Support sending handles to other processes

Needs test.

doc/api/child_processes.markdown

@@ -190,8 +190,8 @@ leaner than `child_process.exec`. It has the same options.
 This is a special case of the `spawn()` functionality for spawning Node
 processes. In addition to having all the methods in a normal ChildProcess
 instance, the returned object has a communication channel built-in. The
-channel is written to with `child.send(message)` and messages are recieved
-by a `'message'` event on the child.
+channel is written to with `child.send(message, [sendStream])` and messages
+are recieved by a `'message'` event on the child.
 
 For example:
 
@@ -224,6 +224,10 @@ These child Nodes are still whole new instances of V8. Assume at least 30ms
 startup and 10mb memory for each new Node. That is, you cannot create many
 thousands of them.
 
+The `sendStream` option to `child.send()` is for sending a `net.Socket`
+or `net.Server` object to another process. Child will receive the handle as
+as second argument to the `message` event.
+
 
 ### child.kill(signal='SIGTERM')
 

lib/child_process_uv.js

@@ -73,7 +73,7 @@ function setupChannel(target, channel) {
 
   var jsonBuffer = '';
 
-  channel.onread = function(pool, offset, length) {
+  channel.onread = function(pool, offset, length, recvStream) {
     if (pool) {
       for (var i = 0; i < length; i++) {
         if (pool[offset + i] === LF) {
@@ -82,7 +82,7 @@ function setupChannel(target, channel) {
           jsonBuffer = pool.toString('ascii', i, length);
           offset = i + 1;
 
-          target.emit('message', message);
+          target.emit('message', message, recvStream);
         }
       }
     } else {
@@ -91,11 +91,14 @@ function setupChannel(target, channel) {
     }
   };
 
-  target.send = function(message, fd) {
-    if (fd) throw new Error("not yet implemented");
-
+  target.send = function(message, sendStream) {
     if (!target._channel) throw new Error("channel closed");
 
+    // Open up net.Socket instances
+    if (sendStream instanceof require('net').Socket) {
+      sendStream = sendStream._handle;
+    }
+
     // For overflow protection don't write if channel queue is too deep.
     if (channel.writeQueueSize > 1024 * 1024) {
       return false; 
@@ -103,7 +106,7 @@ function setupChannel(target, channel) {
 
     var buffer = Buffer(JSON.stringify(message) + '\n');
 
-    var writeReq = channel.write(buffer);
+    var writeReq = channel.write(buffer, 0, buffer.length, sendStream);
 
     if (!writeReq) {
       throw new Error(errno + " cannot write to IPC channel.");

src/stream_wrap.cc

@@ -292,8 +292,7 @@ Handle<Value> StreamWrap::Write(const Arguments& args) {
   } else {
     uv_stream_t* send_stream = NULL;
 
-    if (args.Length() > 3) {
-      assert(args[3]->IsObject());
+    if (args[3]->IsObject()) {
       Local<Object> send_stream_obj = args[3]->ToObject();
       assert(send_stream_obj->InternalFieldCount() > 0);
       StreamWrap* send_stream_wrap = static_cast<StreamWrap*>(