websocket: pass failure cause through to error event

lib/web/websocket/connection.js

@@ -316,7 +316,7 @@ function failWebsocketConnection (handler, code, reason, cause) {
 
   if (isConnecting(handler.readyState)) {
     // If the connection was not established, we must still emit an 'error' and 'close' events
-    handler.onSocketClose()
+    handler.onSocketClose(cause)
   } else if (handler.socket?.destroyed === false) {
     handler.socket.destroy()
   }

lib/web/websocket/websocket.js

@@ -92,7 +92,7 @@ class WebSocket extends EventTarget {
 
       this.#handler.socket.destroy()
     },
-    onSocketClose: () => this.#onSocketClose(),
+    onSocketClose: (cause) => this.#onSocketClose(cause),
     onPing: (body) => {
       if (channels.ping.hasSubscribers) {
         channels.ping.publish({
@@ -565,7 +565,7 @@ class WebSocket extends EventTarget {
    * @see https://websockets.spec.whatwg.org/#feedback-from-the-protocol
    * @see https://datatracker.ietf.org/doc/html/rfc6455#section-7.1.4
    */
-  #onSocketClose () {
+  #onSocketClose (cause) {
     // If the TCP connection was closed after the
     // WebSocket closing handshake was completed, the WebSocket connection
     // is said to have been closed _cleanly_.
@@ -599,7 +599,7 @@ class WebSocket extends EventTarget {
       code = 1006
 
       fireEvent('error', this, (type, init) => new ErrorEvent(type, init), {
-        error: new TypeError(reason)
+        error: new TypeError(reason, cause ? { cause } : undefined)
       })
     }
 

test/websocket/issue-4273.js

@@ -5,12 +5,14 @@ const { WebSocket } = require('../..')
 const { once } = require('node:events')
 
 test('first error than close event is fired on failed connection', async (t) => {
-  t.plan(1)
+  t.plan(3)
 
-  const ws = new WebSocket('ws://localhost:1')
+  const ws = new WebSocket('ws://localhost:999')
 
   ws.addEventListener('error', (ev) => {
     t.assert.ok(ev.error instanceof TypeError)
+    t.assert.ok(ev.error.cause, 'error should have a cause')
+    t.assert.strictEqual(ev.error.cause.code, 'ECONNREFUSED', 'error should have a cause code of ECONNREFUSED')
   })
 
   await once(ws, 'close')