ut_metadata

Extension for Peers to Send Metadata Files (BEP 9)

ut_metadata

Node.js 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.

npm install ut_metadata

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:

var Protocol = require('bittorrent-protocol')
var net = require('net')
 
net.createServer(function (socket) {
  var wire = new Protocol()
  socket.pipe(wire).pipe(socket)
 
  // handle handshake 
  wire.on('handshake', function (infoHashpeerId) {
    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:

var Protocol = require('bittorrent-protocol')
var net = require('net')
var ut_metadata = require('ut_metadata')
 
net.createServer(function (socket) {
  var 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', function (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', function (err) {
    console.log(err.message)
  })
 
  // handle handshake 
  wire.on('handshake', function (infoHashpeerId) {
    wire.handshake(new Buffer('my info hash'), new Buffer('my peer id'))
  })
 
}).listen(6881)

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.

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

Ask the peer to send metadata.

Stop asking the peer to send 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.

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

wire.ut_metadata.on('metadata', function (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.

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', function (err) {
  console.log(err.message)
})

MIT. Copyright (c) Feross Aboukhadijeh.