libtorrent todo-list

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

../src/torrent.cpp:6125

			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

should this really be a public symbol? also, make this a shared_ptr instead

../include/libtorrent/natpmp.hpp:56

#include "libtorrent/io_service_fwd.hpp"
#include "libtorrent/socket.hpp"
#include "libtorrent/address.hpp"
#include "libtorrent/thread.hpp"
#include "libtorrent/error_code.hpp"
#include "libtorrent/intrusive_ptr_base.hpp"
#include "libtorrent/deadline_timer.hpp"

#include <boost/function/function1.hpp>
#include <boost/function/function4.hpp>

namespace libtorrent
{

// int: port mapping index
// int: external port
// std::string: error message
typedef boost::function<void(int, address, int, error_code const&)> portmap_callback_t;
typedef boost::function<void(char const*)> log_callback_t;

class TORRENT_EXPORT natpmp : public intrusive_ptr_base<natpmp>
{
public:
	natpmp(io_service& ios, address const& listen_interface
		, portmap_callback_t const& cb
		, log_callback_t const& lcb);

	void rebind(address const& listen_interface);

	// maps the ports, if a port is set to 0
	// it will not be mapped
	enum protocol_type { none = 0, udp = 1, tcp = 2 };
	int add_mapping(protocol_type p, int external_port, int local_port);
	void delete_mapping(int mapping_index);
	bool get_mapping(int mapping_index, int& local_port, int& external_port, int& protocol) const;

	void close();

private:
	
	void update_mapping(int i, mutex::scoped_lock& l);
	void send_map_request(int i, mutex::scoped_lock& l);
	void send_get_ip_address_request(mutex::scoped_lock& l);
	void resend_request(int i, error_code const& e);
	void on_reply(error_code const& e
		, std::size_t bytes_transferred);
	void try_next_mapping(int i, mutex::scoped_lock& l);
	void update_expiration_timer(mutex::scoped_lock& l);
	void mapping_expired(error_code const& e, int i);
	void close_impl(mutex::scoped_lock& l);

rename this to sha1_hash

../include/libtorrent/peer_id.hpp:61

#include "libtorrent/config.hpp"
#include "libtorrent/assert.hpp"

#if TORRENT_USE_IOSTREAM
#include "libtorrent/escape_string.hpp" // to_hex, from_hex
#include <iostream>
#include <iomanip>
#endif

#ifdef max
#undef max
#endif

#ifdef min
#undef min
#endif

namespace libtorrent
{

	class TORRENT_EXPORT big_number
	{
		// the number of bytes of the number
		enum { number_size = 20 };
	public:
		enum { size = number_size };

		big_number() { clear(); }

		static big_number max()
		{
			big_number ret;
			memset(ret.m_number, 0xff, size);
			return ret;
		}

		static big_number min()
		{
			big_number ret;
			memset(ret.m_number, 0, size);
			return ret;
		}

		explicit big_number(char const* s)
		{
			if (s == 0) clear();
			else std::memcpy(m_number, s, size);
		}

		explicit big_number(std::string const& s)
		{

make this an implementation detail

../include/libtorrent/session.hpp:101

	class port_filter;
	class connection_queue;
	class natpmp;
	class upnp;
	class alert;

	TORRENT_EXPORT session_settings min_memory_usage();
	TORRENT_EXPORT session_settings high_performance_seed();

#ifndef TORRENT_CFG
#error TORRENT_CFG is not defined!
#endif

	void TORRENT_EXPORT TORRENT_CFG();

	namespace aux
	{
		// workaround for microsofts
		// hardware exceptions that makes
		// it hard to debug stuff
#ifdef _MSC_VER
		struct TORRENT_EXPORT eh_initializer
		{
			eh_initializer();
			static void straight_to_debugger(unsigned int, _EXCEPTION_POINTERS*)
			{ throw; }
		};
#else
		struct eh_initializer {};
#endif
		struct session_impl;
	}

	class TORRENT_EXPORT session_proxy
	{
		friend class session;
	public:
		session_proxy() {}
	private:
		session_proxy(boost::shared_ptr<aux::session_impl> impl)
			: m_impl(impl) {}
		boost::shared_ptr<aux::session_impl> m_impl;
	};

#if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_LOGGING || defined TORRENT_ERROR_LOGGING
#define TORRENT_LOGPATH_ARG_DEFAULT , std::string logpath = "."
#else
#define TORRENT_LOGPATH_ARG_DEFAULT
#endif

	// Once it's created, the session object will spawn the main thread that will do all the work.

do these two really need to be exposed to users?

../include/libtorrent/time.hpp:44

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

*/

#ifndef TORRENT_TIME_HPP_INCLUDED
#define TORRENT_TIME_HPP_INCLUDED

#include <boost/version.hpp>
#include "libtorrent/config.hpp"
#include "libtorrent/ptime.hpp"
#include <boost/cstdint.hpp>
#include <string>

namespace libtorrent
{
	TORRENT_EXPORT char const* time_now_string();
	TORRENT_EXPORT std::string log_time();

	TORRENT_EXPORT ptime time_now_hires();
	TORRENT_EXPORT ptime min_time();
	TORRENT_EXPORT ptime max_time();

#if defined TORRENT_USE_BOOST_DATE_TIME

	TORRENT_EXPORT time_duration seconds(int s);
	TORRENT_EXPORT time_duration milliseconds(int s);
	TORRENT_EXPORT time_duration microsec(int s);
	TORRENT_EXPORT time_duration minutes(int s);
	TORRENT_EXPORT time_duration hours(int s);

	TORRENT_EXPORT int total_seconds(time_duration td);
	TORRENT_EXPORT int total_milliseconds(time_duration td);
	TORRENT_EXPORT boost::int64_t total_microseconds(time_duration td);

#elif defined TORRENT_USE_QUERY_PERFORMANCE_TIMER

	namespace aux
	{

move these to time.cpp

../include/libtorrent/time.hpp:68

	TORRENT_EXPORT ptime time_now_hires();
	TORRENT_EXPORT ptime min_time();
	TORRENT_EXPORT ptime max_time();

#if defined TORRENT_USE_BOOST_DATE_TIME

	TORRENT_EXPORT time_duration seconds(int s);
	TORRENT_EXPORT time_duration milliseconds(int s);
	TORRENT_EXPORT time_duration microsec(int s);
	TORRENT_EXPORT time_duration minutes(int s);
	TORRENT_EXPORT time_duration hours(int s);

	TORRENT_EXPORT int total_seconds(time_duration td);
	TORRENT_EXPORT int total_milliseconds(time_duration td);
	TORRENT_EXPORT boost::int64_t total_microseconds(time_duration td);

#elif defined TORRENT_USE_QUERY_PERFORMANCE_TIMER

	namespace aux
	{
		TORRENT_EXPORT boost::int64_t performance_counter_to_microseconds(boost::int64_t pc);
		TORRENT_EXPORT boost::int64_t microseconds_to_performance_counter(boost::int64_t ms);
	}

	inline int total_seconds(time_duration td)
	{
		return int(aux::performance_counter_to_microseconds(td.diff)
			/ 1000000);
	}
	inline int total_milliseconds(time_duration td)
	{
		return int(aux::performance_counter_to_microseconds(td.diff)
			/ 1000);
	}
	inline boost::int64_t total_microseconds(time_duration td)
	{
		return aux::performance_counter_to_microseconds(td.diff);
	}

	inline time_duration microsec(boost::int64_t s)
	{
		return time_duration(aux::microseconds_to_performance_counter(s));
	}
	inline time_duration milliseconds(boost::int64_t s)
	{
		return time_duration(aux::microseconds_to_performance_counter(
			s * 1000));
	}
	inline time_duration seconds(boost::int64_t s)
	{
		return time_duration(aux::microseconds_to_performance_counter(

should this really be a public symbol?

../include/libtorrent/torrent_info.hpp:238

		// if the user wanted to remove this while
		// we were resolving it. In this case, we set
		// the removed flag to true, to make the resolver
		// callback remove it
		bool removed;

		tcp::endpoint endpoint;

		// this is the peer_info field used for the
		// connection, just to count hash failures
		// it's also used to hold the peer_connection
		// pointer, when the web seed is connected
		policy::peer peer_info;
	};

#ifndef BOOST_NO_EXCEPTIONS
	// for backwards compatibility with 0.14
	typedef libtorrent_exception invalid_torrent_file;
#endif

	int TORRENT_EXPORT load_file(std::string const& filename
		, std::vector<char>& v, error_code& ec, int limit = 8000000);

	class TORRENT_EXPORT torrent_info : public intrusive_ptr_base<torrent_info>
	{
	public:

#ifdef TORRENT_DEBUG
		void check_invariant() const;
#endif

#ifndef BOOST_NO_EXCEPTIONS
		torrent_info(lazy_entry const& torrent_file, int flags = 0);
		torrent_info(char const* buffer, int size, int flags = 0);
		torrent_info(std::string const& filename, int flags = 0);
#if TORRENT_USE_WSTRING
		torrent_info(std::wstring const& filename, int flags = 0);
#endif // TORRENT_USE_WSTRING
#endif

		torrent_info(torrent_info const& t, int flags = 0);
		torrent_info(sha1_hash const& info_hash, int flags = 0);
		torrent_info(lazy_entry const& torrent_file, error_code& ec, int flags = 0);
		torrent_info(char const* buffer, int size, error_code& ec, int flags = 0);
		torrent_info(std::string const& filename, error_code& ec, int flags = 0);
#if TORRENT_USE_WSTRING
		torrent_info(std::wstring const& filename, error_code& ec, int flags = 0);
#endif // TORRENT_USE_WSTRING

		~torrent_info();

should this really be a public symbol? also, make this a shared_ptr instead

../include/libtorrent/upnp.hpp:102

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

	extern TORRENT_EXPORT upnp_error_category upnp_category;
#endif

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

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

	void* drain_state();

	enum protocol_type { none = 0, udp = 1, tcp = 2 };
	int add_mapping(protocol_type p, int external_port, int local_port);
	void delete_mapping(int mapping_index);
	bool get_mapping(int mapping_index, int& local_port, int& external_port, int& protocol) const;

	void discover_device();
	void close();

	std::string router_model()
	{
		mutex::scoped_lock l(m_mutex);
		return m_model;
	}

private:

	void discover_device_impl(mutex::scoped_lock& l);
	static address_v4 upnp_multicast_address;
	static udp::endpoint upnp_multicast_endpoint;

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;

m_downloads size will be > 0 just by having pad-files in the torrent. That should be taken into account here.

../src/piece_picker.cpp:1489

	//     have an affinity to pick pieces in the same speed
	//     category.
	// * ignore_whole_pieces
	//     ignores the prefer_whole_pieces parameter (as if
	//     it was 0)

	// only one of rarest_first, sequential can be set

	void piece_picker::pick_pieces(bitfield const& pieces
		, std::vector<piece_block>& interesting_blocks, int num_blocks
		, int prefer_whole_pieces, void* peer, piece_state_t speed
		, int options, std::vector<int> const& suggested_pieces
		, int num_peers) const
	{
		TORRENT_ASSERT(peer == 0 || static_cast<policy::peer*>(peer)->in_use);

		// prevent the number of partial pieces to grow indefinitely
		// make this scale by the number of peers we have. For large
		// scale clients, we would have more peers, and allow a higher
		// threshold for the number of partials
		if (m_downloads.size() > num_peers * 3 / 2) options |= prioritize_partials;

		if (options & ignore_whole_pieces) prefer_whole_pieces = 0;

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

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

		// this will be filled with blocks that we should not request
		// unless we can't find num_blocks among the other ones.
		// blocks that belong to pieces with a mismatching speed
		// category for instance, or if we prefer whole pieces,
		// blocks belonging to a piece that others have
		// downloaded to
		std::vector<piece_block> backup_blocks;
		std::vector<piece_block> backup_blocks2;
		const std::vector<int> empty_vector;
	
		// When prefer_whole_pieces is set (usually set when downloading from
		// fast peers) the partial pieces will not be prioritized, but actually
		// ignored as long as possible. All blocks found in downloading
		// pieces are regarded as backup blocks

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

../src/session_impl.cpp:5157

					}
				}
#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:5908

		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();

will pick_pieces ever return an empty set?

../src/torrent.cpp:8240

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

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

			} while (!interesting_blocks.empty());

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

		// commit all the time critical requests
		for (std::set<peer_connection*>::iterator i = peers_with_requests.begin()
			, end(peers_with_requests.end()); i != end; ++i)
		{
			(*i)->send_block_requests();
		}
	}

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

	void torrent::remove_web_seed(std::string const& url, web_seed_entry::type_t type)
	{
		std::list<web_seed_entry>::iterator i = std::find_if(m_web_seeds.begin(), m_web_seeds.end()
			, (boost::bind(&web_seed_entry::url, _1)

support the option to turn it off

../src/utp_stream.cpp:608

		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;

	// this is true if this socket has subscribed to be notified
	// when this receive round is done
	bool m_subscribe_drained: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;
};

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

../src/utp_stream.cpp:1862

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

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

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

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)

extern int g_failed_announces;
extern int g_announces;

#endif

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

void nop() {}

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

../include/libtorrent/torrent_info.hpp:468

		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

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:2519

		}

		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:5517

	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:5727

	}

	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:6196

	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:1167

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

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

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

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

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

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

		disk_buffer_holder buffer(m_ses, j.buffer);

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

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

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

../src/torrent.cpp:5411

						? (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:6051

		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:6292

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

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

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

		send_upload_only();

		state_updated();

		m_completed_time = time(0);

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

		if (m_abort) return;

		m_policy.recalculate_connect_candidates();

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

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

../src/torrent_info.cpp:181

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

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

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

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

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

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

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

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

../src/torrent_info.cpp:385

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

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

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

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

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

			// This is a memory optimization! Instead of having
			// each entry keep a string for its filename, make it
			// simply point into the info-section buffer
			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:416

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

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

			// This is a memory optimization! Instead of having
			// each entry keep a string for its filename, make it
			// simply point into the info-section buffer
			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:699

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

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

		sha1_hash target(msg_keys[0]->string_ptr());

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

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

		int port = int(msg_keys[1]->int_value());

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

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

../include/libtorrent/ip_voter.hpp:100

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

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

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

	private:

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

}

#endif

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

../include/libtorrent/utp_stream.hpp:351

		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:655

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

	int bt_peer_connection::get_syncoffset(char const* src, int src_size,
		char const* target, int target_size) const
	{
		TORRENT_ASSERT(target_size >= src_size);
		TORRENT_ASSERT(src_size > 0);
		TORRENT_ASSERT(src);
		TORRENT_ASSERT(target);

		int traverse_limit = target_size - src_size;

		for (int i = 0; i < traverse_limit; ++i)
		{
			char const* target_ptr = target + i;
			if (std::equal(src, src+src_size, target_ptr))
				return i;
		}

//	    // Partial sync
// 		for (int i = 0; i < target_size; ++i)
// 		{
// 			// first is iterator in src[] at which mismatch occurs
// 			// second is iterator in target[] at which mismatch occurs
// 			std::pair<const char*, const char*> ret;
// 			int src_sync_size;
//  			if (i > traverse_limit) // partial sync test
//  			{
//  				ret = std::mismatch(src, src + src_size - (i - traverse_limit), &target[i]);
//  				src_sync_size = ret.first - src;
//  				if (src_sync_size == (src_size - (i - traverse_limit)))
//  					return i;
//  			}
//  			else // complete sync test
// 			{
// 				ret = std::mismatch(src, src + src_size, &target[i]);
// 				src_sync_size = ret.first - src;
// 				if (src_sync_size == src_size)
// 					return i;
// 			}
// 		}

        // no complete sync

don't trust this blindly

../src/bt_peer_connection.cpp:1754

		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 (m_ses.m_settings.support_share_mode
			&& 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:2075

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

		send_buffer(msg, packet_size);

		if (num_lazy_pieces > 0)
		{
			for (int i = 0; i < num_lazy_pieces; ++i)
			{
#ifdef TORRENT_VERBOSE_LOGGING
				peer_log("==> HAVE    [ piece: %d ]", lazy_pieces[i]);
#endif
				write_have(lazy_pieces[i]);
			}
		}

		if (m_supports_fast)
			send_allowed_set();
	}

#ifndef TORRENT_DISABLE_EXTENSIONS
	void bt_peer_connection::write_extensions()
	{
		INVARIANT_CHECK;

		TORRENT_ASSERT(m_supports_extensions);
		TORRENT_ASSERT(m_sent_handshake);

		entry handshake;
		entry::dictionary_type& m = handshake["m"].dict();

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

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

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

../src/bt_peer_connection.cpp:3317

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

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

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

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

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

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

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

../src/file.cpp:1327

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

		m_page_size = page_size();
	}

#endif

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

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

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

#ifdef TORRENT_DEBUG
		if (m_open_mode & no_buffer)
		{

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

../src/http_tracker_connection.cpp:99

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

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

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

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

		session_settings const& settings = m_ses.settings();

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

move this to proxy_base and use it in all proxies

../src/i2p_stream.cpp: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:2682

#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:2813

		// 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:3925

		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:4509

				// 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:1895

#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:1898

		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;

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

../src/session_impl.cpp:3252

		// --------------------------------------------------------------
		if (!m_paused) m_auto_manage_time_scaler--;
		if (m_auto_manage_time_scaler < 0)
		{
			m_auto_manage_time_scaler = settings().auto_manage_interval;
			recalculate_auto_managed_torrents();
		}

		// --------------------------------------------------------------
		// check for incoming connections that might have timed out
		// --------------------------------------------------------------

		for (connection_map::iterator i = m_connections.begin();
			i != m_connections.end();)
		{
			peer_connection* p = (*i).get();
			++i;
			// ignore connections that already have a torrent, since they
			// are ticked through the torrents' second_tick
			if (!p->associated_torrent().expired()) continue;
			if (m_last_tick - p->connected_time() > seconds(m_settings.handshake_timeout))
				p->disconnect(errors::timed_out);
		}

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

		int congested_torrents = 0;
		int uncongested_torrents = 0;

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

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

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

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

allow extensions to sort torrents for queuing

../src/session_impl.cpp:4312

			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:4468

		{
			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:4502

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

../src/session_impl.cpp:4503

				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:4647

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

			int rate_threshold = 1024;

			for (std::vector<peer_connection*>::const_iterator i = peers.begin()
				, end(peers.end()); i != end; ++i)
			{
				peer_connection const& p = **i;
				int rate = int(p.uploaded_in_last_round()
					* 1000 / total_milliseconds(unchoke_interval));

				if (rate < rate_threshold) break;

				++m_allowed_upload_slots;

make configurable

../src/session_impl.cpp:4661

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

			int rate_threshold = 1024;

			for (std::vector<peer_connection*>::const_iterator i = peers.begin()
				, end(peers.end()); i != end; ++i)
			{
				peer_connection const& p = **i;
				int rate = int(p.uploaded_in_last_round()
					* 1000 / total_milliseconds(unchoke_interval));

				if (rate < rate_threshold) break;

				++m_allowed_upload_slots;

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

		if (m_settings.choking_algorithm == session_settings::bittyrant_choker)
		{
			// if we're using the bittyrant choker, sort peers by their return
			// on investment. i.e. download rate / upload rate
			std::sort(peers.begin(), peers.end()
				, boost::bind(&peer_connection::bittyrant_unchoke_compare, _1, _2));
		}
		else
		{
			// sorts the peers that are eligible for unchoke by download rate and secondary
			// by total upload. The reason for this is, if all torrents are being seeded,
			// the download rate will be 0, and the peers we have sent the least to should
			// be unchoked
			std::sort(peers.begin(), peers.end()
				, boost::bind(&peer_connection::unchoke_compare, _1, _2));
		}

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

if the read fails, set error and exit immediately

../src/storage.cpp:326

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

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

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

if the read fails, set error and exit immediately

../src/storage.cpp:360

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

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

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

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

make this more generic to not just work if files have been renamed, but also if they have been merged into a single file for instance maybe use the same format as .torrent files and reuse some code from torrent_info

../src/storage.cpp:638

		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:1252

			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::rw_mask) == 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(files().file_path(*file_iter, m_save_path), ec);
				return -1;
			}

			if (file_bytes_left != bytes_transferred)
				return bytes_transferred;

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

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

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:5144

		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:5280

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

		if (m_torrent_file->is_merkle_torrent())
		{
			lazy_entry const* mt = rd.dict_find_string("merkle tree");
			if (mt)
			{
				std::vector<sha1_hash> tree;
				tree.resize(m_torrent_file->merkle_tree().size());
				std::memcpy(&tree[0], mt->string_ptr()
					, (std::min)(mt->string_length(), int(tree.size()) * 20));
				if (mt->string_length() < int(tree.size()) * 20)
					std::memset(&tree[0] + mt->string_length() / 20, 0
						, tree.size() - mt->string_length() / 20);
				m_torrent_file->set_merkle_tree(tree);
			}
			else
			{
				TORRENT_ASSERT(false);
			}
		}
	}

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

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

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

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

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

make this more generic to not just work if files have been renamed, but also if they have been merged into a single file for instance. using file_base

../src/torrent.cpp:5468

		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:7945

			}

			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

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

../src/udp_tracker_connection.cpp:552

		}

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

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

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

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

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

		close();
		return true;
	}

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

Make this count Unicode characters instead of bytes on windows

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

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

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

// on windows, NAME_MAX refers to Unicode characters
// on linux it refers to bytes (utf-8 encoded)

// windows
#if defined FILENAME_MAX
#define TORRENT_MAX_PATH FILENAME_MAX

// beos
#elif defined B_PATH_NAME_LENGTH
#define TORRENT_MAX_PATH B_PATH_NAME_LENGTH

// solaris
#elif defined MAXPATH
#define TORRENT_MAX_PATH MAXPATH

// posix
#elif defined NAME_MAX
#define TORRENT_MAX_PATH NAME_MAX

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

#endif

#if defined TORRENT_WINDOWS && !defined TORRENT_MINGW

#include <stdarg.h>

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

why are all these functions exported?

../include/libtorrent/file.hpp:111

		time_t ctime;
		enum {
#if defined TORRENT_WINDOWS
			fifo = 0x1000, // named pipe (fifo)
			character_special = 0x2000,  // character special
			directory = 0x4000,  // directory
			regular_file = 0x8000  // regular
#else
			fifo = 0010000, // named pipe (fifo)
			character_special = 0020000,  // character special
			directory = 0040000,  // directory
			block_special = 0060000,  // block special
			regular_file = 0100000,  // regular
			link = 0120000,  // symbolic link
			socket = 0140000  // socket
#endif
		} modes_t;
		int mode;
	};

	enum stat_flags_t { dont_follow_links = 1 };
	TORRENT_EXPORT void stat_file(std::string f, file_status* s
		, error_code& ec, int flags = 0);
	TORRENT_EXPORT void rename(std::string const& f
		, std::string const& newf, error_code& ec);
	TORRENT_EXPORT void create_directories(std::string const& f
		, error_code& ec);
	TORRENT_EXPORT void create_directory(std::string const& f
		, error_code& ec);
	TORRENT_EXPORT void remove_all(std::string const& f
		, error_code& ec);
	TORRENT_EXPORT void remove(std::string const& f, error_code& ec);
	TORRENT_EXPORT bool exists(std::string const& f);
	TORRENT_EXPORT size_type file_size(std::string const& f);
	TORRENT_EXPORT bool is_directory(std::string const& f
		, error_code& ec);
	TORRENT_EXPORT void recursive_copy(std::string const& old_path
		, std::string const& new_path, error_code& ec);
	TORRENT_EXPORT void copy_file(std::string const& f
		, std::string const& newf, error_code& ec);

	TORRENT_EXPORT std::string split_path(std::string const& f);
	TORRENT_EXPORT char const* next_path_element(char const* p);
	TORRENT_EXPORT std::string extension(std::string const& f);
	TORRENT_EXPORT void replace_extension(std::string& f, std::string const& ext);
	TORRENT_EXPORT bool is_root_path(std::string const& f);
	TORRENT_EXPORT std::string parent_path(std::string const& f);
	TORRENT_EXPORT bool has_parent_path(std::string const& f);
	TORRENT_EXPORT std::string filename(std::string const& f);
	TORRENT_EXPORT std::string combine_path(std::string const& lhs
		, std::string const& rhs);

does this really need to be exported?

../include/libtorrent/file_storage.hpp:74

		std::string path;
		size_type offset; // the offset of this file inside the torrent
		size_type size; // the size of this file
		// the offset in the file where the storage starts.
		// This is always 0 unless parts of the torrent is
		// compressed into a single file, such as a so-called part file.
		size_type file_base;
		std::time_t mtime;
		sha1_hash filehash;
		bool pad_file:1;
		bool hidden_attribute:1;
		bool executable_attribute:1;
		bool symlink_attribute:1;
		std::string symlink_path;
	};

	// this is used internally to hold the file entry
	// it's smaller and optimized for smaller memory
	// footprint, as opposed to file_entry, which is
	// optimized for convenience
	struct TORRENT_EXPORT internal_file_entry
	{
		friend class file_storage;
#ifdef TORRENT_DEBUG
		// for torrent_info::invariant_check
		friend class torrent_info;
#endif
		internal_file_entry()
			: name(0)
			, offset(0)
			, symlink_index(-1)
			, size(0)
			, name_len(0)
			, pad_file(false)
			, hidden_attribute(false)
			, executable_attribute(false)
			, symlink_attribute(false)
			, path_index(-1)
		{}

		internal_file_entry(file_entry const& e)
			: name(0)
			, offset(e.offset)
			, symlink_index(-1)
			, size(e.size)
			, name_len(0)
			, pad_file(e.pad_file)
			, hidden_attribute(e.hidden_attribute)
			, executable_attribute(e.executable_attribute)
			, symlink_attribute(e.symlink_attribute)
			, path_index(-1)

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();
	}

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

../include/libtorrent/torrent_info.hpp:110

		std::string url;
		std::string trackerid;

		// if this tracker has returned an error or warning message
		// that message is stored here
		std::string message;

		// if this tracker failed the last time it was contacted
		// this error code specifies what error occurred
		error_code last_error;

		int next_announce_in() const;
		int min_announce_in() const;

		// the time of next tracker announce
		ptime next_announce;

		// no announces before this time
		ptime min_announce;


		// if this tracker has returned scrape data, these fields are filled
		// in with valid numbers. Otherwise they are set to -1.
		// the number of current downloaders
		int scrape_incomplete;
		// the number of current seeds
		int scrape_complete;
		// the cumulative number of completed downloads, ever
		int scrape_downloaded;

		// the tier this tracker belongs to
		boost::uint8_t tier;

		// the number of times this tracker can fail
		// in a row before it's removed. 0 means unlimited
		boost::uint8_t fail_limit;

		// the number of times in a row this tracker has failed
		boost::uint8_t fails:7;

		// true if we're currently trying to announce with 
		// this tracker
		bool updating:1;

		enum tracker_source
		{
			source_torrent = 1,
			source_client = 2,
			source_magnet_link = 4,
			source_tex = 8
		};