premiere-libtorrent/include/libtorrent/session.hpp

/*

Copyright (c) 2006-2012, Arvid Norberg
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:

    * Redistributions of source code must retain the above copyright
      notice, this list of conditions and the following disclaimer.
    * Redistributions in binary form must reproduce the above copyright
      notice, this list of conditions and the following disclaimer in
      the documentation and/or other materials provided with the distribution.
    * Neither the name of the author nor the names of its
      contributors may be used to endorse or promote products derived
      from this software without specific prior written permission.

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

*/

#ifndef TORRENT_SESSION_HPP_INCLUDED
#define TORRENT_SESSION_HPP_INCLUDED

#include <algorithm>
#include <vector>

#ifdef _MSC_VER
#pragma warning(push, 1)
#endif

#include <boost/limits.hpp>

#ifdef _MSC_VER
#pragma warning(pop)
#endif

#include "libtorrent/config.hpp"
#include "libtorrent/torrent_handle.hpp"
#include "libtorrent/entry.hpp"
#include "libtorrent/session_status.hpp"
#include "libtorrent/version.hpp"
#include "libtorrent/fingerprint.hpp"
#include "libtorrent/disk_io_thread.hpp"
#include "libtorrent/peer_id.hpp"
#include "libtorrent/alert.hpp" // alert::error_notification
#include "libtorrent/add_torrent_params.hpp"
#include "libtorrent/rss.hpp"
#include "libtorrent/build_config.hpp"

#include "libtorrent/storage.hpp"

#ifdef _MSC_VER
#	include <eh.h>
#endif

#ifdef TORRENT_USE_OPENSSL
// this is a nasty openssl macro
#ifdef set_key
#undef set_key
#endif
#endif

namespace libtorrent
{
	struct plugin;
	struct torrent_plugin;
	class torrent;
	struct ip_filter;
	class port_filter;
	class connection_queue;
	class alert;

	// The default values of the session settings are set for a regular bittorrent client running
	// on a desktop system. There are functions that can set the session settings to pre set
	// settings for other environments. These can be used for the basis, and should be tweaked to
	// fit your needs better.
	// 
	// ``min_memory_usage`` returns settings that will use the minimal amount of RAM, at the
	// potential expense of upload and download performance. It adjusts the socket buffer sizes,
	// disables the disk cache, lowers the send buffer watermarks so that each connection only has
	// at most one block in use at any one time. It lowers the outstanding blocks send to the disk
	// I/O thread so that connections only have one block waiting to be flushed to disk at any given
	// time. It lowers the max number of peers in the peer list for torrents. It performs multiple
	// smaller reads when it hashes pieces, instead of reading it all into memory before hashing.
	// 
	// This configuration is inteded to be the starting point for embedded devices. It will
	// significantly reduce memory usage.
	// 
	// ``high_performance_seed`` returns settings optimized for a seed box, serving many peers
	// and that doesn't do any downloading. It has a 128 MB disk cache and has a limit of 400 files
	// in its file pool. It support fast upload rates by allowing large send buffers.
	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
	{
		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

	// The session holds all state that spans multiple torrents. Among other things it runs the network
	// loop and manages all torrents.
	// Once it's created, the session object will spawn the main thread that will do all the work.
	// The main thread will be idle as long it doesn't have any torrents to participate in.
	class TORRENT_EXPORT session: public boost::noncopyable
	{
	public:

		// If the fingerprint in the first overload is omited, the client will get a default
		// fingerprint stating the version of libtorrent. The fingerprint is a short string that will be
		// used in the peer-id to identify the client and the client's version. For more details see the
		// fingerprint class. The constructor that only takes a fingerprint will not open a
		// listen port for the session, to get it running you'll have to call ``session::listen_on()``.
		// The other constructor, that takes a port range and an interface as well as the fingerprint
		// will automatically try to listen on a port on the given interface. For more information about
		// the parameters, see ``listen_on()`` function.
		// 
		// The flags paramater can be used to start default features (upnp & nat-pmp) and default plugins
		// (ut_metadata, ut_pex and smart_ban). The default is to start those things. If you do not want
		// them to start, pass 0 as the flags parameter.
		// 
		// The ``alert_mask`` is the same mask that you would send to set_alert_mask().
		session(fingerprint const& print = fingerprint("LT"
			, LIBTORRENT_VERSION_MAJOR, LIBTORRENT_VERSION_MINOR, 0, 0)
			, int flags = start_default_features | add_default_plugins
			, boost::uint32_t alert_mask = alert::error_notification
			TORRENT_LOGPATH_ARG_DEFAULT)
		{
			TORRENT_CFG();
			init(std::make_pair(0, 0), "0.0.0.0", print, alert_mask);
#if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_LOGGING || defined TORRENT_ERROR_LOGGING
			set_log_path(logpath);
#endif
			start(flags);
		}
		session(fingerprint const& print
			, std::pair<int, int> listen_port_range
			, char const* listen_interface = "0.0.0.0"
			, int flags = start_default_features | add_default_plugins
			, int alert_mask = alert::error_notification
			TORRENT_LOGPATH_ARG_DEFAULT)
		{
			TORRENT_CFG();
			TORRENT_ASSERT(listen_port_range.first > 0);
			TORRENT_ASSERT(listen_port_range.first < listen_port_range.second);
			init(listen_port_range, listen_interface, print, alert_mask);
#if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_LOGGING || defined TORRENT_ERROR_LOGGING
			set_log_path(logpath);
#endif
			start(flags);
		}
			
		// The destructor of session will notify all trackers that our torrents have been shut down.
		// If some trackers are down, they will time out. All this before the destructor of session
		// returns. So, it's advised that any kind of interface (such as windows) are closed before
		// destructing the session object. Because it can take a few second for it to finish. The
		// timeout can be set with ``set_settings()``.
		~session();

		enum save_state_flags_t
		{
			save_settings =     0x001,
			save_dht_settings = 0x002,
			save_dht_state =    0x004,
			save_proxy =        0x008,
			save_i2p_proxy =    0x010,
			save_encryption_settings = 0x020,
			save_as_map =       0x040,
			save_feeds =        0x080

#ifndef TORRENT_NO_DEPRECATE
			,
			save_dht_proxy = save_proxy,
			save_peer_proxy = save_proxy,
			save_web_proxy = save_proxy,
			save_tracker_proxy = save_proxy
#endif
		};

		// loads and saves all session settings, including dht_settings, encryption settings and proxy
		// settings. ``save_state`` writes all keys to the ``entry`` that's passed in, which needs to
		// either not be initialized, or initialized as a dictionary.
		// 
		// ``load_state`` expects a lazy_entry which can be built from a bencoded buffer with
		// lazy_bdecode().
		// 
		// The ``flags`` arguments passed in to ``save_state`` can be used to filter which parts
		// of the session state to save. By default, all state is saved (except for the individual
		// torrents). see save_state_flags_t
		void save_state(entry& e, boost::uint32_t flags = 0xffffffff) const;
		void load_state(lazy_entry const& e);

		// .. note::
		// 	these calls are potentially expensive and won't scale well
		// 	with lots of torrents. If you're concerned about performance, consider
		// 	using ``post_torrent_updates()`` instead.
		// 
		// ``get_torrent_status`` returns a vector of the torrent_status for every
		// torrent which satisfies ``pred``, which is a predicate function which determines
		// if a torrent should be included in the returned set or not. Returning true means
		// it should be included and false means excluded. The ``flags`` argument is the same
		// as to ``torrent_handle::status()``. Since ``pred`` is guaranteed to be called for
		// every torrent, it may be used to count the number of torrents of different categories
		// as well.
		// 
		// ``refresh_torrent_status`` takes a vector of torrent_status structs (for instance
		// the same vector that was returned by get_torrent_status() ) and refreshes the
		// status based on the ``handle`` member. It is possible to use this function by
		// first setting up a vector of default constructed ``torrent_status`` objects, only
		// initializing the ``handle`` member, in order to request the torrent status for
		// multiple torrents in a single call. This can save a significant amount of time
		// if you have a lot of torrents.
		// 
		// Any torrent_status object whose ``handle`` member is not referring to a
		// valid torrent are ignored.
		void get_torrent_status(std::vector<torrent_status>* ret
			, boost::function<bool(torrent_status const&)> const& pred
			, boost::uint32_t flags = 0) const;
		void refresh_torrent_status(std::vector<torrent_status>* ret
			, boost::uint32_t flags = 0) const;

		// This functions instructs the session to post the state_update_alert, containing
		// the status of all torrents whose state changed since the last time this function
		// was called.
		// 
		// Only torrents who has the state subscription flag set will be included. This flag
		// is on by default. See add_torrent_params_.
		void post_torrent_updates();

		// internal
		io_service& get_io_service();

		// ``find_torrent()`` looks for a torrent with the given info-hash. In case there
		// is such a torrent in the session, a torrent_handle to that torrent is returned.
		// In case the torrent cannot be found, an invalid torrent_handle is returned.
		// 
		// See ``torrent_handle::is_valid()`` to know if the torrent was found or not.
		// 
		// ``get_torrents()`` returns a vector of torrent_handles to all the torrents
		// currently in the session.
		torrent_handle find_torrent(sha1_hash const& info_hash) const;
		std::vector<torrent_handle> get_torrents() const;

		// You add torrents through the add_torrent() function where you give an
		// object with all the parameters. The add_torrent() overloads will block
		// until the torrent has been added (or failed to be added) and returns an
		// error code and a torrent_handle. In order to add torrents more efficiently,
		// consider using async_add_torrent() which returns immediately, without
		// waiting for the torrent to add. Notification of the torrent being added is sent
		// as add_torrent_alert.
		// 
		// The overload that does not take an error_code throws an exception on
		// error and is not available when building without exception support.
		// The torrent_handle returned by add_torrent() can be used to retrieve information
		// about the torrent's progress, its peers etc. It is also used to abort a torrent.
		// 
		// If the torrent you are trying to add already exists in the session (is either queued
		// for checking, being checked or downloading) ``add_torrent()`` will throw
		// libtorrent_exception which derives from ``std::exception`` unless duplicate_is_error
		// is set to false. In that case, add_torrent() will return the handle to the existing
		// torrent.
		//
		// all torrent_handles must be destructed before the session is destructed!
#ifndef BOOST_NO_EXCEPTIONS
		torrent_handle add_torrent(add_torrent_params const& params);
#endif
		torrent_handle add_torrent(add_torrent_params const& params, error_code& ec);
		void async_add_torrent(add_torrent_params const& params);
		
#ifndef BOOST_NO_EXCEPTIONS
#ifndef TORRENT_NO_DEPRECATE
		// deprecated in 0.14
		TORRENT_DEPRECATED_PREFIX
		torrent_handle add_torrent(
			torrent_info const& ti
			, std::string const& save_path
			, entry const& resume_data = entry()
			, storage_mode_t storage_mode = storage_mode_sparse
			, bool paused = false
			, storage_constructor_type sc = default_storage_constructor) TORRENT_DEPRECATED;

		// deprecated in 0.14
		TORRENT_DEPRECATED_PREFIX
		torrent_handle add_torrent(
			boost::intrusive_ptr<torrent_info> ti
			, std::string const& save_path
			, entry const& resume_data = entry()
			, storage_mode_t storage_mode = storage_mode_sparse
			, bool paused = false
			, storage_constructor_type sc = default_storage_constructor
			, void* userdata = 0) TORRENT_DEPRECATED;

		// deprecated in 0.14
		TORRENT_DEPRECATED_PREFIX
		torrent_handle add_torrent(
			char const* tracker_url
			, sha1_hash const& info_hash
			, char const* name
			, std::string const& save_path
			, entry const& resume_data = entry()
			, storage_mode_t storage_mode = storage_mode_sparse
			, bool paused = false
			, storage_constructor_type sc = default_storage_constructor
			, void* userdata = 0) TORRENT_DEPRECATED;
#endif
#endif

		// In case you want to destruct the session asynchrounously, you can request a session
		// destruction proxy. If you don't do this, the destructor of the session object will
		// block while the trackers are contacted. If you keep one ``session_proxy`` to the
		// session when destructing it, the destructor will not block, but start to close down
		// the session, the destructor of the proxy will then synchronize the threads. So, the
		// destruction of the session is performed from the ``session`` destructor call until the
		// ``session_proxy`` destructor call. The ``session_proxy`` does not have any operations
		// on it (since the session is being closed down, no operations are allowed on it). The
		// only valid operation is calling the destructor::
		// 
		// 	class session_proxy
		// 	{
		// 	public:
		// 		session_proxy();
		// 		~session_proxy()
		// 	};
		session_proxy abort() { return session_proxy(m_impl); }

		// Pausing the session has the same effect as pausing every torrent in it, except that
		// torrents will not be resumed by the auto-manage mechanism. Resuming will restore the
		// torrents to their previous paused state. i.e. the session pause state is separate from
		// the torrent pause state. A torrent is inactive if it is paused or if the session is
		// paused.
		void pause();
		void resume();
		bool is_paused() const;

		// returns session wide-statistics and status. For more information, see the ``session_status`` struct.
		session_status status() const;

		// Returns status of the disk cache for this session.
		// For more information, see the cache_status type.
		cache_status get_cache_status() const;

		// fills out the supplied vector with information for
		// each piece that is currently in the disk cache for the torrent with the
		// specified info-hash (``ih``).
		void get_cache_info(sha1_hash const& ih
			, std::vector<cached_piece_info>& ret) const;

		// This adds an RSS feed to the session. The feed will be refreshed
		// regularly and optionally add all torrents from the feed, as they
		// appear.
		//
		// Before adding the feed, you must set the ``url`` field to the
		// feed's url. It may point to an RSS or an atom feed.
		// The returned feed_handle is a handle which is used to interact
		// with the feed, things like forcing a refresh or querying for
		// information about the items in the feed. For more information,
		// see feed_handle.
		feed_handle add_feed(feed_settings const& feed);

		// Removes a feed from being watched by the session. When this
		// call returns, the feed handle is invalid and won't refer
		// to any feed.
		void remove_feed(feed_handle h);

		// Returns a list of all RSS feeds that are being watched by the session.
		void get_feeds(std::vector<feed_handle>& f) const;

		// starts/stops UPnP, NATPMP or LSD port mappers
		// they are stopped by default
		// These functions are not available in case ``TORRENT_DISABLE_DHT`` is
		// defined. ``start_dht`` starts the dht node and makes the trackerless service
		// available to torrents. The startup state is optional and can contain nodes
		// and the node id from the previous session. The dht node state is a bencoded
		// dictionary with the following entries:
		// 
		// nodes
		// 	A list of strings, where each string is a node endpoint encoded in binary. If
		// 	the string is 6 bytes long, it is an IPv4 address of 4 bytes, encoded in
		// 	network byte order (big endian), followed by a 2 byte port number (also
		// 	network byte order). If the string is 18 bytes long, it is 16 bytes of IPv6
		// 	address followed by a 2 bytes port number (also network byte order).
		// 
		// node-id
		// 	The node id written as a readable string as a hexadecimal number.
		// 
		// ``dht_state`` will return the current state of the dht node, this can be used
		// to start up the node again, passing this entry to ``start_dht``. It is a good
		// idea to save this to disk when the session is closed, and read it up again
		// when starting.
		// 
		// If the port the DHT is supposed to listen on is already in use, and exception
		// is thrown, ``asio::error``.
		// 
		// ``stop_dht`` stops the dht node.
		// 
		// ``add_dht_node`` adds a node to the routing table. This can be used if your
		// client has its own source of bootstrapping nodes.
		// 
		// ``set_dht_settings`` sets some parameters availavle to the dht node. See
		// dht_settings for more information.
		//
		// ``is_dht_running()`` returns true if the DHT support has been started and false
		// otherwise.
		void start_dht();
		void stop_dht();
		void set_dht_settings(dht_settings const& settings);
		bool is_dht_running() const;

		// ``add_dht_node`` takes a host name and port pair. That endpoint will be
		// pinged, and if a valid DHT reply is received, the node will be added to
		// the routing table.
		// 
		// ``add_dht_router`` adds the given endpoint to a list of DHT router nodes.
		// If a search is ever made while the routing table is empty, those nodes will
		// be used as backups. Nodes in the router node list will also never be added
		// to the regular routing table, which effectively means they are only used
		// for bootstrapping, to keep the load off them.
		// 
		// An example routing node that you could typically add is
		// ``router.bittorrent.com``.
		void add_dht_node(std::pair<std::string, int> const& node);
		void add_dht_router(std::pair<std::string, int> const& node);

#ifndef TORRENT_NO_DEPRECATE
		// deprecated in 0.15
		// use save_state and load_state instead
		TORRENT_DEPRECATED_PREFIX
		entry dht_state() const TORRENT_DEPRECATED;
		TORRENT_DEPRECATED_PREFIX
		void start_dht(entry const& startup_state) TORRENT_DEPRECATED;
#endif

		// This function adds an extension to this session. The argument is a function
		// object that is called with a ``torrent*`` and which should return a
		// ``boost::shared_ptr<torrent_plugin>``. To write custom plugins, see
		// `libtorrent plugins`_. For the typical bittorrent client all of these
		// extensions should be added. The main plugins implemented in libtorrent are:
		// 
		// metadata extension
		// 	Allows peers to download the metadata (.torren files) from the swarm
		// 	directly. Makes it possible to join a swarm with just a tracker and
		// 	info-hash.
		// 
		// ::
		// 
		// 	#include <libtorrent/extensions/metadata_transfer.hpp>
		// 	ses.add_extension(&libtorrent::create_metadata_plugin);
		// 
		// uTorrent metadata
		// 	Same as ``metadata extension`` but compatible with uTorrent.
		// 
		// ::
		// 
		// 	#include <libtorrent/extensions/ut_metadata.hpp>
		// 	ses.add_extension(&libtorrent::create_ut_metadata_plugin);
		// 
		// uTorrent peer exchange
		// 	Exchanges peers between clients.
		// 
		// ::
		// 
		// 	#include <libtorrent/extensions/ut_pex.hpp>
		// 	ses.add_extension(&libtorrent::create_ut_pex_plugin);
		// 
		// smart ban plugin
		// 	A plugin that, with a small overhead, can ban peers
		// 	that sends bad data with very high accuracy. Should
		// 	eliminate most problems on poisoned torrents.
		// 
		// ::
		// 
		// 	#include <libtorrent/extensions/smart_ban.hpp>
		// 	ses.add_extension(&libtorrent::create_smart_ban_plugin);
		// 
		// 
		// .. _`libtorrent plugins`: libtorrent_plugins.html
		void add_extension(boost::function<boost::shared_ptr<torrent_plugin>(torrent*, void*)> ext);
		void add_extension(boost::shared_ptr<plugin> ext);

		// These functions are not available if ``TORRENT_DISABLE_GEO_IP`` is defined. They
		// expects a path to the `MaxMind ASN database`_ and `MaxMind GeoIP database`_
		// respectively. This will be used to look up which AS and country peers belong to.
		// 
		// ``as_for_ip`` returns the AS number for the IP address specified. If the IP is not
		// in the database or the ASN database is not loaded, 0 is returned.
		// 
		// .. _`MaxMind ASN database`: http://www.maxmind.com/app/asnum
		// .. _`MaxMind GeoIP database`: http://www.maxmind.com/app/geolitecountry
#ifndef TORRENT_DISABLE_GEO_IP
		void load_asnum_db(char const* file);
		void load_country_db(char const* file);
		int as_for_ip(address const& addr);
#ifndef TORRENT_NO_DEPRECATE
#if TORRENT_USE_WSTRING
		// all wstring APIs are deprecated since 0.16.11
		// instead, use the wchar -> utf8 conversion functions
		// and pass in utf8 strings
		TORRENT_DEPRECATED_PREFIX
		void load_country_db(wchar_t const* file) TORRENT_DEPRECATED;
		TORRENT_DEPRECATED_PREFIX
		void load_asnum_db(wchar_t const* file) TORRENT_DEPRECATED;
#endif // TORRENT_USE_WSTRING
#endif // TORRENT_NO_DEPRECATE
#endif // TORRENT_DISABLE_GEO_IP

#ifndef TORRENT_NO_DEPRECATE
		// deprecated in 0.15
		// use load_state and save_state instead
		TORRENT_DEPRECATED_PREFIX
		void load_state(entry const& ses_state) TORRENT_DEPRECATED;
		TORRENT_DEPRECATED_PREFIX
		entry state() const TORRENT_DEPRECATED;
#endif

		// Sets a filter that will be used to reject and accept incoming as well as outgoing
		// connections based on their originating ip address. The default filter will allow
		// connections to any ip address. To build a set of rules for which addresses are
		// accepted and not, see ip_filter.
		// 
		// Each time a peer is blocked because of the IP filter, a peer_blocked_alert is
		// generated.
		// ``get_ip_filter()`` Returns the ip_filter currently in the session. See ip_filter.
		void set_ip_filter(ip_filter const& f);
		ip_filter get_ip_filter() const;
		
		// apply port_filter ``f`` to incoming and outgoing peers.
		// a port filter will reject making outgoing peer connections
		// to certain remote ports. The main intention is to be able
		// to avoid triggering certain anti-virus software by connecting
		// to SMTP, FTP ports.
		void set_port_filter(port_filter const& f);

		// sets and gets the raw peer ID used by libtorrent. When anonymous
		// mode is set the peer ID is randomized per peer anyway.
		void set_peer_id(peer_id const& pid);
		peer_id id() const;

		// sets the key sent to trackers. If it's not set, it is initialized
		// by libtorrent. The key may be used by the tracker to identify the
		// peer potentially across you changing your IP.
		void set_key(int key);


		// ``is_listening()`` will tell you whether or not the session has successfully
		// opened a listening port. If it hasn't, this function will return false, and
		// then you can use ``listen_on()`` to make another attempt.
		// 
		// ``listen_port()`` returns the port we ended up listening on. Since you just pass
		// a port-range to the constructor and to ``listen_on()``, to know which port it
		// ended up using, you have to ask the session using this function.
		// 
		// ``listen_on()`` will change the listen port and/or the listen interface. If the
		// session is already listening on a port, this socket will be closed and a new socket
		// will be opened with these new settings. The port range is the ports it will try
		// to listen on, if the first port fails, it will continue trying the next port within
		// the range and so on. The interface parameter can be left as 0, in that case the
		// os will decide which interface to listen on, otherwise it should be the ip-address
		// of the interface you want the listener socket bound to. ``listen_on()`` returns the
		// error code of the operation in ``ec``. If this indicates success, the session is
		// listening on a port within the specified range. If it fails, it will also
		// generate an appropriate alert (listen_failed_alert).
		// 
		// If all ports in the specified range fails to be opened for listening, libtorrent will
		// try to use port 0 (which tells the operating system to pick a port that's free). If
		// that still fails you may see a listen_failed_alert with port 0 even if you didn't
		// ask to listen on it.
		// 
		// It is possible to prevent libtorrent from binding to port 0 by passing in the flag
		// ``session::no_system_port`` in the ``flags`` argument.
		// 
		// The interface parameter can also be a hostname that will resolve to the device you
		// want to listen on. If you don't specify an interface, libtorrent may attempt to
		// listen on multiple interfaces (typically 0.0.0.0 and ::). This means that if your
		// IPv6 interface doesn't work, you may still see a listen_failed_alert, even though
		// the IPv4 port succeeded.
		// 
		// The ``flags`` parameter can either be 0 or ``session::listen_reuse_address``, which
		// will set the reuse address socket option on the listen socket(s). By default, the
		// listen socket does not use reuse address. If you're running a service that needs
		// to run on a specific port no matter if it's in use, set this flag.
		// 
		// If you're also starting the DHT, it is a good idea to do that after you've called
		// ``listen_on()``, since the default listen port for the DHT is the same as the tcp
		// listen socket. If you start the DHT first, it will assume the tcp port is free and
		// open the udp socket on that port, then later, when ``listen_on()`` is called, it
		// may turn out that the tcp port is in use. That results in the DHT and the bittorrent
		// socket listening on different ports. If the DHT is active when ``listen_on`` is
		// called, the udp port will be rebound to the new port, if it was configured to use
		// the same port as the tcp socket, and if the listen_on call failed to bind to the
		// same port that the udp uses.
		// 
		// If you want the OS to pick a port for you, pass in 0 as both first and second.
		// 
		// The reason why it's a good idea to run the DHT and the bittorrent socket on the same
		// port is because that is an assumption that may be used to increase performance. One
		// way to accelerate the connecting of peers on windows may be to first ping all peers
		// with a DHT ping packet, and connect to those that responds first. On windows one
		// can only connect to a few peers at a time because of a built in limitation (in XP
		// Service pack 2).
		void listen_on(
			std::pair<int, int> const& port_range
			, error_code& ec
			, const char* net_interface = 0
			, int flags = 0);
		unsigned short listen_port() const;
		unsigned short ssl_listen_port() const;
		bool is_listening() const;

		// if the listen port failed in some way
		// you can retry to listen on another port-
		// range with this function. If the listener
		// succeeded and is currently listening,
		// a call to this function will shut down the
		// listen port and reopen it using these new
		// properties (the given interface and port range).
		// As usual, if the interface is left as 0
		// this function will return false on failure.
		// If it fails, it will also generate alerts describing
		// the error. It will return true on success.
		enum listen_on_flags_t
		{
#ifndef TORRENT_NO_DEPRECATE
			// this is always on starting with 0.16.2
			listen_reuse_address = 0x01,
#endif
			listen_no_system_port = 0x02
		};

#ifndef TORRENT_NO_DEPRECATE
		// deprecated in 0.16
		TORRENT_DEPRECATED_PREFIX
		bool listen_on(
			std::pair<int, int> const& port_range
			, const char* net_interface = 0
			, int flags = 0) TORRENT_DEPRECATED;
#endif

		enum options_t
		{
			delete_files = 1
		};

		enum session_flags_t
		{
			add_default_plugins = 1,
			start_default_features = 2
		};

		// ``remove_torrent()`` will close all peer connections associated with the torrent and tell
		// the tracker that we've stopped participating in the swarm. This operation cannot fail.
		// When it completes, you will receive a torrent_removed_alert.
		//
		// The optional second argument ``options`` can be used to delete all the files downloaded
		// by this torrent. To do so, pass in the value ``session::delete_files``. The removal
		// of the torrent is asyncronous, there is no guarantee that adding the same torrent
		// immediately after it was removed will not throw a libtorrent_exception exception. Once
		// the torrent is deleted, a torrent_deleted_alert is posted.
		void remove_torrent(const torrent_handle& h, int options = 0);

		// Sets the session settings and the packet encryption settings respectively.
		// See session_settings and pe_settings for more information on available
		// options.
		void set_settings(session_settings const& s);
		session_settings settings() const;
#ifndef TORRENT_DISABLE_ENCRYPTION
		void set_pe_settings(pe_settings const& settings);
		pe_settings get_pe_settings() const;
#endif

		// These functions sets and queries the proxy settings to be used for the session.
		//
		// For more information on what settings are available for proxies, see
		// proxy_settings. If the session is not in anonymous mode, proxies that
		// aren't working or fail, will automatically be disabled and packets will
		// flow without using any proxy. If you want to enforce using a proxy, even when
		// the proxy doesn't work, enable anonymous_mode in session_settings.
		void set_proxy(proxy_settings const& s);
		proxy_settings proxy() const;

#ifdef TORRENT_STATS
		void enable_stats_logging(bool s);
#endif

#ifndef TORRENT_NO_DEPRECATE
		// deprecated in 0.16
		// Get the number of uploads.
		TORRENT_DEPRECATED_PREFIX
		int num_uploads() const TORRENT_DEPRECATED;

		// Get the number of connections. This number also contains the
		// number of half open connections.
		TORRENT_DEPRECATED_PREFIX
		int num_connections() const TORRENT_DEPRECATED;

		// deprecated in 0.15.
		TORRENT_DEPRECATED_PREFIX
		void set_peer_proxy(proxy_settings const& s) TORRENT_DEPRECATED;
		TORRENT_DEPRECATED_PREFIX
		void set_web_seed_proxy(proxy_settings const& s) TORRENT_DEPRECATED;
		TORRENT_DEPRECATED_PREFIX
		void set_tracker_proxy(proxy_settings const& s) TORRENT_DEPRECATED;

		TORRENT_DEPRECATED_PREFIX
		proxy_settings peer_proxy() const TORRENT_DEPRECATED;
		TORRENT_DEPRECATED_PREFIX
		proxy_settings web_seed_proxy() const TORRENT_DEPRECATED;
		TORRENT_DEPRECATED_PREFIX
		proxy_settings tracker_proxy() const TORRENT_DEPRECATED;

		TORRENT_DEPRECATED_PREFIX
		void set_dht_proxy(proxy_settings const& s) TORRENT_DEPRECATED;
		TORRENT_DEPRECATED_PREFIX
		proxy_settings dht_proxy() const TORRENT_DEPRECATED;
#endif // TORRENT_NO_DEPRECATE

#if TORRENT_USE_I2P
		// ``set_i2p_proxy`` sets the i2p_ proxy, and tries to open a persistant
		// connection to it. The only used fields in the proxy settings structs
		// are ``hostname`` and ``port``.
		//
		// ``i2p_proxy`` returns the current i2p proxy in use.
		//
		// .. _i2p: http://www.i2p2.de
		void set_i2p_proxy(proxy_settings const& s);
		proxy_settings i2p_proxy() const;
#endif

#ifndef TORRENT_NO_DEPRECATE
		// deprecated in 0.16
		TORRENT_DEPRECATED_PREFIX
		int upload_rate_limit() const TORRENT_DEPRECATED;
		TORRENT_DEPRECATED_PREFIX
		int download_rate_limit() const TORRENT_DEPRECATED;
		TORRENT_DEPRECATED_PREFIX
		int local_upload_rate_limit() const TORRENT_DEPRECATED;
		TORRENT_DEPRECATED_PREFIX
		int local_download_rate_limit() const TORRENT_DEPRECATED;
		TORRENT_DEPRECATED_PREFIX
		int max_half_open_connections() const TORRENT_DEPRECATED;

		TORRENT_DEPRECATED_PREFIX
		void set_local_upload_rate_limit(int bytes_per_second) TORRENT_DEPRECATED;
		TORRENT_DEPRECATED_PREFIX
		void set_local_download_rate_limit(int bytes_per_second) TORRENT_DEPRECATED;
		TORRENT_DEPRECATED_PREFIX
		void set_upload_rate_limit(int bytes_per_second) TORRENT_DEPRECATED;
		TORRENT_DEPRECATED_PREFIX
		void set_download_rate_limit(int bytes_per_second) TORRENT_DEPRECATED;
		TORRENT_DEPRECATED_PREFIX
		void set_max_uploads(int limit) TORRENT_DEPRECATED;
		TORRENT_DEPRECATED_PREFIX
		void set_max_connections(int limit) TORRENT_DEPRECATED;
		TORRENT_DEPRECATED_PREFIX
		void set_max_half_open_connections(int limit) TORRENT_DEPRECATED;

		TORRENT_DEPRECATED_PREFIX
		int max_connections() const TORRENT_DEPRECATED;
		TORRENT_DEPRECATED_PREFIX
		int max_uploads() const TORRENT_DEPRECATED;
#endif

		// ``pop_alert()`` is used to ask the session if any errors or events has occurred. With
		// set_alert_mask() you can filter which alerts to receive through ``pop_alert()``.
		// For information about the alert categories, see alerts_.
		// 
		// ``pop_alerts()`` pops all pending alerts in a single call. In high performance environments
		// with a very high alert churn rate, this can save significant amount of time compared to
		// popping alerts one at a time. Each call requires one round-trip to the network thread. If
		// alerts are produced in a higher rate than they can be popped (when popped one at a time)
		// it's easy to get stuck in an infinite loop, trying to drain the alert queue. Popping the entire
		// queue at once avoids this problem.
		// 
		// However, the ``pop_alerts`` function comes with significantly more responsibility. You pass
		// in an *empty* ``std::dequeue<alert*>`` to it. If it's not empty, all elements in it will
		// be deleted and then cleared. All currently pending alerts are returned by being swapped
		// into the passed in container. The responsibility of deleting the alerts is transferred
		// to the caller. This means you need to call delete for each item in the returned dequeue.
		// It's probably a good idea to delete the alerts as you handle them, to save one extra
		// pass over the dequeue.
		// 
		// Alternatively, you can pass in the same container the next time you call ``pop_alerts``.
		// 
		// ``wait_for_alert`` blocks until an alert is available, or for no more than ``max_wait``
		// time. If ``wait_for_alert`` returns because of the time-out, and no alerts are available,
		// it returns 0. If at least one alert was generated, a pointer to that alert is returned.
		// The alert is not popped, any subsequent calls to ``wait_for_alert`` will return the
		// same pointer until the alert is popped by calling ``pop_alert``. This is useful for
		// leaving any alert dispatching mechanism independent of this blocking call, the dispatcher
		// can be called and it can pop the alert independently.
		// 
		// In the python binding, ``wait_for_alert`` takes the number of milliseconds to wait as an integer.
		// 
		// To control the max number of alerts that's queued by the session, see
		// ``session_settings::alert_queue_size``.
		// 
		// save_resume_data_alert and save_resume_data_failed_alert are always posted, regardelss
		// of the alert mask.
		std::auto_ptr<alert> pop_alert();
		void pop_alerts(std::deque<alert*>* alerts);
		alert const* wait_for_alert(time_duration max_wait);

#ifndef TORRENT_NO_DEPRECATE
		TORRENT_DEPRECATED_PREFIX
		void set_severity_level(alert::severity_t s) TORRENT_DEPRECATED;

		TORRENT_DEPRECATED_PREFIX
		size_t set_alert_queue_size_limit(size_t queue_size_limit_) TORRENT_DEPRECATED;
#endif

		// Changes the mask of which alerts to receive. By default only errors are reported.
		// ``m`` is a bitmask where each bit represents a category of alerts.
		//
		// See category_t enum for options.
		void set_alert_mask(boost::uint32_t m);

		// This sets a function to be called (from within libtorrent's netowrk thread) every time an alert
		// is posted. Since the function (``fun``) is run in libtorrent's internal thread, it may not call
		// any of libtorrent's external API functions. Doing so results in a dead lock.
		// 
		// The main intention with this function is to support integration with platform-dependent message
		// queues or signalling systems. For instance, on windows, one could post a message to an HNWD or
		// on linux, write to a pipe or an eventfd.
		void set_alert_dispatch(boost::function<void(std::auto_ptr<alert>)> const& fun);

		connection_queue& get_connection_queue();

		// Starts and stops Local Service Discovery. This service will broadcast
		// the infohashes of all the non-private torrents on the local network to
		// look for peers on the same swarm within multicast reach.
		//
		// It is turned off by default.
		void start_lsd();
		void stop_lsd();

		// Starts and stops the UPnP service. When started, the listen port and the DHT
		// port are attempted to be forwarded on local UPnP router devices.
		// 
		// The upnp object returned by ``start_upnp()`` can be used to add and remove
		// arbitrary port mappings. Mapping status is returned through the
		// portmap_alert and the portmap_error_alert. The object will be valid until
		// ``stop_upnp()`` is called. See upnp-and-nat-pmp_.
		// 
		// It is off by default.
 		void start_upnp();
		void stop_upnp();

		// Starts and stops the NAT-PMP service. When started, the listen port and the DHT
		// port are attempted to be forwarded on the router through NAT-PMP.
		// 
		// The natpmp object returned by ``start_natpmp()`` can be used to add and remove
		// arbitrary port mappings. Mapping status is returned through the
		// portmap_alert and the portmap_error_alert. The object will be valid until
		// ``stop_natpmp()`` is called. See upnp-and-nat-pmp_.
		// 
		// It is off by default.
		void start_natpmp();
		void stop_natpmp();
		
	private:

		void init(std::pair<int, int> listen_range, char const* listen_interface
			, fingerprint const& id, boost::uint32_t alert_mask);
		void set_log_path(std::string const& p);
		void start(int flags);

		// data shared between the main thread
		// and the working thread
		boost::shared_ptr<aux::session_impl> m_impl;
	};

}

#endif // TORRENT_SESSION_HPP_INCLUDED