emitting proxySocket on proxyServer

- emitted once proxySocket was created and socket was piped into it
- needed to support sniffing messages coming from proxy target

README.md

@@ -190,6 +190,7 @@ http.createServer(function (req, res) {
 
 * `error`: The error event is emitted if the request to the target fail.
 * `proxyRes`: This event is emitted if the request to the target got a response.
+* `proxySocket`: This event is emitted once the proxy websocket was created and piped into the target websocket.
 
 ```js
 var httpProxy = require('http-proxy');
@@ -220,6 +221,13 @@ proxy.on('proxyRes', function (proxyRes, req, res) {
   console.log('RAW Response from the target', JSON.stringify(proxyRes.headers, true, 2));
 });
 
+//
+// Listen for the `proxySocket` event on `proxy`.
+//
+proxy.on('proxySocket', function (proxySocket) {
+  // listen for messages coming FROM the target here
+  proxySocket.on('data', hybiParseAndLogMessage);
+});
 ```
 
 #### Using HTTPS

lib/http-proxy/passes/ws-incoming.js

@@ -108,6 +108,7 @@ var passes = exports;
         return i + ": " + proxyRes.headers[i];
       }).join('\r\n') + '\r\n\r\n');
       proxySocket.pipe(socket).pipe(proxySocket);
+      server.emit('proxySocket', proxySocket);
     });
 
     return proxyReq.end(); // XXX: CHECK IF THIS IS THIS CORRECT