AnyEvent::BitTorrent - Yet Another BitTorrent Client Module


        use AnyEvent::BitTorrent;
        my $client = AnyEvent::BitTorrent->new( path => 'some.torrent' );


This is a painfully simple BitTorrent client written on a whim that implements the absolute basics. For a full list of what's currently supported, what you will likely find in a future version, and what you'll never get from this, see the section entitled "This Module is Lame!"


The API, much like the module itself, is simple.

Anything you find by skimming the source is likely not ready for public use and will be subject to change before v1.0.0. Here's the public interface as of this version:

new( ... )

        my $c = AnyEvent::BitTorrent->new(
                path         => 'some/legal.torrent',
                basedir      => './storage/',
                port         => 6881,
                on_hash_pass => sub { ... },
                on_hash_fail => sub { ... },
                state        => 'stopped',
                piece_cache  => $quick_restore

This constructor understands the following arguments:


This is the only required parameter. It's the path to a valid .torrent file.


This is the base directory all data will be stored in and/or read from. Multifile torrents will create another directory below this to store all files.

By default, this is the current working directory when new( ... ) is called.


This is the preferred port local host binds and expects incoming peers to connect to.

By default, this is a zero; the system will pick a port number randomly.


This is a subroutine called whenever a piece fails to pass hashcheck. The callback is handed the piece's index.


This is a subroutine called whenever a piece passes its hashcheck. The callback is handed the piece's index.


This must be one of the following:


This is the default. The client will attempt to create new connections, make and fill requests, etc. This is normal client behavior.


In this state, connections will be made and accepted but no piece requests will be made or filled. To resume full, normal behavior, you must call start( ).


Everything is put on hold. No new outgoing connections are attempted and incoming connections are rejected. To resume full, normal behavior, you must call start( ).


This is the index list returned by piece_cache( ) in a previous instance. Using this should make a complete resume system a trivial task.

hashcheck( [...] )

This method expects...

...a list of integers. You could use this to check a range of pieces (a single file, for example).
        $client->hashcheck( 1 .. 5, 34 .. 56 );
...a single integer. Only that specific piece is checked.
        $client->hashcheck( 17 );
        $client->hashcheck( );

As pieces pass or fail, your on_hash_pass and on_hash_fail callbacks are triggered.

start( )

Sends a 'started' event to trackers and starts performing as a client is expected. New connections are made and accepted, requests are made and filled, etc.

stop( )

Sends a stopped event to trackers, closes all connections, stops attempting new outgoing connections, rejects incoming connections and closes all open files.

pause( )

The client remains mostly active; new connections will be made and accepted, etc. but no requests will be made or filled while the client is paused.

infohash( )

Returns the 20-byte SHA1 hash of the value of the info key from the metadata file.

peerid( )

Returns the 20 byte string used to identify the client. Please see the spec below.

port( )

Returns the port number the client is listening on.

size( )

Returns the total size of all files described in the torrent's metadata.

name( )

Returns the UTF-8 encoded string the metadata suggests we save the file (or directory, in the case of multi-file torrents) under.

uploaded( )

Returns the total amount uploaded to remote peers.

downloaded( )

Returns the total amount downloaded from other peers.

left( )

Returns the approximate amount based on the pieces we still want multiplied by the size of pieces.

piece_length( )

Returns the number of bytes in each piece the file or files are split into. For the purposes of transfer, files are split into fixed-size pieces which are all the same length except for possibly the last one which may be truncated.

bitfield( )

Returns a packed binary string in ascending order (ready for vec()). Each index that the client has is set to one and the rest are set to zero.

wanted( )

Returns a packed binary string in ascending order (ready for vec()). Each index that the client has or simply does not want is set to zero and the rest are set to one.

This value is calculated every time the method is called. Keep that in mind.

complete( )

Returns true if we have downloaded everything we wanted which is not to say that we have all data and can seed.

seed( )

Returns true if we have all data related to the torrent.

files( )

Returns a list of hash references with the following keys:


Which is the size of file in bytes.


Which is the absolute path of the file.


Download priority for this file. By default, all files have a priority of 1. There is no built in scale; the higher the priority, the better odds a piece from it will be downloaded first. Setting a file's priority to 1000 while the rest are still at 1 will likely force the file to complete before any other file is started.

We do not download files with a priority of zero.

peers( )

Returns the list of currently connected peers. The organization of these peers is not yet final so... don't write anything you don't expect to break before we hit v1.0.0.

state( )

Returns active if the client is started, paused if client is paused, and stopped if the client is currently stopped.

piece_cache( )

Pieces which overlap files with zero priority are stored in a part file which is indexed internally. To save this index (for resume, etc.) store the values returned by this method and pass it to new( ).

trackers( )

Returns a list of hashes, each representing a single tier of trackers as defined by BEP12. The hashes contain the following keys:


The is a count of complete peers (seeds) as returned by the most recent announce.


This is a running total of the number of failed announces we've had in a row. This value is reset when we have a successful announce.


The is a count of incomplete peers (leechers) as returned by the most recent announce.


Which is a compact collection of IPv4 peers returned by the tracker. See BEP23.


Which is a compact collection of IPv6 peers returned by the tracker. See BEP07.


Which is a list of URLs.

This Module is Lame!

Yeah, I said it.

There are a few things a BitTorrent client must implement (to some degree) in order to interact with other clients in a modern day swarm. AnyEvent::BitTorrent is meant to meet that bare minimum but it's based on Moo so you could always subclass it to add more advanced functionality. Hint, hint!

What is currently supported?

Basic stuff. We can make and handle piece requests. Deal with cancels, disconnect idle peers, unchoke folks, fast extensions, file download priorities. Normal... stuff. HTTP trackers.

What will probably be supported in the future?

DHT (which will likely be in a separate dist), IPv6 stuff... I'll get around to those.

Long term, UDP trackers may be supported.

For a detailed list, see the TODO file included with this distribution.

What will likely never be supported?

We can't have nice things. Protocol encryption, uTP, endgame tricks, ...these will probably never be included in AnyEvent::BitTorrent.

What should I use instead?

If you're reading all of this with a scowl, there are many alternatives to this module, most of which are sure to be better suited for advanced users. I suggest (in no particular order):

BitFlu. It's written in Perl but you'll still need to be on a Linux, *BSD, et al. system to use it.
Net::BitTorrent the future. I do not suggest using either the current stable or unstable versions found on CPAN. The next version is being worked on and will be based on Reflex.

If you're working on a Perl based client and would like me to link to it, send a bug report to the tracker listed below.

Subclassing AnyEvent::BitTorrent


If you subclass this module and change the way it functions to that which in any way proves harmful to individual peers or the swarm at large, rather than damage AnyEvent::BitTorrent's reputation, override the peerid attribute. Thanks.

PeerID Specification

AnyEvent::BitTorrent may be identified in a swarm by its peer id. As of this version, our peer id is in 'Azureus style' with a single digit for the Major version, two digits for the minor version, and a single character to indicate stability (stable releases marked with S, unstable releases marked with U). It looks sorta like:

        -AB110S-  Stable v1.10.0 relese (typically found on CPAN, tagged in repo)
        -AB110U-  Unstable v1.10.X release (private builds, early testing, etc.)

Bug Reports

If email is better for you, my address is mentioned below but I would rather have bugs sent through the issue tracker found at

Please check the ToDo file included with this distribution in case your bug is already known (...I probably won't file bug reports to myself).

See Also

Net::BitTorrent::Protocol - The package which does all of the wire protocol level heavy lifting.


Sanko Robinson <> -


License and Legal

Copyright (C) 2011-2016 by Sanko Robinson <>

This program is free software; you can redistribute it and/or modify it under the terms of The Artistic License 2.0. See the LICENSE file included with this distribution or notes on the Artistic License 2.0 for clarification.

When separated from the distribution, all original POD documentation is covered by the Creative Commons Attribution-Share Alike 3.0 License. See the clarification of the CCA-SA3.0.

Neither this module nor the Author is affiliated with BitTorrent, Inc.