libtorrent todo-list

in order to support SSL over uTP, the utp_socket manager either needs to be able to receive packets on multiple ports, or we need to peek into the first few bytes the payload stream of a socket to determine whether or not it's an SSL connection. (The former is simpler but won't do as well with NATs)

../src/session_impl.cpp:667

		, m_disconnect_time_scaler(90)
		, m_auto_scrape_time_scaler(180)
		, m_next_explicit_cache_torrent(0)
		, m_cache_rotation_timer(0)
		, m_peak_up_rate(0)
		, m_peak_down_rate(0)
		, m_incoming_connection(false)
		, m_created(time_now_hires())
		, m_last_tick(m_created)
		, m_last_second_tick(m_created - milliseconds(900))
		, m_last_disk_performance_warning(min_time())
		, m_last_disk_queue_performance_warning(min_time())
		, m_last_choke(m_created)
		, m_next_rss_update(min_time())
#ifndef TORRENT_DISABLE_DHT
		, m_dht_announce_timer(m_io_service)
		, m_dht_interval_update_torrents(0)
#endif
		, m_external_udp_port(0)
		, m_udp_socket(m_io_service, m_half_open)
		, m_utp_socket_manager(m_settings, m_udp_socket
			, boost::bind(&session_impl::incoming_connection, this, _1))
		, m_boost_connections(0)
		, m_timer(m_io_service)
		, m_lsd_announce_timer(m_io_service)
		, m_host_resolver(m_io_service)
		, m_current_connect_attempts(0)
		, m_tick_residual(0)
		, m_non_filtered_torrents(0)
#if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_LOGGING || defined TORRENT_ERROR_LOGGING
		, m_logpath(".")
#endif
#ifndef TORRENT_DISABLE_GEO_IP
		, m_asnum_db(0)
		, m_country_db(0)
#endif
		, m_total_failed_bytes(0)
		, m_total_redundant_bytes(0)
		, m_pending_auto_manage(false)
		, m_need_auto_manage(false)
#if (defined TORRENT_DEBUG || TORRENT_RELEASE_ASSERTS) && defined BOOST_HAS_PTHREADS
		, m_network_thread(0)
#endif
	{
#if defined TORRENT_DEBUG || TORRENT_RELEASE_ASSERTS
		m_posting_torrent_updates = false;
#endif

		memset(m_redundant_bytes, 0, sizeof(m_redundant_bytes));
		m_udp_socket.set_rate_limit(m_settings.dht_upload_rate_limit);

if peer is a really good peer, maybe we shouldn't disconnect it

../src/torrent.cpp:6177

			return false;
		}
		TORRENT_ASSERT(m_connections.find(p) == m_connections.end());
		m_connections.insert(p);
#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 policy
		// 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())
			{
				peer->disconnect(errors::too_many_connections);
				p->peer_disconnected_other();
			}
			else
			{
				p->disconnect(errors::too_many_connections);
				// 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 policy know we're removing it
				remove_peer(p);
				return false;
			}
		}

#if defined TORRENT_DEBUG && !defined TORRENT_DISABLE_INVARIANT_CHECKS
		m_policy.check_invariant();
#endif

		if (m_share_mode)
			recalc_share_mode();

		return true;
	}

	bool torrent::want_more_peers() const
	{
		return m_connections.size() < m_max_connections
			&& !is_paused()
			&& ((m_state != torrent_status::checking_files

rename this class to find_peers, since that's what it does find_data is an unnecessarily generic name

../include/libtorrent/kademlia/find_data.hpp:60

#include <libtorrent/kademlia/node_id.hpp>
#include <libtorrent/kademlia/routing_table.hpp>
#include <libtorrent/kademlia/rpc_manager.hpp>
#include <libtorrent/kademlia/observer.hpp>
#include <libtorrent/kademlia/msg.hpp>

#include <boost/optional.hpp>
#include <boost/function/function1.hpp>
#include <boost/function/function2.hpp>

namespace libtorrent { namespace dht
{

typedef std::vector<char> packet_t;

class rpc_manager;
class node_impl;

// -------- find data -----------

class find_data : public traversal_algorithm
{
public:
	typedef boost::function<void(std::vector<tcp::endpoint> const&)> data_callback;
	typedef boost::function<void(std::vector<std::pair<node_entry, std::string> > const&, bool)> nodes_callback;

	void got_peers(std::vector<tcp::endpoint> const& peers);
	void got_write_token(node_id const& n, std::string const& write_token)
	{ m_write_tokens[n] = write_token; }

	find_data(node_impl& node, node_id target
		, data_callback const& dcallback
		, nodes_callback const& ncallback
		, bool noseeds);

	virtual void start();

	virtual char const* name() const;

	node_id const target() const { return m_target; }

protected:

	virtual void done();
	observer_ptr new_observer(void* ptr, udp::endpoint const& ep, node_id const& id);
	virtual bool invoke(observer_ptr o);

	data_callback m_data_callback;
	nodes_callback m_nodes_callback;
	std::map<node_id, std::string> m_write_tokens;
	node_id const m_target;

will pick_pieces ever return an empty set?

../src/torrent.cpp:8347

				if (added_request)
				{
					peers_with_requests.insert(peers_with_requests.begin(), &c);
					if (i->first_requested == min_time()) i->first_requested = now;

					if (!c.can_request_time_critical())
					{
						peers.erase(p);
					}
					else
					{
						// resort p, since it will have a higher download_queue_time now
						while (p != peers.end()-1 && (*p)->download_queue_time() > (*(p+1))->download_queue_time())
						{
							std::iter_swap(p, p+1);
							++p;
						}
					}
				}

			} while (!interesting_blocks.empty());

			peers.insert(peers.begin(), ignore_peers.begin(), ignore_peers.end());
			ignore_peers.clear();
		}

		// 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(m_ses.is_network_thread());
		std::set<std::string> ret;
		for (std::list<web_seed_entry>::const_iterator i = m_web_seeds.begin()
			, end(m_web_seeds.end()); i != end; ++i)
		{
			if (i->peer_info.banned) continue;
			if (i->type != type) continue;
			ret.insert(i->url);
		}
		return ret;
	}

	void torrent::remove_web_seed(std::string const& url, web_seed_entry::type_t type)
	{
		std::list<web_seed_entry>::iterator i = std::find_if(m_web_seeds.begin(), m_web_seeds.end()

we might want to do something else here as well, to resend the packet immediately without it being an MTU probe

../src/utp_stream.cpp:1862

//	if ((rand() % 100) > 0)
#endif
	m_sm->send_packet(udp::endpoint(m_remote_address, m_port)
		, (char const*)h, p->size, ec
		, p->mtu_probe ? utp_socket_manager::dont_fragment : 0);

	++m_out_packets;
	m_sm->inc_stats_counter(utp_socket_manager::packets_out);

	if (ec == error::message_size)
	{
#if TORRENT_UTP_LOG
		UTP_LOGV("%8p: error sending packet: %s\n", this, ec.message().c_str());
#endif
		// if we fail even though this is not a probe, we're screwed
		// since we'd have to repacketize
		TORRENT_ASSERT(p->mtu_probe);
		m_mtu_ceiling = p->size - 1;
		if (m_mtu_floor > m_mtu_ceiling) m_mtu_floor = m_mtu_ceiling;
		update_mtu_limits();
		p->mtu_probe = false;
		if (m_mtu_seq == m_ack_nr)
			m_mtu_seq = 0;
		ec.clear();

#if TORRENT_UTP_LOG
		UTP_LOGV("%8p: re-sending\n", this);
#endif
		m_sm->send_packet(udp::endpoint(m_remote_address, m_port)
			, (char const*)h, p->size, ec, 0);
	}

	if (ec == error::would_block || ec == error::try_again)
	{
#if TORRENT_UTP_LOG
		UTP_LOGV("%8p: socket stalled\n", this);
#endif
		if (!m_stalled)
		{
			m_stalled = true;
			m_sm->subscribe_writable(this);
		}
	}
	else if (ec)
	{
		TORRENT_ASSERT(stack_alloced != bool(payload_size));
		if (payload_size) free(p);
		m_error = ec;
		m_state = UTP_STATE_ERROR_WAIT;
		test_socket_state();
		return false;

sequence number, source IP and connection ID should be verified before accepting a reset packet

../src/utp_stream.cpp:2505

		m_reply_micro = boost::uint32_t(total_microseconds(receive_time - min_time()))
			- ph->timestamp_microseconds;
		boost::uint32_t prev_base = m_their_delay_hist.initialized() ? m_their_delay_hist.base() : 0;
		their_delay = m_their_delay_hist.add_sample(m_reply_micro, step);
		int base_change = m_their_delay_hist.base() - prev_base;
		UTP_LOGV("%8p: their_delay::add_sample:%u prev_base:%u new_base:%u\n"
			, this, m_reply_micro, prev_base, m_their_delay_hist.base());

		if (prev_base && base_change < 0 && base_change > -10000 && m_delay_hist.initialized())
		{
			// their base delay went down. This is caused by clock drift. To compensate,
			// adjust our base delay upwards
			// don't adjust more than 10 ms. If the change is that big, something is probably wrong
			m_delay_hist.adjust_base(-base_change);
		}

		UTP_LOGV("%8p: incoming packet reply_micro:%u base_change:%d\n"
			, this, m_reply_micro, prev_base ? base_change : 0);
	}

	if (ph->get_type() == ST_RESET)
	{
		UTP_LOGV("%8p: incoming packet type:RESET\n", this);
		m_error = asio::error::connection_reset;
		m_state = UTP_STATE_ERROR_WAIT;
		test_socket_state();
		return true;
	}

	// is this ACK valid? If the other end is ACKing
	// a packet that hasn't been sent yet
	// just ignore it. A 3rd party could easily inject a packet
	// like this in a stream, don't sever it because of it.
	// since m_seq_nr is the sequence number of the next packet
	// we'll send (and m_seq_nr-1 was the last packet we sent),
	// if the ACK we got is greater than the last packet we sent
	// something is wrong.
	// If our state is state_none, this packet must be a syn packet
	// and the ack_nr should be ignored
	boost::uint16_t cmp_seq_nr = (m_seq_nr - 1) & ACK_MASK;
#if TORRENT_UT_SEQ
	if (m_state == UTP_STATE_SYN_SENT && ph->get_type() == ST_STATE)
		cmp_seq_nr = m_seq_nr;
#endif
	if (m_state != UTP_STATE_NONE
		&& compare_less_wrap(cmp_seq_nr, ph->ack_nr, ACK_MASK))
	{
		UTP_LOGV("%8p: incoming packet ack_nr:%d our seq_nr:%d (ignored)\n"
			, this, int(ph->ack_nr), m_seq_nr);
		m_sm->inc_stats_counter(utp_socket_manager::redundant_pkts_in);
		return true;

make this configurable in dht_settings

../src/kademlia/node.cpp:64

#include "libtorrent/socket.hpp"
#include "libtorrent/random.hpp"
#include "libtorrent/aux_/session_impl.hpp"
#include "libtorrent/kademlia/node_id.hpp"
#include "libtorrent/kademlia/rpc_manager.hpp"
#include "libtorrent/kademlia/routing_table.hpp"
#include "libtorrent/kademlia/node.hpp"

#include "libtorrent/kademlia/refresh.hpp"
#include "libtorrent/kademlia/find_data.hpp"

#include "ed25519.h"

namespace libtorrent { namespace dht
{

void incoming_error(entry& e, char const* msg, int error_code = 203);

using detail::write_endpoint;

enum { announce_interval = 30 };

#ifdef TORRENT_DHT_VERBOSE_LOGGING
TORRENT_DEFINE_LOG(node)

extern int g_failed_announces;
extern int g_announces;

#endif

// remove peers that have timed out
void purge_peers(std::set<peer_entry>& peers)
{
	for (std::set<peer_entry>::iterator i = peers.begin()
		  , end(peers.end()); i != end;)
	{
		// the peer has timed out
		if (i->added + minutes(int(announce_interval * 1.5f)) < time_now())
		{
#ifdef TORRENT_DHT_VERBOSE_LOGGING
			TORRENT_LOG(node) << "peer timed out at: " << i->addr;
#endif
			peers.erase(i++);
		}
		else
			++i;
	}
}

void nop() {}

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:120

	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 = receive_buffer().left() - m_parser.body_start();
			TORRENT_ASSERT(receive_buffer_size <= t->block_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);

peers should really be corked/uncorked outside of all completed disk operations

../src/peer_connection.cpp:2568

		}

		if (is_disconnecting()) return;

#ifdef TORRENT_STATS
		++m_ses.m_incoming_piece_picks;
#endif
		request_a_block(*t, *this);
		send_block_requests();
	}

	void peer_connection::on_disk_write_complete(int ret, disk_io_job const& j
		, peer_request p, boost::shared_ptr<torrent> t)
	{
#ifdef TORRENT_STATS
		++m_ses.m_num_messages[aux::session_impl::on_disk_write_counter];
#endif
		TORRENT_ASSERT(m_ses.is_network_thread());

		// flush send buffer at the end of this scope
		cork _c(*this);

		INVARIANT_CHECK;

		m_outstanding_writing_bytes -= p.length;
		TORRENT_ASSERT(m_outstanding_writing_bytes >= 0);

#if defined(TORRENT_VERBOSE_LOGGING) || defined(TORRENT_LOGGING)
//		(*m_ses.m_logger) << time_now_string() << " *** DISK_WRITE_COMPLETE [ p: "
//			<< p.piece << " o: " << p.start << " ]\n";
#endif

		if (!t)
		{
			disconnect(j.error);
			return;
		}

		// in case the outstanding bytes just dropped down
		// to allow to receive more data
		setup_receive(read_async);

		piece_block block_finished(p.piece, p.start / t->block_size());

		if (ret == -1)
		{
			// handle_disk_error may disconnect us
			t->handle_disk_error(j, this);
			return;
		}

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:5694

	void session_impl::on_port_mapping(int mapping, address const& ip, int port
		, error_code const& ec, int map_transport)
	{
		TORRENT_ASSERT(is_network_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.post_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.post_alert(portmap_alert(mapping, port
					, map_transport));
			return;
		}

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

	session_status session_impl::status() const
	{
//		INVARIANT_CHECK;
		TORRENT_ASSERT(is_network_thread());

report errors as alerts

../src/session_impl.cpp:5904

	}

	void session_impl::add_dht_router(std::pair<std::string, int> const& node)
	{
#if defined TORRENT_ASIO_DEBUGGING
		add_outstanding_async("session_impl::on_dht_router_name_lookup");
#endif
		char port[7];
		snprintf(port, sizeof(port), "%d", node.second);
		tcp::resolver::query q(node.first, port);
		m_host_resolver.async_resolve(q,
			boost::bind(&session_impl::on_dht_router_name_lookup, this, _1, _2));
	}

	void session_impl::on_dht_router_name_lookup(error_code const& e
		, tcp::resolver::iterator host)
	{
#if defined TORRENT_ASIO_DEBUGGING
		complete_async("session_impl::on_dht_router_name_lookup");
#endif
		if (e) return;
		while (host != tcp::resolver::iterator())
		{
			// router nodes should be added before the DHT is started (and bootstrapped)
			udp::endpoint ep(host->endpoint().address(), host->endpoint().port());
			if (m_dht) m_dht->add_router_node(ep);
			m_dht_router_nodes.push_back(ep);
			++host;
		}
	}
#endif

	void session_impl::maybe_update_udp_mapping(int nat, int local_port, int external_port)
	{
		int local, external, protocol;
		if (nat == 0 && m_natpmp.get())
		{
			if (m_udp_mapping[nat] != -1)
			{
				if (m_natpmp->get_mapping(m_udp_mapping[nat], local, external, protocol))
				{
					// we already have a mapping. If it's the same, don't do anything
					if (local == local_port && external == external_port && protocol == natpmp::udp)
						return;
				}
				m_natpmp->delete_mapping(m_udp_mapping[nat]);
			}
			m_udp_mapping[nat] = m_natpmp->add_mapping(natpmp::udp
				, local_port, external_port);
			return;
		}

we only need to do this if our global IPv4 address has changed since the DHT (currently) only supports IPv4. Since restarting the DHT is kind of expensive, it would be nice to not do it unnecessarily

../src/session_impl.cpp:6375

	void session_impl::set_external_address(address const& ip
		, int source_type, address const& source)
	{
#if defined TORRENT_VERBOSE_LOGGING
		session_log(": set_external_address(%s, %d, %s)", print_address(ip).c_str()
			, source_type, print_address(source).c_str());
#endif

		if (!m_external_ip.cast_vote(ip, source_type, source)) return;

#if defined TORRENT_VERBOSE_LOGGING
		session_log("  external IP updated");
#endif

		if (m_alerts.should_post<external_ip_alert>())
			m_alerts.post_alert(external_ip_alert(ip));

		// since we have a new external IP now, we need to
		// restart the DHT with a new node ID
#ifndef TORRENT_DISABLE_DHT
		if (m_dht)
		{
			entry s = m_dht->state();
			int cur_state = 0;
			int prev_state = 0;
			entry* nodes1 = s.find_key("nodes");
			if (nodes1 && nodes1->type() == entry::list_t) cur_state = nodes1->list().size();
			entry* nodes2 = m_dht_state.find_key("nodes");
			if (nodes2 && nodes2->type() == entry::list_t) prev_state = nodes2->list().size();
			if (cur_state > prev_state) m_dht_state = s;
			start_dht(m_dht_state);
		}
#endif
	}

	void session_impl::free_disk_buffer(char* buf)
	{
		m_disk_thread.free_buffer(buf);
	}

	char* session_impl::allocate_disk_buffer(char const* category)
	{
		return m_disk_thread.allocate_buffer(category);
	}
	
	char* session_impl::allocate_buffer()
	{
		TORRENT_ASSERT(is_network_thread());

#ifdef TORRENT_DISK_STATS
		TORRENT_ASSERT(m_buffer_allocations >= 0);

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:1161

			if (c) c->disconnect(errors::no_memory);
			return;
		}

		// notify the user of the error
		if (alerts().should_post<file_error_alert>())
			alerts().post_alert(file_error_alert(j.error_file, get_handle(), j.error));

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

		if (j.action == disk_io_job::write
			&& (j.error == boost::system::errc::read_only_file_system
			|| j.error == boost::system::errc::permission_denied
			|| j.error == boost::system::errc::operation_not_permitted
			|| j.error == boost::system::errc::no_space_on_device
			|| j.error == boost::system::errc::file_too_large))
		{
			// if we failed to write, stop downloading and just
			// keep seeding.
			set_upload_mode(true);
			return;
		}

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

	void torrent::on_disk_read_complete(int ret, disk_io_job const& j, peer_request r, read_piece_struct* rp)
	{
		TORRENT_ASSERT(m_ses.is_network_thread());

		disk_buffer_holder buffer(m_ses, j.buffer);

		--rp->blocks_left;
		if (ret != r.length)
		{
			rp->fail = true;
			rp->error = j.error;
			handle_disk_error(j);
		}
		else
		{
			std::memcpy(rp->piece_data.get() + r.start, j.buffer, r.length);
		}

		if (rp->blocks_left == 0)
		{
			int size = m_torrent_file->piece_size(r.piece);
			if (rp->fail)
			{

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

../src/torrent.cpp:5439

						? (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
		if (!m_trackers.empty())
		{
			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_entry>::const_iterator i = m_web_seeds.begin()
				, end(m_web_seeds.end()); i != end; ++i)
			{
				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:6344

		TORRENT_ASSERT(is_finished());
		TORRENT_ASSERT(m_state != torrent_status::finished && m_state != torrent_status::seeding);

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

		// 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();

		m_completed_time = time(0);

		// disconnect all seeds
		if (settings().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())
				{
#if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_ERROR_LOGGING
					p->peer_log("*** SEED, CLOSING CONNECTION");
#endif
					seeds.push_back(p);
				}
			}
			std::for_each(seeds.begin(), seeds.end()
				, boost::bind(&peer_connection::disconnect, _1, errors::torrent_finished, 0));
		}

		if (m_abort) return;

		m_policy.recalculate_connect_candidates();

		TORRENT_ASSERT(m_storage);
		// we need to keep the object alive during this operation
		m_storage->async_release_files(
			boost::bind(&torrent::on_files_released, shared_from_this(), _1, _2));
		
		// this torrent just completed downloads, which means it will fall
		// under a different limit with the auto-manager. Make sure we
		// update auto-manage torrents in that case
		if (m_auto_managed)

we might save constructing a std::string if this would take a char const* instead

../src/torrent_info.cpp:181

			{
				tmp_path += i[0];
				tmp_path += i[1];
				tmp_path += i[2];
				tmp_path += i[3];
				i += 3;
				continue;
			}

			tmp_path += "_";
			valid_encoding = false;
		}
		// the encoding was not valid utf-8
		// save the original encoding and replace the
		// commonly used path with the correctly
		// encoded string
		if (!valid_encoding) target = tmp_path;
		return valid_encoding;
	}

	bool valid_path_element(std::string const& element)
	{
		if (element.empty()
			|| element == "." || element == ".."
			|| element[0] == '/' || element[0] == '\\'
			|| element[element.size()-1] == ':')
			return false;
		return true;
	}

	TORRENT_EXTRA_EXPORT void trim_path_element(std::string& element)
	{
		const int max_path_len = TORRENT_MAX_PATH;

		// on windows, the max path is expressed in
		// unicode characters, not bytes
#if defined TORRENT_WINDOWS
		std::wstring path_element;
		utf8_wchar(element, path_element);
		if (path_element.size() <= max_path_len) return;

		// truncate filenames that are too long. But keep extensions!
		std::wstring ext;
		wchar_t const* ext1 = wcsrchr(path_element.c_str(), '.');
		if (ext1 != NULL) ext = ext1;

		if (ext.size() > 15)
		{
			path_element.resize(max_path_len);
		}
		else

this logic should be a separate step done once the torrent is loaded, and the original filenames should be preserved!

../src/torrent_info.cpp:385

	
			while (*s1 != 0 || *s2 != 0)
			{
				c1 = to_lower(*s1);
				c2 = to_lower(*s2);
				if (c1 < c2) return true;
				if (c1 > c2) return false;
				++s1;
				++s2;
			}
			return false;
		}
	};

	bool extract_files(lazy_entry const& list, file_storage& target
		, std::string const& root_dir, ptrdiff_t info_ptr_diff)
	{
		if (list.type() != lazy_entry::list_t) return false;
		target.reserve(list.list_size());

		std::set<std::string, string_less_no_case> files;

		for (int i = 0, end(list.list_size()); i < end; ++i)
		{
			lazy_entry const* file_hash = 0;
			time_t mtime = 0;
			file_entry e;
			lazy_entry const* fee = 0;
			if (!extract_single_file(*list.list_at(i), e, root_dir
				, &file_hash, &fee, &mtime))
				return false;

			// as long as this file already exists
			// increase the counter
			int cnt = 0;
			while (!files.insert(e.path).second)
			{
				++cnt;
				char suffix[50];
				snprintf(suffix, sizeof(suffix), "%d%s", cnt, extension(e.path).c_str());
				replace_extension(e.path, suffix);
			}
			target.add_file(e, file_hash ? file_hash->string_ptr() + info_ptr_diff : 0);

			// This is a memory optimization! Instead of having
			// each entry keep a string for its filename, make it
			// simply point into the info-section buffer
			int last_index = target.num_files() - 1;

once the filename renaming is removed from here this check can be removed as well

../src/torrent_info.cpp:416

			if (!extract_single_file(*list.list_at(i), e, root_dir
				, &file_hash, &fee, &mtime))
				return false;

			// as long as this file already exists
			// increase the counter
			int cnt = 0;
			while (!files.insert(e.path).second)
			{
				++cnt;
				char suffix[50];
				snprintf(suffix, sizeof(suffix), "%d%s", cnt, extension(e.path).c_str());
				replace_extension(e.path, suffix);
			}
			target.add_file(e, file_hash ? file_hash->string_ptr() + info_ptr_diff : 0);

			// This is a memory optimization! Instead of having
			// each entry keep a string for its filename, make it
			// simply point into the info-section buffer
			int last_index = target.num_files() - 1;
			if (fee && target.file_name(last_index) == fee->string_value())
			{
				// this string pointer does not necessarily point into
				// the m_info_section buffer.
				char const* str_ptr = fee->string_ptr() + info_ptr_diff;
				target.rename_file_borrow(last_index, str_ptr, fee->string_length());
			}
		}
		return true;
	}

	int merkle_get_parent(int tree_node)
	{
		// node 0 doesn't have a parent
		TORRENT_ASSERT(tree_node > 0);
		return (tree_node - 1) / 2;
	}

	int merkle_get_sibling(int tree_node)
	{
		// node 0 doesn't have a sibling
		TORRENT_ASSERT(tree_node > 0);
		// even numbers have their sibling to the left
		// odd numbers have their sibling to the right
		return tree_node + (tree_node&1?1:-1);
	}

	int merkle_num_nodes(int leafs)
	{
		TORRENT_ASSERT(leafs > 0);
		return (leafs << 1) - 1;

find_node should write directly to the response entry

../src/kademlia/node.cpp:739

		{
			TORRENT_LOG(node) << " values: " << reply["values"].list().size();
		}
#endif
	}
	else if (strcmp(query, "find_node") == 0)
	{
		key_desc_t msg_desc[] = {
			{"target", lazy_entry::string_t, 20, 0},
		};

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

		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 (strcmp(query, "announce_peer") == 0)
	{
		key_desc_t msg_desc[] = {
			{"info_hash", lazy_entry::string_t, 20, 0},
			{"port", lazy_entry::int_t, 0, 0},
			{"token", lazy_entry::string_t, 0, 0},
			{"n", lazy_entry::string_t, 0, key_desc_t::optional},
			{"seed", lazy_entry::int_t, 0, key_desc_t::optional},
			{"implied_port", lazy_entry::int_t, 0, key_desc_t::optional},
		};

		lazy_entry const* msg_keys[6];
		if (!verify_message(arg_ent, msg_desc, msg_keys, 6, error_string, sizeof(error_string)))
		{
#ifdef TORRENT_DHT_VERBOSE_LOGGING
			++g_failed_announces;
#endif
			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();

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:100

		bloom_filter<32> m_external_address_voters;
		std::vector<external_ip_t> m_external_addresses;
		address m_external_address;
	};

	// 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

implement blocking write. Low priority since it's not used (yet)

../include/libtorrent/utp_stream.hpp:376

		for (typename Mutable_Buffers::const_iterator i = buffers.begin()
			, end(buffers.end()); i != end; ++i)
		{
			using asio::buffer_cast;
			using asio::buffer_size;
			add_read_buffer(buffer_cast<void*>(*i), buffer_size(*i));
#if defined TORRENT_DEBUG || TORRENT_RELEASE_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 Handler>
	void async_write_some(boost::asio::null_buffers const& buffers, Handler const& handler)
	{
		TORRENT_ASSERT(false);
	}

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

../include/libtorrent/web_peer_connection.hpp:127

	private:

		bool maybe_harvest_block();

		// returns the block currently being
		// downloaded. And the progress of that
		// block. If the peer isn't downloading
		// a piece for the moment, the boost::optional
		// will be invalid.
		boost::optional<piece_block_progress> downloading_piece_progress() const;

		// this has one entry per http-request
		// (might be more than the bt requests)
		std::deque<int> m_file_requests;

		std::string m_url;
			
		// this is used for intermediate storage of pieces
		// that are received in more than one HTTP response
		std::vector<char> m_piece;
		
		// the number of bytes received in the current HTTP
		// response. used to know where in the buffer the
		// next response starts
		size_type m_received_body;

		// position in the current range response
		size_type m_range_pos;

		// the position in the current block
		int m_block_pos;

		// 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
		size_type 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;
	};
}

#endif // TORRENT_WEB_PEER_CONNECTION_HPP_INCLUDED

this could be optimized using knuth morris pratt

../src/bt_peer_connection.cpp:655

		if (m_encrypted && m_rc4_encrypted)
		{
			fun = encrypt;
			userdata = m_enc_handler.get();
		}
#endif
		
		peer_connection::send_buffer(buf, size, flags, fun, userdata);
	}

	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:2074

			if (msg[5 + k / 8] & (0x80 >> (k % 8))) bitfield_string[k] = '1';
			else bitfield_string[k] = '0';
		}
		peer_log("==> BITFIELD [ %s ]", bitfield_string.c_str());
#endif
#if defined TORRENT_DEBUG || TORRENT_RELEASE_ASSERTS
		m_sent_bitfield = true;
#endif

		send_buffer(msg, packet_size);

		if (num_lazy_pieces > 0)
		{
			for (int i = 0; i < num_lazy_pieces; ++i)
			{
#ifdef TORRENT_VERBOSE_LOGGING
				peer_log("==> 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();

		// only send the port in case we bade the connection
		// on incoming connections the other end already knows
		// our listen port
		if (!m_ses.m_settings.anonymous_mode)
		{
			if (is_outgoing()) handshake["p"] = m_ses.listen_port();
			handshake["v"] = m_ses.settings().handshake_client_version.empty()
				? m_ses.settings().user_agent : m_ses.settings().handshake_client_version;
		}

		std::string remote_address;
		std::back_insert_iterator<std::string> out(remote_address);
		detail::write_address(remote().address(), out);
		handshake["yourip"] = remote_address;

move the erasing into the loop above remove all payload ranges that has been sent

../src/bt_peer_connection.cpp:3316

			for (std::vector<range>::iterator i = m_payloads.begin();
				i != m_payloads.end(); ++i)
			{
				i->start -= bytes_transferred;
				if (i->start < 0)
				{
					if (i->start + i->length <= 0)
					{
						amount_payload += i->length;
					}
					else
					{
						amount_payload += -i->start;
						i->length -= -i->start;
						i->start = 0;
					}
				}
			}
		}

		m_payloads.erase(
			std::remove_if(m_payloads.begin(), m_payloads.end(), range_below_zero)
			, m_payloads.end());

		TORRENT_ASSERT(amount_payload <= (int)bytes_transferred);
		m_statistics.sent_bytes(amount_payload, bytes_transferred - amount_payload);
		
		if (amount_payload > 0)
		{
			boost::shared_ptr<torrent> t = associated_torrent().lock();
			TORRENT_ASSERT(t);
			if (t) t->update_last_upload();
		}
	}

#if defined TORRENT_DEBUG && !defined TORRENT_DISABLE_INVARIANT_CHECKS
	void bt_peer_connection::check_invariant() const
	{
		boost::shared_ptr<torrent> t = associated_torrent().lock();

#ifndef TORRENT_DISABLE_ENCRYPTION
		TORRENT_ASSERT( (bool(m_state != read_pe_dhkey) || m_dh_key_exchange.get())
				|| !is_outgoing());

		TORRENT_ASSERT(!m_rc4_encrypted || m_enc_handler.get());
#endif
		if (!in_handshake())
		{
			TORRENT_ASSERT(m_sent_handshake);
		}

is there any way to pre-fetch data from a file on windows?

../src/file.cpp:1327

	void file::init_file()
	{
		if (m_page_size != 0) return;

		m_page_size = page_size();
	}

#endif

	void file::hint_read(size_type file_offset, int len)
	{
#if defined POSIX_FADV_WILLNEED
		posix_fadvise(m_fd, file_offset, len, POSIX_FADV_WILLNEED);
#elif defined F_RDADVISE
		radvisory r;
		r.ra_offset = file_offset;
		r.ra_count = len;
		fcntl(m_fd, F_RDADVISE, &r);
#else
#endif
	}

	size_type file::readv(size_type file_offset, iovec_t const* bufs, int num_bufs, error_code& ec)
	{
#ifdef TORRENT_WINDOWS
		if (m_file_handle == INVALID_HANDLE_VALUE)
		{
			ec = error_code(ERROR_INVALID_HANDLE, get_system_category());
			return -1;
		}
#else
		if (m_fd == -1)
		{
			ec = error_code(EBADF, get_system_category());
			return -1;
		}
#endif
		TORRENT_ASSERT((m_open_mode & rw_mask) == read_only || (m_open_mode & rw_mask) == read_write);
		TORRENT_ASSERT(bufs);
		TORRENT_ASSERT(num_bufs > 0);
		TORRENT_ASSERT(is_open());

#if defined TORRENT_WINDOWS || defined TORRENT_LINUX || defined TORRENT_DEBUG
		// make sure m_page_size is initialized
		init_file();
#endif

#ifdef TORRENT_DEBUG
		if (m_open_mode & no_buffer)
		{

support authentication (i.e. user name and password) in the URL

../src/http_tracker_connection.cpp:99

		, aux::session_impl const& ses
		, proxy_settings const& ps
		, std::string const& auth
#if TORRENT_USE_I2P
		, i2p_connection* i2p_conn
#endif
		)
		: tracker_connection(man, req, ios, c)
		, m_man(man)
		, m_ses(ses)
		, m_ps(ps)
		, m_cc(cc)
		, m_ios(ios)
#if TORRENT_USE_I2P
		, m_i2p_conn(i2p_conn)
#endif
	{}

	void http_tracker_connection::start()
	{
		std::string url = tracker_req().url;

		if (tracker_req().kind == tracker_request::scrape_request)
		{
			// find and replace "announce" with "scrape"
			// in request

			std::size_t pos = url.find("announce");
			if (pos == std::string::npos)
			{
				m_ios.post(boost::bind(&http_tracker_connection::fail_disp, self()
					, error_code(errors::scrape_not_available)));
				return;
			}
			url.replace(pos, 8, "scrape");
		}
		
#if TORRENT_USE_I2P
		bool i2p = is_i2p_url(url);
#else
		static const bool i2p = false;
#endif

		session_settings const& settings = m_ses.settings();

		// if request-string already contains
		// some parameters, append an ampersand instead
		// of a question mark
		size_t arguments_start = url.find('?');
		if (arguments_start != std::string::npos)
			url += "&";

move this to proxy_base and use it in all proxies

../src/i2p_stream.cpp:181

	{
		m_state = sam_idle;

		std::string name = m_sam_socket->name_lookup();
		if (!m_name_lookup.empty())
		{
			std::pair<std::string, name_lookup_handler>& nl = m_name_lookup.front();
			do_name_lookup(nl.first, nl.second);
			m_name_lookup.pop_front();
		}

		if (ec)
		{
			handler(ec, 0);
			return;
		}

		handler(ec, name.c_str());
	}

	bool i2p_stream::handle_error(error_code const& e, boost::shared_ptr<handler_type> const& h)
	{
		if (!e) return false;
//		fprintf(stderr, "i2p error \"%s\"\n", e.message().c_str());
		(*h)(e);
		error_code ec;
		close(ec);
		return true;
	}

	void i2p_stream::do_connect(error_code const& e, tcp::resolver::iterator i
		, boost::shared_ptr<handler_type> h)
	{
		if (e || i == tcp::resolver::iterator())
		{
			(*h)(e);
			error_code ec;
			close(ec);
			return;
		}

#if defined TORRENT_ASIO_DEBUGGING
		add_outstanding_async("i2p_stream::connected");
#endif
		m_sock.async_connect(i->endpoint(), boost::bind(
			&i2p_stream::connected, this, _1, h));
	}

	void i2p_stream::connected(error_code const& e, boost::shared_ptr<handler_type> h)
	{
#if defined TORRENT_ASIO_DEBUGGING

use compare_less_wrap for this comparison as well

../src/packet_buffer.cpp:176

		while (new_size < size)
			new_size <<= 1;

		void** new_storage = (void**)malloc(sizeof(void*) * new_size);

		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::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;

this might need something more so that once we have the metadata we can construct a full bitfield

../src/peer_connection.cpp:2731

#ifdef TORRENT_VERBOSE_LOGGING
		peer_log("*** THIS IS A SEED [ p: %p ]", m_peer_info);
#endif

		t->get_policy().set_seed(m_peer_info, true);
		m_upload_only = true;
		m_bitfield_received = true;

		// if we don't have metadata yet
		// just remember the bitmask
		// don't update the piecepicker
		// (since it doesn't exist yet)
		if (!t->ready_for_connections())
		{
			// assume seeds are interesting when we
			// don't even have the metadata
			t->get_policy().peer_is_interesting(*this);

			disconnect_if_redundant();
			return;
		}

		TORRENT_ASSERT(!m_have_piece.empty());
		m_have_piece.set_all();
		m_num_pieces = m_have_piece.size();
		
		t->peer_has_all(this);

		// if we're finished, we're not interested
		if (t->is_upload_only()) send_not_interested();
		else t->get_policy().peer_is_interesting(*this);

		disconnect_if_redundant();
	}
	
	// -----------------------------
	// --------- HAVE NONE ---------
	// -----------------------------

	void peer_connection::incoming_have_none()
	{
		INVARIANT_CHECK;

#ifdef TORRENT_VERBOSE_LOGGING
		peer_log("<== HAVE_NONE");
#endif

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

sort the allowed fast set in priority order

../src/peer_connection.cpp:2862

		// this piece index later
		m_allowed_fast.push_back(index);

		// 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->valid_metadata()
			&& t->has_picker()
			&& t->picker().piece_priority(index) > 0)
		{
			t->get_policy().peer_is_interesting(*this);
		}
	}

	std::vector<int> const& peer_connection::allowed_fast()
	{
		boost::shared_ptr<torrent> t = m_torrent.lock();
		TORRENT_ASSERT(t);

		return m_allowed_fast;
	}

	bool peer_connection::can_request_time_critical() const
	{
		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;
	}

	void peer_connection::make_time_critical(piece_block const& block)
	{
		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;
#if defined TORRENT_DEBUG || TORRENT_RELEASE_ASSERTS
		boost::shared_ptr<torrent> t = m_torrent.lock();
		TORRENT_ASSERT(t);
		TORRENT_ASSERT(t->has_picker());
		TORRENT_ASSERT(t->picker().is_requested(block));
#endif

peers should really be corked/uncorked outside of all completed disk operations

../src/peer_connection.cpp:4575

				// this means we're in seed mode and we haven't yet
				// verified this piece (r.piece)
				t->filesystem().async_read_and_hash(r, boost::bind(&peer_connection::on_disk_read_complete
					, self(), _1, _2, r), cache.second);
				t->verified(r.piece);
			}

			m_reading_bytes += r.length;

			m_requests.erase(m_requests.begin());
			sent_a_piece = true;
		}

		if (t->share_mode() && sent_a_piece)
			t->recalc_share_mode();
	}

	void peer_connection::on_disk_read_complete(int ret, disk_io_job const& j, peer_request r)
	{
		// flush send buffer at the end of this scope
		cork _c(*this);

#ifdef TORRENT_STATS
		++m_ses.m_num_messages[aux::session_impl::on_disk_read_counter];
#endif
		TORRENT_ASSERT(m_ses.is_network_thread());

		m_reading_bytes -= r.length;

		disk_buffer_holder buffer(m_ses, j.buffer);
#if TORRENT_DISK_STATS
		if (j.buffer) m_ses.m_disk_thread.rename_buffer(j.buffer, "received send buffer");
#endif

		boost::shared_ptr<torrent> t = m_torrent.lock();
		if (!t)
		{
			disconnect(j.error);
			return;
		}
		
		if (ret != r.length)
		{
			if (ret == -3)
			{
#if defined TORRENT_VERBOSE_LOGGING
				peer_log("==> REJECT_PIECE [ piece: %d s: %d l: %d ]"
					, r.piece , r.start , r.length);
#endif
				write_reject_request(r);
				if (t->seed_mode()) t->leave_seed_mode(false);

only allow _one_ connection to use this override at a time

../src/policy.cpp:857

				" external: " << external.external_address(m_peers[candidate]->address()) <<
				" t: " << (session_time - m_peers[candidate]->last_connected) <<
				" ]\n";
		}
#endif

		if (candidate == -1) return m_peers.end();
		return m_peers.begin() + candidate;
	}

	bool policy::new_connection(peer_connection& c, int session_time)
	{
		TORRENT_ASSERT(!c.is_outgoing());

		INVARIANT_CHECK;

		// if the connection comes from the tracker,
		// it's probably just a NAT-check. Ignore the
		// num connections constraint then.

		error_code ec;
		TORRENT_ASSERT(c.remote() == c.get_socket()->remote_endpoint(ec) || ec);
		TORRENT_ASSERT(!m_torrent->is_paused());

#if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_LOGGING
		if (c.remote().address() == m_torrent->current_tracker().address())
		{
			m_torrent->debug_log("overriding connection limit for tracker NAT-check");
		}
#endif

		iterator iter;
		peer* i = 0;

		bool found = false;
		if (m_torrent->settings().allow_multiple_connections_per_ip)
		{
			tcp::endpoint remote = c.remote();
			std::pair<iterator, iterator> range = find_peers(remote.address());
			iter = std::find_if(range.first, range.second, match_peer_endpoint(remote));
	
			if (iter != range.second)
			{
				TORRENT_ASSERT((*iter)->in_use);
				found = true;
			}
		}
		else
		{
			iter = std::lower_bound(
				m_peers.begin(), m_peers.end()

how do we deal with our external address changing? Pass in a force-update maybe? and keep a version number in policy

../src/policy.cpp:1897

#endif
		, on_parole(false)
		, banned(false)
#ifndef TORRENT_DISABLE_DHT
		, added_to_dht(false)
#endif
		, supports_utp(true) // assume peers support utp
		, confirmed_supports_utp(false)
		, supports_holepunch(false)
		, web_seed(false)
#if defined TORRENT_DEBUG || TORRENT_RELEASE_ASSERTS
		, in_use(false)
#endif
	{
		TORRENT_ASSERT((src & 0xff) == src);
	}

	// TOOD: pass in both an IPv6 and IPv4 address here
	boost::uint32_t policy::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;
	}

	size_type policy::peer::total_download() const
	{
		if (connection != 0)
		{
			TORRENT_ASSERT(prev_amount_download == 0);
			return connection->statistics().total_payload_download();
		}
		else
		{
			return size_type(prev_amount_download) << 10;
		}
	}

	size_type policy::peer::total_upload() const
	{
		if (connection != 0)
		{
			TORRENT_ASSERT(prev_amount_upload == 0);
			return connection->statistics().total_payload_upload();
		}
		else
		{
			return size_type(prev_amount_upload) << 10;
		}

recalculate all connect candidates for all torrents

../src/session_impl.cpp:1942

		m_upload_rate.close();

		// #error closing the udp socket here means that
		// the uTP connections cannot be closed gracefully
		m_udp_socket.close();
		m_external_udp_port = 0;

#ifndef TORRENT_DISABLE_GEO_IP
		if (m_asnum_db) GeoIP_delete(m_asnum_db);
		if (m_country_db) GeoIP_delete(m_country_db);
		m_asnum_db = 0;
		m_country_db = 0;
#endif

		m_disk_thread.abort();
	}

	void session_impl::set_port_filter(port_filter const& f)
	{
		m_port_filter = f;
	}

	void session_impl::set_ip_filter(ip_filter const& f)
	{
		INVARIANT_CHECK;

		m_ip_filter = f;

		// Close connections whose endpoint is filtered
		// by the new ip-filter
		for (torrent_map::iterator i = m_torrents.begin()
			, end(m_torrents.end()); i != end; ++i)
			i->second->ip_filter_updated();
	}

	ip_filter const& session_impl::get_ip_filter() const
	{
		return m_ip_filter;
	}

	void session_impl::update_disk_thread_settings()
	{
		disk_io_job j;
		j.buffer = (char*)new session_settings(m_settings);
		j.action = disk_io_job::update_settings;
		m_disk_thread.add_job(j);
	}

	template <class Socket>
	void static set_socket_buffer_size(Socket& s, session_settings const& sett, error_code& ec)
	{

have a separate list for these connections, instead of having to loop through all of them

../src/session_impl.cpp:3372

		// --------------------------------------------------------------
		if (!m_paused) m_auto_manage_time_scaler--;
		if (m_auto_manage_time_scaler < 0)
		{
			m_auto_manage_time_scaler = settings().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;
			if (m_last_tick - p->connected_time() > seconds(m_settings.handshake_timeout))
				p->disconnect(errors::timed_out);
		}

		// --------------------------------------------------------------
		// second_tick every torrent
		// --------------------------------------------------------------

		int congested_torrents = 0;
		int uncongested_torrents = 0;

		// count the number of seeding torrents vs. downloading
		// torrents we are running
		int num_seeds = 0;
		int num_downloads = 0;

		// count the number of peers of downloading torrents
		int num_downloads_peers = 0;

		torrent_map::iterator least_recently_scraped = m_torrents.end();
		int num_paused_auto_managed = 0;

		int num_checking = 0;
		int num_queued = 0;
		for (torrent_map::iterator i = m_torrents.begin();
			i != m_torrents.end();)
		{
			torrent& t = *i->second;
			TORRENT_ASSERT(!t.is_aborted());
			if (t.statistics().upload_rate() * 11 / 10 > t.upload_limit())
				++congested_torrents;

allow extensions to sort torrents for queuing

../src/session_impl.cpp:4459

			else if (!t->is_paused())
			{
				TORRENT_ASSERT(t->m_resume_data_loaded || !t->valid_metadata());
				--hard_limit;
			  	if (is_active(t, settings()))
				{
					// this is not an auto managed torrent,
					// if it's running and active, decrease the
					// counters.
					if (t->is_finished())
						--num_seeds;
					else
						--num_downloaders;
				}
			}
		}

		bool handled_by_extension = false;

#ifndef TORRENT_DISABLE_EXTENSIONS
#endif

		if (!handled_by_extension)
		{
			std::sort(downloaders.begin(), downloaders.end()
				, boost::bind(&torrent::sequence_number, _1) < boost::bind(&torrent::sequence_number, _2));

			std::sort(seeds.begin(), seeds.end()
				, boost::bind(&torrent::seed_rank, _1, boost::ref(m_settings))
				> boost::bind(&torrent::seed_rank, _2, boost::ref(m_settings)));
		}

		if (settings().auto_manage_prefer_seeds)
		{
			auto_manage_torrents(seeds, dht_limit, tracker_limit, lsd_limit
				, hard_limit, num_seeds);
			auto_manage_torrents(downloaders, dht_limit, tracker_limit, lsd_limit
				, hard_limit, num_downloaders);
		}
		else
		{
			auto_manage_torrents(downloaders, dht_limit, tracker_limit, lsd_limit
				, hard_limit, num_downloaders);
			auto_manage_torrents(seeds, dht_limit, tracker_limit, lsd_limit
				, hard_limit, num_seeds);
		}
	}

	void session_impl::recalculate_optimistic_unchoke_slots()
	{
		TORRENT_ASSERT(is_network_thread());

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:4615

		{
			if (m_boost_connections > max_connections)
			{
				m_boost_connections -= max_connections;
				max_connections = 0;
			}
			else
			{
				max_connections -= m_boost_connections;
				m_boost_connections = 0;
			}
		}

		// 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
		int limit = (std::min)(m_settings.connections_limit - num_connections(), free_slots);
		if (m_settings.smooth_connects && max_connections > (limit+1) / 2)
			max_connections = (limit+1) / 2;

		if (!m_torrents.empty()
			&& free_slots > -m_half_open.limit()
			&& num_connections() < m_settings.connections_limit
			&& !m_abort
			&& m_settings.connection_speed > 0
			&& max_connections > 0)
		{
			// this is the maximum number of connections we will
			// attempt this tick
			int average_peers = 0;
			if (num_downloads > 0)
				average_peers = num_downloads_peers / num_downloads;

			if (m_next_connect_torrent == m_torrents.end())
				m_next_connect_torrent = m_torrents.begin();

			int steps_since_last_connect = 0;
			int num_torrents = int(m_torrents.size());
			for (;;)
			{
				torrent& t = *m_next_connect_torrent->second;
				if (t.want_more_peers())
				{
					TORRENT_ASSERT(t.allows_peers());
					// have a bias to give more connection attempts
					// to downloading torrents than seed, and even
					// more to downloading torrents with less than
					// average number of connections
					int num_attempts = 1;
					if (!t.is_finished())
					{

make this bias configurable

../src/session_impl.cpp:4649

also take average_peers into account, to create a bias for downloading torrents with < average peers

../src/session_impl.cpp:4650

				average_peers = num_downloads_peers / num_downloads;

			if (m_next_connect_torrent == m_torrents.end())
				m_next_connect_torrent = m_torrents.begin();

			int steps_since_last_connect = 0;
			int num_torrents = int(m_torrents.size());
			for (;;)
			{
				torrent& t = *m_next_connect_torrent->second;
				if (t.want_more_peers())
				{
					TORRENT_ASSERT(t.allows_peers());
					// have a bias to give more connection attempts
					// to downloading torrents than seed, and even
					// more to downloading torrents with less than
					// average number of connections
					int num_attempts = 1;
					if (!t.is_finished())
					{
						TORRENT_ASSERT(m_num_active_downloading > 0);
						num_attempts += m_num_active_finished / m_num_active_downloading;
					}
					while (m_current_connect_attempts < num_attempts)
					{
						TORRENT_TRY
						{
							++m_current_connect_attempts;
							if (t.try_connect_peer())
							{
								--max_connections;
								--free_slots;
								steps_since_last_connect = 0;
#ifdef TORRENT_STATS
								++m_connection_attempts;
#endif
							}
						}
						TORRENT_CATCH(std::bad_alloc&)
						{
							// we ran out of memory trying to connect to a peer
							// lower the global limit to the number of peers
							// we already have
							m_settings.connections_limit = num_connections();
							if (m_settings.connections_limit < 2) m_settings.connections_limit = 2;
						}
						if (!t.want_more_peers()) break;
						if (free_slots <= -m_half_open.limit()) return;
						if (max_connections == 0) return;
						if (num_connections() >= m_settings.connections_limit) return;
					}

make configurable

../src/session_impl.cpp:4794

#ifdef TORRENT_DEBUG
			for (std::vector<peer_connection*>::const_iterator i = peers.begin()
				, end(peers.end()), prev(peers.end()); i != end; ++i)
			{
				if (prev != end)
				{
					boost::shared_ptr<torrent> t1 = (*prev)->associated_torrent().lock();
					TORRENT_ASSERT(t1);
					boost::shared_ptr<torrent> t2 = (*i)->associated_torrent().lock();
					TORRENT_ASSERT(t2);
					TORRENT_ASSERT((*prev)->uploaded_in_last_round() * 1000
						* (1 + t1->priority()) / total_milliseconds(unchoke_interval)
						>= (*i)->uploaded_in_last_round() * 1000
						* (1 + t2->priority()) / total_milliseconds(unchoke_interval));
				}
				prev = i;
			}
#endif

			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;

				++m_allowed_upload_slots;

make configurable

../src/session_impl.cpp:4808

						>= (*i)->uploaded_in_last_round() * 1000
						* (1 + t2->priority()) / total_milliseconds(unchoke_interval));
				}
				prev = i;
			}
#endif

			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;

				++m_allowed_upload_slots;

				rate_threshold += 1024;
			}
			// allow one optimistic unchoke
			++m_allowed_upload_slots;
		}

		if (m_settings.choking_algorithm == session_settings::bittyrant_choker)
		{
			// if we're using the bittyrant choker, sort peers by their return
			// on investment. i.e. download rate / upload rate
			std::sort(peers.begin(), peers.end()
				, boost::bind(&peer_connection::bittyrant_unchoke_compare, _1, _2));
		}
		else
		{
			// 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
			std::sort(peers.begin(), peers.end()
				, boost::bind(&peer_connection::unchoke_compare, _1, _2));
		}

		// auto unchoke
		int upload_limit = m_bandwidth_channel[peer_connection::upload_channel]->throttle();
		if (m_settings.choking_algorithm == session_settings::auto_expand_choker
			&& upload_limit > 0)
		{
			// if our current upload rate is less than 90% of our 
			// limit AND most torrents are not "congested", i.e.
			// they are not holding back because of a per-torrent

if the read fails, set error and exit immediately

../src/storage.cpp:324

			if (m_storage->disk_pool()) block_size = m_storage->disk_pool()->block_size();
			int size = slot_size;
			int num_blocks = (size + block_size - 1) / block_size;

			// when we optimize for speed we allocate all the buffers we
			// need for the rest of the piece, and read it all in one call
			// and then hash it. When optimizing for memory usage, we read
			// one block at a time and hash it. This ends up only using a
			// single buffer
			if (m_storage->settings().optimize_hashing_for_speed)
			{
				file::iovec_t* bufs = TORRENT_ALLOCA(file::iovec_t, num_blocks);
				for (int i = 0; i < num_blocks; ++i)
				{
					bufs[i].iov_base = m_storage->disk_pool()->allocate_buffer("hash temp");
					bufs[i].iov_len = (std::min)(block_size, size);
					size -= bufs[i].iov_len;
				}
				// deliberately pass in 0 as flags, to disable random_access
				num_read = m_storage->readv(bufs, slot, ph.offset, num_blocks, 0);

				for (int i = 0; i < num_blocks; ++i)
				{
					if (small_hash && small_piece_size <= block_size)
					{
						ph.h.update((char const*)bufs[i].iov_base, small_piece_size);
						*small_hash = hasher(ph.h).final();
						small_hash = 0; // avoid this case again
						if (int(bufs[i].iov_len) > small_piece_size)
							ph.h.update((char const*)bufs[i].iov_base + small_piece_size
								, bufs[i].iov_len - small_piece_size);
					}
					else
					{
						ph.h.update((char const*)bufs[i].iov_base, bufs[i].iov_len);
						small_piece_size -= bufs[i].iov_len;
					}
					ph.offset += bufs[i].iov_len;
					m_storage->disk_pool()->free_buffer((char*)bufs[i].iov_base);
				}
			}
			else
			{
				file::iovec_t buf;
				disk_buffer_holder holder(*m_storage->disk_pool()
					, m_storage->disk_pool()->allocate_buffer("hash temp"));
				buf.iov_base = holder.get();
				for (int i = 0; i < num_blocks; ++i)
				{
					buf.iov_len = (std::min)(block_size, size);
					// deliberately pass in 0 as flags, to disable random_access

if the read fails, set error and exit immediately

../src/storage.cpp:358

					{
						ph.h.update((char const*)bufs[i].iov_base, bufs[i].iov_len);
						small_piece_size -= bufs[i].iov_len;
					}
					ph.offset += bufs[i].iov_len;
					m_storage->disk_pool()->free_buffer((char*)bufs[i].iov_base);
				}
			}
			else
			{
				file::iovec_t buf;
				disk_buffer_holder holder(*m_storage->disk_pool()
					, m_storage->disk_pool()->allocate_buffer("hash temp"));
				buf.iov_base = holder.get();
				for (int i = 0; i < num_blocks; ++i)
				{
					buf.iov_len = (std::min)(block_size, size);
					// deliberately pass in 0 as flags, to disable random_access
					int ret = m_storage->readv(&buf, slot, ph.offset, 1, 0);
					if (ret > 0) num_read += ret;

					if (small_hash && small_piece_size <= block_size)
					{
						if (small_piece_size > 0) ph.h.update((char const*)buf.iov_base, small_piece_size);
						*small_hash = hasher(ph.h).final();
						small_hash = 0; // avoid this case again
						if (int(buf.iov_len) > small_piece_size)
							ph.h.update((char const*)buf.iov_base + small_piece_size
								, buf.iov_len - small_piece_size);
					}
					else
					{
						ph.h.update((char const*)buf.iov_base, buf.iov_len);
						small_piece_size -= buf.iov_len;
					}

					ph.offset += buf.iov_len;
					size -= buf.iov_len;
				}
			}
			if (error()) return 0;
		}
		return num_read;
	}

	default_storage::default_storage(file_storage const& fs, file_storage const* mapped, std::string const& path
		, file_pool& fp, std::vector<boost::uint8_t> const& file_prio)
		: m_files(fs)
		, m_file_priority(file_prio)
		, m_pool(fp)
		, m_page_size(page_size())

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:629

		for (;;)
		{
			if (file_offset < m_files.file_size(file_index))
				break;

			file_offset -= m_files.file_size(file_index);
			++file_index;
			TORRENT_ASSERT(file_index != files().num_files());
		}
	
		error_code ec;
		boost::intrusive_ptr<file> file_handle = open_file(file_index, file::read_only, ec);
		if (!file_handle || ec) return slot;

		size_type data_start = file_handle->sparse_end(file_offset);
		return int((data_start + m_files.piece_length() - 1) / m_files.piece_length());
	}

	bool default_storage::verify_resume_data(lazy_entry const& rd, error_code& error)
	{
		lazy_entry const* 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);
			}
		}
		
		lazy_entry const* 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));
		}

		std::vector<std::pair<size_type, std::time_t> > file_sizes;
		lazy_entry const* file_sizes_ent = rd.dict_find_list("file sizes");
		if (file_sizes_ent == 0)
		{
			error = errors::missing_file_sizes;
			return false;
		}
		
		for (int i = 0; i < file_sizes_ent->list_size(); ++i)
		{

what if file_base is used to merge several virtual files into a single physical file? We should probably disable this if file_base is used. This is not a widely used feature though

../src/storage.cpp:1238

			int bytes_transferred = 0;
			// if the file is opened in no_buffer mode, and the
			// read is unaligned, we need to fall back on a slow
			// special read that reads aligned buffers and copies
			// it into the one supplied
			size_type adjusted_offset = files().file_base(file_index) + file_offset;
			if ((file_handle->open_mode() & file::no_buffer)
				&& ((adjusted_offset & (file_handle->pos_alignment()-1)) != 0
				|| (uintptr_t(tmp_bufs->iov_base) & (file_handle->buf_alignment()-1)) != 0))
			{
				bytes_transferred = (int)(this->*op.unaligned_op)(file_handle, adjusted_offset
					, tmp_bufs, num_tmp_bufs, ec);
				if ((op.mode & file::rw_mask) == file::read_write
					&& adjusted_offset + bytes_transferred >= files().file_size(file_index)
					&& (file_handle->pos_alignment() > 0 || file_handle->size_alignment() > 0))
				{
					// we were writing, and we just wrote the last block of the file
					// we likely wrote a bit too much, since we're restricted to
					// a specific alignment for writes. Make sure to truncate the size

					file_handle->set_size(files().file_size(file_index), ec);
				}
			}
			else
			{
				bytes_transferred = (int)((*file_handle).*op.regular_op)(adjusted_offset
					, tmp_bufs, num_tmp_bufs, ec);
				TORRENT_ASSERT(bytes_transferred <= bufs_size(tmp_bufs, num_tmp_bufs));
			}
			file_offset = 0;

			if (ec)
			{
				set_error(files().file_path(file_index, m_save_path), ec);
				return -1;
			}

			if (file_bytes_left != bytes_transferred)
				return bytes_transferred;

			advance_bufs(current_buf, bytes_transferred);
			TORRENT_ASSERT(count_bufs(current_buf, bytes_left - file_bytes_left) <= num_bufs);
		}
		return size;
	}

	// these functions are inefficient, but should be fairly uncommon. The read
	// case happens if unaligned files are opened in no_buffer mode or if clients
	// makes unaligned requests (and the disk cache is disabled or fully utilized
	// for write cache).

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:1362

			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));

#if defined(TORRENT_VERBOSE_LOGGING) || defined(TORRENT_LOGGING)
		std::string names;
		bool match = false;
#endif
		for (int i = 0; i < sk_GENERAL_NAME_num(gens); ++i)
		{
			GENERAL_NAME* gen = sk_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;

#if defined(TORRENT_VERBOSE_LOGGING) || defined(TORRENT_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)
			{
#if defined(TORRENT_VERBOSE_LOGGING) || defined(TORRENT_LOGGING)
				match = true;

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:5172

		if (m_seed_mode) m_verified.resize(m_torrent_file->num_pieces(), false);
		super_seeding(rd.dict_find_int_value("super_seeding", 0));

		m_last_scrape = rd.dict_find_int_value("last_scrape", 0);
		m_last_download = rd.dict_find_int_value("last_download", 0);
		m_last_upload = rd.dict_find_int_value("last_upload", 0);

		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.m_uuids.insert(std::make_pair(m_uuid.empty()
				? m_url : m_uuid, me));
		}

		lazy_entry const* 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;

		lazy_entry const* file_priority = rd.dict_find_list("file_priority");
		if (file_priority && file_priority->list_size()
			== m_torrent_file->num_files())
		{
			for (int i = 0; i < file_priority->list_size(); ++i)
				m_file_priority[i] = file_priority->list_int_value_at(i, 1);
			update_piece_priorities();
		}

		lazy_entry const* piece_priority = rd.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)

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:5308

				add_web_seed(url, web_seed_entry::http_seed);
			}
		}

		if (m_torrent_file->is_merkle_torrent())
		{
			lazy_entry const* 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);
			}
		}
	}

	boost::intrusive_ptr<torrent_info> torrent::get_torrent_copy()
	{
		if (!m_torrent_file->is_valid()) return boost::intrusive_ptr<torrent_info>();

		// copy the torrent_info object
		return boost::intrusive_ptr<torrent_info>(new torrent_info(*m_torrent_file));
	}
	
	void torrent::write_resume_data(entry& ret) const
	{
		using namespace libtorrent::detail; // for write_*_endpoint()
		ret["file-format"] = "libtorrent resume file";
		ret["file-version"] = 1;
		ret["libtorrent-version"] = LIBTORRENT_VERSION;

		ret["total_uploaded"] = m_total_uploaded;
		ret["total_downloaded"] = m_total_downloaded;

		ret["active_time"] = m_active_time;
		ret["finished_time"] = m_finished_time;
		ret["seeding_time"] = m_seeding_time;
		ret["last_seen_complete"] = m_last_seen_complete;

		ret["num_complete"] = m_complete;
		ret["num_incomplete"] = m_incomplete;
		ret["num_downloaded"] = m_downloaded;

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:5496

		entry::string_type& pieces = ret["pieces"].string();
		pieces.resize(m_torrent_file->num_pieces());
		if (is_seed())
		{
			std::memset(&pieces[0], 1, pieces.size());
		}
		else
		{
			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());
			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

		// failcount is a 5 bit value
		int max_failcount = (std::min)(settings().max_failcount, 31);

		int num_saved_peers = 0;

		for (policy::const_iterator i = m_policy.begin_peer()
			, end(m_policy.end_peer()); i != end; ++i)
		{
			error_code ec;
			policy::peer const* p = *i;
			address addr = p->address();

go through the pieces we have and count the total number of downloaders we have. Only count peers that are interested in us since some peers might not send have messages for pieces we have it num_interested == 0, we need to pick a new piece

../src/torrent.cpp:8026

			}

			rarest_pieces.clear();
			rarest_rarity = pp.peer_count;
			rarest_pieces.push_back(i);
		}

		if (prio_updated)
			m_policy.recalculate_connect_candidates();

		// now, rarest_pieces is a list of all pieces that are the rarest ones.
		// and rarest_rarity is the number of peers that have the rarest pieces

		// if there's only a single peer that doesn't have the rarest piece
		// it's impossible for us to download one piece and upload it
		// twice. i.e. we cannot get a positive share ratio
		if (num_peers - rarest_rarity < settings().share_mode_target) return;

		// we might be able to do better than a share ratio of 2 if there are
		// enough downloaders of the pieces we already have.

		// now, pick one of the rarest pieces to download
		int pick = random() % rarest_pieces.size();
		bool was_finished = is_finished();
		m_picker->set_piece_priority(rarest_pieces[pick], 1);
		update_peer_interest(was_finished);

		m_policy.recalculate_connect_candidates();
	}

	void torrent::refresh_explicit_cache(int cache_size)
	{
		TORRENT_ASSERT(m_ses.is_network_thread());
		if (!ready_for_connections()) return;

		if (m_abort) return;
		TORRENT_ASSERT(m_storage);

		// rotate the cached pieces

		// add blocks_per_piece / 2 in order to round to closest whole piece
		int blocks_per_piece = m_torrent_file->piece_length() / block_size();
		int num_cache_pieces = (cache_size + blocks_per_piece / 2) / blocks_per_piece;
		if (num_cache_pieces > m_torrent_file->num_pieces())
			num_cache_pieces = m_torrent_file->num_pieces();

		std::vector<int> avail_vec;
		if (has_picker())
		{
			m_picker->get_availability(avail_vec);
		}

it would be more efficient to not use a string here. however, the problem is that some trackers will respond with actual strings. For example i2p trackers

../src/udp_tracker_connection.cpp:552

		}

		boost::shared_ptr<request_callback> cb = requester();
#if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_LOGGING
		if (cb)
		{
			boost::shared_ptr<request_callback> cb = requester();
			cb->debug_log("<== UDP_TRACKER_RESPONSE [ url: %s ]", tracker_req().url.c_str());
		}
#endif

		if (!cb)
		{
			close();
			return true;
		}

		std::vector<peer_entry> peer_list;
		for (int i = 0; i < num_peers; ++i)
		{
			peer_entry e;
			char ip_string[100];
			unsigned int a = detail::read_uint8(buf);
			unsigned int b = detail::read_uint8(buf);
			unsigned int c = detail::read_uint8(buf);
			unsigned int d = detail::read_uint8(buf);
			snprintf(ip_string, 100, "%u.%u.%u.%u", a, b, c, d);
			e.ip = ip_string;
			e.port = detail::read_uint16(buf);
			e.pid.clear();
			peer_list.push_back(e);
		}

		std::list<address> ip_list;
		for (std::list<tcp::endpoint>::const_iterator i = m_endpoints.begin()
			, end(m_endpoints.end()); i != end; ++i)
		{
			ip_list.push_back(i->address());
		}

		cb->tracker_response(tracker_req(), m_target.address(), ip_list
			, peer_list, interval, min_interval, complete, incomplete, 0, address(), "" /*trackerid*/);

		close();
		return true;
	}

	bool udp_tracker_connection::on_scrape_response(char const* buf, int size)
	{
		restart_read_timeout();
		int action = detail::read_int32(buf);

this loop may not be very efficient

../src/utp_stream.cpp:1573

	TORRENT_ASSERT(p->header_size >= sizeof(utp_header) + sack_size + 2);
	memmove(ptr, ptr + sack_size + 2, p->size - p->header_size);
	p->header_size -= sack_size + 2;
	p->size -= sack_size + 2;
}

// 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)
bool utp_socket_impl::send_pkt(int flags)
{
	INVARIANT_CHECK;

	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 = (packet*)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;
	}

instad of refreshing a bucket by using find_nodes, ping each node periodically

../src/kademlia/routing_table.cpp:265

		os << "]\n";
	}
}

#endif

void routing_table::touch_bucket(node_id const& target)
{
	table_t::iterator i = find_bucket(target);
	i->last_active = time_now();
}

// returns true if lhs is in more need of a refresh than rhs
bool compare_bucket_refresh(routing_table_node const& lhs, routing_table_node const& rhs)
{
	// add the number of nodes to prioritize buckets with few nodes in them
	return lhs.last_active + seconds(lhs.live_nodes.size() * 5)
		< rhs.last_active + seconds(rhs.live_nodes.size() * 5);
}

bool routing_table::need_refresh(node_id& target) const
{
	ptime now = time_now();

	// refresh our own bucket once every 15 minutes
	if (now - m_last_self_refresh > minutes(15))
	{
		m_last_self_refresh = now;
		target = m_id;
#ifdef TORRENT_DHT_VERBOSE_LOGGING
		TORRENT_LOG(table) << "need_refresh [ bucket: self target: " << target << " ]";
#endif
		return true;
	}

	if (m_buckets.empty()) return false;

	table_t::const_iterator i = std::min_element(m_buckets.begin(), m_buckets.end()
		, &compare_bucket_refresh);

	if (now - i->last_active < minutes(15)) return false;
	if (now - m_last_refresh < seconds(45)) return false;

	// generate a random node_id within the given bucket
	target = generate_random_id();
	int num_bits = std::distance(m_buckets.begin(), i) + 1;
	node_id mask(0);
	for (int i = 0; i < num_bits; ++i) mask[i/8] |= 0x80 >> (i&7);

	// target = (target & ~mask) | (root & mask)
	node_id root = m_id;

Make this count Unicode characters instead of bytes on windows

../include/libtorrent/config.hpp:305

// ==== eCS(OS/2) ===
#elif defined __OS2__
#define TORRENT_OS2
#define TORRENT_HAS_FALLOCATE 0
#define TORRENT_USE_IFCONF 1
#define TORRENT_USE_SYSCTL 1
#define TORRENT_USE_MLOCK 0
#define TORRENT_USE_IPV6 0
#define TORRENT_ICONV_ARG (const char**)
#define TORRENT_USE_WRITEV 0
#define TORRENT_USE_READV 0

#else
#warning unknown OS, assuming BSD
#define TORRENT_BSD
#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

// posix
#elif defined NAME_MAX
#define TORRENT_MAX_PATH NAME_MAX

// none of the above
#else
// this is the maximum number of characters in a
// path element / filename on windows
#define TORRENT_MAX_PATH 255
#warning unknown platform, assuming the longest path is 255

#endif

#if defined TORRENT_WINDOWS && !defined TORRENT_MINGW

#include <stdarg.h>

// internal

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:166

	{
		return m_sock.get_option(opt, ec);
	}

#ifndef BOOST_NO_EXCEPTIONS
	void bind(endpoint_type const& endpoint)
	{
//		m_sock.bind(endpoint);
	}
#endif

	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& p)
	{
//		m_sock.open(p);
	}
#endif

	void open(protocol_type const& p, error_code& ec)
	{
		// 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();
	}

include the number of peers received from this tracker, at last announce

../include/libtorrent/torrent_info.hpp:123

		// 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
		ptime next_announce;

		// no announces before this time
		ptime 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
		enum tracker_source

support using the windows API for UPnP operations as well

../include/libtorrent/upnp.hpp:121

	{
		virtual const char* name() const BOOST_SYSTEM_NOEXCEPT;
		virtual std::string message(int ev) const BOOST_SYSTEM_NOEXCEPT;
		virtual boost::system::error_condition default_error_condition(int ev) const BOOST_SYSTEM_NOEXCEPT
		{ return boost::system::error_condition(ev, *this); }
	};

	extern TORRENT_EXPORT upnp_error_category upnp_category;
#endif

// int: port-mapping index
// address: external address as queried from router
// int: external port
// std::string: error message
// an empty string as error means success
// a port-mapping index of -1 means it's
// an informational log message
typedef boost::function<void(int, address, int, error_code const&)> portmap_callback_t;
typedef boost::function<void(char const*)> log_callback_t;

class TORRENT_EXTRA_EXPORT upnp : public intrusive_ptr_base<upnp>
{
public:
	upnp(io_service& ios, connection_queue& cc
		, address const& listen_interface, std::string const& user_agent
		, portmap_callback_t const& cb, log_callback_t const& lcb
		, bool ignore_nonrouters, void* state = 0);
	~upnp();

	void* drain_state();

	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);