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"

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 initiazlied.

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.

dht_nodes name save_path

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.

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 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().

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 refer to a magnet link or a regular http URL.

If it refers to an HTTP URL, the info-hash for the added torrent will not be the true info-hash of the .torrent. Instead a placeholder, unique, info-hash is used which is later updated once the .torrent file has been downloaded.

Once the info-hash change happens, a torrent_update_alert is posted.

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.

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

cache_status()

cache_status ();

initializes all counters to 0

blocks_written

the total number of 16 KiB blocks written to disk since this session was started.

writes

the total number of write operations performed since this session was started.

The ratio (blocks_written - writes) / blocks_written represents the number of saved write operations per total write operations. i.e. a kind of cache hit ratio for the write cahe.

blocks_read

the number of blocks that were requested from the bittorrent engine (from peers), that were served from disk or cache.

blocks_read_hit

the number of blocks that was just copied from the read cache

The ratio blocks_read_hit / blocks_read is the cache hit ratio for the read cache.

reads

the number of read operations used

queued_bytes

the number of bytes waiting, in the disk job queue, to be written or inserted into the disk cache

cache_size

the number of 16 KiB blocks currently in the disk cache (both read and write). This includes both read and write cache.

read_cache_size

the number of 16KiB blocks in the read cache.

total_used_buffers

the total number of buffers currently in use. This includes the read/write disk cache as well as send and receive buffers used in peer connections.

average_queue_time

the number of microseconds an average disk I/O job has to wait in the job queue before it get processed.

average_read_time

the time read jobs takes on average to complete (not including the time in the queue), in microseconds. This only measures read cache misses.

average_write_time

the time write jobs takes to complete, on average, in microseconds. This does not include the time the job sits in the disk job queue or in the write cache, only blocks that are flushed to disk.

average_hash_time average_job_time average_sort_time

the time hash jobs takes to complete on average, in microseconds. Hash jobs include running SHA-1 on the data (which for the most part is done incrementally) and sometimes reading back parts of the piece. It also includes checking files without valid resume data.

job_queue_length

the number of jobs in the job queue.

cumulative_job_time cumulative_read_time cumulative_write_time cumulative_hash_time cumulative_sort_time

the number of milliseconds spent in all disk jobs, and specific ones since the start of the session. Times are specified in milliseconds

total_read_back

the number of bytes that had to be read back from disk because they were flushed before the SHA-1 hash got to hash them. If this is large, a larger cache could significantly improve performance

read_queue_size

number of read jobs in the disk job queue

session_proxy()

session_proxy ();

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

session()

session (fingerprint const& print = fingerprint("LT"
      , LIBTORRENT_VERSION_MAJOR, LIBTORRENT_VERSION_MINOR, 0, 0)
      , int flags = start_default_features | add_default_plugins
      , boost::uint32_t alert_mask = alert::error_notification
      TORRENT_LOGPATH_ARG_DEFAULT);
session (fingerprint const& print
      , std::pair<int, int> listen_port_range
      , char const* listen_interface = "0.0.0.0"
      , int flags = start_default_features | add_default_plugins
      , int alert_mask = alert::error_notification
      TORRENT_LOGPATH_ARG_DEFAULT);

If the fingerprint in the first overload is omited, the client will get a default fingerprint stating the version of libtorrent. The fingerprint is a short string that will be used in the peer-id to identify the client and the client's version. For more details see the fingerprint class. The constructor that only takes a fingerprint will not open a listen port for the session, to get it running you'll have to call session::listen_on(). The other constructor, that takes a port range and an interface as well as the fingerprint will automatically try to listen on a port on the given interface. For more information about the parameters, see listen_on() function.

The flags paramater can be used to start default features (upnp & nat-pmp) and default plugins (ut_metadata, ut_pex and smart_ban). The default is to start those things. If you do not want them to start, pass 0 as the flags parameter.

The alert_mask is the same mask that you would send to set_alert_mask().

~session()

~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 set_settings().

load_state() save_state()

void load_state (lazy_entry const& e);
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 lazy_entry which can be built from a bencoded buffer with lazy_bdecode().

The flags arguments passed in to save_state can be used to filter which parts of the session state to save. By default, all state is saved (except for the individual torrents). see save_state_flags_t

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;

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 ();

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.

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!

abort()

session_proxy abort ();

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

class session_proxy
{
public:
        session_proxy();
        ~session_proxy()
};

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.

status()

session_status status () const;

returns session wide-statistics and status. For more information, see the session_status struct.

get_cache_status()

cache_status get_cache_status () const;

Returns status of the disk cache for this session. For more information, see the cache_status type.

get_cache_info()

void get_cache_info (sha1_hash const& ih
      , std::vector<cached_piece_info>& ret) const;

fills out the supplied vector with information for each piece that is currently in the disk cache for the torrent with the specified info-hash (ih).

add_feed()

feed_handle add_feed (feed_settings const& feed);

This adds an RSS feed to the session. The feed will be refreshed regularly and optionally add all torrents from the feed, as they appear.

Before adding the feed, you must set the url field to the feed's url. It may point to an RSS or an atom feed. The returned feed_handle is a handle which is used to interact with the feed, things like forcing a refresh or querying for information about the items in the feed. For more information, see feed_handle.

remove_feed()

void remove_feed (feed_handle h);

Removes a feed from being watched by the session. When this call returns, the feed handle is invalid and won't refer to any feed.

get_feeds()

void get_feeds (std::vector<feed_handle>& f) const;

Returns a list of all RSS feeds that are being watched by the session.

is_dht_running() start_dht() set_dht_settings() stop_dht()

bool is_dht_running () const;
void start_dht ();
void stop_dht ();
void set_dht_settings (dht_settings const& settings);

starts/stops UPnP, NATPMP or LSD port mappers they are stopped by default These functions are not available in case TORRENT_DISABLE_DHT is defined. start_dht starts the dht node and makes the trackerless service available to torrents. The startup state is optional and can contain nodes and the node id from the previous session. The dht node state is a bencoded dictionary with the following entries:

nodes

A list of strings, where each string is a node endpoint encoded in binary. If the string is 6 bytes long, it is an IPv4 address of 4 bytes, encoded in network byte order (big endian), followed by a 2 byte port number (also network byte order). If the string is 18 bytes long, it is 16 bytes of IPv6 address followed by a 2 bytes port number (also network byte order).

node-id

The node id written as a readable string as a hexadecimal number.

dht_state will return the current state of the dht node, this can be used to start up the node again, passing this entry to start_dht. It is a good idea to save this to disk when the session is closed, and read it up again when starting.

If the port the DHT is supposed to listen on is already in use, and exception is thrown, asio::error.

stop_dht stops the dht node.

add_dht_node adds a node to the routing table. This can be used if your client has its own source of bootstrapping nodes.

set_dht_settings sets some parameters availavle to the dht node. See dht_settings for more information.

is_dht_running() returns true if the DHT support has been started and false otherwise.

add_dht_router() add_dht_node()

void add_dht_router (std::pair<std::string, int> const& 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.

add_dht_router adds the given endpoint to a list of DHT router nodes. If a search is ever made while the routing table is empty, those nodes will be used as backups. Nodes in the router node list will also never be added to the regular routing table, which effectively means they are only used for bootstrapping, to keep the load off them.

An example routing node that you could typically add is router.bittorrent.com.

add_extension()

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

This function adds an extension to this session. The argument is a function object that is called with a torrent* and which should return a boost::shared_ptr<torrent_plugin>. To write custom plugins, see libtorrent plugins. For the typical bittorrent client all of these extensions should be added. The main plugins implemented in libtorrent are:

metadata extension

Allows peers to download the metadata (.torren files) from the swarm directly. Makes it possible to join a swarm with just a tracker and info-hash.

#include <libtorrent/extensions/metadata_transfer.hpp>
ses.add_extension(&libtorrent::create_metadata_plugin);

uTorrent metadata

Same as metadata extension but compatible with uTorrent.

#include <libtorrent/extensions/ut_metadata.hpp>
ses.add_extension(&libtorrent::create_ut_metadata_plugin);

uTorrent peer exchange

Exchanges peers between clients.

#include <libtorrent/extensions/ut_pex.hpp>
ses.add_extension(&libtorrent::create_ut_pex_plugin);

smart ban plugin

A plugin that, with a small overhead, can ban peers that sends bad data with very high accuracy. Should eliminate most problems on poisoned torrents.

#include <libtorrent/extensions/smart_ban.hpp>
ses.add_extension(&libtorrent::create_smart_ban_plugin);

load_asnum_db() load_country_db() as_for_ip()

void load_country_db (char const* file);
void load_asnum_db (char const* file);
int as_for_ip (address const& addr);

These functions are not available if TORRENT_DISABLE_GEO_IP is defined. They expects a path to the MaxMind ASN database and MaxMind GeoIP database respectively. This will be used to look up which AS and country peers belong to.

as_for_ip returns the AS number for the IP address specified. If the IP is not in the database or the ASN database is not loaded, 0 is returned.

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.

set_peer_id() id()

peer_id id () const;
void set_peer_id (peer_id const& pid);

sets and gets the raw peer ID used by libtorrent. When anonymous mode is set the peer ID is randomized per peer anyway.

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() listen_on() ssl_listen_port() is_listening()

void listen_on (
      std::pair<int, int> const& port_range
      , error_code& ec
      , const char* net_interface = 0
      , int flags = 0);
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 use listen_on() to make another attempt.

listen_port() returns the port we ended up listening on. Since you just pass a port-range to the constructor and to listen_on(), to know which port it ended up using, you have to ask the session using this function.

listen_on() will change the listen port and/or the listen interface. If the session is already listening on a port, this socket will be closed and a new socket will be opened with these new settings. The port range is the ports it will try to listen on, if the first port fails, it will continue trying the next port within the range and so on. The interface parameter can be left as 0, in that case the os will decide which interface to listen on, otherwise it should be the ip-address of the interface you want the listener socket bound to. listen_on() returns the error code of the operation in ec. If this indicates success, the session is listening on a port within the specified range. If it fails, it will also generate an appropriate alert (listen_failed_alert).

If all ports in the specified range fails to be opened for listening, libtorrent will try to use port 0 (which tells the operating system to pick a port that's free). If that still fails you may see a listen_failed_alert with port 0 even if you didn't ask to listen on it.

It is possible to prevent libtorrent from binding to port 0 by passing in the flag session::no_system_port in the flags argument.

The interface parameter can also be a hostname that will resolve to the device you want to listen on. If you don't specify an interface, libtorrent may attempt to listen on multiple interfaces (typically 0.0.0.0 and ::). This means that if your IPv6 interface doesn't work, you may still see a listen_failed_alert, even though the IPv4 port succeeded.

The flags parameter can either be 0 or session::listen_reuse_address, which will set the reuse address socket option on the listen socket(s). By default, the listen socket does not use reuse address. If you're running a service that needs to run on a specific port no matter if it's in use, set this flag.

If you're also starting the DHT, it is a good idea to do that after you've called listen_on(), since the default listen port for the DHT is the same as the tcp listen socket. If you start the DHT first, it will assume the tcp port is free and open the udp socket on that port, then later, when listen_on() is called, it may turn out that the tcp port is in use. That results in the DHT and the bittorrent socket listening on different ports. If the DHT is active when listen_on is called, the udp port will be rebound to the new port, if it was configured to use the same port as the tcp socket, and if the listen_on call failed to bind to the same port that the udp uses.

If you want the OS to pick a port for you, pass in 0 as both first and second.

The reason why it's a good idea to run the DHT and the bittorrent socket on the same port is because that is an assumption that may be used to increase performance. One way to accelerate the connecting of peers on windows may be to first ping all peers with a DHT ping packet, and connect to those that responds first. On windows one can only connect to a few peers at a time because of a built in limitation (in XP Service pack 2).

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 asyncronous, there is no guarantee that adding the same torrent immediately after it was removed will not throw a libtorrent_exception exception. Once the torrent is deleted, a torrent_deleted_alert is posted.

set_pe_settings() settings() get_pe_settings() set_settings()

session_settings settings () const;
void set_settings (session_settings const& s);
pe_settings get_pe_settings () const;
void set_pe_settings (pe_settings const& settings);

Sets the session settings and the packet encryption settings respectively. See session_settings and pe_settings for more information on available options.

set_proxy() proxy()

void set_proxy (proxy_settings const& s);
proxy_settings proxy () const;

These functions sets and queries the proxy settings to be used for the session.

For more information on what settings are available for proxies, see proxy_settings. If the session is not in anonymous mode, proxies that aren't working or fail, will automatically be disabled and packets will flow without using any proxy. If you want to enforce using a proxy, even when the proxy doesn't work, enable anonymous_mode in session_settings.

i2p_proxy() set_i2p_proxy()

proxy_settings i2p_proxy () const;
void set_i2p_proxy (proxy_settings const& s);

set_i2p_proxy sets the i2p proxy, and tries to open a persistant connection to it. The only used fields in the proxy settings structs are hostname and port.

i2p_proxy returns the current i2p proxy in use.

pop_alert() pop_alerts() wait_for_alert()

void pop_alerts (std::deque<alert*>* alerts);
std::auto_ptr<alert> pop_alert ();
alert const* wait_for_alert (time_duration max_wait);

pop_alert() is used to ask the session if any errors or events has occurred. With set_alert_mask() you can filter which alerts to receive through pop_alert(). For information about the alert categories, see alerts.

pop_alerts() pops all pending alerts in a single call. In high performance environments with a very high alert churn rate, this can save significant amount of time compared to popping alerts one at a time. Each call requires one round-trip to the network thread. If alerts are produced in a higher rate than they can be popped (when popped one at a time) it's easy to get stuck in an infinite loop, trying to drain the alert queue. Popping the entire queue at once avoids this problem.

However, the pop_alerts function comes with significantly more responsibility. You pass in an empty std::dequeue<alert*> to it. If it's not empty, all elements in it will be deleted and then cleared. All currently pending alerts are returned by being swapped into the passed in container. The responsibility of deleting the alerts is transferred to the caller. This means you need to call delete for each item in the returned dequeue. It's probably a good idea to delete the alerts as you handle them, to save one extra pass over the dequeue.

Alternatively, you can pass in the same container the next time you call pop_alerts.

wait_for_alert blocks until an alert is available, or for no more than max_wait time. If wait_for_alert returns because of the time-out, and no alerts are available, it returns 0. If at least one alert was generated, a pointer to that alert is returned. The alert is not popped, any subsequent calls to wait_for_alert will return the same pointer until the alert is popped by calling pop_alert. This is useful for leaving any alert dispatching mechanism independent of this blocking call, the dispatcher can be called and it can pop the alert independently.

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

To control the max number of alerts that's queued by the session, see session_settings::alert_queue_size.

save_resume_data_alert and save_resume_data_failed_alert are always posted, regardelss of the alert mask.

set_alert_mask()

void set_alert_mask (boost::uint32_t m);

Changes the mask of which alerts to receive. By default only errors are reported. m is a bitmask where each bit represents a category of alerts.

See category_t enum for options.

set_alert_dispatch()

void set_alert_dispatch (boost::function<void(std::auto_ptr<alert>)> const& fun);

This sets a function to be called (from within libtorrent's netowrk thread) every time an alert is posted. Since the function (fun) is run in libtorrent's internal thread, it may not call any of libtorrent's external API functions. Doing so results in a dead lock.

The main intention with this function is to support integration with platform-dependent message queues or signalling systems. For instance, on windows, one could post a message to an HNWD or on linux, write to a pipe or an eventfd.

start_lsd() stop_lsd()

void stop_lsd ();
void start_lsd ();

Starts and stops Local Service Discovery. This service will broadcast the infohashes of all the non-private torrents on the local network to look for peers on the same swarm within multicast reach.

It is turned off by default.

stop_upnp() start_upnp()

void stop_upnp ();
void start_upnp ();

Starts and stops the UPnP service. When started, the listen port and the DHT port are attempted to be forwarded on local UPnP router devices.

The upnp object returned by start_upnp() can be used to add and remove arbitrary port mappings. Mapping status is returned through the portmap_alert and the portmap_error_alert. The object will be valid until stop_upnp() is called. See upnp and nat pmp.

It is off by default.

start_natpmp() stop_natpmp()

void stop_natpmp ();
void start_natpmp ();

Starts and stops the NAT-PMP service. When started, the listen port and the DHT port are attempted to be forwarded on the router through NAT-PMP.

The natpmp object returned by start_natpmp() can be used to add and remove arbitrary port mappings. Mapping status is returned through the portmap_alert and the portmap_error_alert. The object will be valid until stop_natpmp() is called. See upnp and nat pmp.

It is off by default.

enum save_state_flags_t

Declared in "libtorrent/session.hpp"

enum listen_on_flags_t

Declared in "libtorrent/session.hpp"

enum options_t

Declared in "libtorrent/session.hpp"

enum session_flags_t

Declared in "libtorrent/session.hpp"

min_memory_usage() high_performance_seed()

Declared in "libtorrent/session.hpp"

session_settings min_memory_usage ();
session_settings high_performance_seed ();

The default values of the session settings are set for a regular bittorrent client running on a desktop system. There are functions that can set the session settings to pre set settings for other environments. These can be used for the basis, and should be tweaked to fit your needs better.

min_memory_usage returns settings that will use the minimal amount of RAM, at the potential expense of upload and download performance. It adjusts the socket buffer sizes, disables the disk cache, lowers the send buffer watermarks so that each connection only has at most one block in use at any one time. It lowers the outstanding blocks send to the disk I/O thread so that connections only have one block waiting to be flushed to disk at any given time. It lowers the max number of peers in the peer list for torrents. It performs multiple smaller reads when it hashes pieces, instead of reading it all into memory before hashing.

This configuration is inteded to be the starting point for embedded devices. It will significantly reduce memory usage.

high_performance_seed returns settings optimized for a seed box, serving many peers and that doesn't do any downloading. It has a 128 MB disk cache and has a limit of 400 files in its file pool. It support fast upload rates by allowing large send buffers.