http: fix client request.end() EPIPE race

request.end() would sometimes try to write a zero-length buffer to the socket.
Don't do that, it triggers an unnecessary EPIPE when the other end has closed
the connection.

Fixes #3257.

lib/http.js

@@ -475,6 +475,10 @@ OutgoingMessage.prototype._send = function(data, encoding) {
 
 
 OutgoingMessage.prototype._writeRaw = function(data, encoding) {
+  if (data.length === 0) {
+    return true;
+  }
+
   if (this.connection &&
       this.connection._httpMessage === this &&
       this.connection.writable) {

test/simple/test-http-client-pipe-end.js

@@ -0,0 +1,58 @@
+// 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.
+
+// see https://github.com/joyent/node/issues/3257
+
+var common = require('../common');
+var assert = require('assert');
+var http = require('http');
+
+var server = http.createServer(function(req, res) {
+  req.once('end', function() {
+    res.writeHead(200);
+    res.end();
+    server.close();
+  });
+});
+
+server.listen(common.PIPE, function() {
+  var req = http.request({
+    socketPath: common.PIPE,
+    headers: {'Content-Length':'1'},
+    method: 'POST',
+    path: '/'
+  });
+
+  req.write('.');
+
+  sched(function() { req.end() }, 5);
+});
+
+// schedule a callback after `ticks` event loop ticks
+function sched(cb, ticks) {
+  function fn() {
+    if (--ticks)
+      process.nextTick(fn);
+    else
+      cb();
+  }
+  process.nextTick(fn);
+}