How node.js is integrated with chromium

Overview

We keep the modification minimal on both Node and Chromium. Only 2 things are done: main loop integration and context bridging.

Both node.js and Chromium have their main loops. So it would take some efforts to make it run in Chromium. One of the founding feature of node-webkit is to call Node functions directly from DOM, so we integrate them into the same thread. That requires the integration of the main loop of Node and the one from Chromium Render process.

In order to make the objects from Node and DOM to refer to each other, Node is made to use the same V8 engine instance as the one in Chromium. The objects from the 2 worlds are in 2 contexts respectively, to keep their namespace clean.

Main Loop Integration

Chromium internally use class MessageLoop and MessagePump to support its events loop, since node uses libuv to support its events loop, we need to implement a new MessagePump which uses libuv as its underlying events library. The new type of Message Pump is used only in the render process, where the WebKit engine resides.

See base/message_pump_uv.cc, base/message_pump_uv.cc, base/message_loop.cc and base/message_loop.h to understand our work.

On Mac things are a lot different, see base/message_pump_mac.h and base/message_pump_mac.mm.

Context bridging: Insert node's symbols into webkit

This is the most important and trickiest part of node-webkit, first we initialize a context for node, and make node setup all its stuff under it, see content/renderer/renderer_main.cc, then when WebKit has installed DOM into its context, we move everything from node to WebKit, see third_party/WebKit/Source/WebCore/bindings/v8/V8DOMWindowShell.cpp in line 346.

Make Node start with render process

Though node has a Start function that setups everything, it will redirect everything into its own message loop, so we split the Start function into several parts, see third_party/node/src/node.cc.

And since node itself expects to execute a script file, there are many logics that deal with script execution in third_party/node/src/node.js, we heavily modified that part and used some tricks to make its module system run under node-webkit.

Another modification resided under third_party/WebKit/Source/WebCore/bindings/v8/V8DOMWindowShell.cpp in line 363, we inserted some script after WebKit is initialized, so node can get a right pathname and filename which is vital to require function.