ut_metadata

BitTorrent Extension for Peers to Send Metadata Files (BEP 9)

JavaScript implementation of the Extension for Peers to Send Metadata Files (BEP 9). Use with bittorrent-protocol.

The purpose of this extension is to allow clients to join a swarm and complete a download without the need of downloading a .torrent file first. This extension instead allows clients to download the metadata from peers. It makes it possible to support magnet links, a link on a web page only containing enough information to join the swarm (the info hash).

Works in the browser with browserify! This module is used by WebTorrent.

install

npm install ut_metadata

usage

This package should be used with bittorrent-protocol, which supports a plugin-like system for extending the protocol with additional functionality.

Say you're already using bittorrent-protocol. Your code might look something like this:

const Protocol = require('bittorrent-protocol')
const net = require('net')
 
net.createServer(socket => {
  var wire = new Protocol()
  socket.pipe(wire).pipe(socket)
 
  // handle handshake
  wire.on('handshake', (infoHash, peerId) => {
    wire.handshake(new Buffer('my info hash'), new Buffer('my peer id'))
  })
 
}).listen(6881)

To add support for BEP 9, simply modify your code like this:

const Protocol = require('bittorrent-protocol')
const net = require('net')
const ut_metadata = require('ut_metadata')
 
net.createServer(socket => {
  const wire = new Protocol()
  socket.pipe(wire).pipe(socket)
 
  // initialize the extension
  wire.use(ut_metadata())
 
  // all `ut_metadata` functionality can now be accessed at wire.ut_metadata
 
  // ask the peer to send us metadata
  wire.ut_metadata.fetch()
 
  // 'metadata' event will fire when the metadata arrives and is verified to be correct!
  wire.ut_metadata.on('metadata', metadata => {
    // got metadata!
 
    // Note: the event will not fire if the peer does not support ut_metadata, if they
    // don't have metadata yet either, if they repeatedly send invalid data, or if they
    // simply don't respond.
  })
 
  // optionally, listen to the 'warning' event if you want to know that metadata is
  // probably not going to arrive for one of the above reasons.
  wire.ut_metadata.on('warning', err => {
    console.log(err.message)
  })
 
  // handle handshake
  wire.on('handshake', (infoHash, peerId) => {
    wire.handshake(new Buffer('my info hash'), new Buffer('my peer id'))
  })
 
}).listen(6881)

api

ut_metadata([metadata])

Initialize the extension. If you have the torrent metadata (Buffer), pass it into the ut_metadata constructor so it's made available to the peer.

const metadata = fs.readFileSync(__dirname + '/file.torrent')
wire.use(ut_metadata(metadata))

ut_metadata.fetch()

Ask the peer to send metadata.

ut_metadata.cancel()

Stop asking the peer to send metadata.

ut_metadata.setMetadata(metadata)

Set the metadata. If you didn't have the metadata at the time ut_metadata was initialized, but you end up getting it from another peer (or somewhere else), you should call setMetadata so the metadata will be available to the peer.

ut_metadata.on('metadata', function (metadata) {})

Fired when metadata is available and verified to be correct. Called with a single parameter of type Buffer.

wire.ut_metadata.on('metadata', metadata => {
  console.log(Buffer.isBuffer(metadata)) // true
})

Note: the event will not fire if the peer does not support ut_metadata, if they don't have metadata yet either, if they repeatedly send invalid data, or if they simply don't respond.

ut_metadata.on('warning', function (err) {})

Fired if:

• the peer does not support ut_metadata
• the peer doesn't have metadata yet
• the peer repeatedly sent invalid data

wire.ut_metadata.on('warning', err => {
  console.log(err.message)
})

license

MIT. Copyright (c) Feross Aboukhadijeh and WebTorrent, LLC.