# Node

Evented I/O for V8 javascript.

An example of a web server written with Node which responds with "Hello World" after waiting two seconds:

    include("/utils.js");
    include("/http.js");
    createServer(function (req, res) {
      setTimeout(function () {
        res.sendHeader(200, {"Content-Type": "text/plain"});
        res.sendBody("Hello World");
        res.finish();
      }, 2000);
    }).listen(8000);
    puts("Server running at http://127.0.0.1:8000/");

To run the server, put the code into a file `example.js` and execute it with the `node` program

    % /usr/local/bin/node example.js
    Server running at http://127.0.0.1:8000/

See the API documentation for more examples.

## About

Node's goal is to provide an easy way to build scalable network programs. In the above example, the two second delay does not prevent the server from handling new requests. Node tells the operating system (through `epoll`, `kqueue`, `/dev/poll`, or `select`) that it should be notified when the 2 seconds are up or if a new connection is made—then it goes to sleep. If someone new connects, then it executes the callback, if the timeout expires, it executes the inner callback. Each connection is only a small heap allocation.

This is in contrast to today's more common concurrency model where OS threads are employed. Thread-based networking is relatively inefficient and very difficult to use. Node will show much better memory efficiency under high-loads than systems which allocate 2mb thread stacks for each connection. Furthermore, users of Node are free from worries of dead-locking the process—there are no locks. Almost no function in Node directly performs I/O, so the process never blocks. Because nothing blocks, less-than-expert programmers are able to develop fast systems.

Node is similar in design to and influenced by systems like Ruby's Event Machine or Python's Twisted. Node takes the event model a bit further—it presents the event loop as a language construct instead of as a library. In other systems there is always a blocking call to start the event-loop. Typically one defines behavior through callbacks at the beginning of a script and at the end starts a server through a blocking call like `EventMachine::run()`. In Node there is no such start-the-event-loop call. Node simply enters the event loop after executing the input script. Node exits the event loop when there are no more callbacks to perform. This behavior is like browser javascript—the event loop is hidden from the user.

HTTP is a first class protocol in Node. Node's HTTP library has grown out of the author's experiences developing and working with web servers. For example, streaming data through most web frameworks is impossible. Node attempts to correct these problems in its HTTP parser and API. Coupled with Node's purely evented infrastructure, it makes a good foundation for web libraries or frameworks.

But what about multiple-processor concurrency? Threads are necessary to scale programs to multi-core computers. Processes are necessary to scale to multi-core computers, not memory-sharing threads. The fundamentals of scalable systems are fast networking and non-blocking design—the rest is message passing. In future versions, Node will be able to fork new processes (using the Web Workers API ), but this is something that fits well into the current design.

## Download

git repo

2009.09.30 node-0.1.13.tar.gz

## Build

Node eventually wants to support all POSIX operating systems (including Windows with MinGW) but at the moment it is only being tested on Linux, Macintosh, and FreeBSD. The build system requires Python 2.4 or better. V8, on which Node is built, supports only IA-32 and ARM processors. V8 is included in the Node distribution. There are no other dependencies.

    ./configure
    make
    make install

Then have a look at the API documentation.

To run the tests

    make test

## Demo

A chat room demo is running at chat.tinyclouds.org. The source code for the chat room is at http://github.com/ry/node_chat. The chat room is not stable and might occasionally be down.

## Community

For help and discussion subscribe to the mailing list at http://groups.google.com/group/nodejs or send an email to nodejs+subscribe@googlegroups.com.

For real-time discussion, check irc.freenode.net #node.js.

Projects/libraries which are using/for Node.js

## Benchmarks

2009.09.06 narwhal, node, v8cgi, thin/eventmachine