NAME

Net::BitTorrent - Complete, Modern BitTorrent Client Library

SYNOPSIS

use v5.40;
use Net::BitTorrent;
use Net::BitTorrent::Types qw[:encryption];

# Initialize the client
my $client = Net::BitTorrent->new(
    upnp_enabled => 1,
    encryption   => ENCRYPTION_REQUIRED # or 'required'
);

# Unified add() handles magnets, .torrents, or v1/v2 infohashes
# Supports 20/32-byte binary or 40/64-character hex strings
my $torrent = $client->add("magnet:?xt=urn:btih:...", "./downloads");

# Simple event handling
$client->on(torrent_added => sub ($nb, $t) {
    say "New swarm added: " . $t->name;
    $t->start();
});

# Advanced: Manual event loop integration
# while (1) {
#     $client->tick(0.1);
#     select(undef, undef, undef, 0.1);
# }

# Wait for all downloads to finish
$client->wait();

# Graceful shutdown
$client->shutdown();

DESCRIPTION

Net::BitTorrent is a comprehensive, high-performance BitTorrent client library rewritten from the ground up for Modern Perl (v5.40+) using the native class feature.

The library is designed around three core principles:

• 1. Loop-agnosticism: The core logic is decoupled from I/O. You can drive it with a simple while loop, integrate it into IO::Async, Mojo::IOLoop, or even run it in a synchronous environment.
• 2. BitTorrent v2 first: Full support for BEP 52 (BitTorrent v2), including SHA-256 infohashes, Merkle tree block verification, and hybrid v1/v2 swarms.
• 3. Security: Features like BEP 42 (DHT Security), Protocol Encryption (MSE/PE), and peer reputation tracking are built-in and enabled by default.

How Everything Fits Together

Net::BitTorrent uses a hierarchical architecture to manage the complexities of the protocol:

1. The Client (Net::BitTorrent)

The entry point. It manages multiple swarms, global rate limits, decentralized discovery (DHT/LPD), and unified UDP packet routing. It also provides a centralized "hashing queue" to prevent block verification from starving your CPU.

2. Torrents (Net::BitTorrent::Torrent)

Orchestrates a single swarm. It manages its own list of discovered peers, the Piece Picker (rarest-first logic), and communicates with the Trackers. It acts as the bridge between the network (Peers) and the local disk (Storage).

3. Peers (Net::BitTorrent::Peer)

Tracks the state of a single connection (choking, interested, transfer rates). It uses a Protocol Handler to speak the wire protocol and a Net::BitTorrent::Transport (TCP or uTP) to move bytes.

4. Storage (Net::BitTorrent::Storage)

Manages files on disk. It uses Merkle trees for per-block verification (v2) and handles the "virtual contiguous file" mapping required for v1 compatibility. It includes an asynchronous disk cache to keep the main loop fast.

METHODS

new( %params )

Creates a new client instance.

my $client = Net::BitTorrent->new(
    port         => 6881,
    encryption   => 'required', # 'none', 'preferred', or 'required'
    upnp_enabled => 1
);

This method initializes the BitTorrent engine with custom configuration.

Expected parameters:

• port - optional

  The port to listen on for incoming connections. Defaults to a random port in the dynamic range.

• user_agent - optional

  The user agent string reported to trackers and peers.

• encryption - optional

  The encryption requirement level. Can be none, preferred, or required (default).

• upnp_enabled - optional

  Whether to attempt UPnP port mapping. Defaults to false.

• bepXX - optional

  Toggles for specific BEPs (e.g., bep05 => 0 to disable DHT). Defaults to enabled for supported BEPs.

on( $event, $callback )

Registers a global callback for client-level events.

$client->on(torrent_added => sub ($nb, $torrent) {
    warn "Added: " . $torrent->name;
});

This method allows you to react to system-wide changes or automate actions for newly added swarms.

Expected parameters:

• $event

  The name of the event to listen for (e.g., torrent_added).

• $callback

  The code reference to execute when the event is emitted.

add( $thing, $base_path, [%args] )

The recommended, unified method for adding a swarm.

# Add a .torrent file
$client->add("ubuntu.torrent", "./iso");

# Add a magnet link
$client->add("magnet:?xt=urn:btih:...", "./data");

This method automatically detects the type of the first parameter and adds the corresponding swarm. It returns a Net::BitTorrent::Torrent object on success.

Expected parameters:

• $thing

  The resource to add. Can be a file path, a Magnet URI, or an infohash (hex or binary).

• $base_path

  The directory where the torrent's data will be stored.

• %args - optional

  Optional parameters to pass to the Net::BitTorrent::Torrent constructor.

add_torrent( $path, $base_path, [%args] )

Adds a torrent from a local .torrent file.

my $t = $client->add_torrent("linux.torrent", "/downloads");

This method is for adding a swarm specifically from a metadata file. It returns a Net::BitTorrent::Torrent object.

Expected parameters:

• $path

  The path to the .torrent file.

• $base_path

  The directory where the torrent's data will be stored.

• %args - optional

  Optional parameters to pass to the Net::BitTorrent::Torrent constructor.

add_infohash( $ih, $base_path, [%args] )

Adds a torrent by its info hash.

my $t = $client->add_infohash(pack('H*', '...'), './data');

This method is useful for bootstrapping a swarm when only the hash is known. It returns a Net::BitTorrent::Torrent object.

Expected parameters:

• $ih

  The infohash. Can be a 20-byte (v1) or 32-byte (v2) binary string, or a 40/64 character hex string.

• $base_path

  The directory where the torrent's data will be stored.

• %args - optional

  Optional parameters to pass to the Net::BitTorrent::Torrent constructor.

add_magnet( $uri, $base_path, [%args] )

Adds a torrent from a Magnet URI.

my $t = $client->add_magnet("magnet:?xt=urn:btmh:...", "./data");

This method allows adding resources from web links. It returns a Net::BitTorrent::Torrent object.

Expected parameters:

• $uri

  The Magnet URI.

• $base_path

  The directory where the torrent's data will be stored.

• %args - optional

  Optional parameters to pass to the Net::BitTorrent::Torrent constructor.

torrents( )

Returns a list of all active torrents.

my $list = $client->torrents( );

This method returns an array reference containing all currently managed Net::BitTorrent::Torrent objects.

finished( )

Returns a list of completed torrents.

my $done = $client->finished();

This method returns an array reference of all managed torrents that have completed their download.

wait( [$condition], [$timeout] )

Blocks execution until a condition is met.

$client->wait();

This method runs the internal event loop until the provided condition returns true or a timeout is reached. It returns a boolean indicating if the condition was met.

Expected parameters:

• $condition - optional

  A code reference that returns true to stop waiting. Defaults to waiting for all torrents to finish.

• $timeout - optional

  The maximum number of seconds to wait.

tick( [$timeout] )

The "heartbeat" of the library.

$client->tick(0.1);

This method performs discovery, updates swarm logic, and handles network I/O.

Expected parameters:

• $timeout - optional

  The duration in seconds since the last call. Defaults to 0.1.

save_state( $path )

Persists session state to a file.

$client->save_state('session.json');

This method saves the current client state to a JSON file.

Expected parameters:

• $path

  The file path where the state will be saved.

load_state( $path )

Restores session state from a file.

$client->load_state('session.json');

This method loads client state from a JSON file.

Expected parameters:

• $path

  The file path to load the state from.

dht_get( $target, $callback )

Retrieves data from the DHT.

$client->dht_get($target_hash, sub ($value, $node) { ... });

This method initiates a DHT lookup for the specified target hash.

Expected parameters:

• $target

  The 20-byte SHA-1 hash of the data key.

• $callback

  The code reference called when data is found.

dht_put( $value, [$callback] )

Stores data in the DHT.

$client->dht_put('My Shared Note');

This method stores immutable data in the DHT.

Expected parameters:

• $value

  The data to store.

• $callback - optional

  The code reference called when the store operation completes.

dht_scrape( $infohash, $callback )

Performs a decentralized scrape.

$client->dht_scrape($infohash, sub ($stats) { ... });

This method queries the DHT for seeder and leecher counts.

Expected parameters:

• $infohash

  The infohash to scrape.

• $callback

  The code reference called with the scrape results.

shutdown( )

Gracefully stops the client.

$client->shutdown();

This method stops all swarms, unmaps ports, and releases resources.

features( )

Returns the enabled features.

my $f = $client->features();

This method returns a hash reference containing the status of various BEPs.

set_limit_down( $val )

Sets the global download rate limit.

$client->set_limit_down( 1024 * 1024 ); # 1MiB/s

This method sets the maximum download rate in bytes per second.

Expected parameters:

• $val

  The limit in bytes per second. Use 0 for unlimited.

hashing_queue_size( )

Returns the number of pieces waiting for verification.

my $size = $client->hashing_queue_size();

This method returns the current size of the background hashing queue.

queue_verification( $torrent, $index, $data )

Queues a piece for background verification.

$client->queue_verification( $torrent, $index, $data );

This method adds a piece to the throttled background hashing queue.

Expected parameters:

• $torrent

  The Net::BitTorrent::Torrent object the piece belongs to.

• $index

  The piece index.

• $data

  The piece data.

SUPPORTED BEPS

• BEP 03: The BitTorrent Protocol (TCP)
• BEP 05: Mainline DHT
• BEP 06: Fast Extension
• BEP 09: Metadata Exchange
• BEP 10: Extension Protocol
• BEP 11: Peer Exchange (PEX)
• BEP 14: Local Peer Discovery (LPD)
• BEP 29: uTP (UDP Transport)
• BEP 42: DHT Security Extensions
• BEP 52: BitTorrent v2
• BEP 53: Magnet URI Extension

AUTHOR

Sanko Robinson sanko@cpan.org

COPYRIGHT

Copyright (C) 2008-2026 by Sanko Robinson.

This library is free software; you can redistribute it and/or modify it under the terms of the Artistic License 2.0.