Add minimum timeout option

Fix #403

README.md

@@ -152,6 +152,13 @@ Where `options` is a hash which can contain:
     If you don't specify this option, the default is to use the default random
     string generator to generate 8-character long session ids.
 
+  * **timeout (number)**
+
+    Specify a minimum timeout in milliseconds to use for the transport connections.
+    By default this is dynamically calculated based on the measured RTT and
+    the number of expected round trips. This setting will establish a minimum,
+    but if the calculated timeout is higher, that will be used.
+
 Although the 'SockJS' object tries to emulate the 'WebSocket'
 behaviour, it's impossible to support all of its features. An
 important SockJS limitation is the fact that you're not allowed to

lib/main.js

@@ -49,6 +49,7 @@ function SockJS(url, protocols, options) {
   }
   this._transportsWhitelist = options.transports;
   this._transportOptions = options.transportOptions || {};
+  this._timeout = options.timeout || 0;
 
   var sessionId = options.sessionId || 8;
   if (typeof sessionId === 'function') {
@@ -209,7 +210,7 @@ SockJS.prototype._connect = function() {
     }
 
     // calculate timeout based on RTO and round trips. Default to 5s
-    var timeoutMs = (this._rto * Transport.roundTrips) || 5000;
+    var timeoutMs = Math.max(this._timeout, (this._rto * Transport.roundTrips) || 5000);
     this._transportTimeoutId = setTimeout(this._transportTimeout.bind(this), timeoutMs);
     debug('using timeout', timeoutMs);