.
			seeding_piece_quota,

			max_rejects,

			// ``recv_socket_buffer_size`` and ``send_socket_buffer_size``
			// specifies the buffer sizes set on peer sockets. 0 (which is the
			// default) means the OS default (i.e. don't change the buffer sizes).
			// The socket buffer sizes are changed using setsockopt() with
			// SOL_SOCKET/SO_RCVBUF and SO_SNDBUFFER.
			recv_socket_buffer_size,
			send_socket_buffer_size,

			// ``file_checks_delay_per_block`` is the number of milliseconds to
			// sleep in between disk read operations when checking torrents. This
			// defaults to 0, but can be set to higher numbers to slow down the
			// rate at which data is read from the disk while checking. This may
			// be useful for background tasks that doesn't matter if they take a
			// bit longer, as long as they leave disk I/O time for other
			// processes.
			file_checks_delay_per_block,

			// ``read_cache_line_size`` is the number of blocks to read into the
			// read cache when a read cache miss occurs. Setting this to 0 is
			// essentially the same thing as disabling read cache. The number of
			// blocks read into the read cache is always capped by the piece
			// boundary.
			// 
			// When a piece in the write cache has ``write_cache_line_size``
			// contiguous blocks in it, they will be flushed. Setting this to 1
			// effectively disables the write cache.
			read_cache_line_size,
			write_cache_line_size,

make this a raw pointer. perhaps keep the shared_ptr around further down the object to maintain an owner

../include/libtorrent/torrent.hpp:195

		// connection to pick up
		peer_request restart_request;
		std::vector<char> restart_piece;
	};

	struct TORRENT_EXTRA_EXPORT torrent_hot_members
	{
		torrent_hot_members(aux::session_interface& ses
			, add_torrent_params const& p, int block_size);

	protected:
		// the piece picker. This is allocated lazily. When we don't
		// have anything in the torrent (for instance, if it hasn't
		// been started yet) or if we have everything, there is no
		// picker. It's allocated on-demand the first time we need
		// it in torrent::need_picker(). In order to tell the
		// difference between having everything and nothing in
		// the case there is no piece picker, see m_have_all.
		boost::scoped_ptr<piece_picker> m_picker;

		boost::shared_ptr<torrent_info> m_torrent_file;

		// a back reference to the session
		// this torrent belongs to.
		aux::session_interface& m_ses;

		// this vector is sorted at all times, by the pointer value.
		// use sorted_insert() and sorted_find() on it. The GNU STL
		// implementation on Darwin uses significantly less memory to
		// represent a vector than a set, and this set is typically
		// relatively small, and it's cheap to copy pointers.
		std::vector<peer_connection*> m_connections;

		// the scrape data from the tracker response, this
		// is optional and may be 0xffffff
		boost::uint32_t m_complete:24;

		// set to true when this torrent may not download anything
		bool m_upload_mode:1;

		// this is set to false as long as the connections
		// of this torrent hasn't been initialized. If we
		// have metadata from the start, connections are
		// initialized immediately, if we didn't have metadata,
		// they are initialized right after files_checked().
		// valid_resume_data() will return false as long as
		// the connections aren't initialized, to avoid
		// them from altering the piece-picker before it
		// has been initialized with files_checked().
		bool m_connections_initialized:1;

this wastes 5 bits per file

../include/libtorrent/torrent.hpp:1244

		typedef std::list<boost::shared_ptr<torrent_plugin> > extension_list_t;
		extension_list_t m_extensions;
#endif

		// used for tracker announces
		deadline_timer m_tracker_timer;

		// used to detect when we are active or inactive for long enough
		// to trigger the auto-manage logic
		deadline_timer m_inactivity_timer;

		// this is the upload and download statistics for the whole torrent.
		// it's updated from all its peers once every second.
		libtorrent::stat m_stat;

		// -----------------------------

		// this vector is allocated lazily. If no file priorities are
		// ever changed, this remains empty. Any unallocated slot
		// implicitly means the file has priority 1.
		std::vector<boost::uint8_t> m_file_priority;

		// this object is used to track download progress of individual files
		aux::file_progress m_file_progress;

		// these are the pieces we're currently
		// suggesting to peers.
		std::vector<suggest_piece_t> m_suggested_pieces;

		std::vector<announce_entry> m_trackers;
		// this is an index into m_trackers

		// this list is sorted by time_critical_piece::deadline
		std::vector<time_critical_piece> m_time_critical_pieces;

		std::string m_trackerid;
#ifndef TORRENT_NO_DEPRECATE
		// deprecated in 1.1
		std::string m_username;
		std::string m_password;
#endif

		std::string m_save_path;

		// if we don't have the metadata, this is a url to
		// the torrent file
		std::string m_url;

		// if this was added from an RSS feed, this is the unique
		// identifier in the feed.
		std::string m_uuid;

These two bitfields should probably be coalesced into one

../include/libtorrent/torrent.hpp:1302

		// the .torrent file from m_url
//		std::vector<char> m_torrent_file_buf;

		// this is a list of all pieces that we have announced
		// as having, without actually having yet. If we receive
		// a request for a piece in this list, we need to hold off
		// on responding until we have completed the piece and
		// verified its hash. If the hash fails, send reject to
		// peers with outstanding requests, and dont_have to other
		// peers. This vector is ordered, to make lookups fast.
		std::vector<int> m_predictive_pieces;

		// the performance counters of this session
		counters& m_stats_counters;

		// each bit represents a piece. a set bit means
		// the piece has had its hash verified. This
		// is only used in seed mode (when m_seed_mode
		// is true)

		bitfield m_verified;
		// this means there is an outstanding, async, operation
		// to verify each piece that has a 1
		bitfield m_verifying;

		// set if there's an error on this torrent
		error_code m_error;

		// used if there is any resume data
		boost::scoped_ptr<resume_data_t> m_resume_data;

		// if the torrent is started without metadata, it may
		// still be given a name until the metadata is received
		// once the metadata is received this field will no
		// longer be used and will be reset
		boost::scoped_ptr<std::string> m_name;

		storage_constructor_type m_storage_constructor;

		// the posix time this torrent was added and when
		// it was completed. If the torrent isn't yet
		// completed, m_completed_time is 0
		time_t m_added_time;
		time_t m_completed_time;

		// this was the last time _we_ saw a seed in this swarm
		time_t m_last_seen_complete;

		// this is the time last any of our peers saw a seed
		// in this swarm
		time_t m_swarm_last_seen_complete;

there may be some opportunities to optimize the size if torrent_info. specifically to turn some std::string and std::vector into pointers

../include/libtorrent/torrent_info.hpp:117

		// The URL of the web seed
		std::string url;

		// Optional authentication. If this is set, it's passed
		// in as HTTP basic auth to the web seed. The format is:
		// username:password.
		std::string auth;

		// Any extra HTTP headers that need to be passed to the web seed
		headers_t extra_headers;

		// The type of web seed (see type_t)
		boost::uint8_t type;
	};

#ifndef BOOST_NO_EXCEPTIONS
	// for backwards compatibility with 0.14
	typedef libtorrent_exception invalid_torrent_file;
#endif

	class TORRENT_EXPORT torrent_info
	{
	public:

		// The constructor that takes an info-hash  will initialize the info-hash
		// to the given value, but leave all other fields empty. This is used
		// internally when downloading torrents without the metadata. The
		// metadata will be created by libtorrent as soon as it has been
		// downloaded from the swarm.
		// 
		// The constructor that takes a bdecode_node will create a torrent_info
		// object from the information found in the given torrent_file. The
		// bdecode_node represents a tree node in an bencoded file. To load an
		// ordinary .torrent file into a bdecode_node, use bdecode().
		// 
		// The version that takes a buffer pointer and a size will decode it as a
		// .torrent file and initialize the torrent_info object for you.
		// 
		// The version that takes a filename will simply load the torrent file
		// and decode it inside the constructor, for convenience. This might not
		// be the most suitable for applications that want to be able to report
		// detailed errors on what might go wrong.
		//
		// There is an upper limit on the size of the torrent file that will be
		// loaded by the overload taking a filename. If it's important that even
		// very large torrent files are loaded, use one of the other overloads.
		// 
		// The overloads that takes an ``error_code const&`` never throws if an
		// error occur, they will simply set the error code to describe what went
		// wrong and not fully initialize the torrent_info object. The overloads
		// that do not take the extra error_code parameter will always throw if

this should be unique_ptr in the future

../include/libtorrent/tracker_manager.hpp:392

		// this is only used for SOCKS packets, since
		// they may be addressed to hostname
		virtual bool incoming_packet(error_code const& e, char const* hostname
			, char const* buf, int size) TORRENT_OVERRIDE;

		void update_transaction_id(
			boost::shared_ptr<udp_tracker_connection> c
			, boost::uint64_t tid);

		aux::session_settings const& settings() const { return m_settings; }
		udp_socket& get_udp_socket() { return m_udp_socket; }
		resolver_interface& host_resolver() { return m_host_resolver; }

	private:

		typedef mutex mutex_t;
		mutable mutex_t m_mutex;

		// maps transactionid to the udp_tracker_connection
		typedef boost::unordered_map<boost::uint32_t
			, boost::shared_ptr<udp_tracker_connection> > udp_conns_t;
		udp_conns_t m_udp_conns;

		typedef std::vector<boost::shared_ptr<http_tracker_connection> > http_conns_t;
		http_conns_t m_http_conns;

		class udp_socket& m_udp_socket;
		resolver_interface& m_host_resolver;
		aux::session_settings const& m_settings;
		counters& m_stats_counters;
#if !defined TORRENT_DISABLE_LOGGING || TORRENT_USE_ASSERTS
		aux::session_logger& m_ses;
#endif

		bool m_abort;
	};
}

#endif // TORRENT_TRACKER_MANAGER_HPP_INCLUDED

support using the windows API for UPnP operations as well

../include/libtorrent/upnp.hpp:132

	std::list<std::string> tag_stack;
	std::string control_url;
	std::string service_type;
	std::string model;
	std::string url_base;
	bool top_tags(const char* str1, const char* str2)
	{
		std::list<std::string>::reverse_iterator i = tag_stack.rbegin();
		if (i == tag_stack.rend()) return false;
		if (!string_equal_no_case(i->c_str(), str2)) return false;
		++i;
		if (i == tag_stack.rend()) return false;
		if (!string_equal_no_case(i->c_str(), str1)) return false;
		return true;
	}
};

TORRENT_EXTRA_EXPORT void find_control_url(int type, char const* string
	, int str_len, parse_state& state);

class TORRENT_EXTRA_EXPORT upnp : public boost::enable_shared_from_this<upnp>
{
public:
	upnp(io_service& ios
		, address const& listen_interface, std::string const& user_agent
		, portmap_callback_t const& cb, log_callback_t const& lcb
		, bool ignore_nonrouters);
	~upnp();

	void start();

	enum protocol_type { none = 0, udp = 1, tcp = 2 };

	// Attempts to add a port mapping for the specified protocol. Valid protocols are
	// ``upnp::tcp`` and ``upnp::udp`` for the UPnP class and ``natpmp::tcp`` and
	// ``natpmp::udp`` for the NAT-PMP class.
	//
	// ``external_port`` is the port on the external address that will be mapped. This
	// is a hint, you are not guaranteed that this port will be available, and it may
	// end up being something else. In the portmap_alert_ notification, the actual
	// external port is reported.
	//
	// ``local_port`` is the port in the local machine that the mapping should forward
	// to.
	//
	// The return value is an index that identifies this port mapping. This is used
	// to refer to mappings that fails or succeeds in the portmap_error_alert_ and
	// portmap_alert_ respectively. If The mapping fails immediately, the return value
	// is -1, which means failure. There will not be any error alert notification for
	// mappings that fail with a -1 return value.
	int add_mapping(protocol_type p, int external_port, int local_port);

implement blocking write. Low priority since it's not used (yet)

../include/libtorrent/utp_stream.hpp:424

		for (typename Mutable_Buffers::const_iterator i = buffers.begin()
			, end(buffers.end()); i != end; ++i)
		{
			using boost::asio::buffer_cast;
			using boost::asio::buffer_size;
			add_read_buffer(buffer_cast<void*>(*i), buffer_size(*i));
#if TORRENT_USE_ASSERTS
			buf_size += buffer_size(*i);
#endif
		}
		std::size_t ret = read_some(true);
		TORRENT_ASSERT(ret <= buf_size);
		TORRENT_ASSERT(ret > 0);
		return ret;
	}

	template <class Const_Buffers>
	std::size_t write_some(Const_Buffers const& /* buffers */, error_code& /* ec */)
	{
		TORRENT_ASSERT(false && "not implemented!");
		return 0;
	}

#ifndef BOOST_NO_EXCEPTIONS
	template <class Mutable_Buffers>
	std::size_t read_some(Mutable_Buffers const& buffers)
	{
		error_code ec;
		std::size_t ret = read_some(buffers, ec);
		if (ec)
			boost::throw_exception(boost::system::system_error(ec));
		return ret;
	}

	template <class Const_Buffers>
	std::size_t write_some(Const_Buffers const& buffers)
	{
		error_code ec;
		std::size_t ret = write_some(buffers, ec);
		if (ec)
			boost::throw_exception(boost::system::system_error(ec));
		return ret;
	}
#endif

	template <class Const_Buffers, class Handler>
	void async_write_some(Const_Buffers const& buffers, Handler const& handler)
	{
		if (m_impl == 0)
		{
			m_io_service.post(boost::bind<void>(handler

since this is a public function, it should probably be moved out of this header and into one with other public functions.

../include/libtorrent/kademlia/item.hpp:61

#include <boost/array.hpp>

namespace libtorrent { namespace dht
{

// calculate the target hash for an immutable item.
sha1_hash TORRENT_EXTRA_EXPORT item_target_id(
	std::pair<char const*, int> v);

// calculate the target hash for a mutable item.
sha1_hash TORRENT_EXTRA_EXPORT item_target_id(std::pair<char const*, int> salt
	, char const* pk);

bool TORRENT_EXTRA_EXPORT verify_mutable_item(
	std::pair<char const*, int> v
	, std::pair<char const*, int> salt
	, boost::uint64_t seq
	, char const* pk
	, char const* sig);


// given a byte range ``v`` and an optional byte range ``salt``, a
// sequence number, public key ``pk`` (must be 32 bytes) and a secret key
// ``sk`` (must be 64 bytes), this function produces a signature which
// is written into a 64 byte buffer pointed to by ``sig``. The caller
// is responsible for allocating the destination buffer that's passed in
// as the ``sig`` argument. Typically it would be allocated on the stack.
void TORRENT_EXPORT sign_mutable_item(
	std::pair<char const*, int> v
	, std::pair<char const*, int> salt
	, boost::uint64_t seq
	, char const* pk
	, char const* sk
	, char* sig);

enum
{
	item_pk_len = 32,
	item_sk_len = 64,
	item_sig_len = 64
};

class TORRENT_EXTRA_EXPORT item
{
public:
	item() : m_seq(0), m_mutable(false)  {}
	item(char const* pk, std::string const& salt);
	item(entry const& v) { assign(v); }
	item(entry const& v
		, std::pair<char const*, int> salt
		, boost::uint64_t seq, char const* pk, char const* sk);

should this be renamed m_outgoing_interfaces?

../include/libtorrent/aux_/session_impl.hpp:859

			// client with the tracker only. It is randomized
			// at startup
			int m_key;

			// the addresses or device names of the interfaces we are supposed to
			// listen on. if empty, it means that we should let the os decide
			// which interface to listen on
			std::vector<std::pair<std::string, int> > m_listen_interfaces;

			// keep this around until everything uses the list of interfaces
			// instead.
			tcp::endpoint m_listen_interface;

			// the network interfaces outgoing connections are opened through. If
			// there is more then one, they are used in a round-robin fashion
			// each element is a device name or IP address (in string form) and
			// a port number. The port determines which port to bind the listen
			// socket to, and the device or IP determines which network adapter
			// to be used. If no adapter with the specified name exists, the listen
			// socket fails.
			std::vector<std::string> m_net_interfaces;

			// if we're listening on an IPv6 interface
			// this is one of the non local IPv6 interfaces
			// on this machine
			tcp::endpoint m_ipv6_interface;
			tcp::endpoint m_ipv4_interface;

			// since we might be listening on multiple interfaces
			// we might need more than one listen socket
			std::list<listen_socket_t> m_listen_sockets;

#if TORRENT_USE_I2P
			i2p_connection m_i2p_conn;
			boost::shared_ptr<socket_type> m_i2p_listen_socket;
#endif

#ifdef TORRENT_USE_OPENSSL
			ssl::context* ssl_ctx() { return &m_ssl_ctx; }
			void on_incoming_utp_ssl(boost::shared_ptr<socket_type> const& s);
			void ssl_handshake(error_code const& ec, boost::shared_ptr<socket_type> s);
#endif

			// when as a socks proxy is used for peers, also
			// listen for incoming connections on a socks connection
			boost::shared_ptr<socket_type> m_socks_listen_socket;
			boost::uint16_t m_socks_listen_port;

			// round-robin index into m_net_interfaces
			mutable boost::uint8_t m_interface_index;

replace this by a proper asio timer

../include/libtorrent/aux_/session_impl.hpp:911

			void open_new_incoming_socks_connection();

			enum listen_on_flags_t
			{
				open_ssl_socket = 0x10
			};

			listen_socket_t setup_listener(std::string const& device
				, boost::asio::ip::tcp const& protocol, int port, int flags
				, error_code& ec);

#ifndef TORRENT_DISABLE_DHT
			entry m_dht_state;
#endif

			// this is initialized to the unchoke_interval
			// session_setting and decreased every second.
			// when it reaches zero, it is reset to the
			// unchoke_interval and the unchoke set is
			// recomputed.
			int m_unchoke_time_scaler;

			// this is used to decide when to recalculate which
			// torrents to keep queued and which to activate

replace this by a proper asio timer

../include/libtorrent/aux_/session_impl.hpp:916

				open_ssl_socket = 0x10
			};

			listen_socket_t setup_listener(std::string const& device
				, boost::asio::ip::tcp const& protocol, int port, int flags
				, error_code& ec);

#ifndef TORRENT_DISABLE_DHT
			entry m_dht_state;
#endif

			// this is initialized to the unchoke_interval
			// session_setting and decreased every second.
			// when it reaches zero, it is reset to the
			// unchoke_interval and the unchoke set is
			// recomputed.
			int m_unchoke_time_scaler;

			// this is used to decide when to recalculate which
			// torrents to keep queued and which to activate
			int m_auto_manage_time_scaler;

			// works like unchoke_time_scaler but it
			// is only decresed when the unchoke set
			// is recomputed, and when it reaches zero,
			// the optimistic unchoke is moved to another peer.

replace this by a proper asio timer

../include/libtorrent/aux_/session_impl.hpp:923

#ifndef TORRENT_DISABLE_DHT
			entry m_dht_state;
#endif

			// this is initialized to the unchoke_interval
			// session_setting and decreased every second.
			// when it reaches zero, it is reset to the
			// unchoke_interval and the unchoke set is
			// recomputed.
			int m_unchoke_time_scaler;

			// this is used to decide when to recalculate which
			// torrents to keep queued and which to activate
			int m_auto_manage_time_scaler;

			// works like unchoke_time_scaler but it
			// is only decresed when the unchoke set
			// is recomputed, and when it reaches zero,
			// the optimistic unchoke is moved to another peer.
			int m_optimistic_unchoke_time_scaler;

			// works like unchoke_time_scaler. Each time
			// it reaches 0, and all the connections are
			// used, the worst connection will be disconnected
			// from the torrent with the most peers
			int m_disconnect_time_scaler;

			// when this scaler reaches zero, it will
			// scrape one of the auto managed, paused,
			// torrents.
			int m_auto_scrape_time_scaler;

			// the index of the torrent that we'll
			// refresh the next time
			int m_next_explicit_cache_torrent;

			// this is a counter of the number of seconds until
			// the next time the read cache is rotated, if we're
			// using an explicit read read cache.
			int m_cache_rotation_timer;

			// the index of the torrent that we'll
			// refresh the next time
			int m_next_suggest_torrent;

			// this is a counter of the number of seconds until
			// the next time the suggest pieces are refreshed
			int m_suggest_timer;

			// statistics gathered from all torrents.

it would be nice to not have this be part of session_interface

../include/libtorrent/aux_/session_interface.hpp:241

		// load the specified torrent. also evict one torrent, except
		// for the one specified, if we are at the limit of loaded torrents
		virtual bool load_torrent(torrent* t) = 0;

		// bump the specified torrent to make it the most recently used one
		// in the torrent LRU (i.e. the least likely to get unloaded)
		virtual void bump_torrent(torrent* t, bool back = true) = 0;

		// ask for which interface and port to bind outgoing peer connections on
		virtual tcp::endpoint bind_outgoing_socket(socket_type& s, address const&
			remote_address, error_code& ec) const = 0;
		virtual bool verify_bound_address(address const& addr, bool utp
			, error_code& ec) = 0;

#ifndef TORRENT_DISABLE_MUTABLE_TORRENTS
		virtual std::vector<boost::shared_ptr<torrent> > find_collection(
			std::string const& collection) const = 0;
#endif

		virtual proxy_settings proxy() const = 0;

#if TORRENT_USE_I2P
		virtual proxy_settings i2p_proxy() const = 0;
		virtual char const* i2p_session() const = 0;
#endif

		virtual void prioritize_connections(boost::weak_ptr<torrent> t) = 0;

		virtual tcp::endpoint get_ipv6_interface() const = 0;
		virtual tcp::endpoint get_ipv4_interface() const = 0;

		virtual void trigger_auto_manage() = 0;

		virtual void apply_settings_pack(boost::shared_ptr<settings_pack> pack) = 0;
		virtual session_settings const& settings() const = 0;

		virtual void queue_tracker_request(tracker_request& req
			, boost::weak_ptr<request_callback> c) = 0;

		// peer-classes
		virtual void set_peer_classes(peer_class_set* s, address const& a, int st) = 0;
		virtual peer_class_pool const& peer_classes() const = 0;
		virtual peer_class_pool& peer_classes() = 0;
		virtual bool ignore_unchoke_slots_set(peer_class_set const& set) const = 0;
		virtual int copy_pertinent_channels(peer_class_set const& set
			, int channel, bandwidth_channel** dst, int max) = 0;
		virtual int use_quota_overhead(peer_class_set& set, int amount_down, int amount_up) = 0;

		virtual bandwidth_manager* get_bandwidth_manager(int channel) = 0;

make this a bitfield

../include/libtorrent/aux_/session_settings.hpp:78

	if ((name & settings_pack::type_mask) != settings_pack:: type ## _type_base) return default_val; \
	return m_ ## type ## s[name - settings_pack:: type ## _type_base]

	struct TORRENT_EXTRA_EXPORT session_settings
	{
		friend void libtorrent::save_settings_to_dict(
			aux::session_settings const& s, entry::dictionary_type& sett);

		void set_str(int name, std::string const& value) { SET(string); }
		std::string const& get_str(int name) const { GET(string, m_strings[0]); }
		void set_int(int name, int value) { SET(int); }
		int get_int(int name) const { GET(int, 0); }
		void set_bool(int name, bool value) { SET(bool); }
		bool get_bool(int name) const { GET(bool, false); }

		session_settings();

	private:
		std::string m_strings[settings_pack::num_string_settings];
		int m_ints[settings_pack::num_int_settings];
		bool m_bools[settings_pack::num_bool_settings];
	};

#undef GET
#undef SET

} }

#endif