| libtorrent

Author: | Arvid Norberg, arvid@libtorrent.org
Version: | 1.1.5

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# Core

Table of contents

- Core
  - add_torrent_params
  - announce_entry
  - cache_status
  - bt_peer_connection_handle
  - peer_info
  - peer_request
  - session_proxy
  - session
  - session_handle
  - stats_metric
  - block_info
  - partial_piece_info
  - torrent_handle
  - web_seed_entry
  - torrent_info
  - torrent_status
  - dht_storage_counters
  - dht_storage_interface
  - generate_fingerprint()
  - to_hex()
  - from_hex()
  - make_magnet_uri()
  - session_stats_metrics()
  - find_metric_idx()
  - hash_value()
  - hash_value()
  - is_utp_stream_logging()
  - set_utp_stream_logging()
  - version()
  - dht_default_storage_constructor()
  - sign_mutable_item()
  - verify_message()

## add_torrent_params

Declared in "libtorrent/add_torrent_params.hpp"

The add_torrent_params is a parameter pack for adding torrents to a session. The key fields when adding a torrent are:

- ti - when you have a .torrent file
- url - when you have a magnet link
- info_hash - when all you have is an info-hash (this is similar to a magnet link)

one of those fields need to be set. Another mandatory field is `save_path`. The add_torrent_params object is passed into one of the `session::add_torrent()` overloads or `session::async_add_torrent()`.

If you only specify the info-hash, the torrent file will be downloaded from peers, which requires them to support the metadata extension. For the metadata extension to work, libtorrent must be built with extensions enabled (`TORRENT_DISABLE_EXTENSIONS` must not be defined). It also takes an optional `name` argument. This may be left empty in case no name should be assigned to the torrent. In case it's not, the name is used for the torrent as long as it doesn't have metadata. See `torrent_handle::name`.

    struct add_torrent_params
    {
       add_torrent_params (storage_constructor_type sc = default_storage_constructor);

       enum flags_t
       {
          flag_seed_mode,
          flag_override_resume_data,
          flag_upload_mode,
          flag_share_mode,
          flag_apply_ip_filter,
          flag_paused,
          flag_auto_managed,
          flag_duplicate_is_error,
          flag_merge_resume_trackers,
          flag_update_subscribe,
          flag_super_seeding,
          flag_sequential_download,
          flag_use_resume_save_path,
          flag_pinned,
          flag_merge_resume_http_seeds,
          flag_stop_when_ready,
       };

       int version;
       boost::shared_ptr<torrent_info> ti;
       std::vector<std::string> trackers;
       std::vector<std::string> url_seeds;
       std::vector<std::pair<std::string, int> > dht_nodes;
       std::string name;
       std::string save_path;
       std::vector<char> resume_data;
       storage_mode_t storage_mode;
       storage_constructor_type storage;
       void* userdata;
       std::vector<boost::uint8_t> file_priorities;
       std::string trackerid;
       std::string url;
       std::string uuid;
       std::string source_feed_url;
       boost::uint64_t flags;
       sha1_hash info_hash;
       int max_uploads;
       int max_connections;
       int upload_limit;
       int download_limit;
    };

### add_torrent_params()

    add_torrent_params (storage_constructor_type sc = default_storage_constructor);

The constructor can be used to initialize the storage constructor, which determines the storage mechanism for the downloaded or seeding data for the torrent. For more information, see the `storage` field.

### enum flags_t

Declared in "libtorrent/add_torrent_params.hpp"

name | value | description
--- | --- | ---

flag_seed_mode

1

If `flag_seed_mode` is set, libtorrent will assume that all files are present for this torrent and that they all match the hashes in the torrent file. Each time a peer requests to download a block, the piece is verified against the hash, unless it has been verified already. If a hash fails, the torrent will automatically leave the seed mode and recheck all the files. The use case for this mode is if a torrent is created and seeded, or if the user already know that the files are complete, this is a way to avoid the initial file checks, and significantly reduce the startup time.

Setting `flag_seed_mode` on a torrent without metadata (a .torrent file) is a no-op and will be ignored.

If resume data is passed in with this torrent, the seed mode saved in there will override the seed mode you set here.

flag_override_resume_data

2

If `flag_override_resume_data` is set, flags set for this torrent in this `add_torrent_params` object will take precedence over whatever states are saved in the resume data. For instance, the `paused`, `auto_managed`, `sequential_download`, `seed_mode`, `super_seeding`, `max_uploads`, `max_connections`, `upload_limit` and `download_limit` are all affected by this flag. The intention of this flag is to have any field in add_torrent_params configuring the torrent override the corresponding configuration from the resume file, with the one exception of save resume data, which has its own flag (for historic reasons). "file_priorities" and "save_path" are not affected by this flag.

flag_upload_mode

4

If `flag_upload_mode` is set, the torrent will be initialized in upload-mode, which means it will not make any piece requests. This state is typically entered on disk I/O errors, and if the torrent is also auto managed, it will be taken out of this state periodically. This mode can be used to avoid race conditions when adjusting priorities of pieces before allowing the torrent to start downloading.

If the torrent is auto-managed (`flag_auto_managed`), the torrent will eventually be taken out of upload-mode, regardless of how it got there. If it's important to manually control when the torrent leaves upload mode, don't make it auto managed.

flag_share_mode

8

determines if the torrent should be added in share mode or not. Share mode indicates that we are not interested in downloading the torrent, but merely want to improve our share ratio (i.e. increase it). A torrent started in share mode will do its best to never download more than it uploads to the swarm. If the swarm does not have enough demand for upload capacity, the torrent will not download anything. This mode is intended to be safe to add any number of torrents to, without manual screening, without the risk of downloading more than is uploaded.

A torrent in share mode sets the priority to all pieces to 0, except for the pieces that are downloaded, when pieces are decided to be downloaded. This affects the progress bar, which might be set to "100% finished" most of the time. Do not change file or piece priorities for torrents in share mode, it will make it not work.

The share mode has one setting, the share ratio target, see `settings_pack::share_mode_target` for more info.

flag_apply_ip_filter | 16 | determines if the IP filter should apply to this torrent or not. By default all torrents are subject to filtering by the IP filter (i.e. this flag is set by default). This is useful if certain torrents needs to be exempt for some reason, being an auto-update torrent for instance.
flag_paused | 32 | specifies whether or not the torrent is to be started in a paused state. I.e. it won't connect to the tracker or any of the peers until it's resumed. This is typically a good way of avoiding race conditions when setting configuration options on torrents before starting them.

flag_auto_managed

64

If the torrent is auto-managed (`flag_auto_managed`), the torrent may be resumed at any point, regardless of how it paused. If it's important to manually control when the torrent is paused and resumed, don't make it auto managed.

If `flag_auto_managed` is set, the torrent will be queued, started and seeded automatically by libtorrent. When this is set, the torrent should also be started as paused. The default queue order is the order the torrents were added. They are all downloaded in that order. For more details, see queuing.

If you pass in resume data, the auto_managed state of the torrent when the resume data was saved will override the auto_managed state you pass in here. You can override this by setting `override_resume_data`.

flag_duplicate_is_error | 128 |

flag_merge_resume_trackers

256

defaults to off and specifies whether tracker URLs loaded from resume data should be added to the trackers in the torrent or replace the trackers. When replacing trackers (i.e. this flag is not set), any trackers passed in via add_torrent_params are also replaced by any trackers in the resume data. The default behavior is to have the resume data override the .torrent file _and_ the trackers added in add_torrent_params.

flag_update_subscribe | 512 | on by default and means that this torrent will be part of state updates when calling post_torrent_updates().
flag_super_seeding | 1024 | sets the torrent into super seeding mode. If the torrent is not a seed, this flag has no effect. It has the same effect as calling `torrent_handle::super_seeding(true)` on the torrent handle immediately after adding it.
flag_sequential_download | 2048 | sets the sequential download state for the torrent. It has the same effect as calling `torrent_handle::sequential_download(true)` on the torrent handle immediately after adding it.
flag_use_resume_save_path | 4096 | if this flag is set, the save path from the resume data file, if present, is honored. This defaults to not being set, in which case the save_path specified in add_torrent_params is always used.
flag_pinned | 8192 | indicates that this torrent should never be unloaded from RAM, even if unloading torrents are allowed in general. Setting this makes the torrent exempt from loading/unloading management.

flag_merge_resume_http_seeds

32768

defaults to off and specifies whether web seed URLs loaded from resume data should be added to the ones in the torrent file or replace them. No distinction is made between the two different kinds of web seeds (BEP 17 and BEP 19). When replacing web seeds (i.e. when this flag is not set), any web seeds passed in via add_torrent_params are also replaced. The default behavior is to have any web seeds in the resume data take precedence over whatever is passed in here as well as the .torrent file.

flag_stop_when_ready | 16384 | the stop when ready flag. Setting this flag is equivalent to calling torrent_handle::stop_when_ready() immediately after the torrent is added.

version
  filled in by the constructor and should be left untouched. It is used for forward binary compatibility.

ti
  torrent_info object with the torrent to add. Unless the url or info_hash is set, this is required to be initialized.

trackers
  If the torrent doesn't have a tracker, but relies on the DHT to find peers, the `trackers` can specify tracker URLs for the torrent.

url_seeds
  url seeds to be added to the torrent (BEP 17).

dht_nodes name
  a list of hostname and port pairs, representing DHT nodes to be added to the session (if DHT is enabled). The hostname may be an IP address.

save_path

  the path where the torrent is or will be stored. Note that this may also be stored in resume data. If you want the save path saved in the resume data to be used, you need to set the flag_use_resume_save_path flag.

  Note

  On windows this path (and other paths) are interpreted as UNC paths. This means they must use backslashes as directory separators and may not contain the special directories "." or "..".

  Setting this to an absolute path performs slightly better than a relative path.

resume_data
  The optional parameter, `resume_data` can be given if up to date fast-resume data is available. The fast-resume data can be acquired from a running torrent by calling save_resume_data() on torrent_handle. See fast resume. The `vector` that is passed in will be swapped into the running torrent instance with `std::vector::swap()`.

storage_mode
  One of the values from storage_mode_t. For more information, see storage allocation.

storage
  can be used to customize how the data is stored. The default storage will simply write the data to the files it belongs to, but it could be overridden to save everything to a single file at a specific location or encrypt the content on disk for instance. For more information about the storage_interface that needs to be implemented for a custom storage, see storage_interface.

userdata
  The `userdata` parameter is optional and will be passed on to the extension constructor functions, if any (see torrent_handle::add_extension()).

file_priorities
  can be set to control the initial file priorities when adding a torrent. The semantics are the same as for `torrent_handle::prioritize_files()`. The file priorities specified in here take precedence over those specified in the resume data, if any.

trackerid
  the default tracker id to be used when announcing to trackers. By default this is empty, and no tracker ID is used, since this is an optional argument. If a tracker returns a tracker ID, that ID is used instead of this.

url
  If you specify a `url`, the torrent will be set in `downloading_metadata` state until the .torrent file has been downloaded. If there's any error while downloading, the torrent will be stopped and the torrent error state (`torrent_status::error`) will indicate what went wrong. The `url` may be set to a magnet link.

uuid
  if `uuid` is specified, it is used to find duplicates. If another torrent is already running with the same UUID as the one being added, it will be considered a duplicate. This is mainly useful for RSS feed items which has UUIDs specified.

source_feed_url
  should point to the URL of the RSS feed this torrent comes from, if it comes from an RSS feed.

flags

  flags controlling aspects of this torrent and how it's added. See flags_t for details.

  Note

  The `flags` field is initialized with default flags by the constructor. In order to preserve default behavior when clearing or setting other flags, make sure to bitwise OR or in a flag or bitwise AND the inverse of a flag to clear it.

info_hash
  set this to the info hash of the torrent to add in case the info-hash is the only known property of the torrent. i.e. you don't have a .torrent file nor a magnet link.

max_uploads max_connections upload_limit download_limit

  `max_uploads`, `max_connections`, `upload_limit`, `download_limit` correspond to the `set_max_uploads()`, `set_max_connections()`, `set_upload_limit()` and `set_download_limit()` functions on torrent_handle. These values let you initialize these settings when the torrent is added, instead of calling these functions immediately following adding it.

  -1 means unlimited on these settings just like their counterpart functions on torrent_handle

  For fine grained control over rate limits, including making them apply to local peers, see peer classes.

## announce_entry

Declared in "libtorrent/announce_entry.hpp"

this class holds information about one bittorrent tracker, as it relates to a specific torrent.

    struct announce_entry
    {
       announce_entry (std::string const& u);
       announce_entry (announce_entry const&) = default;
       ~announce_entry ();
       announce_entry& operator= (announce_entry const&) = default;
       announce_entry ();
       int next_announce_in () const;
       int min_announce_in () const;
       void reset ();
       void failed (aux::session_settings const& sett, int retry_interval = 0);
       bool can_announce (time_point now, bool is_seed) const;
       bool is_working () const;
       void trim ();

       enum tracker_source
       {
          source_torrent,
          source_client,
          source_magnet_link,
          source_tex,
       };

       std::string url;
       std::string trackerid;
       std::string message;
       error_code last_error;
       time_point next_announce;
       time_point min_announce;
       int scrape_incomplete;
       int scrape_complete;
       int scrape_downloaded;
       boost::uint8_t tier;
       boost::uint8_t fail_limit;
       boost::uint8_t fails:7;
       bool updating:1;
       boost::uint8_t source:4;
       bool verified:1;
       bool start_sent:1;
       bool complete_sent:1;
       bool send_stats:1;
    };

### announce_entry() ~announce_entry() operator=()

    announce_entry (std::string const& u);
    announce_entry (announce_entry const&) = default;
    ~announce_entry ();
    announce_entry& operator= (announce_entry const&) = default;
    announce_entry ();

constructs a tracker announce entry with `u` as the URL.

### min_announce_in() next_announce_in()

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

returns the number of seconds to the next announce on this tracker. `min_announce_in()` returns the number of seconds until we are allowed to force another tracker update with this tracker.

If the last time this tracker was contacted failed, `last_error` is the error code describing what error occurred.

### reset()

    void reset ();

reset announce counters and clears the started sent flag. The announce_entry will look like we've never talked to the tracker.

### failed()

    void failed (aux::session_settings const& sett, int retry_interval = 0);

updates the failure counter and time-outs for re-trying. This is called when the tracker announce fails.

### can_announce()

    bool can_announce (time_point now, bool is_seed) const;

returns true if we can announce to this tracker now. The current time is passed in as `now`. The `is_seed` argument is necessary because once we become a seed, we need to announce right away, even if the re-announce timer hasn't expired yet.

### is_working()

    bool is_working () const;

returns true if the last time we tried to announce to this tracker succeeded, or if we haven't tried yet.

### trim()

    void trim ();

trims whitespace characters from the beginning of the URL.

### enum tracker_source

Declared in "libtorrent/announce_entry.hpp"

name | value | description
--- | --- | ---
source_torrent | 1 | the tracker was part of the .torrent file
source_client | 2 | the tracker was added programatically via the add_troacker()_ function
source_magnet_link | 4 | the tracker was part of a magnet link
source_tex | 8 | the tracker was received from the swarm via tracker exchange

url
  tracker URL as it appeared in the torrent file

trackerid
  the current `&trackerid=` argument passed to the tracker. this is optional and is normally empty (in which case no trackerid is sent).

message
  if this tracker has returned an error or warning message that message is stored here

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

next_announce
  the time of next tracker announce

min_announce
  no announces before this time

scrape_incomplete scrape_complete scrape_downloaded
  if this tracker has returned scrape data, these fields are filled in with valid numbers. Otherwise they are set to -1. the number of current downloaders

tier
  the tier this tracker belongs to

fail_limit
  the max number of failures to announce to this tracker in a row, before this tracker is not used anymore. 0 means unlimited

fails
  the number of times in a row we have failed to announce to this tracker.

updating
  true while we're waiting for a response from the tracker.

source
  a bitmask specifying which sources we got this tracker from.

verified
  set to true the first time we receive a valid response from this tracker.

start_sent
  set to true when we get a valid response from an announce with event=started. If it is set, we won't send start in the subsequent announces.

complete_sent
  set to true when we send a event=completed.

send_stats
  this is false the stats sent to this tracker will be 0

## cache_status

Declared in "libtorrent/disk_io_thread.hpp"

this struct holds a number of statistics counters relevant for the disk io thread and disk cache.

    struct cache_status
    {
       cache_status ();

       std::vector<cached_piece_info> pieces;
    };

### cache_status()

    cache_status ();

initializes all counters to 0

## bt_peer_connection_handle

Declared in "libtorrent/peer_connection_handle.hpp"

    struct bt_peer_connection_handle : public peer_connection_handle
    {
       explicit bt_peer_connection_handle (peer_connection_handle pc);
       bool support_extensions () const;
       bool packet_finished () const;
       bool supports_encryption () const;
       void switch_recv_crypto (boost::shared_ptr<crypto_plugin> crypto);
       void switch_send_crypto (boost::shared_ptr<crypto_plugin> crypto);
       boost::shared_ptr<bt_peer_connection> native_handle () const;
    };

## peer_info

Declared in "libtorrent/peer_info.hpp"

holds information and statistics about one peer that libtorrent is connected to

    struct peer_info
    {
       enum peer_flags_t
       {
          interesting,
          choked,
          remote_interested,
          remote_choked,
          supports_extensions,
          local_connection,
          handshake,
          connecting,
          on_parole,
          seed,
          optimistic_unchoke,
          snubbed,
          upload_only,
          endgame_mode,
          holepunched,
          i2p_socket,
          utp_socket,
          ssl_socket,
          rc4_encrypted,
          plaintext_encrypted,
       };

       enum peer_source_flags
       {
          tracker,
          dht,
          pex,
          lsd,
          resume_data,
          incoming,
       };

       enum connection_type_t
       {
          standard_bittorrent,
          web_seed,
          http_seed,
       };

       enum bw_state
       {
          bw_idle,
          bw_limit,
          bw_network,
          bw_disk,
       };

       std::string client;
       bitfield pieces;
       boost::int64_t total_download;
       boost::int64_t total_upload;
       time_duration last_request;
       time_duration last_active;
       time_duration download_queue_time;
       boost::uint32_t flags;
       boost::uint32_t source;
       int up_speed;
       int down_speed;
       int payload_up_speed;
       int payload_down_speed;
       peer_id pid;
       int queue_bytes;
       int request_timeout;
       int send_buffer_size;
       int used_send_buffer;
       int receive_buffer_size;
       int used_receive_buffer;
       int num_hashfails;
       int download_queue_length;
       int timed_out_requests;
       int busy_requests;
       int requests_in_buffer;
       int target_dl_queue_length;
       int upload_queue_length;
       int failcount;
       int downloading_piece_index;
       int downloading_block_index;
       int downloading_progress;
       int downloading_total;
       int connection_type;
       int remote_dl_rate;
       int pending_disk_bytes;
       int pending_disk_read_bytes;
       int send_quota;
       int receive_quota;
       int rtt;
       int num_pieces;
       int download_rate_peak;
       int upload_rate_peak;
       float progress;
       int progress_ppm;
       int estimated_reciprocation_rate;
       tcp::endpoint ip;
       tcp::endpoint local_endpoint;
       char read_state;
       char write_state;
    };

### enum peer_flags_t

Declared in "libtorrent/peer_info.hpp"

name | value | description
--- | --- | ---
interesting | 1 | we are interested in pieces from this peer.
choked | 2 | we have choked this peer.
remote_interested | 4 | the peer is interested in us
remote_choked | 8 | the peer has choked us.
supports_extensions | 16 | means that this peer supports the extension protocol.
local_connection | 32 | The connection was initiated by us, the peer has a listen port open, and that port is the same as in the address of this peer. If this flag is not set, this peer connection was opened by this peer connecting to us.
handshake | 64 | The connection is opened, and waiting for the handshake. Until the handshake is done, the peer cannot be identified.
connecting | 128 | The connection is in a half-open state (i.e. it is being connected).
on_parole | 512 | The peer has participated in a piece that failed the hash check, and is now "on parole", which means we're only requesting whole pieces from this peer until it either fails that piece or proves that it doesn't send bad data.
seed | 1024 | This peer is a seed (it has all the pieces).
optimistic_unchoke | 2048 | This peer is subject to an optimistic unchoke. It has been unchoked for a while to see if it might unchoke us in return an earn an upload/unchoke slot. If it doesn't within some period of time, it will be choked and another peer will be optimistically unchoked.
snubbed | 4096 | This peer has recently failed to send a block within the request timeout from when the request was sent. We're currently picking one block at a time from this peer.
upload_only | 8192 | This peer has either explicitly (with an extension) or implicitly (by becoming a seed) told us that it will not downloading anything more, regardless of which pieces we have.
endgame_mode | 16384 | This means the last time this peer picket a piece, it could not pick as many as it wanted because there were not enough free ones. i.e. all pieces this peer has were already requested from other peers.
holepunched | 32768 | This flag is set if the peer was in holepunch mode when the connection succeeded. This typically only happens if both peers are behind a NAT and the peers connect via the NAT holepunch mechanism.
i2p_socket | 65536 | indicates that this socket is runnin on top of the I2P transport.
utp_socket | 131072 | indicates that this socket is a uTP socket
ssl_socket | 262144 | indicates that this socket is running on top of an SSL (TLS) channel
rc4_encrypted | 1048576 | this connection is obfuscated with RC4
plaintext_encrypted | 2097152 | the handshake of this connection was obfuscated with a diffie-hellman exchange

### enum peer_source_flags

Declared in "libtorrent/peer_info.hpp"

name | value | description
--- | --- | ---
tracker | 1 | The peer was received from the tracker.
dht | 2 | The peer was received from the kademlia DHT.
pex | 4 | The peer was received from the peer exchange extension.
lsd | 8 | The peer was received from the local service discovery (The peer is on the local network).
resume_data | 16 | The peer was added from the fast resume data.
incoming | 32 | we received an incoming connection from this peer

### enum connection_type_t

Declared in "libtorrent/peer_info.hpp"

name | value | description
--- | --- | ---
standard_bittorrent | 0 | Regular bittorrent connection
web_seed | 1 | HTTP connection using the BEP 19 protocol
http_seed | 2 | HTTP connection using the BEP 17 protocol

### enum bw_state

Declared in "libtorrent/peer_info.hpp"

name | value | description
--- | --- | ---
bw_idle | 0 | The peer is not waiting for any external events to send or receive data.
bw_limit | 1 | The peer is waiting for the rate limiter.
bw_network | 2 | The peer has quota and is currently waiting for a network read or write operation to complete. This is the state all peers are in if there are no bandwidth limits.
bw_disk | 4 | The peer is waiting for the disk I/O thread to catch up writing buffers to disk before downloading more.

client
  a string describing the software at the other end of the connection. In some cases this information is not available, then it will contain a string that may give away something about which software is running in the other end. In the case of a web seed, the server type and version will be a part of this string.

pieces
  a bitfield, with one bit per piece in the torrent. Each bit tells you if the peer has that piece (if it's set to 1) or if the peer miss that piece (set to 0).

total_download total_upload
  the total number of bytes downloaded from and uploaded to this peer. These numbers do not include the protocol chatter, but only the payload data.

last_request last_active
  the time since we last sent a request to this peer and since any transfer occurred with this peer

download_queue_time
  the time until all blocks in the request queue will be downloaded

flags
  tells you in which state the peer is in. It is set to any combination of the peer_flags_t enum.

source
  a combination of flags describing from which sources this peer was received. See peer_source_flags.

up_speed down_speed
  the current upload and download speed we have to and from this peer (including any protocol messages). updated about once per second

payload_up_speed payload_down_speed
  The transfer rates of payload data only updated about once per second

pid
  the peer's id as used in the bit torrent protocol. This id can be used to extract 'fingerprints' from the peer. Sometimes it can tell you which client the peer is using. See identify_client()_

request_timeout
  the number of seconds until the current front piece request will time out. This timeout can be adjusted through `settings_pack::request_timeout`. -1 means that there is not outstanding request.

send_buffer_size used_send_buffer
  the number of bytes allocated and used for the peer's send buffer, respectively.

receive_buffer_size used_receive_buffer
  the number of bytes allocated and used as receive buffer, respectively.

num_hashfails
  the number of pieces this peer has participated in sending us that turned out to fail the hash check.

download_queue_length
  this is the number of requests we have sent to this peer that we haven't got a response for yet

timed_out_requests
  the number of block requests that have timed out, and are still in the download queue

busy_requests
  the number of busy requests in the download queue. A busy request is a request for a block we've also requested from a different peer

requests_in_buffer
  the number of requests messages that are currently in the send buffer waiting to be sent.

target_dl_queue_length
  the number of requests that is tried to be maintained (this is typically a function of download speed)

upload_queue_length
  the number of piece-requests we have received from this peer that we haven't answered with a piece yet.

failcount
  the number of times this peer has "failed". i.e. failed to connect or disconnected us. The failcount is decremented when we see this peer in a tracker response or peer exchange message.

downloading_piece_index downloading_block_index downloading_progress downloading_total
  You can know which piece, and which part of that piece, that is currently being downloaded from a specific peer by looking at these four members. `downloading_piece_index` is the index of the piece that is currently being downloaded. This may be set to -1 if there's currently no piece downloading from this peer. If it is >= 0, the other three members are valid. `downloading_block_index` is the index of the block (or sub-piece) that is being downloaded. `downloading_progress` is the number of bytes of this block we have received from the peer, and `downloading_total` is the total number of bytes in this block.

connection_type
  the kind of connection this peer uses. See connection_type_t.

remote_dl_rate
  an estimate of the rate this peer is downloading at, in bytes per second.

pending_disk_bytes
  the number of bytes this peer has pending in the disk-io thread. Downloaded and waiting to be written to disk. This is what is capped by `settings_pack::max_queued_disk_bytes`.

pending_disk_read_bytes
  number of outstanding bytes to read from disk

send_quota receive_quota
  the number of bytes this peer has been assigned to be allowed to send and receive until it has to request more quota from the bandwidth manager.

rtt
  an estimated round trip time to this peer, in milliseconds. It is estimated by timing the the TCP `connect()`. It may be 0 for incoming connections.

num_pieces
  the number of pieces this peer has.

download_rate_peak upload_rate_peak
  the highest download and upload rates seen on this connection. They are given in bytes per second. This number is reset to 0 on reconnect.

progress
  the progress of the peer in the range [0, 1]. This is always 0 when floating point operations are disabled, instead use `progress_ppm`.

progress_ppm
  indicates the download progress of the peer in the range [0, 1000000] (parts per million).

estimated_reciprocation_rate
  this is an estimation of the upload rate, to this peer, where it will unchoke us. This is a coarse estimation based on the rate at which we sent right before we were choked. This is primarily used for the bittyrant choking algorithm.

ip
  the IP-address to this peer. The type is an asio endpoint. For more info, see the asio documentation.

local_endpoint
  the IP and port pair the socket is bound to locally. i.e. the IP address of the interface it's going out over. This may be useful for multi-homed clients with multiple interfaces to the internet.

read_state write_state
  bitmasks indicating what state this peer is in with regards to sending and receiving data. The states are declared in the bw_state enum.

## peer_request

Declared in "libtorrent/peer_request.hpp"

represents a byte range within a piece. Internally this is is used for incoming piece requests.

    struct peer_request
    {
       bool operator== (peer_request const& r) const;

       int piece;
       int start;
       int length;
    };

### operator==()

    bool operator== (peer_request const& r) const;

returns true if the right hand side peer_request refers to the same range as this does.

piece
  the index of the piece in which the range starts.

start
  the offset within that piece where the range starts.

length
  the size of the range, in bytes.

## session_proxy

Declared in "libtorrent/session.hpp"

this is a holder for the internal session implementation object. Once the session destruction is explicitly initiated, this holder is used to synchronize the completion of the shutdown. The lifetime of this object may outlive session, causing the session destructor to not block. The session_proxy destructor will block however, until the underlying session is done shutting down.

    class session_proxy
    {
       ~session_proxy ();
       session_proxy (session_proxy const&) = default;
       session_proxy& operator= (session_proxy const&) = default;
       session_proxy ();
    };

### session_proxy() ~session_proxy() operator=()

    ~session_proxy ();
    session_proxy (session_proxy const&) = default;
    session_proxy& operator= (session_proxy const&) = default;
    session_proxy ();

default constructor, does not refer to any session implementation object.

## session

Declared in "libtorrent/session.hpp"

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.

You have some control over session configuration through the `session::apply_settings()` member function. To change one or more configuration options, create a settings_pack. object and fill it with the settings to be set and pass it in to `session::apply_settings()`.

see apply_settings().

    class session : public boost::noncopyable, public session_handle
    {
       session (settings_pack const& pack = settings_pack()
          , int flags = start_default_features | add_default_plugins);
       session (settings_pack const& pack
          , io_service& ios
          , int flags = start_default_features | add_default_plugins);
       ~session ();
       session_proxy abort ();
    };

### session()

    session (settings_pack const& pack = settings_pack()
          , int flags = start_default_features | add_default_plugins);

Constructs the session objects which acts as the container of torrents. It provides configuration options across torrents (such as rate limits, disk cache, ip filter etc.). In order to avoid a race condition between starting the session and configuring it, you can pass in a settings_pack object. Its settings will take effect before the session starts up.

The `flags` parameter 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 features. If you do not want them to start, pass 0 as the flags parameter.

### session()

    session (settings_pack const& pack
          , io_service& ios
          , int flags = start_default_features | add_default_plugins);

overload of the constructor that takes an external io_service to run the session object on. This is primarily useful for tests that may want to run multiple sessions on a single io_service, or low resource systems where additional threads are expensive and sharing an io_service with other events is fine.

Warning

The session object does not cleanly terminate with an external `io_service`. The `io_service::run()` call _must_ have returned before it's safe to destruct the session. Which means you MUST call session::abort() and save the session_proxy first, then destruct the session object, then sync with the io_service, then destruct the session_proxy object.

### ~session()

    ~session ();

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 apply_settings().

### abort()

    session_proxy abort ();

In case you want to destruct the session asynchronously, 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_handle

Declared in "libtorrent/session_handle.hpp"

    struct session_handle
    {
       session_handle ();
       session_handle (aux::session_impl* impl);
       bool is_valid () const;
       void load_state (bdecode_node const& e, boost::uint32_t flags = 0xffffffff);
       void save_state (entry& e, boost::uint32_t flags = 0xffffffff) const;
       void refresh_torrent_status (std::vector<torrent_status>* ret
          , boost::uint32_t flags = 0) const;
       void get_torrent_status (std::vector<torrent_status>* ret
          , boost::function<bool(torrent_status const&)> const& pred
          , boost::uint32_t flags = 0) const;
       void post_torrent_updates (boost::uint32_t flags = 0xffffffff);
       void post_session_stats ();
       void post_dht_stats ();
       torrent_handle find_torrent (sha1_hash const& info_hash) const;
       std::vector<torrent_handle> get_torrents () const;
       void async_add_torrent (add_torrent_params const& params);
       torrent_handle add_torrent (add_torrent_params const& params, error_code& ec);
       torrent_handle add_torrent (add_torrent_params const& params);
       void resume ();
       void pause ();
       bool is_paused () const;
       void set_load_function (user_load_function_t fun);
       void get_cache_info (cache_status* ret, torrent_handle h = torrent_handle(), int flags = 0) const;
       bool is_dht_running () const;
       dht_settings get_dht_settings () const;
       void set_dht_settings (dht_settings const& settings);
       void set_dht_storage (dht::dht_storage_constructor_type sc);
       void add_dht_node (std::pair<std::string, int> const& node);
       void dht_get_item (sha1_hash const& target);
       void dht_get_item (boost::array<char, 32> key
          , std::string salt = std::string());
       sha1_hash dht_put_item (entry data);
       void dht_put_item (boost::array<char, 32> key
          , boost::function<void(entry&, boost::array<char,64>&
          , boost::uint64_t&, std::string const&)> cb
          , std::string salt = std::string());
       void dht_get_peers (sha1_hash const& info_hash);
       void dht_announce (sha1_hash const& info_hash, int port = 0, int flags = 0);
       void dht_direct_request (udp::endpoint ep, entry const& e, void* userdata = 0);
       void add_extension (boost::function<boost::shared_ptr<torrent_plugin>(
          torrent_handle const&, void*)> ext);
       void add_extension (boost::shared_ptr<plugin> ext);
       ip_filter get_ip_filter () const;
       void set_ip_filter (ip_filter const& f);
       void set_port_filter (port_filter const& f);
       peer_id id () const;
       void set_key (int key);
       bool is_listening () const;
       unsigned short listen_port () const;
       unsigned short ssl_listen_port () const;
       void set_peer_class_filter (ip_filter const& f);
       void set_peer_class_type_filter (peer_class_type_filter const& f);
       int create_peer_class (char const* name);
       void delete_peer_class (int cid);
       peer_class_info get_peer_class (int cid);
       void set_peer_class (int cid, peer_class_info const& pci);
       void remove_torrent (const torrent_handle& h, int options = 0);
       settings_pack get_settings () const;
       void apply_settings (settings_pack const& s);
       void pop_alerts (std::vector<alert*>* alerts);
       void set_alert_notify (boost::function<void()> const& fun);
       alert* wait_for_alert (time_duration max_wait);
       void delete_port_mapping (int handle);
       int add_port_mapping (protocol_type t, int external_port, int local_port);
       aux::session_impl* native_handle () const;

       enum save_state_flags_t
       {
          save_settings,
          save_dht_settings,
          save_dht_state,
          save_encryption_settings,
       };

       enum options_t
       {
          delete_files,
          delete_partfile,
       };

       enum session_flags_t
       {
          add_default_plugins,
          start_default_features,
       };

       enum protocol_type
       {
          udp,
          tcp,
       };
    };

### load_state() save_state()

    void load_state (bdecode_node const& e, boost::uint32_t flags = 0xffffffff);
    void save_state (entry& e, boost::uint32_t flags = 0xffffffff) const;

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 bdecode_node which can be built from a bencoded buffer with bdecode().

The `flags` argument is used to filter which parts of the session state to save or load. By default, all state is saved/restored (except for the individual torrents). see save_state_flags_t

When saving settings, there are two fields that are not loaded. `peer_fingerprint` and `user_agent`. Those are left as configured by the `session_settings` passed to the session constructor or subsequently set via apply_settings().

### get_torrent_status() refresh_torrent_status()

    void refresh_torrent_status (std::vector<torrent_status>* ret
          , boost::uint32_t flags = 0) const;
    void get_torrent_status (std::vector<torrent_status>* ret
          , boost::function<bool(torrent_status const&)> const& pred
          , boost::uint32_t flags = 0) const;

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.

### post_torrent_updates()

    void post_torrent_updates (boost::uint32_t flags = 0xffffffff);

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. the `flags` argument is the same as for torrent_handle::status(). see torrent_handle::status_flags_t.

### post_session_stats()

    void post_session_stats ();

This function will post a session_stats_alert object, containing a snapshot of the performance counters from the internals of libtorrent. To interpret these counters, query the session via session_stats_metrics().

For more information, see the session statistics section.

### post_dht_stats()

    void post_dht_stats ();

This will cause a dht_stats_alert to be posted.

### find_torrent() get_torrents()

    torrent_handle find_torrent (sha1_hash const& info_hash) const;
    std::vector<torrent_handle> get_torrents () const;

`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.

### add_torrent() async_add_torrent()

    void async_add_torrent (add_torrent_params const& params);
    torrent_handle add_torrent (add_torrent_params const& params, error_code& ec);
    torrent_handle add_torrent (add_torrent_params const& params);

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!

### pause() resume() is_paused()

    void resume ();
    void pause ();
    bool is_paused () const;

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.

### set_load_function()

    void set_load_function (user_load_function_t fun);

the feature of dynamically loading/unloading torrents is deprecated and discouraged

This function enables dynamic loading of torrent files. When a torrent is unloaded but needs to be available in memory, this function is called from within the libtorrent network thread. From within this thread, you can not use any of the public APIs of libtorrent itself. The the info-hash of the torrent is passed in to the function and it is expected to fill in the passed in `vector<char>` with the .torrent file corresponding to it.

If there is an error loading the torrent file, the `error_code` (`ec`) should be set to reflect the error. In such case, the torrent itself is stopped and set to an error state with the corresponding error code.

Given that the function is called from the internal network thread of libtorrent, it's important to not stall. libtorrent will not be able to send nor receive any data until the function call returns.

The signature of the function to pass in is:

    void fun(sha1_hash const& info_hash, std::vector<char>& buf, error_code& ec);

### get_cache_info()

    void get_cache_info (cache_status* ret, torrent_handle h = torrent_handle(), int flags = 0) const;

Fills in the cache_status struct with information about the given torrent. If `flags` is `session::disk_cache_no_pieces` the `cache_status::pieces` field will not be set. This may significantly reduce the cost of this call.

### get_dht_settings() is_dht_running() set_dht_settings()

    bool is_dht_running () const;
    dht_settings get_dht_settings () const;
    void set_dht_settings (dht_settings const& settings);

`set_dht_settings` sets some parameters available 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.

`get_dht_settings()` returns the current settings

### set_dht_storage()

    void set_dht_storage (dht::dht_storage_constructor_type sc);

`set_dht_storage` set a dht custom storage constructor function to be used internally when the dht is created.

Since the dht storage is a critical component for the dht behavior, this function will only be effective the next time the dht is started. If you never touch this feature, a default map-memory based storage is used.

If you want to make sure the dht is initially created with your custom storage, create a session with the setting `settings_pack::enable_dht` to false, set your constructor function and call `apply_settings` with `settings_pack::enable_dht` to true.

### add_dht_node()

    void add_dht_node (std::pair<std::string, int> const& node);

`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.

### dht_get_item()

    void dht_get_item (sha1_hash const& target);

query the DHT for an immutable item at the `target` hash. the result is posted as a dht_immutable_item_alert.

### dht_get_item()

    void dht_get_item (boost::array<char, 32> key
          , std::string salt = std::string());

query the DHT for a mutable item under the public key `key`. this is an ed25519 key. `salt` is optional and may be left as an empty string if no salt is to be used. if the item is found in the DHT, a dht_mutable_item_alert is posted.

### dht_put_item()

    sha1_hash dht_put_item (entry data);

store the given bencoded data as an immutable item in the DHT. the returned hash is the key that is to be used to look the item up again. It's just the SHA-1 hash of the bencoded form of the structure.

### dht_put_item()

    void dht_put_item (boost::array<char, 32> key
          , boost::function<void(entry&, boost::array<char,64>&
          , boost::uint64_t&, std::string const&)> cb
          , std::string salt = std::string());

store a mutable item. The `key` is the public key the blob is to be stored under. The optional `salt` argument is a string that is to be mixed in with the key when determining where in the DHT the value is to be stored. The callback function is called from within the libtorrent network thread once we've found where to store the blob, possibly with the current value stored under the key. The values passed to the callback functions are:

entry& value
  the current value stored under the key (may be empty). Also expected to be set to the value to be stored by the function.
boost::array<char,64>& signature
  the signature authenticating the current value. This may be zeros if there is currently no value stored. The function is expected to fill in this buffer with the signature of the new value to store. To generate the signature, you may want to use the `sign_mutable_item` function.
boost::uint64_t& seq
  current sequence number. May be zero if there is no current value. The function is expected to set this to the new sequence number of the value that is to be stored. Sequence numbers must be monotonically increasing. Attempting to overwrite a value with a lower or equal sequence number will fail, even if the signature is correct.
std::string const& salt
  this is the salt that was used for this put call.

Since the callback function `cb` is called from within libtorrent, it is critical to not perform any blocking operations. Ideally not even locking a mutex. Pass any data required for this function along with the function object's context and make the function entirely self-contained. The only reason data blob's value is computed via a function instead of just passing in the new value is to avoid race conditions. If you want to update the value in the DHT, you must first retrieve it, then modify it, then write it back. The way the DHT works, it is natural to always do a lookup before storing and calling the callback in between is convenient.

### dht_direct_request()

    void dht_direct_request (udp::endpoint ep, entry const& e, void* userdata = 0);

Send an arbitrary DHT request directly to the specified endpoint. This function is intended for use by plugins. When a response is received or the request times out, a dht_direct_response_alert will be posted with the response (if any) and the userdata pointer passed in here. Since this alert is a response to an explicit call, it will always be posted, regardless of the alert mask.

### add_extension()

    void add_extension (boost::function<boost::shared_ptr<torrent_plugin>(
          torrent_handle const&, void*)> ext);
    void add_extension (boost::shared_ptr<plugin> ext);

This function adds an extension to this session. The argument is a function object that is called with a `torrent_handle` 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 (.torrent 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);

### get_ip_filter() set_ip_filter()

    ip_filter get_ip_filter () const;
    void set_ip_filter (ip_filter const& f);

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.

### set_port_filter()

    void set_port_filter (port_filter const& f);

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.

### id()

    peer_id id () const;

returns the raw peer ID used by libtorrent. When anonymous mode is set the peer ID is randomized per peer.

### set_key()

    void set_key (int key);

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.

### listen_port() ssl_listen_port() is_listening()

    bool is_listening () const;
    unsigned short listen_port () const;
    unsigned short ssl_listen_port () const;

`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 set a new settings_pack::listen_interfaces to try another interface and port to bind to.

`listen_port()` returns the port we ended up listening on.

### set_peer_class_filter()

    void set_peer_class_filter (ip_filter const& f);

Sets the peer class filter for this session. All new peer connections will take this into account and be added to the peer classes specified by this filter, based on the peer's IP address.

The ip-filter essentially maps an IP -> uint32. Each bit in that 32 bit integer represents a peer class. The least significant bit represents class 0, the next bit class 1 and so on.

For more info, see ip_filter.

For example, to make all peers in the range 200.1.1.0 - 200.1.255.255 belong to their own peer class, apply the following filter:

    ip_filter f;
    int my_class = ses.create_peer_class("200.1.x.x IP range");
    f.add_rule(address_v4::from_string("200.1.1.0")
            , address_v4::from_string("200.1.255.255")
            , 1 << my_class);
    ses.set_peer_class_filter(f);

This setting only applies to new connections, it won't affect existing peer connections.

This function is limited to only peer class 0-31, since there are only 32 bits in the IP range mapping. Only the set bits matter; no peer class will be removed from a peer as a result of this call, peer classes are only added.

The `peer_class` argument cannot be greater than 31. The bitmasks representing peer classes in the `peer_class_filter` are 32 bits.

For more information, see peer classes.

### set_peer_class_type_filter()

    void set_peer_class_type_filter (peer_class_type_filter const& f);

Sets and gets the peer class type filter. This is controls automatic peer class assignments to peers based on what kind of socket it is.

It does not only support assigning peer classes, it also supports removing peer classes based on socket type.

The order of these rules being applied are:

1. peer-class IP filter
2. peer-class type filter, removing classes
3. peer-class type filter, adding classes

For more information, see peer classes. TODO: add get_peer_class_type_filter() as well

### create_peer_class()

    int create_peer_class (char const* name);

Creates a new peer class (see peer classes) with the given name. The returned integer is the new peer class identifier. Peer classes may have the same name, so each invocation of this function creates a new class and returns a unique identifier.

Identifiers are assigned from low numbers to higher. So if you plan on using certain peer classes in a call to set_peer_class_filter(), make sure to create those early on, to get low identifiers.

For more information on peer classes, see peer classes.

### delete_peer_class()

    void delete_peer_class (int cid);

This call dereferences the reference count of the specified peer class. When creating a peer class it's automatically referenced by 1. If you want to recycle a peer class, you may call this function. You may only call this function once per peer class you create. Calling it more than once for the same class will lead to memory corruption.

Since peer classes are reference counted, this function will not remove the peer class if it's still assigned to torrents or peers. It will however remove it once the last peer and torrent drops their references to it.

There is no need to call this function for custom peer classes. All peer classes will be properly destructed when the session object destructs.

For more information on peer classes, see peer classes.

### get_peer_class() set_peer_class()

    peer_class_info get_peer_class (int cid);
    void set_peer_class (int cid, peer_class_info const& pci);

These functions queries information from a peer class and updates the configuration of a peer class, respectively.

`cid` must refer to an existing peer class. If it does not, the return value of `get_peer_class()` is undefined.

`set_peer_class()` sets all the information in the `peer_class_info` object in the specified peer class. There is no option to only update a single property.

A peer or torrent belonging to more than one class, the highest priority among any of its classes is the one that is taken into account.

For more information, see peer classes.

### remove_torrent()

    void remove_torrent (const torrent_handle& h, int options = 0);

`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 asynchronous, 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.

### get_settings() apply_settings()

    settings_pack get_settings () const;
    void apply_settings (settings_pack const& s);

Applies the settings specified by the settings_pack `s`. This is an asynchronous operation that will return immediately and actually apply the settings to the main thread of libtorrent some time later.

### pop_alerts() wait_for_alert() set_alert_notify()

    void pop_alerts (std::vector<alert*>* alerts);
    void set_alert_notify (boost::function<void()> const& fun);
    alert* wait_for_alert (time_duration max_wait);

Alerts is the main mechanism for libtorrent to report errors and events. `pop_alerts` fills in the vector passed to it with pointers to new alerts. The session still owns these alerts and they will stay valid until the next time `pop_alerts` is called. You may not delete the alert objects.

It is safe to call `pop_alerts` from multiple different threads, as long as the alerts themselves are not accessed once another thread calls `pop_alerts`. Doing this requires manual synchronization between the popping threads.

`wait_for_alert` will block the current thread for `max_wait` time duration, or until another alert is posted. If an alert is available at the time of the call, it returns immediately. The returned alert pointer is the head of the alert queue. `wait_for_alert` does not pop alerts from the queue, it merely peeks at it. The returned alert will stay valid until `pop_alerts` is called twice. The first time will pop it and the second will free it.

If there is no alert in the queue and no alert arrives within the specified timeout, `wait_for_alert` returns NULL.

In the python binding, `wait_for_alert` takes the number of milliseconds to wait as an integer.

The alert queue in the session will not grow indefinitely. Make sure to pop periodically to not miss notifications. To control the max number of alerts that's queued by the session, see `settings_pack::alert_queue_size`.

Some alerts are considered so important that they are posted even when the alert queue is full. Some alerts are considered mandatory and cannot be disabled by the `alert_mask`. For instance, save_resume_data_alert and save_resume_data_failed_alert are always posted, regardless of the alert mask.

To control which alerts are posted, set the alert_mask (settings_pack::alert_mask).

the `set_alert_notify` function lets the client set a function object to be invoked every time the alert queue goes from having 0 alerts to 1 alert. This function is called from within libtorrent, it may be the main thread, or it may be from within a user call. The intention of of the function is that the client wakes up its main thread, to poll for more alerts using `pop_alerts()`. If the notify function fails to do so, it won't be called again, until `pop_alerts` is called for some other reason. For instance, it could signal an eventfd, post a message to an HWND or some other main message pump. The actual retrieval of alerts should not be done in the callback. In fact, the callback should not block. It should not perform any expensive work. It really should just notify the main application thread.

### add_port_mapping() delete_port_mapping()

    void delete_port_mapping (int handle);
    int add_port_mapping (protocol_type t, int external_port, int local_port);

add_port_mapping adds a port forwarding on UPnP and/or NAT-PMP, whichever is enabled. The return value is a handle referring to the port mapping that was just created. Pass it to delete_port_mapping() to remove it.

### native_handle()

    aux::session_impl* native_handle () const;

This function is intended only for use by plugins. This type does not have a stable API and should be relied on as little as possible.

### enum save_state_flags_t

Declared in "libtorrent/session_handle.hpp"

name | value | description
--- | --- | ---
save_settings | 1 | saves settings (i.e. the settings_pack)
save_dht_settings | 2 | saves dht_settings
save_dht_state | 4 | saves dht state such as nodes and node-id, possibly accelerating joining the DHT if provided at next session startup.
save_encryption_settings | 32 | save pe_settings

### enum options_t

Declared in "libtorrent/session_handle.hpp"

name | value | description
--- | --- | ---
delete_files | 1 | delete the files belonging to the torrent from disk. including the part-file, if there is one
delete_partfile | 2 | delete just the part-file associated with this torrent

### enum session_flags_t

Declared in "libtorrent/session_handle.hpp"

name | value | description
--- | --- | ---
add_default_plugins | 1 | this will add common extensions like ut_pex, ut_metadata, lt_tex smart_ban and possibly others.
start_default_features | 2 | this will start features like DHT, local service discovery, UPnP and NAT-PMP.

### enum protocol_type

Declared in "libtorrent/session_handle.hpp"

name | value | description
--- | --- | ---
udp | 1 |
tcp | 2 |

## stats_metric

Declared in "libtorrent/session_stats.hpp"

describes one statistics metric from the session. For more information, see the session statistics section.

    struct stats_metric
    {
       enum metric_type_t
       {
          type_counter,
          type_gauge,
       };

       char const* name;
       int value_index;
       metric_type_t type;
    };

### enum metric_type_t

Declared in "libtorrent/session_stats.hpp"

name | value | description
--- | --- | ---
type_counter | 0 |
type_gauge | 1 |

## block_info

Declared in "libtorrent/torrent_handle.hpp"

holds the state of a block in a piece. Who we requested it from and how far along we are at downloading it.

    struct block_info
    {
       void set_peer (tcp::endpoint const& ep);
       tcp::endpoint peer () const;

       enum block_state_t
       {
          none,
          requested,
          writing,
          finished,
       };

       unsigned bytes_progress:15;
       unsigned block_size:15;
       unsigned state:2;
       unsigned num_peers:14;
    };

### set_peer() peer()

    void set_peer (tcp::endpoint const& ep);
    tcp::endpoint peer () const;

The peer is the ip address of the peer this block was downloaded from.

### enum block_state_t

Declared in "libtorrent/torrent_handle.hpp"

name | value | description
--- | --- | ---
none | 0 | This block has not been downloaded or requested form any peer.
requested | 1 | The block has been requested, but not completely downloaded yet.
writing | 2 | The block has been downloaded and is currently queued for being written to disk.
finished | 3 | The block has been written to disk.

bytes_progress
  the number of bytes that have been received for this block

block_size
  the total number of bytes in this block.

state
  the state this block is in (see block_state_t)

num_peers
  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.

## partial_piece_info

Declared in "libtorrent/torrent_handle.hpp"

This class holds information about pieces that have outstanding requests or outstanding writes

    struct partial_piece_info
    {
       int piece_index;
       int blocks_in_piece;
       int finished;
       int writing;
       int requested;
       block_info* blocks;
    };

piece_index
  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.

blocks_in_piece
  the number of blocks in this piece

finished
  the number of blocks that are in the finished state

writing
  the number of blocks that are in the writing state

requested
  the number of blocks that are in the requested state

blocks

  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.

## torrent_handle

Declared in "libtorrent/torrent_handle.hpp"

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 libtorrent_exception 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_handle
    {
       torrent_handle ();
       torrent_handle (torrent_handle const& t);
       torrent_handle& operator= (torrent_handle const&) = default;
       void add_piece (int piece, char const* data, int flags = 0) const;
       void read_piece (int piece) const;
       bool have_piece (int piece) const;
       void get_peer_info (std::vector<peer_info>& v) const;
       torrent_status status (boost::uint32_t flags = 0xffffffff) const;
       void get_download_queue (std::vector<partial_piece_info>& queue) const;
       void reset_piece_deadline (int index) const;
       void clear_piece_deadlines () const;
       void set_piece_deadline (int index, int deadline, int flags = 0) const;
       void set_priority (int prio) const;
       void file_progress (std::vector<boost::int64_t>& progress, int flags = 0) const;
       void file_status (std::vector<pool_file_status>& status) const;
       void clear_error () const;
       std::vector<announce_entry> trackers () const;
       void replace_trackers (std::vector<announce_entry> const&) const;
       void add_tracker (announce_entry const&) const;
       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;
       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;
       void add_extension (
          boost::function<boost::shared_ptr<torrent_plugin>(torrent_handle const&, void*)> const& ext
          , void* userdata = 0);
       bool set_metadata (char const* metadata, int size) const;
       bool is_valid () const;
       void pause (int flags = 0) const;
       void resume () const;
       void stop_when_ready (bool b) const;
       void set_upload_mode (bool b) const;
       void set_share_mode (bool b) const;
       void flush_cache () const;
       void apply_ip_filter (bool b) const;
       void force_recheck () const;
       void save_resume_data (int flags = 0) const;
       bool need_save_resume_data () const;
       void auto_managed (bool m) const;
       void queue_position_down () const;
       void queue_position_top () const;
       int queue_position () const;
       void queue_position_bottom () const;
       void queue_position_up () const;
       void queue_position_set (int p) const;
       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);
       storage_interface* get_storage_impl () const;
       shared_ptr<const torrent_info> torrent_file () const;
       void piece_availability (std::vector<int>& avail) const;
       int piece_priority (int index) const;
       std::vector<int> piece_priorities () const;
       void piece_priority (int index, int priority) const;
       void prioritize_pieces (std::vector<int> const& pieces) const;
       void prioritize_pieces (std::vector<std::pair<int, int> > const& pieces) const;
       int file_priority (int index) const;
       void prioritize_files (std::vector<int> const& files) const;
       void file_priority (int index, int priority) const;
       std::vector<int> file_priorities () const;
       void force_reannounce (int seconds = 0, int tracker_index = -1) const;
       void force_dht_announce () const;
       void scrape_tracker (int idx = -1) const;
       int upload_limit () const;
       int download_limit () const;
       void set_upload_limit (int limit) const;
       void set_download_limit (int limit) const;
       void set_pinned (bool p) const;
       void set_sequential_download (bool sd) const;
       void connect_peer (tcp::endpoint const& adr, int source = 0
          , int flags = 0x1 + 0x4 + 0x8) const;
       int max_uploads () const;
       void set_max_uploads (int max_uploads) const;
       int max_connections () const;
       void set_max_connections (int max_connections) const;
       void move_storage (std::string const& save_path, int flags = 0) const;
       void rename_file (int index, std::string const& new_name) const;
       void super_seeding (bool on) const;
       sha1_hash info_hash () const;
       bool operator!= (const torrent_handle& h) const;
       bool operator< (const torrent_handle& h) const;
       bool operator== (const torrent_handle& h) const;
       boost::uint32_t id () const;
       boost::shared_ptr<torrent> native_handle () const;

       enum flags_t
       {
          overwrite_existing,
       };

       enum status_flags_t
       {
          query_distributed_copies,
          query_accurate_download_counters,
          query_last_seen_complete,
          query_pieces,
          query_verified_pieces,
          query_torrent_file,
          query_name,
          query_save_path,
       };

       enum deadline_flags
       {
          alert_when_available,
       };

       enum file_progress_flags_t
       {
          piece_granularity,
       };

       enum pause_flags_t
       {
          graceful_pause,
       };

       enum save_resume_flags_t
       {
          flush_disk_cache,
          save_info_dict,
          only_if_modified,
       };
    };

### torrent_handle()

    torrent_handle ();

constructs a torrent handle that does not refer to a torrent. i.e. is_valid() will return false.

### add_piece()

    void add_piece (int piece, char const* data, int flags = 0) const;

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.

### read_piece()

    void read_piece (int piece) 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.

### have_piece()

    bool have_piece (int piece) const;

Returns true if this piece has been completely downloaded, and false otherwise.

### get_peer_info()

    void get_peer_info (std::vector<peer_info>& v) const;

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 libtorrent_exception exception. Each entry in the vector contains information about that particular peer. See peer_info.

### status()

    torrent_status status (boost::uint32_t flags = 0xffffffff) const;

`status()` will return a structure with information about the status of this torrent. If the torrent_handle is invalid, it will throw libtorrent_exception 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 the status_flags_t enum.

### get_download_queue()

    void get_download_queue (std::vector<partial_piece_info>& queue) 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.

### clear_piece_deadlines() reset_piece_deadline() set_piece_deadline()

    void reset_piece_deadline (int index) const;
    void clear_piece_deadlines () const;
    void set_piece_deadline (int index, int deadline, int flags = 0) const;

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.

The `flags` parameter can be used to ask libtorrent to post 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.

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.

### set_priority()

    void set_priority (int prio) const;

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.

### file_progress()

    void file_progress (std::vector<boost::int64_t>& progress, int flags = 0) const;

This function fills in the supplied vector with the 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.

### file_status()

    void file_status (std::vector<pool_file_status>& status) const;

This function fills in the passed in vector with status about files that are open for this torrent. Any file that is not open in this torrent, 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 pool_file_status.

### clear_error()

    void clear_error () 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.

### add_tracker() replace_trackers() trackers()

    std::vector<announce_entry> trackers () const;
    void replace_trackers (std::vector<announce_entry> const&) const;
    void add_tracker (announce_entry const&) 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.

### url_seeds() add_url_seed() remove_url_seed()

    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;

`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.

### http_seeds() remove_http_seed() add_http_seed()

    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;

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.

### add_extension()

    void add_extension (
          boost::function<boost::shared_ptr<torrent_plugin>(torrent_handle const&, void*)> const& ext
          , void* userdata = 0);

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.

### set_metadata()

    bool set_metadata (char const* metadata, int size) const;

`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.

### is_valid()

    bool is_valid () const;

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.

### pause() resume()

    void pause (int flags = 0) const;
    void resume () const;

`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`.

The `flags` argument to pause can be set to `torrent_handle::graceful_pause` which 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.

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.

### stop_when_ready()

    void stop_when_ready (bool b) const;

set or clear the stop-when-ready flag. When this flag is set, the torrent will force stop whenever it transitions from a non-data-transferring state into a data-transferring state (referred to as being ready to download or seed). This is useful for torrents that should not start downloading or seeding yet, but want to be made ready to do so. A torrent may need to have its files checked for instance, so it needs to be started and possibly queued for checking (auto-managed and started) but as soon as it's done, it should be stopped.

Force stopped means auto-managed is set to false and it's paused. As if auto_manage(false) and pause() were called on the torrent.

Note that the torrent may transition into a downloading state while calling this function, and since the logic is edge triggered you may miss the edge. To avoid this race, if the torrent already is in a downloading state when this call is made, it will trigger the stop-when-ready immediately.

When the stop-when-ready logic fires, the flag is cleared. Any subsequent transitions between downloading and non-downloading states will not be affected, until this function is used to set it again.

The behavior is more robust when setting this flag as part of adding the torrent. See add_torrent_params.

The stop-when-ready flag fixes the inherent race condition of waiting for the state_changed_alert and then call pause(). The download/seeding will most likely start in between posting the alert and receiving the call to pause.

### set_upload_mode()

    void set_upload_mode (bool b) const;

Explicitly sets the upload mode of the torrent. In upload mode, the torrent will not request any pieces. If the torrent is auto managed, it will automatically be taken out of upload mode periodically (see `settings_pack::optimistic_disk_retry`). Torrents are automatically put in upload mode whenever they encounter a disk write error.

`m` should be true to enter upload mode, and false to leave it.

To test if a torrent is in upload mode, call `torrent_handle::status()` and inspect `torrent_status::upload_mode`.

### set_share_mode()

    void set_share_mode (bool b) const;

Enable or disable share mode for this torrent. When in share mode, the torrent will not necessarily be downloaded, especially not the whole of it. Only parts that are likely to be distributed to more than 2 other peers are downloaded, and only if the previous prediction was correct.

### flush_cache()

    void flush_cache () 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.

### apply_ip_filter()

    void apply_ip_filter (bool b) const;

Set to true to apply the session global IP filter to this torrent (which is the default). Set to false to make this torrent ignore the IP filter.

### force_recheck()

    void force_recheck () 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.

### save_resume_data()

    void save_resume_data (int flags = 0) const;

`save_resume_data()` asks libtorrent to generate fast-resume data for this torrent.

The `flags` argument is a bitmask of flags ORed together. see save_resume_flags_t

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:

    extern int outstanding_resume_data; // global counter of outstanding resume data
    std::vector<torrent_handle> handles = ses.get_torrents();
    ses.pause();
    for (torrent_handle i : handles)
    {
            torrent_handle& h = *i;
            if (!h.is_valid()) continue;
            torrent_status s = h.status();
            if (!s.has_metadata) continue;
            if (!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 == 0) 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 == 0)
                    {
                            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);
                    out.unsetf(std::ios_base::skipws);
                    bencode(std::ostream_iterator<char>(out), *rd->resume_data);
                    --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.

### need_save_resume_data()

    bool need_save_resume_data () 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 alert is posted. It is important to make sure this alert is received and handled in order for this function to be meaningful.

### auto_managed()

    void auto_managed (bool m) const;

changes whether the torrent is auto managed or not. For more info, see queuing.

### queue_position() queue_position_up() queue_position_bottom() queue_position_down() queue_position_top()

    void queue_position_down () const;
    void queue_position_top () const;
    int queue_position () const;
    void queue_position_bottom () const;
    void queue_position_up () 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_set()

    void queue_position_set (int p) 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

### set_ssl_certificate_buffer() set_ssl_certificate()

    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);

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. This overload is only available when libtorrent is built against boost 1.54 or later.

`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.

### get_storage_impl()

    storage_interface* get_storage_impl () const;

Returns the storage implementation for this torrent. This depends on the storage constructor function that was passed to add_torrent.

### torrent_file()

    shared_ptr<const torrent_info> torrent_file () 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 NULL pointer). The torrent may be in a state without metadata only if it was started without a .torrent file, e.g. by using the libtorrent extension of just supplying a tracker and info-hash.

### piece_availability()

    void piece_availability (std::vector<int>& avail) const;

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.

### piece_priority() prioritize_pieces() piece_priorities()

    int piece_priority (int index) const;
    std::vector<int> piece_priorities () const;
    void piece_priority (int index, int priority) const;
    void prioritize_pieces (std::vector<int> const& pieces) const;
    void prioritize_pieces (std::vector<std::pair<int, int> > const& pieces) 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. For instance, magnet links and torrents added by URL 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.

`piece_priorities` returns a vector with one element for each piece in the torrent. Each element is the current priority of that piece.

### file_priorities() prioritize_files() file_priority()

    int file_priority (int index) const;
    void prioritize_files (std::vector<int> const& files) const;
    void file_priority (int index, int priority) const;
    std::vector<int> file_priorities () const;

`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.

`file_priorities()` returns a vector with the priorities of all files.

The priority values are the same as for piece_priority().

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.

### force_reannounce() force_dht_announce()

    void force_reannounce (int seconds = 0, int tracker_index = -1) const;
    void force_dht_announce () const;

`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.

`force_dht_announce` will announce the torrent to the DHT immediately.

### scrape_tracker()

    void scrape_tracker (int idx = -1) const;

`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.

### set_upload_limit() upload_limit() download_limit() set_download_limit()

    int upload_limit () const;
    int download_limit () const;
    void set_upload_limit (int limit) const;
    void set_download_limit (int limit) 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.

### set_pinned()

    void set_pinned (bool p) const;

A pinned torrent may not be unloaded by libtorrent. When the dynamic loading and unloading of torrents is enabled (by setting a load function on the session), this can be used to exempt certain torrents from the unloading logic.

Magnet links, and other torrents that start out without having metadata are pinned automatically. This is to give the client a chance to get the metadata and save it before it's unloaded. In this case, it may be useful to unpin the torrent once its metadata has been saved to disk.

For more information about dynamically loading and unloading torrents, see dynamic loading of torrent files.

### set_sequential_download()

    void set_sequential_download (bool sd) const;

`set_sequential_download()` enables or disables sequential download. When enabled, the piece picker will pick pieces in sequence instead of rarest first. In this mode, piece priorities are ignored, with the exception of priority 7, which are still preferred over the sequential piece order.

Enabling sequential download will affect the piece distribution negatively in the swarm. It should be used sparingly.

### connect_peer()

    void connect_peer (tcp::endpoint const& adr, int source = 0
          , int flags = 0x1 + 0x4 + 0x8) 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 libtorrent_exception. 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.

`flags` are the same flags that are passed along with the `ut_pex` extension.

0x01 | peer supports encryption.
0x02 | peer is a seed
0x04 | supports uTP. If this is not set, the peer will only be contacted over TCP.
0x08 | supports hole punching protocol. If this flag is received from a peer, it can be used as a rendezvous point in case direct connections to the peer fail

### max_uploads() set_max_uploads()

    int max_uploads () const;
    void set_max_uploads (int max_uploads) 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.

### max_connections() set_max_connections()

    int max_connections () const;
    void set_max_connections (int max_connections) 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.

### move_storage()

    void move_storage (std::string const& save_path, int flags = 0) const;

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 = 0
> - fail_if_exist = 1
> - dont_replace = 2

`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 takes the existing file in the target directory, if there is one. The source files will still be removed in that case.

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.

### rename_file()

    void rename_file (int index, std::string const& new_name) const;

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.

### super_seeding()

    void super_seeding (bool on) const;

Enables or disabled super seeding/initial seeding for this torrent. The torrent needs to be a seed for this to take effect.

### info_hash()

    sha1_hash info_hash () const;

`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.

### operator!=() operator<() operator==()

    bool operator!= (const torrent_handle& h) const;
    bool operator< (const torrent_handle& h) const;
    bool operator== (const torrent_handle& h) const;

comparison operators. The order of the torrents is unspecified but stable.

### native_handle()

    boost::shared_ptr<torrent> native_handle () const;

This function is intended only for use by plugins and the alert dispatch function. This type does not have a stable API and should be relied on as little as possible.

### enum flags_t

Declared in "libtorrent/torrent_handle.hpp"

name | value | description
--- | --- | ---
overwrite_existing | 1 |

### enum status_flags_t

Declared in "libtorrent/torrent_handle.hpp"

name | value | description
--- | --- | ---
query_distributed_copies | 1 | calculates `distributed_copies`, `distributed_full_copies` and `distributed_fraction`.
query_accurate_download_counters | 2 | includes partial downloaded blocks in `total_done` and `total_wanted_done`.
query_last_seen_complete | 4 | includes `last_seen_complete`.
query_pieces | 8 | includes `pieces`.
query_verified_pieces | 16 | includes `verified_pieces` (only applies to torrents in seed mode).
query_torrent_file | 32 | includes `torrent_file`, which is all the static information from the .torrent file.
query_name | 64 | 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.
query_save_path | 128 | includes `save_path`, the path to the directory the files of the torrent are saved to.

### enum deadline_flags

Declared in "libtorrent/torrent_handle.hpp"

name | value | description
--- | --- | ---
alert_when_available | 1 |

### enum file_progress_flags_t

Declared in "libtorrent/torrent_handle.hpp"

name | value | description
--- | --- | ---
piece_granularity | 1 | 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.

### enum pause_flags_t

Declared in "libtorrent/torrent_handle.hpp"

name | value | description
--- | --- | ---
graceful_pause | 1 |

### enum save_resume_flags_t

Declared in "libtorrent/torrent_handle.hpp"

name | value | description
--- | --- | ---
flush_disk_cache | 1 | 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.
save_info_dict | 2 | 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).
only_if_modified | 4 | 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.

## web_seed_entry

Declared in "libtorrent/torrent_info.hpp"

the web_seed_entry holds information about a web seed (also known as URL seed or HTTP seed). It is essentially a URL with some state associated with it. For more information, see BEP 17 and BEP 19.

    struct web_seed_entry
    {
       web_seed_entry (std::string const& url_, type_t type_
          , std::string const& auth_ = std::string()
          , headers_t const& extra_headers_ = headers_t());
       bool operator== (web_seed_entry const& e) const;
       bool operator< (web_seed_entry const& e) const;

       enum type_t
       {
          url_seed,
          http_seed,
       };

       std::string url;
       std::string auth;
       headers_t extra_headers;
       boost::uint8_t type;
    };

### operator==()

    bool operator== (web_seed_entry const& e) const;

URL and type comparison

### operator<()

    bool operator< (web_seed_entry const& e) const;

URL and type less-than comparison

### enum type_t

Declared in "libtorrent/torrent_info.hpp"

name | value | description
--- | --- | ---
url_seed | 0 |
http_seed | 1 |

url
  The URL of the web seed

auth
  Optional authentication. If this is set, it's passed in as HTTP basic auth to the web seed. The format is: username:password.

extra_headers
  Any extra HTTP headers that need to be passed to the web seed

type
  The type of web seed (see type_t)

## torrent_info

Declared in "libtorrent/torrent_info.hpp"

TODO: there may be some opportunities to optimize the size if torrent_info. specifically to turn some std::string and std::vector into pointers

    class torrent_info
    {
       torrent_info (std::string const& filename, int flags = 0);
       torrent_info (std::string const& filename, error_code& ec, int flags = 0);
       torrent_info (char const* buffer, int size, error_code& ec, int flags = 0);
       torrent_info (sha1_hash const& info_hash, int flags = 0);
       torrent_info (bdecode_node const& torrent_file, error_code& ec, int flags = 0);
       torrent_info (char const* buffer, int size, int flags = 0);
       torrent_info (bdecode_node const& torrent_file, int flags = 0);
       torrent_info (torrent_info const& t);
       ~torrent_info ();
       file_storage const& files () const;
       file_storage const& orig_files () const;
       void rename_file (int index, std::string const& new_filename);
       void remap_files (file_storage const& f);
       std::vector<announce_entry> const& trackers () const;
       void add_tracker (std::string const& url, int tier = 0);
       std::vector<sha1_hash> similar_torrents () const;
       std::vector<std::string> collections () const;
       void add_url_seed (std::string const& url
          , std::string const& extern_auth = std::string()
          , web_seed_entry::headers_t const& extra_headers = web_seed_entry::headers_t());
       std::vector<web_seed_entry> const& web_seeds () const;
       void set_web_seeds (std::vector<web_seed_entry> seeds);
       void add_http_seed (std::string const& url
          , std::string const& extern_auth = std::string()
          , web_seed_entry::headers_t const& extra_headers = web_seed_entry::headers_t());
       boost::int64_t total_size () const;
       int num_pieces () const;
       int piece_length () const;
       const sha1_hash& info_hash () const;
       int num_files () const;
       std::vector<file_slice> map_block (int piece, boost::int64_t offset, int size) const;
       peer_request map_file (int file, boost::int64_t offset, int size) const;
       void unload ();
       void load (char const* buffer, int size, error_code& ec);
       std::string ssl_cert () const;
       bool is_valid () const;
       bool priv () const;
       bool is_i2p () const;
       sha1_hash hash_for_piece (int index) const;
       char const* hash_for_piece_ptr (int index) const;
       int piece_size (int index) const;
       bool is_loaded () const;
       std::vector<sha1_hash> const& merkle_tree () const;
       void set_merkle_tree (std::vector<sha1_hash>& h);
       boost::optional<time_t> creation_date () const;
       const std::string& name () const;
       const std::string& comment () const;
       const std::string& creator () const;
       nodes_t const& nodes () const;
       void add_node (std::pair<std::string, int> const& node);
       bool parse_info_section (bdecode_node const& e, error_code& ec, int flags);
       bdecode_node info (char const* key) const;
       void swap (torrent_info& ti);
       int metadata_size () const;
       boost::shared_array<char> metadata () const;
       bool is_merkle_torrent () const;
       bool parse_torrent_file (bdecode_node const& libtorrent, error_code& ec, int flags);
    };

### torrent_info()

    torrent_info (std::string const& filename, int flags = 0);
    torrent_info (std::string const& filename, error_code& ec, int flags = 0);
    torrent_info (char const* buffer, int size, error_code& ec, int flags = 0);
    torrent_info (sha1_hash const& info_hash, int flags = 0);
    torrent_info (bdecode_node const& torrent_file, error_code& ec, int flags = 0);
    torrent_info (char const* buffer, int size, int flags = 0);
    torrent_info (bdecode_node const& torrent_file, int flags = 0);
    torrent_info (torrent_info const& t);

The constructor that takes an info-hash will initialize the info-hash to the given value, but leave all other fields empty. This is used internally when downloading torrents without the metadata. The metadata will be created by libtorrent as soon as it has been downloaded from the swarm.

The constructor that takes a bdecode_node will create a torrent_info object from the information found in the given torrent_file. The bdecode_node represents a tree node in an bencoded file. To load an ordinary .torrent file into a bdecode_node, use bdecode().

The version that takes a buffer pointer and a size will decode it as a .torrent file and initialize the torrent_info object for you.

The version that takes a filename will simply load the torrent file and decode it inside the constructor, for convenience. This might not be the most suitable for applications that want to be able to report detailed errors on what might go wrong.

There is an upper limit on the size of the torrent file that will be loaded by the overload taking a filename. If it's important that even very large torrent files are loaded, use one of the other overloads.

The overloads that takes an `error_code const&` never throws if an error occur, they will simply set the error code to describe what went wrong and not fully initialize the torrent_info object. The overloads that do not take the extra error_code parameter will always throw if an error occurs. These overloads are not available when building without exception support.

The `flags` argument is currently unused.

### ~torrent_info()

    ~torrent_info ();

frees all storage associated with this torrent_info object

### orig_files() files()

    file_storage const& files () const;
    file_storage const& orig_files () const;

The file_storage object contains the information on how to map the pieces to files. It is separated from the torrent_info object because when creating torrents a storage object needs to be created without having a torrent file. When renaming files in a storage, the storage needs to make its own copy of the file_storage in order to make its mapping differ from the one in the torrent file.

`orig_files()` returns the original (unmodified) file storage for this torrent. This is used by the web server connection, which needs to request files with the original names. Filename may be changed using `torrent_info::rename_file()`.

For more information on the file_storage object, see the separate document on how to create torrents.

### rename_file()

    void rename_file (int index, std::string const& new_filename);

Renames a the file with the specified index to the new name. The new filename is reflected by the `file_storage` returned by `files()` but not by the one returned by `orig_files()`.

If you want to rename the base name of the torrent (for a multi file torrent), you can copy the `file_storage` (see files() and orig_files() ), change the name, and then use remap_files().

The `new_filename` can both be a relative path, in which case the file name is relative to the `save_path` of the torrent. If the `new_filename` is an absolute path (i.e. `is_complete(new_filename) == true`), then the file is detached from the `save_path` of the torrent. In this case the file is not moved when move_storage() is invoked.

### remap_files()

    void remap_files (file_storage const& f);

Remaps the file storage to a new file layout. This can be used to, for instance, download all data in a torrent to a single file, or to a number of fixed size sector aligned files, regardless of the number and sizes of the files in the torrent.

The new specified `file_storage` must have the exact same size as the current one.

### trackers() add_tracker()

    std::vector<announce_entry> const& trackers () const;
    void add_tracker (std::string const& url, int tier = 0);

`add_tracker()` adds a tracker to the announce-list. The `tier` determines the order in which the trackers are to be tried.

The `trackers()` function will return a sorted vector of `announce_entry`. Each announce entry contains a string, which is the tracker url, and a tier index. The tier index is the high-level priority. No matter which trackers that works or not, the ones with lower tier will always be tried before the one with higher tier number. For more information, see announce_entry.

### collections() similar_torrents()

    std::vector<sha1_hash> similar_torrents () const;
    std::vector<std::string> collections () const;

These two functions are related to BEP 38 (mutable torrents). The vectors returned from these correspond to the "similar" and "collections" keys in the .torrent file. Both info-hashes and collections from within the info-dict and from outside of it are included.

### add_url_seed() set_web_seeds() add_http_seed() web_seeds()

    void add_url_seed (std::string const& url
          , std::string const& extern_auth = std::string()
          , web_seed_entry::headers_t const& extra_headers = web_seed_entry::headers_t());
    std::vector<web_seed_entry> const& web_seeds () const;
    void set_web_seeds (std::vector<web_seed_entry> seeds);
    void add_http_seed (std::string const& url
          , std::string const& extern_auth = std::string()
          , web_seed_entry::headers_t const& extra_headers = web_seed_entry::headers_t());

`web_seeds()` returns all url seeds and http seeds in the torrent. Each entry is a `web_seed_entry` and may refer to either a url seed or http seed.

`add_url_seed()` and `add_http_seed()` adds one url to the list of url/http seeds. Currently, the only transport protocol supported for the url is http.

`set_web_seeds()` replaces all web seeds with the ones specified in the `seeds` vector.

The `extern_auth` argument can be used for other authorization schemes than basic HTTP authorization. If set, it will override any username and password found in the URL itself. The string will be sent as the HTTP authorization header's value (without specifying "Basic").

The `extra_headers` argument defaults to an empty list, but can be used to insert custom HTTP headers in the requests to a specific web seed.

See http seeding for more information.

### piece_length() num_pieces() total_size()

    boost::int64_t total_size () const;
    int num_pieces () const;
    int piece_length () const;

`total_size()`, `piece_length()` and `num_pieces()` returns the total number of bytes the torrent-file represents (all the files in it), the number of byte for each piece and the total number of pieces, respectively. The difference between `piece_size()` and `piece_length()` is that `piece_size()` takes the piece index as argument and gives you the exact size of that piece. It will always be the same as `piece_length()` except in the case of the last piece, which may be smaller.

### info_hash()

    const sha1_hash& info_hash () const;

returns the info-hash of the torrent

### num_files()

    int num_files () const;

If you need index-access to files you can use the `num_files()` along with the `file_path()`, `file_size()`-family of functions to access files using indices.

### map_block()

    std::vector<file_slice> map_block (int piece, boost::int64_t offset, int size) const;

This function will map a piece index, a byte offset within that piece and a size (in bytes) into the corresponding files with offsets where that data for that piece is supposed to be stored. See file_slice.

### map_file()

    peer_request map_file (int file, boost::int64_t offset, int size) const;

This function will map a range in a specific file into a range in the torrent. The `file_offset` parameter is the offset in the file, given in bytes, where 0 is the start of the file. See peer_request.

The input range is assumed to be valid within the torrent. `file_offset` + `size` is not allowed to be greater than the file size. `file_index` must refer to a valid file, i.e. it cannot be >= `num_files()`.

### unload() load()

    void unload ();
    void load (char const* buffer, int size, error_code& ec);

load and unload this torrent info

### ssl_cert()

    std::string ssl_cert () const;

Returns the SSL root certificate for the torrent, if it is an SSL torrent. Otherwise returns an empty string. The certificate is the the public certificate in x509 format.

### is_valid()

    bool is_valid () const;

returns true if this torrent_info object has a torrent loaded. This is primarily used to determine if a magnet link has had its metadata resolved yet or not.

### priv()

    bool priv () const;

returns true if this torrent is private. i.e., it should not be distributed on the trackerless network (the kademlia DHT).

### is_i2p()

    bool is_i2p () const;

returns true if this is an i2p torrent. This is determined by whether or not it has a tracker whose URL domain name ends with ".i2p". i2p torrents disable the DHT and local peer discovery as well as talking to peers over anything other than the i2p network.

### hash_for_piece_ptr() hash_for_piece() piece_size()

    sha1_hash hash_for_piece (int index) const;
    char const* hash_for_piece_ptr (int index) const;
    int piece_size (int index) const;

`hash_for_piece()` takes a piece-index and returns the 20-bytes sha1-hash for that piece and `info_hash()` returns the 20-bytes sha1-hash for the info-section of the torrent file. `hash_for_piece_ptr()` returns a pointer to the 20 byte sha1 digest for the piece. Note that the string is not null-terminated.

### set_merkle_tree() merkle_tree()

    std::vector<sha1_hash> const& merkle_tree () const;
    void set_merkle_tree (std::vector<sha1_hash>& h);

`merkle_tree()` returns a reference to the merkle tree for this torrent, if any.

`set_merkle_tree()` moves the passed in merkle tree into the torrent_info object. i.e. `h` will not be identical after the call. You need to set the merkle tree for a torrent that you've just created (as a merkle torrent). The merkle tree is retrieved from the `create_torrent::merkle_tree()` function, and need to be saved separately from the torrent file itself. Once it's added to libtorrent, the merkle tree will be persisted in the resume data.

### creator() creation_date() name() comment()

    boost::optional<time_t> creation_date () const;
    const std::string& name () const;
    const std::string& comment () const;
    const std::string& creator () const;

`name()` returns the name of the torrent.

`comment()` returns the comment associated with the torrent. If there's no comment, it will return an empty string. `creation_date()` returns the creation date of the torrent as time_t (posix time). If there's no time stamp in the torrent file, the optional object will be uninitialized.

Both the name and the comment is UTF-8 encoded strings.

`creator()` returns the creator string in the torrent. If there is no creator string it will return an empty string.

### nodes()

    nodes_t const& nodes () const;

If this torrent contains any DHT nodes, they are put in this vector in their original form (host name and port number).

### add_node()

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

This is used when creating torrent. Use this to add a known DHT node. It may be used, by the client, to bootstrap into the DHT network.

### parse_info_section()

    bool parse_info_section (bdecode_node const& e, error_code& ec, int flags);

populates the torrent_info by providing just the info-dict buffer. This is used when loading a torrent from a magnet link for instance, where we only have the info-dict. The bdecode_node `e` points to a parsed info-dictionary. `ec` returns an error code if something fails (typically if the info dictionary is malformed). `flags` are currently unused.

### info()

    bdecode_node info (char const* key) const;

This function looks up keys from the info-dictionary of the loaded torrent file. It can be used to access extension values put in the .torrent file. If the specified key cannot be found, it returns NULL.

### swap()

    void swap (torrent_info& ti);

swap the content of this and `ti`.

### metadata_size() metadata()

    int metadata_size () const;
    boost::shared_array<char> metadata () const;

`metadata()` returns a the raw info section of the torrent file. The size of the metadata is returned by `metadata_size()`.

### is_merkle_torrent()

    bool is_merkle_torrent () const;

returns whether or not this is a merkle torrent. see BEP 30.

## torrent_status

Declared in "libtorrent/torrent_status.hpp"

holds a snapshot of the status of a torrent, as queried by torrent_handle::status().

    struct torrent_status
    {
       bool operator== (torrent_status const& st) const;

       enum state_t
       {
          checking_files,
          downloading_metadata,
          downloading,
          finished,
          seeding,
          allocating,
          checking_resume_data,
       };

       torrent_handle handle;
       std::string save_path;
       std::string name;
       boost::weak_ptr<const torrent_info> torrent_file;
       time_duration next_announce;
       std::string current_tracker;
       boost::int64_t total_download;
       boost::int64_t total_upload;
       boost::int64_t total_payload_download;
       boost::int64_t total_payload_upload;
       boost::int64_t total_failed_bytes;
       boost::int64_t total_redundant_bytes;
       bitfield pieces;
       bitfield verified_pieces;
       boost::int64_t total_done;
       boost::int64_t total_wanted_done;
       boost::int64_t total_wanted;
       boost::int64_t all_time_upload;
       boost::int64_t all_time_download;
       time_t added_time;
       time_t completed_time;
       time_t last_seen_complete;
       storage_mode_t storage_mode;
       float progress;
       int progress_ppm;
       int queue_position;
       int download_rate;
       int upload_rate;
       int download_payload_rate;
       int upload_payload_rate;
       int num_seeds;
       int num_peers;
       int num_complete;
       int num_incomplete;
       int list_seeds;
       int list_peers;
       int connect_candidates;
       int num_pieces;
       int distributed_full_copies;
       int distributed_fraction;
       float distributed_copies;
       int block_size;
       int num_uploads;
       int num_connections;
       int uploads_limit;
       int connections_limit;
       int up_bandwidth_queue;
       int down_bandwidth_queue;
       int time_since_upload;
       int time_since_download;
       int active_time;
       int finished_time;
       int seeding_time;
       int seed_rank;
       int last_scrape;
       int priority;
       state_t state;
       bool need_save_resume;
       bool ip_filter_applies;
       bool upload_mode;
       bool share_mode;
       bool super_seeding;
       bool paused;
       bool auto_managed;
       bool sequential_download;
       bool is_seeding;
       bool is_finished;
       bool has_metadata;
       bool has_incoming;
       bool seed_mode;
       bool moving_storage;
       bool is_loaded;
       bool announcing_to_trackers;
       bool announcing_to_lsd;
       bool announcing_to_dht;
       bool stop_when_ready;
       sha1_hash info_hash;
    };

### operator==()

    bool operator== (torrent_status const& st) const;

compares if the torrent status objects come from the same torrent. i.e. only the torrent_handle field is compared.

### enum state_t

Declared in "libtorrent/torrent_status.hpp"

name | value | description
--- | --- | ---
checking_files | 1 | The torrent has not started its download yet, and is currently checking existing files.
downloading_metadata | 2 | The torrent is trying to download metadata from peers. This assumes the metadata_transfer extension is in use.
downloading | 3 | The torrent is being downloaded. This is the state most torrents will be in most of the time. The progress meter will tell how much of the files that has been downloaded.
finished | 4 | In this state the torrent has finished downloading but still doesn't have the entire torrent. i.e. some pieces are filtered and won't get downloaded.
seeding | 5 | In this state the torrent has finished downloading and is a pure seeder.
allocating | 6 | If the torrent was started in full allocation mode, this indicates that the (disk) storage for the torrent is allocated.
checking_resume_data | 7 | The torrent is currently checking the fastresume data and comparing it to the files on disk. This is typically completed in a fraction of a second, but if you add a large number of torrents at once, they will queue up.

handle
  a handle to the torrent whose status the object represents.

save_path
  the path to the directory where this torrent's files are stored. It's typically the path as was given to async_add_torrent() or add_torrent() when this torrent was started. This field is only included if the torrent status is queried with `torrent_handle::query_save_path`.

name
  the name of the torrent. Typically this is derived from the .torrent file. In case the torrent was started without metadata, and hasn't completely received it yet, it returns the name given to it when added to the session. See `session::add_torrent`. This field is only included if the torrent status is queried with `torrent_handle::query_name`.

torrent_file
  set to point to the `torrent_info` object for this torrent. It's only included if the torrent status is queried with `torrent_handle::query_torrent_file`.

next_announce
  the time until the torrent will announce itself to the tracker.

current_tracker
  the URL of the last working tracker. If no tracker request has been successful yet, it's set to an empty string.

total_download total_upload
  the number of bytes downloaded and uploaded to all peers, accumulated, this session only. The session is considered to restart when a torrent is paused and restarted again. When a torrent is paused, these counters are reset to 0. If you want complete, persistent, stats, see `all_time_upload` and `all_time_download`.

total_payload_download total_payload_upload
  counts the amount of bytes send and received this session, but only the actual payload data (i.e the interesting data), these counters ignore any protocol overhead. The session is considered to restart when a torrent is paused and restarted again. When a torrent is paused, these counters are reset to 0.

total_failed_bytes
  the number of bytes that has been downloaded and that has failed the piece hash test. In other words, this is just how much crap that has been downloaded since the torrent was last started. If a torrent is paused and then restarted again, this counter will be reset.

total_redundant_bytes
  the number of bytes that has been downloaded even though that data already was downloaded. The reason for this is that in some situations the same data can be downloaded by mistake. When libtorrent sends requests to a peer, and the peer doesn't send a response within a certain timeout, libtorrent will re-request that block. Another situation when libtorrent may re-request blocks is when the requests it sends out are not replied in FIFO-order (it will re-request blocks that are skipped by an out of order block). This is supposed to be as low as possible. This only counts bytes since the torrent was last started. If a torrent is paused and then restarted again, this counter will be reset.

pieces
  a bitmask that represents which pieces we have (set to true) and the pieces we don't have. It's a pointer and may be set to 0 if the torrent isn't downloading or seeding.

verified_pieces
  a bitmask representing which pieces has had their hash checked. This only applies to torrents in seed mode. If the torrent is not in seed mode, this bitmask may be empty.

total_done
  the total number of bytes of the file(s) that we have. All this does not necessarily has to be downloaded during this session (that's `total_payload_download`).

total_wanted_done
  the number of bytes we have downloaded, only counting the pieces that we actually want to download. i.e. excluding any pieces that we have but have priority 0 (i.e. not wanted).

total_wanted
  The total number of bytes we want to download. This may be smaller than the total torrent size in case any pieces are prioritized to 0, i.e. not wanted

all_time_upload all_time_download
  are accumulated upload and download payload byte counters. They are saved in and restored from resume data to keep totals across sessions.

added_time
  the posix-time when this torrent was added. i.e. what `time(NULL)` returned at the time.

completed_time
  the posix-time when this torrent was finished. If the torrent is not yet finished, this is 0.

last_seen_complete
  the time when we, or one of our peers, last saw a complete copy of this torrent.

storage_mode
  The allocation mode for the torrent. See storage_mode_t for the options. For more information, see storage allocation.

progress
  a value in the range [0, 1], that represents the progress of the torrent's current task. It may be checking files or downloading.

progress_ppm

  progress parts per million (progress * 1000000) when disabling floating point operations, this is the only option to query progress

  reflects the same value as `progress`, but instead in a range [0, 1000000] (ppm = parts per million). When floating point operations are disabled, this is the only alternative to the floating point value in progress.

queue_position
  the position this torrent has in the download queue. If the torrent is a seed or finished, this is -1.

download_rate upload_rate
  the total rates for all peers for this torrent. These will usually have better precision than summing the rates from all peers. The rates are given as the number of bytes per second.

download_payload_rate upload_payload_rate
  the total transfer rate of payload only, not counting protocol chatter. This might be slightly smaller than the other rates, but if projected over a long time (e.g. when calculating ETA:s) the difference may be noticeable.

num_seeds
  the number of peers that are seeding that this client is currently connected to.

num_peers
  the number of peers this torrent currently is connected to. Peer connections that are in the half-open state (is attempting to connect) or are queued for later connection attempt do not count. Although they are visible in the peer list when you call get_peer_info().

num_complete num_incomplete
  if the tracker sends scrape info in its announce reply, these fields will be set to the total number of peers that have the whole file and the total number of peers that are still downloading. set to -1 if the tracker did not send any scrape data in its announce reply.

list_seeds list_peers
  the number of seeds in our peer list and the total number of peers (including seeds). We are not necessarily connected to all the peers in our peer list. This is the number of peers we know of in total, including banned peers and peers that we have failed to connect to.

connect_candidates
  the number of peers in this torrent's peer list that is a candidate to be connected to. i.e. It has fewer connect attempts than the max fail count, it is not a seed if we are a seed, it is not banned etc. If this is 0, it means we don't know of any more peers that we can try.

num_pieces
  the number of pieces that has been downloaded. It is equivalent to: `std::accumulate(pieces->begin(), pieces->end())`. So you don't have to count yourself. This can be used to see if anything has updated since last time if you want to keep a graph of the pieces up to date.

distributed_full_copies
  the number of distributed copies of the torrent. Note that one copy may be spread out among many peers. It tells how many copies there are currently of the rarest piece(s) among the peers this client is connected to.

distributed_fraction

  tells the share of pieces that have more copies than the rarest piece(s). Divide this number by 1000 to get the fraction.

  For example, if `distributed_full_copies` is 2 and `distributed_fraction` is 500, it means that the rarest pieces have only 2 copies among the peers this torrent is connected to, and that 50% of all the pieces have more than two copies.

  If we are a seed, the piece picker is deallocated as an optimization, and piece availability is no longer tracked. In this case the distributed copies members are set to -1.

distributed_copies

  the number of distributed copies of the file. note that one copy may be spread out among many peers. This is a floating point representation of the distributed copies.

  the integer part tells how many copies
    there are of the rarest piece(s)
  the fractional part tells the fraction of pieces that
    have more copies than the rarest piece(s).

block_size
  the size of a block, in bytes. A block is a sub piece, it is the number of bytes that each piece request asks for and the number of bytes that each bit in the `partial_piece_info`'s bitset represents, see get_download_queue(). This is typically 16 kB, but it may be larger if the pieces are larger.

num_uploads
  the number of unchoked peers in this torrent.

num_connections
  the number of peer connections this torrent has, including half-open connections that hasn't completed the bittorrent handshake yet. This is always >= `num_peers`.

uploads_limit
  the set limit of upload slots (unchoked peers) for this torrent.

connections_limit
  the set limit of number of connections for this torrent.

up_bandwidth_queue down_bandwidth_queue
  the number of peers in this torrent that are waiting for more bandwidth quota from the torrent rate limiter. This can determine if the rate you get from this torrent is bound by the torrents limit or not. If there is no limit set on this torrent, the peers might still be waiting for bandwidth quota from the global limiter, but then they are counted in the `session_status` object.

time_since_upload time_since_download
  the number of seconds since any peer last uploaded from this torrent and the last time a downloaded piece passed the hash check, respectively. Note, when starting up a torrent that needs its files checked, piece may pass and that will be considered downloading for the purpose of this counter. -1 means there either hasn't been any uploading/downloading, or it was too long ago for libtorrent to remember (currently forgetting happens after about 18 hours)

active_time finished_time seeding_time
  These keep track of the number of seconds this torrent has been active (not paused) and the number of seconds it has been active while being finished and active while being a seed. `seeding_time` should be <= `finished_time` which should be <= `active_time`. They are all saved in and restored from resume data, to keep totals across sessions.

seed_rank
  A rank of how important it is to seed the torrent, it is used to determine which torrents to seed and which to queue. It is based on the peer to seed ratio from the tracker scrape. For more information, see queuing. Higher value means more important to seed

last_scrape
  the number of seconds since this torrent acquired scrape data. If it has never done that, this value is -1.

priority
  the priority of this torrent

state
  the main state the torrent is in. See torrent_status::state_t.

need_save_resume
  true if this torrent has unsaved changes to its download state and statistics since the last resume data was saved.

ip_filter_applies
  true if the session global IP filter applies to this torrent. This defaults to true.

upload_mode
  true if the torrent is blocked from downloading. This typically happens when a disk write operation fails. If the torrent is auto-managed, it will periodically be taken out of this state, in the hope that the disk condition (be it disk full or permission errors) has been resolved. If the torrent is not auto-managed, you have to explicitly take it out of the upload mode by calling set_upload_mode() on the torrent_handle.

share_mode
  true if the torrent is currently in share-mode, i.e. not downloading the torrent, but just helping the swarm out.

super_seeding
  true if the torrent is in super seeding mode

paused
  set to true if the torrent is paused and false otherwise. It's only true if the torrent itself is paused. If the torrent is not running because the session is paused, this is still false. To know if a torrent is active or not, you need to inspect both `torrent_status::paused` and `session::is_paused()`.

auto_managed
  set to true if the torrent is auto managed, i.e. libtorrent is responsible for determining whether it should be started or queued. For more info see queuing

sequential_download
  true when the torrent is in sequential download mode. In this mode pieces are downloaded in order rather than rarest first.

is_seeding
  true if all pieces have been downloaded.

is_finished
  true if all pieces that have a priority > 0 are downloaded. There is only a distinction between finished and seeding if some pieces or files have been set to priority 0, i.e. are not downloaded.

has_metadata
  true if this torrent has metadata (either it was started from a .torrent file or the metadata has been downloaded). The only scenario where this can be false is when the torrent was started torrent-less (i.e. with just an info-hash and tracker ip, a magnet link for instance).

has_incoming
  true if there has ever been an incoming connection attempt to this torrent.

seed_mode
  true if the torrent is in seed_mode. If the torrent was started in seed mode, it will leave seed mode once all pieces have been checked or as soon as one piece fails the hash check.

moving_storage
  this is true if this torrent's storage is currently being moved from one location to another. This may potentially be a long operation if a large file ends up being copied from one drive to another.

is_loaded
  true if this torrent is loaded into RAM. A torrent can be started and still not loaded into RAM, in case it has not had any peers interested in it yet. Torrents are loaded on demand.

announcing_to_trackers announcing_to_lsd announcing_to_dht
  these are set to true if this torrent is allowed to announce to the respective peer source. Whether they are true or false is determined by the queue logic/auto manager. Torrents that are not auto managed will always be allowed to announce to all peer sources.

stop_when_ready
  this reflects whether the `stop_when_ready` flag is currently enabled on this torrent. For more information, see torrent_handle::stop_when_ready().

info_hash
  the info-hash for this torrent

## dht_storage_counters

Declared in "libtorrent/kademlia/dht_storage.hpp"

This structure hold the relevant counters for the storage

    struct dht_storage_counters
    {
       boost::int32_t torrents;
       boost::int32_t peers;
       boost::int32_t immutable_data;
       boost::int32_t mutable_data;
    };

## dht_storage_interface

Declared in "libtorrent/kademlia/dht_storage.hpp"

The DHT storage interface is a pure virtual class that can be implemented to customize how the data for the DHT is stored.

The default storage implementation uses three maps in RAM to save the peers, mutable and immutable items and it's designed to provide a fast and fully compliant behavior of the BEPs.

libtorrent comes with one built-in storage implementation: `dht_default_storage` (private non-accessible class). Its constructor function is called dht_default_storage_constructor().

    struct dht_storage_interface
    {
       virtual bool get_peers (sha1_hash const& info_hash
          , bool noseed, bool scrape
          , entry& peers) const = 0;
       virtual void announce_peer (sha1_hash const& info_hash
          , tcp::endpoint const& endp
          , std::string const& name, bool seed) = 0;
       virtual bool get_immutable_item (sha1_hash const& target
          , entry& item) const = 0;
       virtual void put_immutable_item (sha1_hash const& target
          , char const* buf, int size
          , address const& addr) = 0;
       virtual bool get_mutable_item_seq (sha1_hash const& target
          , boost::int64_t& seq) const = 0;
       virtual bool get_mutable_item (sha1_hash const& target
          , boost::int64_t seq, bool force_fill
          , entry& item) const = 0;
       virtual void put_mutable_item (sha1_hash const& target
          , char const* buf, int size
          , char const* sig
          , boost::int64_t seq
          , char const* pk
          , char const* salt, int salt_size
          , address const& addr) = 0;
       virtual void tick () = 0;
       virtual dht_storage_counters counters () const = 0;
       virtual ~dht_storage_interface ();
    };

### get_peers()

    virtual bool get_peers (sha1_hash const& info_hash
          , bool noseed, bool scrape
          , entry& peers) const = 0;

This function retrieve the peers tracked by the DHT corresponding to the given info_hash. You can specify if you want only seeds and/or you are scraping the data.

For future implementers: If the torrent tracked contains a name, such a name must be stored as a string in peers["n"]

If the scrape parameter is true, you should fill these keys:

    peers["BFpe"] - with the standard bit representation of a
                    256 bloom filter containing the downloaders
    peers["BFsd"] - with the standard bit representation of a
                    256 bloom filter containing the seeders

If the scrape parameter is false, you should fill the key peers["values"] with a list containing a subset of peers tracked by the given info_hash. Such a list should consider the value of dht_settings::max_peers_reply. If noseed is true only peers marked as no seed should be included.

returns true if an entry with the info_hash is found and the data is returned inside the (entry) out parameter peers.

### announce_peer()

    virtual void announce_peer (sha1_hash const& info_hash
          , tcp::endpoint const& endp
          , std::string const& name, bool seed) = 0;

This function is named announce_peer for consistency with the upper layers, but has nothing to do with networking. Its only responsibility is store the peer in such a way that it's returned in the entry with the lookup_peers.

The `name` parameter is the name of the torrent if provided in the announce_peer DHT message. The length of this value should have a maximum length in the final storage. The default implementation truncate the value for a maximum of 50 characters.

### get_immutable_item()

    virtual bool get_immutable_item (sha1_hash const& target
          , entry& item) const = 0;

This function retrieves the immutable item given its target hash.

For future implementers: The value should be returned as an entry in the key item["v"].

returns true if the item is found and the data is returned inside the (entry) out parameter item.

### put_immutable_item()

    virtual void put_immutable_item (sha1_hash const& target
          , char const* buf, int size
          , address const& addr) = 0;

Store the item's data. This layer is only for storage. The authentication of the item is performed by the upper layer.

For implementers: This data can be stored only if the target is not already present. The implementation should consider the value of dht_settings::max_dht_items.

### get_mutable_item_seq()

    virtual bool get_mutable_item_seq (sha1_hash const& target
          , boost::int64_t& seq) const = 0;

This function retrieves the sequence number of a mutable item.

returns true if the item is found and the data is returned inside the out parameter seq.

### get_mutable_item()

    virtual bool get_mutable_item (sha1_hash const& target
          , boost::int64_t seq, bool force_fill
          , entry& item) const = 0;

This function retrieves the mutable stored in the DHT.

For implementers: The item sequence should be stored in the key item["seq"]. if force_fill is true or (0 <= seq and seq < item["seq"]) the following keys should be filled item["v"] - with the value no encoded. item["sig"] - with a string representation of the signature. item["k"] - with a string representation of the public key.

returns true if the item is found and the data is returned inside the (entry) out parameter item.

### put_mutable_item()

    virtual void put_mutable_item (sha1_hash const& target
          , char const* buf, int size
          , char const* sig
          , boost::int64_t seq
          , char const* pk
          , char const* salt, int salt_size
          , address const& addr) = 0;

Store the item's data. This layer is only for storage. The authentication of the item is performed by the upper layer.

For implementers: The sequence number should be checked if the item is already present. The implementation should consider the value of dht_settings::max_dht_items.

### tick()

    virtual void tick () = 0;

This function is called periodically (non-constant frequency).

For implementers: Use this functions for expire peers or items or any other storage cleanup.

## generate_fingerprint()

Declared in "libtorrent/fingerprint.hpp"

    std::string generate_fingerprint (std::string name
       , int major, int minor = 0, int revision = 0, int tag = 0);

This is a utility function to produce a client ID fingerprint formatted to the most common convention.

The name string should contain exactly two characters. These are the characters unique to your client, used to identify it. Make sure not to clash with anybody else. Here are some taken id's:

id chars | client
--- | ---
'AZ' | Azureus
'LT' | libtorrent (default)
'BX' | BittorrentX
'MT' | Moonlight Torrent
'TS' | Torrent Storm
'SS' | Swarm Scope
'XT' | Xan Torrent

There's an informal directory of client id's here.

The `major`, `minor`, `revision` and `tag` parameters are used to identify the version of your client.

## to_hex()

Declared in "libtorrent/hex.hpp"

    void to_hex (char const *in, int len, char* out);
    std::string to_hex (std::string const& s);

The overload taking a `std::string` converts (binary) the string `s` to hexadecimal representation and returns it. The overload taking a `char const*` and a length converts the binary buffer [`in`, `in` + len) to hexadecimal and prints it to the buffer `out`. The caller is responsible for making sure the buffer pointed to by `out` is large enough, i.e. has at least len * 2 bytes of space.

## from_hex()

Declared in "libtorrent/hex.hpp"

    bool from_hex (char const *in, int len, char* out);

converts the buffer [`in`, `in` + len) from hexadecimal to binary. The binary output is written to the buffer pointed to by `out`. The caller is responsible for making sure the buffer at `out` has enough space for the result to be written to, i.e. (len + 1) / 2 bytes.

## make_magnet_uri()

Declared in "libtorrent/magnet_uri.hpp"

    std::string make_magnet_uri (torrent_handle const& handle);
    std::string make_magnet_uri (torrent_info const& info);

Generates a magnet URI from the specified torrent. If the torrent handle is invalid, an empty string is returned.

For more information about magnet links, see magnet links.

## session_stats_metrics()

Declared in "libtorrent/session_stats.hpp"

    std::vector<stats_metric> session_stats_metrics ();

This free function returns the list of available metrics exposed by libtorrent's statistics API. Each metric has a name and a value index. The value index is the index into the array in session_stats_alert where this metric's value can be found when the session stats is sampled (by calling post_session_stats()).

## find_metric_idx()

Declared in "libtorrent/session_stats.hpp"

    int find_metric_idx (char const* name);

given a name of a metric, this function returns the counter index of it, or -1 if it could not be found. The counter index is the index into the values array returned by session_stats_alert.

## hash_value()

Declared in "libtorrent/torrent_handle.hpp"

    std::size_t hash_value (torrent_status const& ts);

allows torrent_handle to be used in unordered_map and unordered_set.

## hash_value()

Declared in "libtorrent/torrent_handle.hpp"

    std::size_t hash_value (torrent_handle const& h);

for boost::hash (and to support using this type in unordered_map etc.)

## is_utp_stream_logging()

Declared in "libtorrent/utp_stream.hpp"

    bool is_utp_stream_logging ();

## set_utp_stream_logging()

Declared in "libtorrent/utp_stream.hpp"

    void set_utp_stream_logging (bool enable);

This function should be used at the very beginning and very end of your program.

## version()

Declared in "libtorrent/version.hpp"

    char const* version ();

returns the libtorrent version as string form in this format: "<major>.<minor>.<tiny>.<tag>"

## dht_default_storage_constructor()

Declared in "libtorrent/kademlia/dht_storage.hpp"

    dht_storage_interface* dht_default_storage_constructor (sha1_hash const& id
       , dht_settings const& settings);

## sign_mutable_item()

Declared in "libtorrent/kademlia/item.hpp"

    void sign_mutable_item (
       std::pair<char const*, int> v
       , std::pair<char const*, int> salt
       , boost::uint64_t seq
       , char const* pk
       , char const* sk
       , char* sig);

given a byte range `v` and an optional byte range `salt`, a sequence number, public key `pk` (must be 32 bytes) and a secret key `sk` (must be 64 bytes), this function produces a signature which is written into a 64 byte buffer pointed to by `sig`. The caller is responsible for allocating the destination buffer that's passed in as the `sig` argument. Typically it would be allocated on the stack.

## verify_message()

Declared in "libtorrent/kademlia/msg.hpp"

    bool verify_message (bdecode_node const& msg, key_desc_t const desc[]
       , bdecode_node ret[], int size, char* error, int error_size);