Refactor the server-side code

lib/common.js

@@ -4,9 +4,18 @@
 
 var querystring = require('querystring')
 
+exports.NUM_ANNOUNCE_PEERS = 50
+exports.MAX_ANNOUNCE_PEERS = 82
+
 exports.CONNECTION_ID = Buffer.concat([ toUInt32(0x417), toUInt32(0x27101980) ])
 exports.ACTIONS = { CONNECT: 0, ANNOUNCE: 1, SCRAPE: 2, ERROR: 3 }
 exports.EVENTS = { update: 0, completed: 1, started: 2, stopped: 3 }
+exports.EVENT_IDS = {
+  0: 'update',
+  1: 'completed',
+  2: 'started',
+  3: 'stopped'
+};
 
 function toUInt32 (n) {
   var buf = new Buffer(4)

lib/parse_http.js

@@ -0,0 +1,58 @@
+var common = require('./common')
+
+var REMOVE_IPV6_RE = /^::ffff:/
+
+module.exports = parseHttpRequest
+
+function parseHttpRequest (req, options) {
+  var s = req.url.split('?')
+  var params = common.querystringParse(s[1])
+
+  if (s[0] === '/announce') {
+    params.action = common.ACTIONS.ANNOUNCE
+
+    params.peer_id = typeof params.peer_id === 'string' && common.binaryToUtf8(params.peer_id)
+    params.port = Number(params.port)
+
+    if (typeof params.info_hash !== 'string') throw new Error('invalid info_hash')
+    if (params.info_hash.length !== 20) throw new Error('invalid info_hash length')
+    if (typeof params.peer_id !== 'string') throw new Error('invalid peer_id')
+    if (params.peer_id.length !== 20) throw new Error('invalid peer_id length')
+    if (!params.port) throw new Error('invalid port')
+
+    params.left = Number(params.left)
+    params.compact = Number(params.compact)
+
+    params.ip = options.trustProxy
+      ? req.headers['x-forwarded-for'] || req.connection.remoteAddress
+      : req.connection.remoteAddress.replace(REMOVE_IPV6_RE, '') // force ipv4
+    params.addr = params.ip + ':' + params.port // TODO: ipv6 brackets?
+
+    params.numwant = Math.min(
+      Number(params.numwant) || common.NUM_ANNOUNCE_PEERS,
+      common.MAX_ANNOUNCE_PEERS
+    )
+
+    return params
+  } else if (s[0] === '/scrape') { // unofficial scrape message
+    params.action = common.ACTIONS.SCRAPE
+
+    if (typeof params.info_hash === 'string') {
+      params.info_hash = [ params.info_hash ]
+    }
+
+    if (params.info_hash) {
+      if (!Array.isArray(params.info_hash)) throw new Error('invalid info_hash array')
+
+      params.info_hash.forEach(function (infoHash) {
+        if (infoHash.length !== 20) {
+          throw new Error('invalid info_hash')
+        }
+      })
+    }
+
+    return params
+  } else {
+    return null
+  }
+}

lib/parse_udp.js

@@ -0,0 +1,80 @@
+var bufferEqual = require('buffer-equal')
+var ipLib = require('ip')
+var common = require('./common')
+
+
+module.exports = parseUdpRequest
+
+function parseUdpRequest (msg, rinfo) {
+  if (msg.length < 16) {
+    throw new Error('received packet is too short')
+  }
+
+  if (rinfo.family !== 'IPv4') {
+    throw new Error('udp tracker does not support IPv6')
+  }
+
+  var params = {
+    connectionId: msg.slice(0, 8), // 64-bit
+    action: msg.readUInt32BE(8),
+    transactionId: msg.readUInt32BE(12)
+  }
+
+  // TODO: randomize:
+  if (!bufferEqual(params.connectionId, common.CONNECTION_ID)) {
+    throw new Error('received packet with invalid connection id')
+  }
+
+  if (params.action === common.ACTIONS.CONNECT) {
+    // No further params
+  } else if (params.action === common.ACTIONS.ANNOUNCE) {
+    params.info_hash = msg.slice(16, 36).toString('binary') // 20 bytes
+    params.peer_id = msg.slice(36, 56).toString('utf8') // 20 bytes
+    params.downloaded = fromUInt64(msg.slice(56, 64)) // TODO: track this?
+    params.left = fromUInt64(msg.slice(64, 72))
+    params.uploaded = fromUInt64(msg.slice(72, 80)) // TODO: track this?
+    params.event = msg.readUInt32BE(80)
+    params.event = common.EVENT_IDS[params.event]
+    if (!params.event) throw new Error('invalid event') // early return
+    params.ip = msg.readUInt32BE(84) // optional
+    params.ip = params.ip ?
+      ipLib.toString(params.ip) :
+      rinfo.address
+    params.key = msg.readUInt32BE(88) // TODO: what is this for?
+    params.numwant = msg.readUInt32BE(92) // optional
+    // never send more than MAX_ANNOUNCE_PEERS or else the UDP packet will get bigger than
+    // 512 bytes which is not safe
+    params.numwant = Math.min(params.numwant || common.NUM_ANNOUNCE_PEERS, common.MAX_ANNOUNCE_PEERS)
+    params.port = msg.readUInt16BE(96) || rinfo.port // optional
+    params.addr = params.ip + ':' + params.port // TODO: ipv6 brackets
+    params.compact = 1 // udp is always compact
+
+  } else if (params.action === common.ACTIONS.SCRAPE) { // scrape message
+    params.info_hash = msg.slice(16, 36).toString('binary') // 20 bytes
+
+    // TODO: support multiple info_hash scrape
+    if (msg.length > 36) {
+      throw new Error('multiple info_hash scrape not supported')
+    }
+  } else {
+    throw new Error('Invalid action in UDP packet: ' + params.action)
+  }
+
+  return params
+}
+
+// HELPER FUNCTIONS
+
+var TWO_PWR_32 = (1 << 16) * 2
+
+/**
+ * Return the closest floating-point representation to the buffer value. Precision will be
+ * lost for big numbers.
+ */
+function fromUInt64 (buf) {
+  var high = buf.readUInt32BE(0) | 0 // force
+  var low = buf.readUInt32BE(4) | 0
+  var lowUnsigned = (low >= 0) ? low : TWO_PWR_32 + low
+
+  return high * TWO_PWR_32 + lowUnsigned
+}

lib/swarm.js

@@ -0,0 +1,118 @@
+var debug = require('debug')('bittorrent-tracker')
+
+module.exports = Swarm
+
+// Regard this as the default implementation of an interface that you
+// need to support when overriding Server.getSwarm()
+function Swarm (infoHash, server) {
+  this.peers = {}
+  this.complete = 0
+  this.incomplete = 0
+  this.emit = server.emit.bind(server)
+}
+
+Swarm.prototype.announce = function (params, cb) {
+  var self = this
+  var peer = self.peers[params.addr]
+
+  // Dispatch announce event
+  if (!params.event || params.event === 'empty') params.event = 'update'
+  var fn = '_onAnnounce_' + params.event
+  if (self[fn]) {
+    self[fn](params, peer, function (err) {
+      // event processed, prepare response:
+
+      if (params.left === 0 && peer) peer.complete = true
+
+      // send peers
+      var peers = self._getPeers(params.numwant)
+
+      cb(null, {
+        complete: self.complete,
+        incomplete: self.incomplete,
+        peers: peers
+      })
+    })
+  } else {
+    cb(new Error('invalid event'))
+  }
+}
+
+Swarm.prototype._onAnnounce_started = function (params, peer, cb) {
+  if (peer) {
+    debug('unexpected `started` event from peer that is already in swarm')
+    return this._onAnnounce_update() // treat as an update
+  }
+  if (params.left === 0) this.complete += 1
+  else this.incomplete += 1
+  peer = this.peers[params.addr] = {
+    ip: params.ip,
+    port: params.port,
+    peerId: params.peer_id
+  }
+  this.emit('start', params.addr)
+
+  cb()
+}
+
+Swarm.prototype._onAnnounce_stopped = function (params, peer, cb) {
+  if (!peer) {
+    debug('unexpected `stopped` event from peer that is not in swarm')
+    return // do nothing
+  }
+  if (peer.complete) this.complete -= 1
+  else this.incomplete -= 1
+  this.peers[params.addr] = null
+  this.emit('stop', params.addr)
+
+  cb()
+}
+
+Swarm.prototype._onAnnounce_completed = function (params, peer, cb) {
+  if (!peer) {
+    debug('unexpected `completed` event from peer that is not in swarm')
+    return start() // treat as a start
+  }
+  if (peer.complete) {
+    debug('unexpected `completed` event from peer that is already marked as completed')
+    return // do nothing
+  }
+  this.complete += 1
+  this.incomplete -= 1
+  peer.complete = true
+  this.emit('complete', params.addr)
+
+  cb()
+}
+
+Swarm.prototype._onAnnounce_update = function (params, peer, cb) {
+  if (!peer) {
+    debug('unexpected `update` event from peer that is not in swarm')
+    return start() // treat as a start
+  }
+  this.emit('update', params.addr)
+
+  cb()
+}
+
+Swarm.prototype._getPeers = function (numwant) {
+  var peers = []
+  for (var peerId in this.peers) {
+    if (peers.length >= numwant) break
+    var peer = this.peers[peerId]
+    if (!peer) continue // ignore null values
+    peers.push({
+      'peer id': peer.peerId,
+      ip: peer.ip,
+      port: peer.port
+    })
+  }
+  return peers
+}
+
+Swarm.prototype.scrape = function (infoHash, params, cb) {
+  cb(null, {
+    complete: this.complete,
+    incomplete: this.incomplete
+  })
+}

package.json

@@ -26,6 +26,7 @@
     "ip": "^0.3.0",
     "once": "^1.3.0",
     "portfinder": "^0.2.1",
+    "run-series": "^1.0.2",
     "string2compact": "^1.1.1"
   },
   "devDependencies": {