feat: ability to subscribe on websocket client/server senders

Author: DudaGod

README.md

@@ -489,6 +489,34 @@ proxy.on('close', function (res, socket, head) {
 
 **[Back to top](#table-of-contents)**
 
+### Listening for websocket proxy request events
+
+* `clientSender`: This event is emitted after websocket sender from client to server is initialized
+* `serverSender`: This event is emitted after websocket sender from server to client is initialized
+
+```js
+httpProxy.createServer({
+  target: 'ws://localhost:9014',
+  ws: true
+}).listen(8014);
+
+proxyServer.on('upgrade', function (req, socket, head) {
+  proxy.ws(req, socket, head);
+});
+
+proxyServer.on('proxyReqWs', (proxyReq, req, socket, options, head) => {
+  proxyReq.on('clientSender', (clientSender) => {
+    clientSender.send('hello, server');
+  });
+
+  proxyReq.on('serverSender', (serverSender) => {
+    serverSender.send('hello, client');
+  });
+});
+```
+
+**[Back to top](#table-of-contents)**
+
 ### Shutdown
 
 * When testing or running server within another program it may be necessary to close the proxy.

lib/http-proxy/ws/interceptor.js

@@ -77,6 +77,7 @@ module.exports = class Interceptor {
     _interceptClientMessages() {
         const receiver = new Receiver(this._clientExtensions);
         const sender = new Sender(this._proxySocket, this._serverExtensions);
+        this._proxyReq.emit('clientSender', sender);
 
         // frame must be masked when send from client to server - https://tools.ietf.org/html/rfc6455#section-5.3
         const options = {mask: true};
@@ -92,6 +93,7 @@ module.exports = class Interceptor {
     _interceptServerMessages() {
         const receiver = new Receiver(this._serverExtensions);
         const sender = new Sender(this._socket, this._clientExtensions);
+        this._proxyReq.emit('serverSender', sender);
 
         const options = {mask: false};
         const dataSender = this._getDataSender({sender, event: 'wsServerMsg', options});