net: Provide better error when writing after FIN

The stock writable stream "write after end" message is overly vague, if
you have clearly not called end() yourself yet.

When we receive a FIN from the other side, and call destroySoon() as a
result, then generate an EPIPE error (which is what would happen if you
did actually write to the socket), with a message explaining what
actually happened.

lib/_stream_writable.js

@@ -126,10 +126,15 @@ Writable.prototype.write = function(chunk, encoding, cb) {
   }
 
   if (state.ended) {
+    var self = this;
     var er = new Error('write after end');
-    if (typeof cb === 'function')
+    // TODO: defer error events consistently everywhere, not just the cb
+    self.emit('error', er);
+    if (typeof cb === 'function') {
+      process.nextTick(function() {
         cb(er);
-    this.emit('error', er);
+      });
+    }
     return;
   }
 

lib/net.js

@@ -240,9 +240,32 @@ function onSocketEnd() {
     this.read(0);
   }
 
-  if (!this.allowHalfOpen)
+  if (!this.allowHalfOpen) {
+    this.write = writeAfterFIN;
     this.destroySoon();
   }
+}
+
+// Provide a better error message when we call end() as a result
+// 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 (typeof encoding === 'function') {
+    cb = encoding;
+    encoding = null;
+  }
+
+  var er = new Error('This socket has been closed by the other party');
+  er.code = 'EPIPE';
+  var self = this;
+  // TODO: defer error events consistently everywhere, not just the cb
+  self.emit('error', er);
+  if (typeof cb === 'function') {
+    process.nextTick(function() {
+      cb(er);
+    });
+  }
+}
 
 exports.Socket = Socket;
 exports.Stream = Socket; // Legacy naming.
@@ -708,6 +731,9 @@ function connect(self, address, port, addressType, localAddress) {
 
 
 Socket.prototype.connect = function(options, cb) {
+  if (this.write !== Socket.prototype.write)
+    this.write = Socket.prototype.write;
+
   if (typeof options !== 'object') {
     // Old API:
     // connect(port, [host], [cb])

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

@@ -0,0 +1,80 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+var common = require('../common');
+var assert = require('assert');
+
+// This is similar to simple/test-socket-write-after-fin, except that
+// we don't set allowHalfOpen.  Then we write after the client has sent
+// a FIN, and this is an error.  However, the standard "write after end"
+// message is too vague, and doesn't actually tell you what happens.
+
+var net = require('net');
+var serverData = '';
+var gotServerEnd = false;
+var clientData = '';
+var gotClientEnd = false;
+var gotServerError = false;
+
+var server = net.createServer(function(sock) {
+  sock.setEncoding('utf8');
+  sock.on('error', function(er) {
+    console.error(er.code + ': ' + er.message);
+    gotServerError = er;
+  });
+
+  sock.on('data', function(c) {
+    serverData += c;
+  });
+  sock.on('end', function() {
+    gotServerEnd = true
+    sock.write(serverData);
+    sock.end();
+  });
+  server.close();
+});
+server.listen(common.PORT);
+
+var sock = net.connect(common.PORT);
+sock.setEncoding('utf8');
+sock.on('data', function(c) {
+  clientData += c;
+});
+
+sock.on('end', function() {
+  gotClientEnd = true;
+});
+
+process.on('exit', function() {
+  assert.equal(clientData, '');
+  assert.equal(serverData, 'hello1hello2hello3\nTHUNDERMUSCLE!');
+  assert(gotClientEnd);
+  assert(gotServerEnd);
+  assert(gotServerError);
+  assert.equal(gotServerError.code, 'EPIPE');
+  assert.notEqual(gotServerError.message, 'write after end');
+  console.log('ok');
+});
+
+sock.write('hello1');
+sock.write('hello2');
+sock.write('hello3\n');
+sock.end('THUNDERMUSCLE!');

test/simple/test-socket-write-after-fin.js

@@ -0,0 +1,64 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+var common = require('../common');
+var assert = require('assert');
+var net = require('net');
+var serverData = '';
+var gotServerEnd = false;
+var clientData = '';
+var gotClientEnd = false;
+
+var server = net.createServer({ allowHalfOpen: true }, function(sock) {
+  sock.setEncoding('utf8');
+  sock.on('data', function(c) {
+    serverData += c;
+  });
+  sock.on('end', function() {
+    gotServerEnd = true
+    sock.end(serverData);
+    server.close();
+  });
+});
+server.listen(common.PORT);
+
+var sock = net.connect(common.PORT);
+sock.setEncoding('utf8');
+sock.on('data', function(c) {
+  clientData += c;
+});
+
+sock.on('end', function() {
+  gotClientEnd = true;
+});
+
+process.on('exit', function() {
+  assert.equal(serverData, clientData);
+  assert.equal(serverData, 'hello1hello2hello3\nTHUNDERMUSCLE!');
+  assert(gotClientEnd);
+  assert(gotServerEnd);
+  console.log('ok');
+});
+
+sock.write('hello1');
+sock.write('hello2');
+sock.write('hello3\n');
+sock.end('THUNDERMUSCLE!');