http: ServerResponse.assignSocket should not throw an internal error

doc/api/errors.md

@@ -1438,6 +1438,12 @@ Status code was outside the regular status code range (100-999).
 
 The client has not sent the entire request within the allowed time.
 
+<a id="ERR_HTTP_SOCKET_ASSIGNED"></a>
+
+### `ERR_HTTP_SOCKET_ASSIGNED`
+
+The given [`ServerResponse`][] was already assigned a socket.
+
 <a id="ERR_HTTP_SOCKET_ENCODING"></a>
 
 ### `ERR_HTTP_SOCKET_ENCODING`
@@ -3590,6 +3596,7 @@ The native call from `process.cpuUsage` could not be processed.
 [`Object.getPrototypeOf`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/getPrototypeOf
 [`Object.setPrototypeOf`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/setPrototypeOf
 [`REPL`]: repl.md
+[`ServerResponse`]: http.md#class-httpserverresponse
 [`Writable`]: stream.md#class-streamwritable
 [`child_process`]: child_process.md
 [`cipher.getAuthTag()`]: crypto.md#ciphergetauthtag

lib/_http_server.js

@@ -75,6 +75,7 @@ const {
   ERR_HTTP_HEADERS_SENT,
   ERR_HTTP_INVALID_STATUS_CODE,
   ERR_HTTP_SOCKET_ENCODING,
+  ERR_HTTP_SOCKET_ASSIGNED,
   ERR_INVALID_ARG_VALUE,
   ERR_INVALID_CHAR,
 } = codes;
@@ -276,7 +277,9 @@ function onServerResponseClose() {
 }
 
 ServerResponse.prototype.assignSocket = function assignSocket(socket) {
-  assert(!socket._httpMessage);
+  if (socket._httpMessage) {
+    throw new ERR_HTTP_SOCKET_ASSIGNED();
+  }
   socket._httpMessage = this;
   socket.on('close', onServerResponseClose);
   this.socket = socket;

lib/internal/errors.js

@@ -1167,6 +1167,8 @@ E('ERR_HTTP_INVALID_HEADER_VALUE',
   'Invalid value "%s" for header "%s"', TypeError);
 E('ERR_HTTP_INVALID_STATUS_CODE', 'Invalid status code: %s', RangeError);
 E('ERR_HTTP_REQUEST_TIMEOUT', 'Request timeout', Error);
+E('ERR_HTTP_SOCKET_ASSIGNED',
+  'ServerResponse has an already assigned socket', Error);
 E('ERR_HTTP_SOCKET_ENCODING',
   'Changing the socket encoding is not allowed per RFC7230 Section 3.', Error);
 E('ERR_HTTP_TRAILER_INVALID',

test/parallel/test-http-server-response-standalone.js

@@ -31,4 +31,10 @@ const ws = new Writable({
 
 res.assignSocket(ws);
 
+assert.throws(function() {
+  res.assignSocket(ws);
+}, {
+  code: 'ERR_HTTP_SOCKET_ASSIGNED'
+});
+
 res.end('hello world');