client: Re-use WebSocket connections

Use a socket pool, so tracker clients share WebSocket objects for the
same server.

In practice, WebSockets are pretty slow to establish, so this gives a
nice performance boost, and saves browser resources.

Author: feross

lib/websocket-tracker.js

@@ -11,6 +11,11 @@ var Socket = require('simple-websocket')
 
 var common = require('./common')
 
+// Use a socket pool, so tracker clients share WebSocket objects for the same server.
+// In practice, WebSockets are pretty slow to establish, so this gives a nice performance
+// boost, and saves browser resources.
+var socketPool = {}
+
 var RECONNECT_VARIANCE = 30 * 1000
 var RECONNECT_MINIMUM = 5 * 1000
 
@@ -26,9 +31,10 @@ function WebSocketTracker (client, announceUrl, opts) {
 
   self._opts = opts
 
+  if (announceUrl[announceUrl.length - 1] === '/') {
+    announceUrl = announceUrl.substring(0, announceUrl.length - 1)
+  }
   self._announceUrl = announceUrl
-  if (self._announceUrl[self._announceUrl.length - 1] !== '/') self._announceUrl += '/'
-  self._announceUrl += '?' + hat(40)
 
   self._peers = {} // peers (offer id -> peer)
   self._socket = null
@@ -102,7 +108,11 @@ WebSocketTracker.prototype._openSocket = function () {
   self._onSocketDataBound = self._onSocketData.bind(self)
   self._onSocketCloseBound = self._onSocketClose.bind(self)
 
-  self._socket = new Socket(self._announceUrl)
+  self._socket = socketPool[self._announceUrl]
+  if (!self._socket) {
+    self._socket = socketPool[self._announceUrl] = new Socket(self._announceUrl)
+  }
+
   self._socket.on('data', self._onSocketDataBound)
   self._socket.on('close', self._onSocketCloseBound)
   self._socket.on('error', self._onSocketErrorBound)
@@ -117,10 +127,22 @@ WebSocketTracker.prototype._onSocketData = function (data) {
   }
 
   if (data.info_hash !== self.client._infoHashBinary) {
-    return self.client.emit('warning', new Error('Invalid tracker response'))
+    debug(
+      'ignoring websocket data from %s for %s (looking for %s: reused socket)',
+      self._announceUrl, common.binaryToHex(data.info_hash), self.client._infoHashHex
+    )
+    return
   }
 
-  debug('received %s from %s', JSON.stringify(data), self._announceUrl)
+  if (data.peer_id && data.peer_id === self.client._peerIdBinary) {
+    // ignore offers/answers from this client
+    return
+  }
+
+  debug(
+    'received %s from %s for %s',
+    JSON.stringify(data), self._announceUrl, self.client._infoHashHex
+  )
 
   var failure = data['failure reason']
   if (failure) return self.client.emit('warning', new Error(failure))
@@ -149,13 +171,8 @@ WebSocketTracker.prototype._onSocketData = function (data) {
     })
   }
 
-  if (self.client._peerIdHex === common.binaryToHex(data.peer_id)) {
-    // ignore offers/answers from this client
-    return
-  }
-
   var peer
-  if (data.offer) {
+  if (data.offer && data.peer_id) {
     peer = new Peer({
       trickle: false,
       config: self.client._rtcConfig,
@@ -177,7 +194,7 @@ WebSocketTracker.prototype._onSocketData = function (data) {
     self.client.emit('peer', peer)
   }
 
-  if (data.answer) {
+  if (data.answer && data.peer_id) {
     peer = self._peers[common.binaryToHex(data.offer_id)]
     if (peer) {
       peer.id = common.binaryToHex(data.peer_id)
@@ -191,18 +208,28 @@ WebSocketTracker.prototype._onSocketData = function (data) {
 
 WebSocketTracker.prototype._onSocketClose = function () {
   var self = this
+  if (self.destroyed) return
   self.destroy()
-  var ms = Math.floor(Math.random() * RECONNECT_VARIANCE) + RECONNECT_MINIMUM
-  setTimeout(function () {
-    self._openSocket()
-  }, ms)
-  debug('reconnecting socket in %s ms', ms)
+  self._startReconnectTimer()
 }
 
 WebSocketTracker.prototype._onSocketError = function (err) {
   var self = this
   if (self.destroyed) return
-  self.client.emit('error', err)
+  self.destroy()
+  // errors will often happen if a tracker is offline, so don't treat it as fatal
+  self.client.emit('warning', err)
+  self._startReconnectTimer()
+}
+
+WebSocketTracker.prototype._startReconnectTimer = function () {
+  var self = this
+  var ms = Math.floor(Math.random() * RECONNECT_VARIANCE) + RECONNECT_MINIMUM
+  setTimeout(function () {
+    self.destroyed = false
+    self._openSocket()
+  }, ms)
+  debug('reconnecting socket in %s ms', ms)
 }
 
 WebSocketTracker.prototype._send = function (params) {