net: Do not destroy socket mid-write

The fix in e0519ace315c7ce14278d5eaab8d1d72a0a0a054 is overly zealous,
and can destroy a socket while there are still outstanding writes in
progress.

Closes GH-5688

lib/net.js

@@ -411,7 +411,8 @@ function maybeDestroy(socket) {
   if (!socket.readable &&
       !socket.writable &&
       !socket.destroyed &&
-      !socket._connecting) {
+      !socket._connecting &&
+      !socket._writableState.length) {
     socket.destroy();
   }
 }

test/simple/test-child-process-stdio-big-write-end.js

@@ -0,0 +1,79 @@
+// 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 BUFSIZE = 1024;
+
+switch (process.argv[2]) {
+  case undefined:
+    return parent();
+  case 'child':
+    return child();
+  default:
+    throw new Error('wtf?');
+}
+
+function parent() {
+  var spawn = require('child_process').spawn;
+  var child = spawn(process.execPath, [__filename, 'child']);
+  var sent = 0;
+
+  var n = '';
+  child.stdout.setEncoding('ascii');
+  child.stdout.on('data', function(c) {
+    n += c;
+  });
+  child.stdout.on('end', function() {
+    assert.equal(+n, sent);
+    console.log('ok');
+  });
+
+  // Write until the buffer fills up.
+  do {
+    var buf = new Buffer(BUFSIZE);
+    buf.fill('.');
+    sent += BUFSIZE;
+  } while (child.stdin.write(buf));
+
+  // then write a bunch more times.
+  for (var i = 0; i < 100; i++) {
+    var buf = new Buffer(BUFSIZE);
+    buf.fill('.');
+    sent += BUFSIZE;
+    child.stdin.write(buf);
+  }
+
+  // now end, before it's all flushed.
+  child.stdin.end();
+
+  // now we wait...
+}
+
+function child() {
+  var received = 0;
+  process.stdin.on('data', function(c) {
+    received += c.length;
+  });
+  process.stdin.on('end', function() {
+    console.log(received);
+  });
+}