net: write syscall optimization and a bytesWritten bug fix

lib/net.js

@@ -154,8 +154,9 @@ function Socket(options) {
 
   initSocketHandle(this);
 
-  this._pendingData = null;
-  this._pendingEncoding = '';
+  // Buffer for the single possible write while connecting: when uncorked
+  // or ended, then written to. Writable will buffer any other writes.
+  this._pendingWrite = null;
 
   // handle strings directly
   this._writableState.decodeStrings = false;
@@ -628,19 +629,18 @@ Socket.prototype.write = function(chunk, encoding, cb) {
 
 
 Socket.prototype._writeGeneric = function(writev, data, encoding, cb) {
-  // If we are still connecting, then buffer this for later.
-  // The Writable logic will buffer up any more writes while
-  // waiting for this one to be done.
+  // If the socket is ended / uncorked while connecting, a single write can
+  // fire through the cork. Buffer it and send it once connected. Writable
+  // will buffer any sequential writes if uncorked.
   if (this._connecting) {
-    this._pendingData = data;
-    this._pendingEncoding = encoding;
+    this._pendingWrite = { data: data, encoding: encoding };
+
     this.once('connect', function() {
+      this._pendingWrite = null;
       this._writeGeneric(writev, data, encoding, cb);
     });
     return;
   }
-  this._pendingData = null;
-  this._pendingEncoding = '';
 
   this._unrefTimer();
 
@@ -730,8 +730,6 @@ function createWriteReq(req, handle, data, encoding) {
 Socket.prototype.__defineGetter__('bytesWritten', function() {
   var bytes = this._bytesDispatched;
   const state = this._writableState;
-  const data = this._pendingData;
-  const encoding = this._pendingEncoding;
 
   if (!state)
     return undefined;
@@ -743,11 +741,24 @@ Socket.prototype.__defineGetter__('bytesWritten', function() {
       bytes += Buffer.byteLength(el.chunk, el.encoding);
   });
 
-  if (data) {
-    if (data instanceof Buffer)
-      bytes += data.length;
-    else
-      bytes += Buffer.byteLength(data, encoding);
+  var buffer = this._pendingWrite;
+  if (Array.isArray(buffer)) {
+    // was a writev, iterate over chunks to get total length
+    for (let i = 0; i < buffer.length; i++) {
+      let chunk = buffer[i];
+
+      if (chunk instanceof Buffer) {
+        bytes += chunk.length;
+      } else {
+        bytes += Buffer.byteLength(chunk.data, chunk.encoding);
+      }
+    }
+  } else if (buffer) {
+    if (buffer.data instanceof Buffer) {
+      bytes += buffer.data.length;
+    } else {
+      bytes += Buffer.byteLength(buffer.data, buffer.encoding);
+    }
   }
 
   return bytes;
@@ -869,6 +880,7 @@ Socket.prototype.connect = function(options, cb) {
   }
 
   if (this.destroyed) {
+    // Recycle the socket.
     this._readableState.reading = false;
     this._readableState.ended = false;
     this._readableState.endEmitted = false;
@@ -899,6 +911,12 @@ Socket.prototype.connect = function(options, cb) {
   this._connecting = true;
   this.writable = true;
 
+  // Cork then uncork upon connecting.
+  this.cork();
+  this.once('connect', function() {
+    this.uncork();
+  });
+
   if (pipe) {
     connect(this, options.path);
   } else {

test/parallel/test-net-socket-byteswritten.js

@@ -0,0 +1,36 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const net = require('net');
+const Buffer = require('buffer').Buffer;
+
+var server = net.createServer(function(socket) {
+  socket.end();
+});
+
+server.listen(common.PORT, common.mustCall(function() {
+  var socket = net.connect(common.PORT);
+
+  // Cork the socket, then write twice; this should cause a writev, which
+  // previously caused an err in the bytesWritten count.
+  socket.cork();
+
+  socket.write('one');
+  socket.write(new Buffer('twø', 'utf8'));
+
+  socket.uncork();
+
+  // one = 3 bytes, twø = 4 bytes
+  assert.equal(socket.bytesWritten, 3 + 4);
+
+  socket.on('connect', common.mustCall(function() {
+    assert.equal(socket.bytesWritten, 3 + 4);
+  }));
+
+  socket.on('end', common.mustCall(function() {
+    assert.equal(socket.bytesWritten, 3 + 4);
+
+    server.close();
+  }));
+}));