net: emit 'close' when socket ends before connect

Don't set `writable` to true when a socket connects if the socket is
already in an ending state.

In the existing code, afterConnect always set `writable` to true.  This
has been the case for a long time, but previous to commit
9b7a691, the socket would still be
destroyed by `destroySoon` and emit a `'close'` event. Since that
commit removed this masking behavior, we have relied on maybeDestroy to
destroy the socket when the readble state is ended, and that won't
happen if `writable` is set to true.

If the socket has `allowHalfOpen` set to true, then `destroy` will still
not be called and `'close'` will not be emitted.

PR-URL: #21290
Fixes: #21268
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

lib/net.js

@@ -1138,7 +1138,8 @@ function afterConnect(status, handle, req, readable, writable) {
 
   if (status === 0) {
     self.readable = readable;
-    self.writable = writable;
+    if (!self._writableState.ended)
+      self.writable = writable;
     self._unrefTimer();
 
     self.emit('connect');

test/parallel/test-net-socket-end-before-connect.js

@@ -0,0 +1,13 @@
+'use strict';
+
+const common = require('../common');
+
+const net = require('net');
+
+const server = net.createServer();
+
+server.listen(common.mustCall(() => {
+  const socket = net.createConnection(server.address().port);
+  socket.on('close', common.mustCall(() => server.close()));
+  socket.end();
+}));