libtorrent todo-list

filter out peers that are disconnecting

src/torrent.cpp:1505

		snprintf(filename, sizeof(filename), "/tmp/%d.pem", rand());
		FILE* f = fopen(filename, "w+");
		fwrite(cert.c_str(), cert.size(), 1, f);
		fclose(f);
		ctx->load_verify_file(filename);
#endif
		// if all went well, set the torrent ssl context to this one
		m_ssl_ctx = ctx;
		// tell the client we need a cert for this torrent
		alerts().post_alert(torrent_need_cert_alert(get_handle()));
#else
		set_error(asio::error::operation_not_supported, "x.509 certificate");
		pause();
#endif
	}

#endif // TORRENT_OPENSSL

	peer_connection* torrent::find_lowest_ranking_peer() const
	{
		const_peer_iterator lowest_rank = std::min_element(begin(), end()
			, boost::bind(&peer_connection::peer_rank, _1)
			< boost::bind(&peer_connection::peer_rank, _2));

		if (lowest_rank == end()) return NULL;
		return *lowest_rank;
	}

	// this may not be called from a constructor because of the call to
	// shared_from_this()
	void torrent::init()
	{
		TORRENT_ASSERT(m_ses.is_network_thread());
		TORRENT_ASSERT(m_torrent_file->is_valid());
		TORRENT_ASSERT(m_torrent_file->num_files() > 0);
		TORRENT_ASSERT(m_torrent_file->total_size() >= 0);

#ifdef TORRENT_USE_OPENSSL
		std::string cert = m_torrent_file->ssl_cert();
		if (!cert.empty()) init_ssl(cert);
#endif

		m_file_priority.resize(m_torrent_file->num_files(), 1);
		m_file_progress.resize(m_torrent_file->num_files(), 0);

		m_block_size_shift = root2((std::min)(int(block_size()), m_torrent_file->piece_length()));

		if (m_torrent_file->num_pieces() > piece_picker::max_pieces)
		{
			set_error(errors::too_many_pieces_in_torrent, "");
			pause();

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

src/torrent.cpp:6004

			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

remove the read timeout concept. This should not be necessary

src/utp_stream.cpp:412

	// these are the callbacks made into the utp_stream object
	// on read/write/connect events
	utp_stream::handler_t m_read_handler;
	utp_stream::handler_t m_write_handler;
	utp_stream::connect_handler_t m_connect_handler;

	// the address of the remote endpoint
	address m_remote_address;

	// the local address
	address m_local_address;

	// the send and receive buffers
	// maps packet sequence numbers
	packet_buffer m_inbuf;
	packet_buffer m_outbuf;

	// timers when we should trigger the read and
	// write callbacks (unless the buffers fill up
	// before)
	ptime m_read_timeout;

remove the write timeout concept. This should not be necessary

src/utp_stream.cpp:415

	utp_stream::handler_t m_read_handler;
	utp_stream::handler_t m_write_handler;
	utp_stream::connect_handler_t m_connect_handler;

	// the address of the remote endpoint
	address m_remote_address;

	// the local address
	address m_local_address;

	// the send and receive buffers
	// maps packet sequence numbers
	packet_buffer m_inbuf;
	packet_buffer m_outbuf;

	// timers when we should trigger the read and
	// write callbacks (unless the buffers fill up
	// before)
	ptime m_read_timeout;

	ptime m_write_timeout;

	// the time when the last packet we sent times out. Including re-sends.
	// if we ever end up not having sent anything in one second (
	// or one mean rtt + 2 average deviations, whichever is greater)
	// we set our cwnd to 1 MSS. This condition can happen either because
	// a packet has timed out and needs to be resent or because our
	// cwnd is set to less than one MSS during congestion control.
	// it can also happen if the other end sends an advertized window
	// size less than one MSS.
	ptime m_timeout;
	
	// the last time we wanted to send more data, but couldn't because
	// it would bring the number of outstanding bytes above the cwnd.
	// this is used to restrict increasing the cwnd size when we're
	// not sending fast enough to need it bigger
	ptime m_last_cwnd_hit;

	// the last time we stepped the timestamp history
	ptime m_last_history_step;

	// the max number of bytes in-flight. This is a fixed point
	// value, to get the true number of bytes, shift right 16 bits
	// the value is always >= 0, but the calculations performed on
	// it in do_ledbat() are signed.
	boost::int64_t m_cwnd;

	timestamp_history m_delay_hist;
	timestamp_history m_their_delay_hist;

	// the number of bytes we have buffered in m_inbuf

this alloca() statement won't necessarily produce correctly aligned memory. do something about that

src/utp_stream.cpp:1685

	bool stack_alloced = false;
#endif

	// payload size being zero means we're just sending
	// an force. We should not pick up the nagle packet
	if (!m_nagle_packet || (payload_size == 0 && force))
	{
		// we only need a heap allocation if we have payload and
		// need to keep the packet around (in the outbuf)
		if (payload_size) 
		{
			p = (packet*)malloc(sizeof(packet) + m_mtu);
			p->allocated = m_mtu;
		}
		else
		{
#ifdef TORRENT_DEBUG
			stack_alloced = true;
#endif
			TORRENT_ASSERT(force);
			p = (packet*)TORRENT_ALLOCA(char, sizeof(packet) + packet_size);
			UTP_LOGV("%8p: allocating %d bytes on the stack\n", this, packet_size);
			p->allocated = packet_size;
		}

		p->size = packet_size;
		p->header_size = packet_size - payload_size;
		p->num_transmissions = 0;
		p->need_resend = false;
		ptr = p->buf;
		h = (utp_header*)ptr;
		ptr += sizeof(utp_header);

		h->extension = sack ? 1 : 0;
		h->connection_id = m_send_id;
		// seq_nr is ignored for ST_STATE packets, so it doesn't
		// matter that we say this is a sequence number we haven't
		// actually sent yet
		h->seq_nr = m_seq_nr;
		h->type_ver = ((payload_size ? ST_DATA : ST_STATE) << 4) | 1;

		write_payload(p->buf + p->header_size, payload_size);
	}
	else
	{
		// pick up the nagle packet and keep adding bytes to it
		p = m_nagle_packet;

		ptr = p->buf + sizeof(utp_header);
		h = (utp_header*)p->buf;
		TORRENT_ASSERT(h->seq_nr == m_seq_nr);

remove this dependency by having the dht observer have its own flags

src/kademlia/rpc_manager.cpp:36

      contributors may be used to endorse or promote products derived
      from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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.

*/

#include "libtorrent/pch.hpp"
#include "libtorrent/socket.hpp"

#include "libtorrent/aux_/session_impl.hpp"

#include <boost/bind.hpp>

#include <libtorrent/io.hpp>
#include <libtorrent/random.hpp>
#include <libtorrent/invariant_check.hpp>
#include <libtorrent/kademlia/node_id.hpp> // for generate_random_id
#include <libtorrent/kademlia/rpc_manager.hpp>
#include <libtorrent/kademlia/logging.hpp>
#include <libtorrent/kademlia/routing_table.hpp>
#include <libtorrent/kademlia/find_data.hpp>
#include <libtorrent/kademlia/refresh.hpp>
#include <libtorrent/kademlia/node.hpp>
#include <libtorrent/kademlia/observer.hpp>
#include <libtorrent/kademlia/dht_observer.hpp>
#include <libtorrent/hasher.hpp>
#include <libtorrent/time.hpp>
#include <time.h> // time()

#ifdef TORRENT_DHT_VERBOSE_LOGGING
#include <fstream>
#endif

namespace libtorrent { namespace dht
{

namespace io = libtorrent::detail;

#ifdef TORRENT_DHT_VERBOSE_LOGGING
TORRENT_DEFINE_LOG(rpc)

take a udp_socket_interface here instead. Move udp_socket_interface down into libtorrent core

include/libtorrent/kademlia/dht_tracker.hpp:79

	struct lazy_entry;
}

namespace libtorrent { namespace dht
{

#ifdef TORRENT_DHT_VERBOSE_LOGGING
	TORRENT_DECLARE_LOG(dht_tracker);
#endif

	struct dht_tracker;

	TORRENT_EXTRA_EXPORT void intrusive_ptr_add_ref(dht_tracker const*);
	TORRENT_EXTRA_EXPORT void intrusive_ptr_release(dht_tracker const*);	

	struct dht_tracker : udp_socket_interface, udp_socket_observer
	{
		friend void intrusive_ptr_add_ref(dht_tracker const*);
		friend void intrusive_ptr_release(dht_tracker const*);

		dht_tracker(libtorrent::aux::session_impl& ses, rate_limited_udp_socket& sock
			, dht_settings const& settings, entry const* state = 0);
		virtual ~dht_tracker();

		void start(entry const& bootstrap);
		void stop();

		void add_node(udp::endpoint node);
		void add_node(std::pair<std::string, int> const& node);
		void add_router_node(udp::endpoint const& node);

		entry state() const;

		void announce(sha1_hash const& ih, int listen_port, bool seed
			, boost::function<void(std::vector<tcp::endpoint> const&)> f);

		void dht_status(session_status& s);
		void network_stats(int& sent, int& received);

		// translate bittorrent kademlia message into the generic kademlia message
		// used by the library
		virtual bool incoming_packet(error_code const& ec
			, udp::endpoint const&, char const* buf, int size);

	private:
	
		boost::intrusive_ptr<dht_tracker> self()
		{ return boost::intrusive_ptr<dht_tracker>(this); }

		void on_name_lookup(error_code const& e
			, udp::resolver::iterator host);

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 char const* name() const { return "get_peers"; }

	node_id const target() const { return m_target; }

protected:

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

private:

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

if we still can't find the torrent, we should probably look for it by url here

src/session_impl.cpp:5113

					}
				}
#if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_LOGGING || defined TORRENT_ERROR_LOGGING
				else
				{
					session_log("metadata info-hash failed");
				}
#endif
			}
#if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_LOGGING || defined TORRENT_ERROR_LOGGING
			else
			{
				session_log("no metadata found");
			}
#endif
		}

		// is the torrent already active?
		boost::shared_ptr<torrent> torrent_ptr = find_torrent(*ih).lock();
		if (!torrent_ptr && !params.uuid.empty()) torrent_ptr = find_torrent(params.uuid).lock();

		if (torrent_ptr)
		{
			if ((params.flags & add_torrent_params::flag_duplicate_is_error) == 0)
			{
				if (!params.uuid.empty() && torrent_ptr->uuid().empty())
					torrent_ptr->set_uuid(params.uuid);
				if (!params.url.empty() && torrent_ptr->url().empty())
					torrent_ptr->set_url(params.url);
				if (!params.source_feed_url.empty() && torrent_ptr->source_feed_url().empty())
					torrent_ptr->set_source_feed_url(params.source_feed_url);
				return torrent_handle(torrent_ptr);
			}

			ec = errors::duplicate_torrent;
			return torrent_handle();
		}

		int queue_pos = 0;
		for (torrent_map::const_iterator i = m_torrents.begin()
			, end(m_torrents.end()); i != end; ++i)
		{
			int pos = i->second->queue_position();
			if (pos >= queue_pos) queue_pos = pos + 1;
		}

		torrent_ptr.reset(new torrent(*this, m_listen_interface
			, 16 * 1024, queue_pos, params, *ih));
		torrent_ptr->start();

#ifndef TORRENT_DISABLE_EXTENSIONS

pass in ec along with the alert

src/torrent.cpp:5789

		if (info_hash != m_torrent_file->info_hash())
		{
			if (alerts().should_post<metadata_failed_alert>())
			{
				alerts().post_alert(metadata_failed_alert(get_handle()));
			}
			return false;
		}

		lazy_entry metadata;
		error_code ec;
		int ret = lazy_bdecode(metadata_buf, metadata_buf + metadata_size, metadata, ec);
		if (ret != 0 || !m_torrent_file->parse_info_section(metadata, ec, 0))
		{
			// this means the metadata is correct, since we
			// verified it against the info-hash, but we
			// failed to parse it. Pause the torrent
			if (alerts().should_post<metadata_failed_alert>())
			{
				alerts().post_alert(metadata_failed_alert(get_handle()));
			}
			set_error(errors::invalid_swarm_metadata, "");
			pause();
			return false;
		}

		if (m_ses.m_alerts.should_post<metadata_received_alert>())
		{
			m_ses.m_alerts.post_alert(metadata_received_alert(
				get_handle()));
		}

		// this makes the resume data "paused" and
		// "auto_managed" fields be ignored. If the paused
		// field is not ignored, the invariant check will fail
		// since we will be paused but without having disconnected
		// any of the peers.
		m_override_resume_data = true;

		// we have to initialize the torrent before we start
		// disconnecting redundant peers, otherwise we'll think
		// we're a seed, because we have all 0 pieces
		init();

		// disconnect redundant peers
		for (std::set<peer_connection*>::iterator i = m_connections.begin()
			, end(m_connections.end()); i != end;)
		{
			std::set<peer_connection*>::iterator p = i++;
			(*p)->disconnect_if_redundant();

support the option to turn it off

src/utp_stream.cpp:617

		UTP_STATE_ERROR_WAIT,

		// there are no more references to this socket
		// and we can delete it
		UTP_STATE_DELETE
	};

	// this is the cursor into m_delay_sample_hist
	boost::uint8_t m_delay_sample_idx:2;

	// the state the socket is in
	boost::uint8_t m_state:3;

	// this is set to true when we receive a fin
	bool m_eof:1;

	// is this socket state attached to a user space socket?
	bool m_attached:1;

	// this is true if nagle is enabled (which it is by default)
	bool m_nagle:1;

	// this is true while the socket is in slow start mode. It's
	// only in slow-start during the start-up phase. Slow start
	// (contrary to what its name suggest) means that we're growing
	// the congestion window (cwnd) exponetially rather than linearly.
	// this is done at startup of a socket in order to find its
	// link capacity faster. This behaves similar to TCP slow start
	bool m_slow_start:1;
	
	// this is true as long as we have as many packets in
	// flight as allowed by the congestion window (cwnd)
	bool m_cwnd_full:1;

	// this is set to true when this socket has added itself to
	// the utp socket manager's list of deferred acks. Once the
	// burst of incoming UDP packets is all drained, the utp socket
	// manager will send acks for all sockets on this list.
	bool m_deferred_ack:1;

	// if this socket tries to send a packet via the utp socket
	// manager, and it fails with EWOULDBLOCK, the socket
	// is stalled and this is set. It's also added to a list
	// of sockets in the utp_socket_manager to be notified of
	// the socket being writable again
	bool m_stalled:1;
};

#if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_LOGGING || defined TORRENT_ERROR_LOGGING
int socket_impl_size() { return sizeof(utp_socket_impl); }
#endif

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:1848

		, boost::uint32_t(h->timestamp_difference_microseconds), int(p->mtu_probe)
		, h->extension);
#endif

	error_code ec;
#ifdef TORRENT_DEBUG
	// simulate 1% packet loss
//	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;

	if (ec == error::message_size)
	{
		m_mtu_ceiling = p->size - 1;
		if (m_mtu_floor > m_mtu_ceiling) m_mtu_floor = m_mtu_ceiling;
		update_mtu_limits();
	}
	else 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;
	}

	if (!m_stalled)
		++p->num_transmissions;

	// if we have payload, we need to save the packet until it's acked
	// and progress m_seq_nr
	if (p->size > p->header_size)
	{
		// if we're sending a payload packet, there should not
		// be a nagle packet waiting for more data

fix this stats logging. For instance, the stats counters could be factored out into its own class, and dht_tracker could take an optional reference to it ++m_replies_sent[e["r"]]; m_replies_bytes_sent[e["r"]] += int(m_send_buf.size());

src/kademlia/dht_tracker.cpp:641

#ifdef TORRENT_DHT_VERBOSE_LOGGING
		std::stringstream log_line;
		lazy_entry print;
		int ret = lazy_bdecode(&m_send_buf[0], &m_send_buf[0] + m_send_buf.size(), print, ec);
		TORRENT_ASSERT(ret == 0);
		log_line << print_entry(print, true);
#endif

		if (m_sock.send(addr, &m_send_buf[0], (int)m_send_buf.size(), ec, send_flags))
		{
			if (ec) return false;

			// account for IP and UDP overhead
			m_sent_bytes += m_send_buf.size() + (addr.address().is_v6() ? 48 : 28);

#ifdef TORRENT_DHT_VERBOSE_LOGGING
			m_total_out_bytes += m_send_buf.size();
		
			if (e["y"].string() == "r")
			{
			}
			else if (e["y"].string() == "q")
			{
				m_queries_out_bytes += m_send_buf.size();
			}
			TORRENT_LOG(dht_tracker) << "==> " << addr << " " << log_line.str();
#endif
			return true;
		}
		else
		{
#ifdef TORRENT_DHT_VERBOSE_LOGGING
			TORRENT_LOG(dht_tracker) << "==> " << addr << " DROPPED " << log_line.str();
#endif
			return false;
		}
	}

}}

make this configurable in dht_settings

src/kademlia/node.cpp:63

#include "libtorrent/alert.hpp"
#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 "libtorrent/rsa.hpp"

namespace libtorrent { namespace dht
{

void incoming_error(entry& e, char const* msg);

using detail::write_endpoint;

enum { announce_interval = 30 };

#ifdef TORRENT_DHT_VERBOSE_LOGGING
TORRENT_DEFINE_LOG(node)
#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() {}

node_impl::node_impl(alert_dispatcher* alert_disp
	, udp_socket_interface* sock
	, dht_settings const& settings, node_id nid, address const& external_address
	, dht_observer* observer)

this should be a deque, since time critical pieces are expected to be popped in the same order as they are sorted. The expectation is that new items are pushed back and items are popped from the front

include/libtorrent/torrent.hpp:1038

		struct time_critical_piece
		{
			// when this piece was first requested
			ptime first_requested;
			// when this piece was last requested
			ptime last_requested;
			// by what time we want this piece
			ptime deadline;
			// 1 = send alert with piece data when available
			int flags;
			// how many peers it's been requested from
			int peers;
			// the piece index
			int piece;
			bool operator<(time_critical_piece const& rhs) const
			{ return deadline < rhs.deadline; }
		};

		// this list is sorted by time_critical_piece::deadline
		std::list<time_critical_piece> m_time_critical_pieces;

		std::string m_trackerid;
		std::string m_username;
		std::string m_password;

		// the network interfaces outgoing connections
		// are opened through. If there is more then one,
		// they are used in a round-robin fasion
		std::vector<union_endpoint> m_net_interfaces;

		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;

		// if this torrent was added by an RSS feed, this is the
		// URL to that feed
		std::string m_source_feed_url;

		// this is used as temporary storage while downloading
		// the .torrent file from m_url
		std::vector<char> m_torrent_file_buf;

		// each bit represents a piece. a set bit means
		// the piece has had its hash verified. This

these strings (m_comment, m_created_by, m_ssl_root_cert) could be lazy_entry* to save memory

include/libtorrent/torrent_info.hpp:455

		std::vector<announce_entry> m_urls;
		std::vector<web_seed_entry> m_web_seeds;
		nodes_t m_nodes;

		// if this is a merkle torrent, this is the merkle
		// tree. It has space for merkle_num_nodes(merkle_num_leafs(num_pieces))
		// hashes
		std::vector<sha1_hash> m_merkle_tree;

		// this is a copy of the info section from the torrent.
		// it use maintained in this flat format in order to
		// make it available through the metadata extension
		boost::shared_array<char> m_info_section;

		// this is a pointer into the m_info_section buffer
		// pointing to the first byte of the first sha-1 hash
		char const* m_piece_hashes;

		// if a comment is found in the torrent file
		// this will be set to that comment
		std::string m_comment;

		// an optional string naming the software used
		// to create the torrent file
		std::string m_created_by;

#ifdef TORRENT_USE_OPENSSL
		// for ssl-torrens, this contains the root
		// certificate, in .pem format (i.e. ascii
		// base64 encoded with head and tails)
		std::string m_ssl_root_cert;
#endif

		// the info section parsed. points into m_info_section
		// parsed lazily
		mutable lazy_entry m_info_dict;

		// if a creation date is found in the torrent file
		// this will be set to that, otherwise it'll be
		// 1970, Jan 1
		time_t m_creation_date;

		// the hash that identifies this torrent
		sha1_hash m_info_hash;

		// the number of bytes in m_info_section
		boost::uint32_t m_info_section_size:24;

		// this is used when creating a torrent. If there's
		// only one file there are cases where it's impossible
		// to know if it should be written as a multifile torrent

replace with a union of address_v4 and address_v6 to not waste space. This struct is instantiated hundreds of times for the routing table

include/libtorrent/kademlia/node_entry.hpp:92

		, id(0)
	{
#ifdef TORRENT_DHT_VERBOSE_LOGGING
		first_seen = time_now();
#endif
	}
	
	bool pinged() const { return timeout_count != 0xffff; }
	void set_pinged() { if (timeout_count == 0xffff) timeout_count = 0; }
	void timed_out() { if (pinged()) ++timeout_count; }
	int fail_count() const { return pinged() ? timeout_count : 0; }
	void reset_fail_count() { if (pinged()) timeout_count = 0; }
	udp::endpoint ep() const { return udp::endpoint(addr, port); }
	bool confirmed() const { return timeout_count == 0; }
	void update_rtt(int new_rtt)
	{
		if (rtt == 0xffff) rtt = new_rtt;
		else rtt = int(rtt) / 3 + int(new_rtt) * 2 / 3;
	}

	address addr;
	boost::uint16_t port;
	// the number of times this node has failed to
	// respond in a row
	boost::uint16_t timeout_count;
	// the average RTT of this node
	boost::uint16_t rtt;
	node_id id;
#ifdef TORRENT_DHT_VERBOSE_LOGGING
	ptime first_seen;
#endif
};

} } // namespace libtorrent::dht

#endif

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:2488

		}

		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:5471

	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:5676

	}

	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:6138

	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:1112

			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;
			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)
			{
				rp->piece_data.reset();

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

src/torrent.cpp:5292

						? (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

ideally, we would disconnect the oldest connection i.e. the one that has waited the longest to connect.

src/torrent.cpp:5930

		if (m_ses.is_aborted())
		{
			p->disconnect(errors::session_closing);
			return false;
		}

		bool maybe_replace_peer = false;

		if (m_connections.size() >= m_max_connections)
		{
			// if more than 10% of the connections are outgoing
			// connection attempts that haven't completed yet,
			// disconnect one of them and let this incoming
			// connection through.
			if (m_num_connecting > m_max_connections / 10)
			{
				// find one of the connecting peers and disconnect it
				// find any peer that's connecting (i.e. a half-open TCP connection)
				// that's also not disconnecting

				std::set<peer_connection*>::iterator i = std::find_if(begin(), end()
					, boost::bind(&peer_connection::is_connecting, _1)
					&& !boost::bind(&peer_connection::is_disconnecting, _1));

				if (i == end())
				{
					// this seems odd, but we might as well handle it
					p->disconnect(errors::too_many_connections);
					return false;
				}
				(*i)->disconnect(errors::too_many_connections);
            
				// if this peer was let in via connections slack,
				// it has done its duty of causing the disconnection
				// of another peer
				p->peer_disconnected_other();
			}
			else
			{
				maybe_replace_peer = true;
			}
		}

		TORRENT_TRY
		{
#ifndef TORRENT_DISABLE_EXTENSIONS
			for (extension_list_t::iterator i = m_extensions.begin()
				, end(m_extensions.end()); i != end; ++i)
			{
				boost::shared_ptr<peer_plugin> pp((*i)->new_connection(p));
				if (pp) p->add_extension(pp);

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:6179

		}
#if defined TORRENT_DEBUG || TORRENT_RELEASE_ASSERTS
		m_finished_alert_posted = true;
#endif

		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
		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)
			m_ses.trigger_auto_manage();

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

src/torrent_info.cpp:187

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

			convert_to_utf8(tmp_path, *i);
			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;
	}

	void trim_path_element(std::string& path_element)
	{
		const int max_path_len = TORRENT_MAX_PATH;
		if (int(path_element.size()) > max_path_len)
		{
			// truncate filenames that are too long. But keep extensions!
			std::string ext = extension(path_element);
			if (ext.size() > 15)
			{
				path_element.resize(max_path_len);
			}
			else
			{
				path_element.resize(max_path_len - ext.size());
				path_element += ext;
			}
		}
	}

	TORRENT_EXTRA_EXPORT std::string sanitize_path(std::string const& p)
	{

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

src/torrent_info.cpp:366

			}
			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());
		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;

			int cnt = 0;
			std::set<std::string, string_less_no_case> files;

			// as long as this file already exists
			// increase the counter
			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
			internal_file_entry const& fe = *target.rbegin();

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

src/torrent_info.cpp:387

				return false;

			int cnt = 0;
			std::set<std::string, string_less_no_case> files;

			// as long as this file already exists
			// increase the counter
			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
			internal_file_entry const& fe = *target.rbegin();
			if (fee && fe.filename() == 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;
				const_cast<internal_file_entry&>(fe).set_name(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:690

		{
			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)
	{
#ifdef TORRENT_DHT_VERBOSE_LOGGING
		extern int g_failed_announces;
#endif
		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},
		};

		lazy_entry const* msg_keys[5];
		if (!verify_message(arg_ent, msg_desc, msg_keys, 5, 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());
		if (port < 0 || port >= 65536)
		{
#ifdef TORRENT_DHT_VERBOSE_LOGGING

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:350

		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 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, asio::error::not_connected, 0));

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:660

		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

don't trust this blindly

src/bt_peer_connection.cpp:1755

		// but where do we put that info?

		int last_seen_complete = boost::uint8_t(root.dict_find_int_value("complete_ago", -1));
		if (last_seen_complete >= 0) set_last_seen_complete(last_seen_complete);
		
		std::string client_info = root.dict_find_string_value("v");
		if (!client_info.empty()) m_client_version = client_info;

		int reqq = int(root.dict_find_int_value("reqq"));
		if (reqq > 0) m_max_out_request_queue = reqq;

		if (root.dict_find_int_value("upload_only", 0))
			set_upload_only(true);

		if (root.dict_find_int_value("share_mode", 0))
			set_share_mode(true);

		std::string myip = root.dict_find_string_value("yourip");
		if (!myip.empty())
		{
			if (myip.size() == address_v4::bytes_type().size())
			{
				address_v4::bytes_type bytes;
				std::copy(myip.begin(), myip.end(), bytes.begin());
				m_ses.set_external_address(address_v4(bytes)
					, aux::session_impl::source_peer, remote().address());
			}
#if TORRENT_USE_IPV6
			else if (myip.size() == address_v6::bytes_type().size())
			{
				address_v6::bytes_type bytes;
				std::copy(myip.begin(), myip.end(), bytes.begin());
				address_v6 ipv6_address(bytes);
				if (ipv6_address.is_v4_mapped())
					m_ses.set_external_address(ipv6_address.to_v4()
						, aux::session_impl::source_peer, remote().address());
				else
					m_ses.set_external_address(ipv6_address
						, aux::session_impl::source_peer, remote().address());
			}
#endif
		}

		// if we're finished and this peer is uploading only
		// disconnect it
		if (t->is_finished() && upload_only()
			&& t->settings().close_redundant_connections
			&& !t->share_mode())
			disconnect(errors::upload_upload_connection);
	}

if we're finished, send upload_only message

src/bt_peer_connection.cpp:2069

			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().user_agent;
		}

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

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

src/bt_peer_connection.cpp:3308

			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();
		}
	}

#ifdef TORRENT_DEBUG
	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:1205

	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:172

	{
		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;
		}

		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 (handle_error(e, h)) return;

		// send hello command
		m_state = read_hello_response;

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:2651

#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:2782

		// 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;
		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
		// ignore it if it's already time critical
		if (rit - m_request_queue.begin() < m_queued_time_critical) return;
		pending_block b = *rit;
		m_request_queue.erase(rit);

we should probably just send a HAVE_ALL here

src/peer_connection.cpp:3892

		std::fill(m_recv_buffer.begin() + m_recv_pos, m_recv_buffer.end(), 0);
#endif

		m_packet_size = packet_size;
	}

	void peer_connection::superseed_piece(int replace_piece, int new_piece)
	{
		if (new_piece == -1)
		{
			if (m_superseed_piece[0] == -1) return;
			m_superseed_piece[0] = -1;
			m_superseed_piece[1] = -1;
			
#ifdef TORRENT_VERBOSE_LOGGING
			peer_log("*** ending super seed mode");
#endif
			boost::shared_ptr<torrent> t = m_torrent.lock();
			assert(t);

			for (int i = 0; i < int(m_have_piece.size()); ++i)
			{
				if (m_have_piece[i] || !t->have_piece(i)) continue;
#ifdef TORRENT_VERBOSE_LOGGING
				peer_log("==> HAVE    [ piece: %d] (ending super seed)", i);
#endif
				write_have(i);
			}
			
			return;
		}

		assert(!has_piece(new_piece));
		
#ifdef TORRENT_VERBOSE_LOGGING
		peer_log("==> HAVE    [ piece: %d ] (super seed)", new_piece);
#endif
		write_have(new_piece);

		if (replace_piece >= 0)
		{
			// move the piece we're replacing to the tail
			if (m_superseed_piece[0] == replace_piece)
				std::swap(m_superseed_piece[0], m_superseed_piece[1]);
		}

		m_superseed_piece[1] = m_superseed_piece[0];
		m_superseed_piece[0] = new_piece;
	}

	void peer_connection::update_desired_queue_size()

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

src/peer_connection.cpp:4475

				// 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:1889

#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:1887

		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);
	}

	void session_impl::set_settings(session_settings const& s)
	{
		INVARIANT_CHECK;

allow extensions to sort torrents for queuing

src/session_impl.cpp:4267

			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:4423

		{
			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:4457

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

src/session_impl.cpp:4458

				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:4602

#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_since_unchoke() * 1000
						* (1 + t1->priority()) / total_milliseconds(unchoke_interval)
						>= (*i)->uploaded_since_unchoke() * 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_since_unchoke()
					* 1000 / total_milliseconds(unchoke_interval));

				if (rate < rate_threshold) break;

				++m_allowed_upload_slots;

make configurable

src/session_impl.cpp:4616

						>= (*i)->uploaded_since_unchoke() * 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_since_unchoke()
					* 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:325

			int block_size = 16 * 1024;
			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;
				}
				num_read = m_storage->readv(bufs, slot, ph.offset, num_blocks);

				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);
					int ret = m_storage->readv(&buf, slot, ph.offset, 1);

if the read fails, set error and exit immediately

src/storage.cpp:358

					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);
					int ret = m_storage->readv(&buf, slot, ph.offset, 1);
					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:623

		for (file_iter = files().begin();;)
		{
			if (file_offset < file_iter->size)
				break;

			file_offset -= file_iter->size;
			++file_iter;
			TORRENT_ASSERT(file_iter != files().end());
		}
	
		error_code ec;
		boost::intrusive_ptr<file> file_handle = open_file(file_iter, 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:1192

			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_iter) + 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::read_write
					&& adjusted_offset + bytes_transferred >= file_iter->size
					&& (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(file_iter->size, 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(combine_path(m_save_path, files().file_path(*file_iter)), 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).

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:5025

		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:5161

				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_seeds"] = m_complete;
		ret["num_incomplete"] = m_incomplete;
		ret["num_downloaders"] = m_downloaders;

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:5349

		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();
			for (torrent_info::file_iterator i = m_torrent_file->begin_files()
				, end(m_torrent_file->end_files()); i != end; ++i)
			{
				fl.push_back(m_torrent_file->files().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:7823

			}

			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;
		// 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);
		}
		else
		{
			// we don't keep track of availability, do it the expensive way
			// do a linear search from the first piece

if there's been long enough since we requested something from this piece, request one of the backup blocks (the one with the least number of requests to it) and update the last request timestamp

src/torrent.cpp:8050

				std::vector<pending_block> const& rq = c.request_queue();

				bool added_request = false;

				if (!interesting_blocks.empty() && std::find_if(rq.begin(), rq.end()
					, has_block(interesting_blocks.front())) != rq.end())
				{
					c.make_time_critical(interesting_blocks.front());
					added_request = true;
				}
				else if (!interesting_blocks.empty())
				{
					if (!c.add_request(interesting_blocks.front(), peer_connection::req_time_critical))
					{
						peers.erase(p);
						continue;
					}
					added_request = true;
				}


				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());
		}

		// 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();
		}
	}

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:548

		}

		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, 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);

Make this count Unicode characters instead of bytes on windows

include/libtorrent/config.hpp:283

// ==== 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>

inline int snprintf(char* buf, int len, char const* fmt, ...)

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:152

	{
		return m_sock.set_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();
	}