premiere-libtorrent/include/libtorrent/torrent_handle.hpp

/*

Copyright (c) 2003-2018, Arvid Norberg
All rights reserved.

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modification, are permitted provided that the following conditions
are met:

    * Redistributions of source code must retain the above copyright
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    * Redistributions in binary form must reproduce the above copyright
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      the documentation and/or other materials provided with the distribution.
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      contributors may be used to endorse or promote products derived
      from this software without specific prior written permission.

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AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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*/

#ifndef TORRENT_TORRENT_HANDLE_HPP_INCLUDED
#define TORRENT_TORRENT_HANDLE_HPP_INCLUDED

#include "libtorrent/config.hpp"

#include <vector>
#include <set>
#include <functional>
#include <memory>

#include "libtorrent/aux_/disable_warnings_push.hpp"
#if TORRENT_ABI_VERSION == 1
// for deprecated force_reannounce
#include <boost/date_time/posix_time/posix_time_duration.hpp>
#endif
#include "libtorrent/aux_/disable_warnings_pop.hpp"

#include "libtorrent/fwd.hpp"
#include "libtorrent/address.hpp"
#include "libtorrent/socket.hpp" // tcp::endpoint
#include "libtorrent/span.hpp"
#include "libtorrent/sha1_hash.hpp"
#include "libtorrent/units.hpp"
#include "libtorrent/aux_/vector.hpp"
#include "libtorrent/storage_defs.hpp"
#include "libtorrent/torrent_flags.hpp"
#include "libtorrent/peer_info.hpp" // for peer_source_flags_t
#include "libtorrent/download_priority.hpp"
#include "libtorrent/pex_flags.hpp"
#include "libtorrent/broadcast_socket.hpp" // for is_v6

namespace libtorrent {
namespace aux {
	struct session_impl;
}

#if TORRENT_ABI_VERSION == 1
	struct peer_list_entry;
#endif
	class torrent;

#ifndef BOOST_NO_EXCEPTIONS
	[[noreturn]] void throw_invalid_handle();
#endif

	using status_flags_t = flags::bitfield_flag<std::uint32_t, struct status_flags_tag>;
	using add_piece_flags_t = flags::bitfield_flag<std::uint8_t, struct add_piece_flags_tag>;
	using pause_flags_t = flags::bitfield_flag<std::uint8_t, struct pause_flags_tag>;
	using deadline_flags_t = flags::bitfield_flag<std::uint8_t, struct deadline_flags_tag>;
	using resume_data_flags_t = flags::bitfield_flag<std::uint8_t, struct resume_data_flags_tag>;
	using reannounce_flags_t = flags::bitfield_flag<std::uint8_t, struct reannounce_flags_tag>;
	using queue_position_t = aux::strong_typedef<int, struct queue_position_tag>;

	// holds the state of a block in a piece. Who we requested
	// it from and how far along we are at downloading it.
	struct TORRENT_EXPORT block_info
	{
		// this is the enum used for the block_info::state field.
		enum block_state_t
		{
			// This block has not been downloaded or requested form any peer.
			none,
			// The block has been requested, but not completely downloaded yet.
			requested,
			// The block has been downloaded and is currently queued for being
			// written to disk.
			writing,
			// The block has been written to disk.
			finished
		};

	private:
		union addr_t
		{
			address_v4::bytes_type v4;
			address_v6::bytes_type v6;
		};
		addr_t addr;

		std::uint16_t port;
	public:

		// The peer is the ip address of the peer this block was downloaded from.
		void set_peer(tcp::endpoint const& ep)
		{
			is_v6_addr = is_v6(ep);
			if (is_v6_addr)
				addr.v6 = ep.address().to_v6().to_bytes();
			else
				addr.v4 = ep.address().to_v4().to_bytes();
			port = ep.port();
		}
		tcp::endpoint peer() const
		{
			if (is_v6_addr)
				return tcp::endpoint(address_v6(addr.v6), port);
			else
				return tcp::endpoint(address_v4(addr.v4), port);
		}

		// the number of bytes that have been received for this block
		unsigned bytes_progress:15;

		// the total number of bytes in this block.
		unsigned block_size:15;

		// the state this block is in (see block_state_t)
		unsigned state:2;

		// the number of peers that is currently requesting this block. Typically
		// this is 0 or 1, but at the end of the torrent blocks may be requested
		// by more peers in parallel to speed things up.
		unsigned num_peers:14;
	private:
		// the type of the addr union
		bool is_v6_addr:1;
	};

	// This class holds information about pieces that have outstanding requests
	// or outstanding writes
	struct TORRENT_EXPORT partial_piece_info
	{
#if TORRENT_ABI_VERSION == 1
#include "libtorrent/aux_/disable_warnings_push.hpp"
		partial_piece_info() = default;
		partial_piece_info(partial_piece_info&&) noexcept = default;
		partial_piece_info(partial_piece_info const&) = default;
		partial_piece_info& operator=(partial_piece_info const&) = default;
		partial_piece_info& operator=(partial_piece_info&&) noexcept = default;
#include "libtorrent/aux_/disable_warnings_pop.hpp"
#endif
		// the index of the piece in question. ``blocks_in_piece`` is the number
		// of blocks in this particular piece. This number will be the same for
		// most pieces, but
		// the last piece may have fewer blocks than the standard pieces.
		piece_index_t piece_index;

		// the number of blocks in this piece
		int blocks_in_piece;

		// the number of blocks that are in the finished state
		int finished;

		// the number of blocks that are in the writing state
		int writing;

		// the number of blocks that are in the requested state
		int requested;

		// this is an array of ``blocks_in_piece`` number of
		// items. One for each block in the piece.
		//
		// .. warning:: This is a pointer that points to an array
		//	that's owned by the session object. The next time
		//	get_download_queue() is called, it will be invalidated.
		block_info* blocks;

#if TORRENT_ABI_VERSION == 1
		// the speed classes. These may be used by the piece picker to
		// coalesce requests of similar download rates
		enum state_t { none, slow, medium, fast };

		// the download speed class this piece falls into.
		// this is used internally to cluster peers of the same
		// speed class together when requesting blocks.
		//
		// set to either ``fast``, ``medium``, ``slow`` or ``none``. It tells
		// which download rate category the peers downloading this piece falls
		// into. ``none`` means that no peer is currently downloading any part of
		// the piece. Peers prefer picking pieces from the same category as
		// themselves. The reason for this is to keep the number of partially
		// downloaded pieces down. Pieces set to ``none`` can be converted into
		// any of ``fast``, ``medium`` or ``slow`` as soon as a peer want to
		// download from it.
		state_t TORRENT_DEPRECATED_MEMBER piece_state;
#endif
	};

	// for std::hash (and to support using this type in unordered_map etc.)
	TORRENT_EXPORT std::size_t hash_value(torrent_handle const& h);

	// You will usually have to store your torrent handles somewhere, since it's
	// the object through which you retrieve information about the torrent and
	// aborts the torrent.
	//
	// .. warning::
	// 	Any member function that returns a value or fills in a value has to be
	// 	made synchronously. This means it has to wait for the main thread to
	// 	complete the query before it can return. This might potentially be
	// 	expensive if done from within a GUI thread that needs to stay
	// 	responsive. Try to avoid querying for information you don't need, and
	// 	try to do it in as few calls as possible. You can get most of the
	// 	interesting information about a torrent from the
	// 	torrent_handle::status() call.
	//
	// The default constructor will initialize the handle to an invalid state.
	// Which means you cannot perform any operation on it, unless you first
	// assign it a valid handle. If you try to perform any operation on an
	// uninitialized handle, it will throw ``invalid_handle``.
	//
	// .. warning::
	// 	All operations on a torrent_handle may throw system_error
	// 	exception, in case the handle is no longer referring to a torrent.
	// 	There is one exception is_valid() will never throw. Since the torrents
	// 	are processed by a background thread, there is no guarantee that a
	// 	handle will remain valid between two calls.
	//
	struct TORRENT_EXPORT torrent_handle
	{
		friend struct aux::session_impl;
		friend struct session_handle;
		friend class torrent;
		friend TORRENT_EXPORT std::size_t hash_value(torrent_handle const& th);

		// constructs a torrent handle that does not refer to a torrent.
		// i.e. is_valid() will return false.
		torrent_handle() noexcept = default;

		// hidden
		torrent_handle(torrent_handle const& t) = default;
		torrent_handle(torrent_handle&& t) noexcept = default;
		torrent_handle& operator=(torrent_handle const&) = default;
		torrent_handle& operator=(torrent_handle&&) noexcept = default;


#if TORRENT_ABI_VERSION == 1
		using flags_t = add_piece_flags_t;
		using status_flags_t = libtorrent::status_flags_t;
		using pause_flags_t = libtorrent::pause_flags_t;
		using save_resume_flags_t = libtorrent::resume_data_flags_t;
		using reannounce_flags_t = libtorrent::reannounce_flags_t;
#endif

		// instruct libtorrent to overwrite any data that may already have been
		// downloaded with the data of the new piece being added.
		static constexpr add_piece_flags_t overwrite_existing = 0_bit;

		// This function will write ``data`` to the storage as piece ``piece``,
		// as if it had been downloaded from a peer. ``data`` is expected to
		// point to a buffer of as many bytes as the size of the specified piece.
		// The data in the buffer is copied and passed on to the disk IO thread
		// to be written at a later point.
		//
		// By default, data that's already been downloaded is not overwritten by
		// this buffer. If you trust this data to be correct (and pass the piece
		// hash check) you may pass the overwrite_existing flag. This will
		// instruct libtorrent to overwrite any data that may already have been
		// downloaded with this data.
		//
		// Since the data is written asynchronously, you may know that is passed
		// or failed the hash check by waiting for piece_finished_alert or
		// hash_failed_alert.
		void add_piece(piece_index_t piece, char const* data, add_piece_flags_t flags = {}) const;

		// This function starts an asynchronous read operation of the specified
		// piece from this torrent. You must have completed the download of the
		// specified piece before calling this function.
		//
		// When the read operation is completed, it is passed back through an
		// alert, read_piece_alert. Since this alert is a response to an explicit
		// call, it will always be posted, regardless of the alert mask.
		//
		// Note that if you read multiple pieces, the read operations are not
		// guaranteed to finish in the same order as you initiated them.
		void read_piece(piece_index_t piece) const;

		// Returns true if this piece has been completely downloaded and written
		// to disk, and false otherwise.
		bool have_piece(piece_index_t piece) const;

#if TORRENT_ABI_VERSION == 1
		// internal
		TORRENT_DEPRECATED
		void get_full_peer_list(std::vector<peer_list_entry>& v) const;
#endif

		// takes a reference to a vector that will be cleared and filled with one
		// entry for each peer connected to this torrent, given the handle is
		// valid. If the torrent_handle is invalid, it will throw
		// system_error exception. Each entry in the vector contains
		// information about that particular peer. See peer_info.
		void get_peer_info(std::vector<peer_info>& v) const;

		// calculates ``distributed_copies``, ``distributed_full_copies`` and
		// ``distributed_fraction``.
		static constexpr status_flags_t query_distributed_copies = 0_bit;

		// includes partial downloaded blocks in ``total_done`` and
		// ``total_wanted_done``.
		static constexpr status_flags_t query_accurate_download_counters = 1_bit;

		// includes ``last_seen_complete``.
		static constexpr status_flags_t query_last_seen_complete = 2_bit;
		// populate the ``pieces`` field in torrent_status.
		static constexpr status_flags_t query_pieces = 3_bit;
		// includes ``verified_pieces`` (only applies to torrents in *seed
		// mode*).
		static constexpr status_flags_t query_verified_pieces = 4_bit;
		// includes ``torrent_file``, which is all the static information from
		// the .torrent file.
		static constexpr status_flags_t query_torrent_file = 5_bit;
		// includes ``name``, the name of the torrent. This is either derived
		// from the .torrent file, or from the ``&dn=`` magnet link argument
		// or possibly some other source. If the name of the torrent is not
		// known, this is an empty string.
		static constexpr status_flags_t query_name = 6_bit;
		// includes ``save_path``, the path to the directory the files of the
		// torrent are saved to.
		static constexpr status_flags_t query_save_path = 7_bit;

		// ``status()`` will return a structure with information about the status
		// of this torrent. If the torrent_handle is invalid, it will throw
		// system_error exception. See torrent_status. The ``flags``
		// argument filters what information is returned in the torrent_status.
		// Some information in there is relatively expensive to calculate, and if
		// you're not interested in it (and see performance issues), you can
		// filter them out.
		//
		// By default everything is included. The flags you can use to decide
		// what to *include* are defined in this class.
		torrent_status status(status_flags_t flags = status_flags_t::all()) const;

		// ``get_download_queue()`` takes a non-const reference to a vector which
		// it will fill with information about pieces that are partially
		// downloaded or not downloaded at all but partially requested. See
		// partial_piece_info for the fields in the returned vector.
		void get_download_queue(std::vector<partial_piece_info>& queue) const;

		// used to ask libtorrent to send an alert once the piece has been
		// downloaded, by passing alert_when_available. When set, the
		// read_piece_alert alert will be delivered, with the piece data, when
		// it's downloaded.
		static constexpr deadline_flags_t alert_when_available = 0_bit;

		// This function sets or resets the deadline associated with a specific
		// piece index (``index``). libtorrent will attempt to download this
		// entire piece before the deadline expires. This is not necessarily
		// possible, but pieces with a more recent deadline will always be
		// prioritized over pieces with a deadline further ahead in time. The
		// deadline (and flags) of a piece can be changed by calling this
		// function again.
		//
		// If the piece is already downloaded when this call is made, nothing
		// happens, unless the alert_when_available flag is set, in which case it
		// will have the same effect as calling read_piece() for ``index``.
		//
		// ``deadline`` is the number of milliseconds until this piece should be
		// completed.
		//
		// ``reset_piece_deadline`` removes the deadline from the piece. If it
		// hasn't already been downloaded, it will no longer be considered a
		// priority.
		//
		// ``clear_piece_deadlines()`` removes deadlines on all pieces in
		// the torrent. As if reset_piece_deadline() was called on all pieces.
		void set_piece_deadline(piece_index_t index, int deadline, deadline_flags_t flags = {}) const;
		void reset_piece_deadline(piece_index_t index) const;
		void clear_piece_deadlines() const;

#if TORRENT_ABI_VERSION == 1
		// This sets the bandwidth priority of this torrent. The priority of a
		// torrent determines how much bandwidth its peers are assigned when
		// distributing upload and download rate quotas. A high number gives more
		// bandwidth. The priority must be within the range [0, 255].
		//
		// The default priority is 0, which is the lowest priority.
		//
		// To query the priority of a torrent, use the
		// ``torrent_handle::status()`` call.
		//
		// Torrents with higher priority will not necessarily get as much
		// bandwidth as they can consume, even if there's is more quota. Other
		// peers will still be weighed in when bandwidth is being distributed.
		// With other words, bandwidth is not distributed strictly in order of
		// priority, but the priority is used as a weight.
		//
		// Peers whose Torrent has a higher priority will take precedence when
		// distributing unchoke slots. This is a strict prioritisation where
		// every interested peer on a high priority torrent will be unchoked
		// before any other, lower priority, torrents have any peers unchoked.
		// deprecated in 1.2
		TORRENT_DEPRECATED
		void set_priority(int prio) const;

#if !TORRENT_NO_FPU
		// fills the specified vector with the download progress [0, 1]
		// of each file in the torrent. The files are ordered as in
		// the torrent_info.
		TORRENT_DEPRECATED
		void file_progress(std::vector<float>& progress) const;
#endif

		TORRENT_DEPRECATED
		void file_status(std::vector<open_file_state>& status) const;
#endif

		// flags to be passed in file_progress().
		enum file_progress_flags_t
		{
			// only calculate file progress at piece granularity. This makes
			// the file_progress() call cheaper and also only takes bytes that
			// have passed the hash check into account, so progress cannot
			// regress in this mode.
			piece_granularity = 1
		};

		// This function fills in the supplied vector with the number of
		// bytes downloaded of each file in this torrent. The progress values are
		// ordered the same as the files in the torrent_info. This operation is
		// not very cheap. Its complexity is *O(n + mj)*. Where *n* is the number
		// of files, *m* is the number of downloading pieces and *j* is the
		// number of blocks in a piece.
		//
		// The ``flags`` parameter can be used to specify the granularity of the
		// file progress. If left at the default value of 0, the progress will be
		// as accurate as possible, but also more expensive to calculate. If
		// ``torrent_handle::piece_granularity`` is specified, the progress will
		// be specified in piece granularity. i.e. only pieces that have been
		// fully downloaded and passed the hash check count. When specifying
		// piece granularity, the operation is a lot cheaper, since libtorrent
		// already keeps track of this internally and no calculation is required.
		void file_progress(std::vector<std::int64_t>& progress, int flags = 0) const;

		// This function returns a vector with status about files
		// that are open for this torrent. Any file that is not open
		// will not be reported in the vector, i.e. it's possible that
		// the vector is empty when returning, if none of the files in the
		// torrent are currently open.
		//
		// See open_file_state
		std::vector<open_file_state> file_status() const;

		// If the torrent is in an error state (i.e. ``torrent_status::error`` is
		// non-empty), this will clear the error and start the torrent again.
		void clear_error() const;

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

		// TODO: 3 unify url_seed and http_seed with just web_seed, using the
		// web_seed_entry.

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

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

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

		// ``set_metadata`` expects the *info* section of metadata. i.e. The
		// buffer passed in will be hashed and verified against the info-hash. If
		// it fails, a ``metadata_failed_alert`` will be generated. If it passes,
		// a ``metadata_received_alert`` is generated. The function returns true
		// if the metadata is successfully set on the torrent, and false
		// otherwise. If the torrent already has metadata, this function will not
		// affect the torrent, and false will be returned.
		bool set_metadata(span<char const> metadata) const;

#if TORRENT_ABI_VERSION == 1
		TORRENT_DEPRECATED
		bool set_metadata(char const* metadata, int size) const
		{ return set_metadata({metadata, size}); }
#endif

		// Returns true if this handle refers to a valid torrent and false if it
		// hasn't been initialized or if the torrent it refers to has been
		// aborted. Note that a handle may become invalid after it has been added
		// to the session. Usually this is because the storage for the torrent is
		// somehow invalid or if the filenames are not allowed (and hence cannot
		// be opened/created) on your filesystem. If such an error occurs, a
		// file_error_alert is generated and all handles that refers to that
		// torrent will become invalid.
		bool is_valid() const;

		// will delay the disconnect of peers that we're still downloading
		// outstanding requests from. The torrent will not accept any more
		// requests and will disconnect all idle peers. As soon as a peer is done
		// transferring the blocks that were requested from it, it is
		// disconnected. This is a graceful shut down of the torrent in the sense
		// that no downloaded bytes are wasted.
		static constexpr pause_flags_t graceful_pause = 0_bit;
		static constexpr pause_flags_t clear_disk_cache = 1_bit;

		// ``pause()``, and ``resume()`` will disconnect all peers and reconnect
		// all peers respectively. When a torrent is paused, it will however
		// remember all share ratios to all peers and remember all potential (not
		// connected) peers. Torrents may be paused automatically if there is a
		// file error (e.g. disk full) or something similar. See
		// file_error_alert.
		//
		// To know if a torrent is paused or not, call
		// ``torrent_handle::status()`` and inspect ``torrent_status::paused``.
		//
		// .. note::
		// 	Torrents that are auto-managed may be automatically resumed again. It
		// 	does not make sense to pause an auto-managed torrent without making it
		// 	not auto-managed first. Torrents are auto-managed by default when added
		// 	to the session. For more information, see queuing_.
		//
		void pause(pause_flags_t flags = {}) const;
		void resume() const;

		// sets and gets the torrent state flags. See torrent_flags_t.
		// The ``set_flags`` overload that take a mask will affect all
		// flags part of the mask, and set their values to what the
		// ``flags`` argument is set to. This allows clearing and
		// setting flags in a single function call.
		// The ``set_flags`` overload that just takes flags, sets all
		// the specified flags and leave any other flags unchanged.
		// ``unset_flags`` clears the specified flags, while leaving
		// any other flags unchanged.
		//
		// The `seed_mode` flag is special, it can only be cleared once the
		// torrent has been added, and it can only be set as part of the
		// add_torrent_params flags, when adding the torrent.
		torrent_flags_t flags() const;
		void set_flags(torrent_flags_t flags, torrent_flags_t mask) const;
		void set_flags(torrent_flags_t flags) const;
		void unset_flags(torrent_flags_t flags) const;

		// Instructs libtorrent to flush all the disk caches for this torrent and
		// close all file handles. This is done asynchronously and you will be
		// notified that it's complete through cache_flushed_alert.
		//
		// Note that by the time you get the alert, libtorrent may have cached
		// more data for the torrent, but you are guaranteed that whatever cached
		// data libtorrent had by the time you called
		// ``torrent_handle::flush_cache()`` has been written to disk.
		void flush_cache() const;

		// ``force_recheck`` puts the torrent back in a state where it assumes to
		// have no resume data. All peers will be disconnected and the torrent
		// will stop announcing to the tracker. The torrent will be added to the
		// checking queue, and will be checked (all the files will be read and
		// compared to the piece hashes). Once the check is complete, the torrent
		// will start connecting to peers again, as normal.
		// The torrent will be placed last in queue, i.e. its queue position
		// will be the highest of all torrents in the session.
		void force_recheck() const;

		// the disk cache will be flushed before creating the resume data.
		// This avoids a problem with file timestamps in the resume data in
		// case the cache hasn't been flushed yet.
		static constexpr resume_data_flags_t flush_disk_cache = 0_bit;

		// the resume data will contain the metadata from the torrent file as
		// well. This is default for any torrent that's added without a
		// torrent file (such as a magnet link or a URL).
		static constexpr resume_data_flags_t save_info_dict = 1_bit;

		// if nothing significant has changed in the torrent since the last
		// time resume data was saved, fail this attempt. Significant changes
		// primarily include more data having been downloaded, file or piece
		// priorities having changed etc. If the resume data doesn't need
		// saving, a save_resume_data_failed_alert is posted with the error
		// resume_data_not_modified.
		static constexpr resume_data_flags_t only_if_modified = 2_bit;

		// ``save_resume_data()`` asks libtorrent to generate fast-resume data for
		// this torrent.
		//
		// This operation is asynchronous, ``save_resume_data`` will return
		// immediately. The resume data is delivered when it's done through an
		// save_resume_data_alert.
		//
		// The fast resume data will be empty in the following cases:
		//
		//	1. The torrent handle is invalid.
		//	2. The torrent hasn't received valid metadata and was started without
		//	   metadata (see libtorrent's metadata-from-peers_ extension)
		//
		// Note that by the time you receive the fast resume data, it may already
		// be invalid if the torrent is still downloading! The recommended
		// practice is to first pause the session, then generate the fast resume
		// data, and then close it down. Make sure to not remove_torrent() before
		// you receive the save_resume_data_alert though. There's no need to
		// pause when saving intermittent resume data.
		//
		//.. warning::
		//   If you pause every torrent individually instead of pausing the
		//   session, every torrent will have its paused state saved in the
		//   resume data!
		//
		//.. warning::
		//   The resume data contains the modification timestamps for all files.
		//   If one file has been modified when the torrent is added again, the
		//   will be rechecked. When shutting down, make sure to flush the disk
		//   cache before saving the resume data. This will make sure that the
		//   file timestamps are up to date and won't be modified after saving
		//   the resume data. The recommended way to do this is to pause the
		//   torrent, which will flush the cache and disconnect all peers.
		//
		//.. note::
		//   It is typically a good idea to save resume data whenever a torrent
		//   is completed or paused. In those cases you don't need to pause the
		//   torrent or the session, since the torrent will do no more writing to
		//   its files. If you save resume data for torrents when they are
		//   paused, you can accelerate the shutdown process by not saving resume
		//   data again for paused torrents. Completed torrents should have their
		//   resume data saved when they complete and on exit, since their
		//   statistics might be updated.
		//
		//	In full allocation mode the resume data is never invalidated by
		//	subsequent writes to the files, since pieces won't move around. This
		//	means that you don't need to pause before writing resume data in full
		//	or sparse mode. If you don't, however, any data written to disk after
		//	you saved resume data and before the session closed is lost.
		//
		// It also means that if the resume data is out dated, libtorrent will
		// not re-check the files, but assume that it is fairly recent. The
		// assumption is that it's better to loose a little bit than to re-check
		// the entire file.
		//
		// It is still a good idea to save resume data periodically during
		// download as well as when closing down.
		//
		// Example code to pause and save resume data for all torrents and wait
		// for the alerts:
		//
		// .. code:: c++
		//
		//	extern int outstanding_resume_data; // global counter of outstanding resume data
		//	std::vector<torrent_handle> handles = ses.get_torrents();
		//	ses.pause();
		//	for (torrent_handle const& h : handles)
		//	{
		//		if (!h.is_valid()) continue;
		//		torrent_status s = h.status();
		//		if (!s.has_metadata || !s.need_save_resume_data()) continue;
		//
		//		h.save_resume_data();
		//		++outstanding_resume_data;
		//	}
		//
		//	while (outstanding_resume_data > 0)
		//	{
		//		alert const* a = ses.wait_for_alert(seconds(10));
		//
		//		// if we don't get an alert within 10 seconds, abort
		//		if (a == nullptr) break;
		//
		//		std::vector<alert*> alerts;
		//		ses.pop_alerts(&alerts);
		//
		//		for (alert* i : alerts)
		//		{
		//			if (alert_cast<save_resume_data_failed_alert>(a))
		//			{
		//				process_alert(a);
		//				--outstanding_resume_data;
		//				continue;
		//			}
		//
		//			save_resume_data_alert const* rd = alert_cast<save_resume_data_alert>(a);
		//			if (rd == nullptr)
		//			{
		//				process_alert(a);
		//				continue;
		//			}
		//
		//			torrent_handle h = rd->handle;
		//			torrent_status st = h.status(torrent_handle::query_save_path
		//				| torrent_handle::query_name);
		//			std::ofstream out((st.save_path
		//				+ "/" + st.name + ".fastresume").c_str()
		//				, std::ios_base::binary);
		//			std::vector<char> buf = write_resume_data_buf(rd->params);
		//			out.write(buf.data(), buf.size());
		//			--outstanding_resume_data;
		//		}
		//	}
		//
		//.. note::
		//	Note how ``outstanding_resume_data`` is a global counter in this
		//	example. This is deliberate, otherwise there is a race condition for
		//	torrents that was just asked to save their resume data, they posted
		//	the alert, but it has not been received yet. Those torrents would
		//	report that they don't need to save resume data again, and skipped by
		//	the initial loop, and thwart the counter otherwise.
		void save_resume_data(resume_data_flags_t flags = {}) const;

		// This function returns true if any whole chunk has been downloaded
		// since the torrent was first loaded or since the last time the resume
		// data was saved. When saving resume data periodically, it makes sense
		// to skip any torrent which hasn't downloaded anything since the last
		// time.
		//
		//.. note::
		//	A torrent's resume data is considered saved as soon as the
		//	save_resume_data_alert is posted. It is important to make sure this
		//	alert is received and handled in order for this function to be
		//	meaningful.
		bool need_save_resume_data() const;

		// Every torrent that is added is assigned a queue position exactly one
		// greater than the greatest queue position of all existing torrents.
		// Torrents that are being seeded have -1 as their queue position, since
		// they're no longer in line to be downloaded.
		//
		// When a torrent is removed or turns into a seed, all torrents with
		// greater queue positions have their positions decreased to fill in the
		// space in the sequence.
		//
		// ``queue_position()`` returns the torrent's position in the download
		// queue. The torrents with the smallest numbers are the ones that are
		// being downloaded. The smaller number, the closer the torrent is to the
		// front of the line to be started.
		//
		// The queue position is also available in the torrent_status.
		//
		// The ``queue_position_*()`` functions adjust the torrents position in
		// the queue. Up means closer to the front and down means closer to the
		// back of the queue. Top and bottom refers to the front and the back of
		// the queue respectively.
		queue_position_t queue_position() const;
		void queue_position_up() const;
		void queue_position_down() const;
		void queue_position_top() const;
		void queue_position_bottom() const;

		// updates the position in the queue for this torrent. The relative order
		// of all other torrents remain intact but their numerical queue position
		// shifts to make space for this torrent's new position
		void queue_position_set(queue_position_t p) const;

		// For SSL torrents, use this to specify a path to a .pem file to use as
		// this client's certificate. The certificate must be signed by the
		// certificate in the .torrent file to be valid.
		//
		// The set_ssl_certificate_buffer() overload takes the actual certificate,
		// private key and DH params as strings, rather than paths to files.
		//
		// ``cert`` is a path to the (signed) certificate in .pem format
		// corresponding to this torrent.
		//
		// ``private_key`` is a path to the private key for the specified
		// certificate. This must be in .pem format.
		//
		// ``dh_params`` is a path to the Diffie-Hellman parameter file, which
		// needs to be in .pem format. You can generate this file using the
		// openssl command like this: ``openssl dhparam -outform PEM -out
		// dhparams.pem 512``.
		//
		// ``passphrase`` may be specified if the private key is encrypted and
		// requires a passphrase to be decrypted.
		//
		// Note that when a torrent first starts up, and it needs a certificate,
		// it will suspend connecting to any peers until it has one. It's
		// typically desirable to resume the torrent after setting the SSL
		// certificate.
		//
		// If you receive a torrent_need_cert_alert, you need to call this to
		// provide a valid cert. If you don't have a cert you won't be allowed to
		// connect to any peers.
		void set_ssl_certificate(std::string const& certificate
			, std::string const& private_key
			, std::string const& dh_params
			, std::string const& passphrase = "");
		void set_ssl_certificate_buffer(std::string const& certificate
			, std::string const& private_key
			, std::string const& dh_params);

		// Returns the storage implementation for this torrent. This depends on the
		// storage constructor function that was passed to add_torrent.
		storage_interface* get_storage_impl() const;

		// Returns a pointer to the torrent_info object associated with this
		// torrent. The torrent_info object may be a copy of the internal object.
		// If the torrent doesn't have metadata, the pointer will not be
		// initialized (i.e. a nullptr). The torrent may be in a state
		// without metadata only if it was started without a .torrent file, e.g.
		// by being added by magnet link
		std::shared_ptr<const torrent_info> torrent_file() const;

#if TORRENT_ABI_VERSION == 1

		// ================ start deprecation ============

		// deprecated in 1.2
		// use set_flags() and unset_flags() instead
		TORRENT_DEPRECATED
		void stop_when_ready(bool b) const;
		TORRENT_DEPRECATED
		void set_upload_mode(bool b) const;
		TORRENT_DEPRECATED
		void set_share_mode(bool b) const;
		TORRENT_DEPRECATED
		void apply_ip_filter(bool b) const;
		TORRENT_DEPRECATED
		void auto_managed(bool m) const;
		TORRENT_DEPRECATED
		void set_pinned(bool p) const;
		TORRENT_DEPRECATED
		void set_sequential_download(bool sd) const;


		// deprecated in 1.0
		// use status() instead (with query_save_path)
		TORRENT_DEPRECATED
		std::string save_path() const;

		// deprecated in 1.0
		// use status() instead (with query_name)
		// returns the name of this torrent, in case it doesn't
		// have metadata it returns the name assigned to it
		// when it was added.
		TORRENT_DEPRECATED
		std::string name() const;

		// use torrent_file() instead
		TORRENT_DEPRECATED
		const torrent_info& get_torrent_info() const;

		// deprecated in 0.16, feature will be removed
		TORRENT_DEPRECATED
		int get_peer_upload_limit(tcp::endpoint ip) const;
		TORRENT_DEPRECATED
		int get_peer_download_limit(tcp::endpoint ip) const;
		TORRENT_DEPRECATED
		void set_peer_upload_limit(tcp::endpoint ip, int limit) const;
		TORRENT_DEPRECATED
		void set_peer_download_limit(tcp::endpoint ip, int limit) const;

		// deprecated in 0.16, feature will be removed
		TORRENT_DEPRECATED
		void set_ratio(float up_down_ratio) const;

		// deprecated in 0.16. use status() instead, and inspect the
		// torrent_status::flags field. Alternatively, call flags() directly on
		// the torrent_handle
		TORRENT_DEPRECATED
		bool is_seed() const;
		TORRENT_DEPRECATED
		bool is_finished() const;
		TORRENT_DEPRECATED
		bool is_paused() const;
		TORRENT_DEPRECATED
		bool is_auto_managed() const;
		TORRENT_DEPRECATED
		bool is_sequential_download() const;
		TORRENT_DEPRECATED
		bool has_metadata() const;
		TORRENT_DEPRECATED
		bool super_seeding() const;

		// deprecated in 0.14
		// use save_resume_data() instead. It is async. and
		// will return the resume data in an alert
		TORRENT_DEPRECATED
		entry write_resume_data() const;

		// ``use_interface()`` sets the network interface this torrent will use
		// when it opens outgoing connections. By default, it uses the same
		// interface as the session uses to listen on. The parameter must be a
		// string containing one or more, comma separated, ip-address (either an
		// IPv4 or IPv6 address). When specifying multiple interfaces, the
		// torrent will round-robin which interface to use for each outgoing
		// connection. This is useful for clients that are multi-homed.
		TORRENT_DEPRECATED
		void use_interface(const char* net_interface) const;
		// ================ end deprecation ============
#endif

		// Fills the specified ``std::vector<int>`` with the availability for
		// each piece in this torrent. libtorrent does not keep track of
		// availability for seeds, so if the torrent is seeding the availability
		// for all pieces is reported as 0.
		//
		// The piece availability is the number of peers that we are connected
		// that has advertised having a particular piece. This is the information
		// that libtorrent uses in order to prefer picking rare pieces.
		void piece_availability(std::vector<int>& avail) const;

		// These functions are used to set and get the priority of individual
		// pieces. By default all pieces have priority 4. That means that the
		// random rarest first algorithm is effectively active for all pieces.
		// You may however change the priority of individual pieces. There are 8
		// priority levels. 0 means not to download the piece at all. Otherwise,
		// lower priority values means less likely to be picked. Piece priority
		// takes precedence over piece availability. Every piece with priority 7
		// will be attempted to be picked before a priority 6 piece and so on.
		//
		// The default priority of pieces is 4.
		//
		// Piece priorities can not be changed for torrents that have not
		// downloaded the metadata yet. Magnet links won't have metadata
		// immediately. see the metadata_received_alert.
		//
		// ``piece_priority`` sets or gets the priority for an individual piece,
		// specified by ``index``.
		//
		// ``prioritize_pieces`` takes a vector of integers, one integer per
		// piece in the torrent. All the piece priorities will be updated with
		// the priorities in the vector.
		// The second overload of ``prioritize_pieces`` that takes a vector of pairs
		// will update the priorities of only select pieces, and leave all other
		// unaffected. Each pair is (piece, priority). That is, the first item is
		// the piece index and the second item is the priority of that piece.
		// Invalid entries, where the piece index or priority is out of range, are
		// not allowed.
		//
		// ``get_piece_priorities`` returns a vector with one element for each piece
		// in the torrent. Each element is the current priority of that piece.
		//
		// It's possible to cancel the effect of *file* priorities by setting the
		// priorities for the affected pieces. Care has to be taken when mixing
		// usage of file- and piece priorities.
		void piece_priority(piece_index_t index, download_priority_t priority) const;
		download_priority_t piece_priority(piece_index_t index) const;
		void prioritize_pieces(std::vector<download_priority_t> const& pieces) const;
		void prioritize_pieces(std::vector<std::pair<piece_index_t, download_priority_t>> const& pieces) const;
		std::vector<download_priority_t> get_piece_priorities() const;

		void set_piece_premiere(piece_index_t index, bool prem) const;
		bool is_piece_premiere(piece_index_t index) const;

#if TORRENT_ABI_VERSION == 1
		TORRENT_DEPRECATED
		void prioritize_pieces(std::vector<int> const& pieces) const;
		TORRENT_DEPRECATED
		void prioritize_pieces(std::vector<std::pair<piece_index_t, int>> const& pieces) const;
		TORRENT_DEPRECATED
		std::vector<int> piece_priorities() const;
#endif

		// ``index`` must be in the range [0, number_of_files).
		//
		// ``file_priority()`` queries or sets the priority of file ``index``.
		//
		// ``prioritize_files()`` takes a vector that has at as many elements as
		// there are files in the torrent. Each entry is the priority of that
		// file. The function sets the priorities of all the pieces in the
		// torrent based on the vector.
		//
		// ``get_file_priorities()`` returns a vector with the priorities of all
		// files.
		//
		// The priority values are the same as for piece_priority(). See
		// download_priority_t.
		//
		// Whenever a file priority is changed, all other piece priorities are
		// reset to match the file priorities. In order to maintain special
		// priorities for particular pieces, piece_priority() has to be called
		// again for those pieces.
		//
		// You cannot set the file priorities on a torrent that does not yet have
		// metadata or a torrent that is a seed. ``file_priority(int, int)`` and
		// prioritize_files() are both no-ops for such torrents.
		//
		// Since changing file priorities may involve disk operations (of moving
		// files in- and out of the part file), the internal accounting of file
		// priorities happen asynchronously. i.e. setting file priorities and then
		// immediately querying them may not yield the same priorities just set.
		// However, the *piece* priorities are updated immediately.
		//
		// when combining file- and piece priorities, the resume file will record
		// both. When loading the resume data, the file priorities will be applied
		// first, then the piece priorities.
		void file_priority(file_index_t index, download_priority_t priority) const;
		download_priority_t file_priority(file_index_t index) const;
		void prioritize_files(std::vector<download_priority_t> const& files) const;
		std::vector<download_priority_t> get_file_priorities() const;

#if TORRENT_ABI_VERSION == 1
		TORRENT_DEPRECATED
		void prioritize_files(std::vector<int> const& files) const;
		TORRENT_DEPRECATED
		std::vector<int> file_priorities() const;
#endif

		// by default, force-reannounce will still honor the min-interval
		// published by the tracker. If this flag is set, it will be ignored
		// and the tracker is announced immediately.
		static constexpr reannounce_flags_t ignore_min_interval = 0_bit;

		// ``force_reannounce()`` will force this torrent to do another tracker
		// request, to receive new peers. The ``seconds`` argument specifies how
		// many seconds from now to issue the tracker announces.
		//
		// If the tracker's ``min_interval`` has not passed since the last
		// announce, the forced announce will be scheduled to happen immediately
		// as the ``min_interval`` expires. This is to honor trackers minimum
		// re-announce interval settings.
		//
		// The ``tracker_index`` argument specifies which tracker to re-announce.
		// If set to -1 (which is the default), all trackers are re-announce.
		//
		// The ``flags`` argument can be used to affect the re-announce. See
		// ignore_min_interval.
		//
		// ``force_dht_announce`` will announce the torrent to the DHT
		// immediately.
		void force_reannounce(int seconds = 0, int tracker_index = -1, reannounce_flags_t = {}) const;
		void force_dht_announce() const;

#if TORRENT_ABI_VERSION == 1
		// forces a reannounce in the specified amount of time.
		// This overrides the default announce interval, and no
		// announce will take place until the given time has
		// timed out.
		TORRENT_DEPRECATED
		void force_reannounce(boost::posix_time::time_duration) const;
#endif

		// ``scrape_tracker()`` will send a scrape request to a tracker. By
		// default (``idx`` = -1) it will scrape the last working tracker. If
		// ``idx`` is >= 0, the tracker with the specified index will scraped.
		//
		// A scrape request queries the tracker for statistics such as total
		// number of incomplete peers, complete peers, number of downloads etc.
		//
		// This request will specifically update the ``num_complete`` and
		// ``num_incomplete`` fields in the torrent_status struct once it
		// completes. When it completes, it will generate a scrape_reply_alert.
		// If it fails, it will generate a scrape_failed_alert.
		void scrape_tracker(int idx = -1) const;

		// ``set_upload_limit`` will limit the upload bandwidth used by this
		// particular torrent to the limit you set. It is given as the number of
		// bytes per second the torrent is allowed to upload.
		// ``set_download_limit`` works the same way but for download bandwidth
		// instead of upload bandwidth. Note that setting a higher limit on a
		// torrent then the global limit
		// (``settings_pack::upload_rate_limit``) will not override the global
		// rate limit. The torrent can never upload more than the global rate
		// limit.
		//
		// ``upload_limit`` and ``download_limit`` will return the current limit
		// setting, for upload and download, respectively.
		//
		// Local peers are not rate limited by default. see peer-classes_.
		void set_upload_limit(int limit) const;
		int upload_limit() const;
		void set_download_limit(int limit) const;
		int download_limit() const;

		// ``connect_peer()`` is a way to manually connect to peers that one
		// believe is a part of the torrent. If the peer does not respond, or is
		// not a member of this torrent, it will simply be disconnected. No harm
		// can be done by using this other than an unnecessary connection attempt
		// is made. If the torrent is uninitialized or in queued or checking
		// mode, this will throw system_error. The second (optional)
		// argument will be bitwise ORed into the source mask of this peer.
		// Typically this is one of the source flags in peer_info. i.e.
		// ``tracker``, ``pex``, ``dht`` etc.
		//
		// For possible values of ``flags``, see pex_flags_t.
		void connect_peer(tcp::endpoint const& adr, peer_source_flags_t source = {}
			, pex_flags_t flags = pex_encryption | pex_utp | pex_holepunch) const;

		// ``set_max_uploads()`` sets the maximum number of peers that's unchoked
		// at the same time on this torrent. If you set this to -1, there will be
		// no limit. This defaults to infinite. The primary setting controlling
		// this is the global unchoke slots limit, set by unchoke_slots_limit in
		// settings_pack.
		//
		// ``max_uploads()`` returns the current settings.
		void set_max_uploads(int max_uploads) const;
		int max_uploads() const;

		// ``set_max_connections()`` sets the maximum number of connection this
		// torrent will open. If all connections are used up, incoming
		// connections may be refused or poor connections may be closed. This
		// must be at least 2. The default is unlimited number of connections. If
		// -1 is given to the function, it means unlimited. There is also a
		// global limit of the number of connections, set by
		// ``connections_limit`` in settings_pack.
		//
		// ``max_connections()`` returns the current settings.
		void set_max_connections(int max_connections) const;
		int max_connections() const;

#if TORRENT_ABI_VERSION == 1
		// sets a username and password that will be sent along in the HTTP-request
		// of the tracker announce. Set this if the tracker requires authorization.
		TORRENT_DEPRECATED
		void set_tracker_login(std::string const& name
			, std::string const& password) const;
#endif

		// Moves the file(s) that this torrent are currently seeding from or
		// downloading to. If the given ``save_path`` is not located on the same
		// drive as the original save path, the files will be copied to the new
		// drive and removed from their original location. This will block all
		// other disk IO, and other torrents download and upload rates may drop
		// while copying the file.
		//
		// Since disk IO is performed in a separate thread, this operation is
		// also asynchronous. Once the operation completes, the
		// ``storage_moved_alert`` is generated, with the new path as the
		// message. If the move fails for some reason,
		// ``storage_moved_failed_alert`` is generated instead, containing the
		// error message.
		//
		// The ``flags`` argument determines the behavior of the copying/moving
		// of the files in the torrent. see move_flags_t.
		//
		// ``always_replace_files`` is the default and replaces any file that
		// exist in both the source directory and the target directory.
		//
		// ``fail_if_exist`` first check to see that none of the copy operations
		// would cause an overwrite. If it would, it will fail. Otherwise it will
		// proceed as if it was in ``always_replace_files`` mode. Note that there
		// is an inherent race condition here. If the files in the target
		// directory appear after the check but before the copy or move
		// completes, they will be overwritten. When failing because of files
		// already existing in the target path, the ``error`` of
		// ``move_storage_failed_alert`` is set to
		// ``boost::system::errc::file_exists``.
		//
		// The intention is that a client may use this as a probe, and if it
		// fails, ask the user which mode to use. The client may then re-issue
		// the ``move_storage`` call with one of the other modes.
		//
		// ``dont_replace`` always keeps the existing file in the target
		// directory, if there is one. The source files will still be removed in
		// that case. Note that it won't automatically re-check files. If an
		// incomplete torrent is moved into a directory with the complete files,
		// pause, move, force-recheck and resume. Without the re-checking, the
		// torrent will keep downloading and files in the new download directory
		// will be overwritten.
		//
		// Files that have been renamed to have absolute paths are not moved by
		// this function. Keep in mind that files that don't belong to the
		// torrent but are stored in the torrent's directory may be moved as
		// well. This goes for files that have been renamed to absolute paths
		// that still end up inside the save path.
		void move_storage(std::string const& save_path
			, move_flags_t flags = move_flags_t::always_replace_files
			) const;

#if TORRENT_ABI_VERSION == 1
		// deprecated in 1.2
		TORRENT_DEPRECATED
		void move_storage(std::string const& save_path, int flags) const;
#endif

		// Renames the file with the given index asynchronously. The rename
		// operation is complete when either a file_renamed_alert or
		// file_rename_failed_alert is posted.
		void rename_file(file_index_t index, std::string const& new_name) const;

#if TORRENT_ABI_VERSION == 1
		// all wstring APIs are deprecated since 0.16.11
		// instead, use the wchar -> utf8 conversion functions
		// and pass in utf8 strings
		TORRENT_DEPRECATED
		void move_storage(std::wstring const& save_path, int flags = 0) const;
		TORRENT_DEPRECATED
		void rename_file(file_index_t index, std::wstring const& new_name) const;

		// Enables or disabled super seeding/initial seeding for this torrent.
		// The torrent needs to be a seed for this to take effect.
		TORRENT_DEPRECATED
		void super_seeding(bool on) const;
#endif // TORRENT_ABI_VERSION

		// ``info_hash()`` returns the info-hash of the torrent. If this handle
		// is to a torrent that hasn't loaded yet (for instance by being added)
		// by a URL, the returned value is undefined.
		sha1_hash info_hash() const;

		// comparison operators. The order of the torrents is unspecified
		// but stable.
		bool operator==(const torrent_handle& h) const
		{ return !m_torrent.owner_before(h.m_torrent) && !h.m_torrent.owner_before(m_torrent); }
		bool operator!=(const torrent_handle& h) const
		{ return m_torrent.owner_before(h.m_torrent) || h.m_torrent.owner_before(m_torrent); }
		bool operator<(const torrent_handle& h) const
		{ return m_torrent.owner_before(h.m_torrent); }

		// returns a unique identifier for this torrent. It's not a dense index.
		// It's not preserved across sessions.
		std::uint32_t id() const
		{
			uintptr_t ret = reinterpret_cast<uintptr_t>(m_torrent.lock().get());
			// a torrent object is about 1024 (2^10) bytes, so
			// it's safe to shift 10 bits
			return std::uint32_t(ret >> 10);
		}

		// This function is intended only for use by plugins and the alert
		// dispatch function. This type does not have a stable ABI and should
		// be relied on as little as possible. Accessing the handle returned by
		// this function is not thread safe outside of libtorrent's internal
		// thread (which is used to invoke plugin callbacks).
		// The ``torrent`` class is not only eligible for changing ABI across
		// minor versions of libtorrent, its layout is also dependent on build
		// configuration. This adds additional requirements on a client to be
		// built with the exact same build configuration as libtorrent itself.
		// i.e. the ``TORRENT_`` macros must match between libtorrent and the
		// client builds.
		std::shared_ptr<torrent> native_handle() const;

	private:

		template<typename Fun, typename... Args>
		void async_call(Fun f, Args&&... a) const;

		template<typename Fun, typename... Args>
		void sync_call(Fun f, Args&&... a) const;

		template<typename Ret, typename Fun, typename... Args>
		Ret sync_call_ret(Ret def, Fun f, Args&&... a) const;

		explicit torrent_handle(std::weak_ptr<torrent> const& t)
		{ if (!t.expired()) m_torrent = t; }

		std::weak_ptr<torrent> m_torrent;
	};
}

namespace std
{
	template <>
	struct hash<libtorrent::torrent_handle>
	{
		std::size_t operator()(libtorrent::torrent_handle const& th) const
		{
			return libtorrent::hash_value(th);
		}
	};
}

#endif // TORRENT_TORRENT_HANDLE_HPP_INCLUDED