Node

Node is a purely asynchronous I/O framework for V8 javascript.

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

new node.http.Server(function (msg) {
  setTimeout(function () {
    msg.sendHeader(200, [["Content-Type", "text/plain"]]);
    msg.sendBody("Hello World");
    msg.finish();
  }, 2000);
}).listen(8000, "localhost");

This script can handle hundreds of concurrent requests while using little CPU or memory—see benchmarks. Check out the documentation for more examples.

Node is free to download, use, and build upon.

Motivation

Evented programming makes sense
1. difference between blocking/non-blocking design
  There are many methods to write internet servers but they can fundamentally be divided into two camps: evented and threaded; non-blocking and blocking. A blocking server accepts a connection and launches a new thread to handle the connection. Because the concurrency is handled by the thread scheduler, a blocking server can make function calls which preform full network requests.
```
var response = db.execute("SELECT * FROM table");
// do something
```
  An evented server manages its concurrency itself. All connections are handled in a single thread and callbacks are executed on certain events: "socket 23 is has data to read", "socket 65's write buffer is empty". An evented server executes small bits of code but never blocks the process. In the evented world callbacks are used instead of functions
```
db.execute("SELECT * FROM table", function (response) {
// do something
});
```
2. I/O latency
```
l1 cache ~ 3
l2 cache ~ 14
     ram ~ 250
    disk ~ 41000000
 network ~ 240000000
```
3. purely evented interfaces rule out a lot of stupidity
Evented programs are more efficient
1. pthread stack size 2mb default stack size on linux (1mb on windows, 64kb on FreeBSD) of course this is adjustable
2. context switching benchmark
3. Apache vs. Nginx
4. event machine vs mongrel (neverblock)
The appropriateness of Javascript
1. No I/O
  Javascript is without I/O. In the browser the DOM provides I/O, but non-browser javascript interpreters have only non-standardized functions to allow them print to console or access the network.
2. No Threads
3. Good compiler
4. Universality of the language
  Contemporary computer infrastructure has two irreplaceable languages: C and Javascript. C is the language of operating systems. POSIX, the universal operating system API, is defined in C. So while you can interface with operating systems in Java and Haskell, those languages access must make system calls in C. Similarly, Javascript is the language of the web operating system. In place of POSIX is the DOM. You can wrap Javascript, you can compile to Javascript, but in the end browsers must be interfaced with in Javascript. Portable low-level systems tend to be written in C and portable web-level systems are written in Javascript.

Benchmarks

TODO

Download

TODO

Build

configure
make
make install

Application Programming Interface

The node executable should be given an argument pointing to a javascript file.

Timers

The timer API is the same as in the browser. The functions setTimeout, setInterval, clearTimeout, and clearInterval

File System

TCP

HTTP (`node.http`)

Node provides a fast web server and client interface. The interface is rather low-level. Node, for example, will not parse application/x-www-form-urlencoded message bodies—that is for higher level code to manage. The interface does abstract the Transfer-Encoding (i.e. chuncked or identity), Message boundarys, and Keep-Alive connections.

HTTP Server (`node.http.Server`)

new Server(request_handler, options)

Creates a new web server. The options argument accepts the same values as the options argument for node.tcp.Server does. The options argument is optional.

The request_handler is a function which is called on each request with a Message object argument.

server.listen(port, hostname)

Begin accepting connections on the specified port and hostname. If the hostname is omitted, the server will accept connections directed to any address.

server.close()

Stops the server. Requests currently in progress will not be interrupted.

HTTP Request Message (`node.http.Message`)

This object is only created internally—not by the user. It is passed as an argument to the request_handler function in a web server.

msg.method

The request method as a string. Read only. Example: "GET", "DELETE".

msg.uri

The request URI as a string. Read only. Example: "/index.html?hello=world".

msg.headers

The request headers expressed as an array of 2-element arrays. Read only. Example:

[ ["Content-Length", "123"]
, ["Content-Type", "text/plain"]
, ["Connection", "keep-alive"]
, ["Accept", "*/*"]
]

msg.http_version

The HTTP protocol version as a string. Read only. Examples: "1.1", "1.0"

msg.connection

A reference to the node.tcp.Connection object. Read only. Note that multiple messages can be sent on a single connection.

msg.onBody

Callback. Should be set by the user to be informed of when a piece of the message body is received. Example:

msg.onBody = function (chunk) {
  puts("part of the body: " + chunk);
}

A chunk of the body is given as the single argument. The transfer-encoding has been removed.

The body chunk is either a String in the case of utf8 encoding or an array of numbers in the case of raw encoding.

msg.onBodyComplete

Callback. Made exactly once for each message. No arguments. After onBodyComplete is executed onBody will no longer be called.

msg.setBodyEncoding(encoding)

Set the encoding for the request body. Either "utf8" or "raw". Defaults to raw. TODO

msg.sendHeader(status_code, headers)

Sends a response header to the request. The status code is a 3-digit HTTP status code, like 404. The second argument, headers, should be an array of 2-element arrays, representing the response headers.

Example:

var body = "hello world";
msg.sendHeader( 200
              , [ ["Content-Length", body.length] 
                , ["Content-Type", "text/plain"] 
                ]
              );

This method must only be called once on a message and it must be called before msg.finish() is called.

msg.sendBody(chunk)

This method must be called after sendHeader was called. It sends a chunk of the response body. This method may be called multiple times to provide successive parts of the body.

msg.finish()

This method signals that all of the response headers and body has been sent; that server should consider this message complete. The method, msg.finish(), MUST be called on each response.

Modules

Node has simple module loading. Here is an example. This is the file foo.js:

include("mjsunit");

function onLoad () {
  assertEquals(1, 2);
}

Here the module mjsunit has provided the function assertEquals().

The module file, mjsunit.js, must be in the same directory as foo.js for include() to work. The include() function will insert all the exported objects from the module into the global namespace.

Because file loading does not happen instantaneously, and because Node has a policy of never blocking, the callback onLoad() is provided to notify the user when all the exported functions are completely loaded.

To export an object, add to the special object exports. Let's look at how mjsunit.js does this

function fail (expected, found, name_opt) {
  // ...
}

function deepEquals (a, b) {
  // ...
}

exports.assertEquals = function (expected, found, name_opt) {
  if (!deepEquals(found, expected)) {
    fail(expected, found, name_opt);
  }
};

The functions fail and deepEquals are not exported and remain private to the module.

In addition to include() a module can use require(). Instead of loading the exported objects into the global namespace, it will return a namespace object. Again, the members of the namespace object can only be guaranteed to exist after the onLoad() callback is made. For example:

var mjsunit = require("mjsunit");

function onLoad () {
  mjsunit.assertEquals(1, 2);
}