net: Fix invalid write after end error

lib/net.js

@@ -30,6 +30,7 @@ const {
   NumberParseInt,
   ObjectDefineProperty,
   ObjectSetPrototypeOf,
+  ReflectApply,
   Symbol,
 } = primordials;
 
@@ -434,6 +435,11 @@ function afterShutdown() {
 // of the other side sending a FIN.  The standard 'write after end'
 // is overly vague, and makes it seem like the user's code is to blame.
 function writeAfterFIN(chunk, encoding, cb) {
+  if (!this.writableEnded) {
+    return ReflectApply(
+      stream.Duplex.prototype.write, this, [chunk, encoding, cb]);
+  }
+
   if (typeof encoding === 'function') {
     cb = encoding;
     encoding = null;
@@ -947,7 +953,6 @@ Socket.prototype.connect = function(...args) {
   this._unrefTimer();
 
   this.connecting = true;
-  this.writable = true;
 
   if (pipe) {
     validateString(path, 'options.path');

test/parallel/test-net-writable.js

@@ -0,0 +1,15 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const net = require('net');
+
+const server = net.createServer(common.mustCall(function(s) {
+  server.close();
+  s.end();
+})).listen(0, 'localhost', common.mustCall(function() {
+  const socket = net.connect(this.address().port, 'localhost');
+  socket.on('end', common.mustCall(() => {
+    assert.strictEqual(socket.writable, true);
+    socket.write('hello world');
+  }));
+}));

test/parallel/test-socket-write-after-fin-error.js

@@ -26,8 +26,10 @@ const server = net.createServer(function(sock) {
   });
   sock.on('end', function() {
     gotServerEnd = true;
-    sock.write(serverData);
-    sock.end();
+    setImmediate(() => {
+      sock.write(serverData);
+      sock.end();
+    });
   });
   server.close();
 });