net: Fix string-concat hot path bug

Also removes functionality added in f9fec3a2d6
because it changes API. (That patch shouldn't have been added anyway.)

lib/net.js

@@ -349,11 +349,13 @@ Socket.prototype.write = function(data /* [encoding], [fd], [cb] */) {
         if (!this._writeQueueCallbacks[last]) {
           this._writeQueueCallbacks[last] = cb;
         } else {
-          // awful
-          this._writeQueueCallbacks[last] = function() {
-            this._writeQueueCallbacks[last]();
-            cb();
-          };
+          var original = this._writeQueueCallbacks[last];
+
+          if (Array.isArray(original)) {
+            original.push(cb);
+          } else {
+            this._writeQueueCallbacks[last] = [ original, cb ];
+          }
         }
       }
     } else {
@@ -465,7 +467,13 @@ Socket.prototype._writeOut = function(data, encoding, fd, cb) {
       return false;
     } else {
       if (cb) {
-        process.nextTick(cb);
+        if (Array.isArray(cb)) {
+          for (var i = 0; i < cb.length; i++) {
+            if (cb[i]) cb[i]();
+          }
+        } else {
+          cb();
+        }
       }
       return true;
     }

test/simple/test-net-write-callbacks.js

@@ -0,0 +1,56 @@
+// 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 net = require('net');
+var assert = require('assert');
+
+var cbcount = 0;
+var N = 500000;
+
+var server = net.Server(function(socket) {
+  socket.on('data', function(d) {
+    console.error("got %d bytes", d.length);
+  });
+
+  socket.on('end', function() {
+    console.error("end");
+    socket.destroy();
+    server.close();
+  });
+});
+
+server.listen(common.PORT, function() {
+  var client = net.createConnection(common.PORT);
+
+  client.on('connect', function() {
+    for (var i = 0; i < N; i++) {
+      client.write("hello world", function() {
+        cbcount++;
+      });
+    }
+    client.end();
+  });
+});
+
+process.on('exit', function() {
+  assert.equal(N, cbcount);
+});