node/doc/api.markdown

node(1) -- evented I/O for V8 JavaScript
========================================

## Synopsis

An example of a web server written with Node which responds with "Hello
World":

    var sys = require("sys"),
      http = require("http");

    http.createServer(function (request, response) {
      response.writeHead(200, {"Content-Type": "text/plain"});
      response.end("Hello World\n");
    }).listen(8000);

    sys.puts("Server running at http://127.0.0.1:8000/");

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

    > node example.js
    Server running at http://127.0.0.1:8000/

All of the examples in the documentation can be run similarly.


## String Encodings and Buffers

Pure Javascript is Unicode friendly but not nice to pure binary data.  When
dealing with TCP streams or the file system, it's necessary to handle octet
streams. Node has several strategies for manipulating, creating, and
consuming octet streams.

Raw data is stored in instances of the `Buffer` class. A `Buffer` is similar
to an array of integers but correspond to a raw memory allocation outside
the V8 heap. A `Buffer` cannot be resized.
Access the class at `require('buffer').Buffer`.

- **`new Buffer(size)`**: Allocates a new buffer of `size` octets.

- **`buffer[index]`**: Get and set the octet at `index`. The value can be
between 0x00 and 0xFF.

- **`buffer.length`**: length in octets.

- **`buffer.copy(targetBuffer, targetStart, start, end)`**:
Does a memcpy() between buffers.

- **`buffer.slice(start, end)`**: Returns a new buffer which references the
same memory as the old, but offset and cropped by the `start` and `end`
indexes. **Modifying the new buffer slice will modify memory in the original
buffer!**

Node supports 3 string encodings. UTF-8 (`"utf8"`), ASCII (`"ascii"`), and
Binary (`"binary"`). `"ascii"` and `"binary"` only look at the first 8 bits
of the 16bit JavaScript string characters. The following `Buffer` methods
allow decoding and encoding of strings:

- **`buffer.write(string, encoding, offset)`**: Writes `string` to the buffer at
`offset` using the given encoding. Returns number of octets written.  If
`buffer` did not contain enough space to fit the entire string it will write
a partial amount of the string. In the case of `encoding=='utf8'`, the
method will not write partial characters.

- **`buffer.toString(encoding, start, end)`**: Decodes and returns a string assuming
in the given encoding beginning at `start` and ending at `end`.



## Events

Many objects in Node emit events: a TCP server emits an event each time
there is a stream, a child process emits an event when it exits. All
objects which emit events are instances of `events.EventEmitter`.

Events are represented by a camel-cased string. Here are some examples:
`"stream"`, `"data"`, `"messageBegin"`.

Functions can be then be attached to objects, to be executed when an event
is emitted. These functions are called _listeners_.


### events.EventEmitter

`require("events")` to access the events module.

All EventEmitters emit the event `"newListener"` when new listeners are
added.

- **`"newListener"`** - `callback(event, listener)`:
This event is made any time someone adds a new listener.


### emitter.addListener(event, listener)

Adds a listener to the end of the listeners array for the specified event.

    server.addListener('stream', function (stream) {
      sys.puts("someone connected!");
    });


### emitter.removeListener(event, listener)

Remove a listener from the listener array for the specified event.
**Caution**: changes array indices in the listener array behind the listener.


### emitter.removeAllListeners(event)

Removes all listeners from the listener array for the specified event.


### emitter.listeners(event)

Returns an array of listeners for the specified event. This array can be
manipulated, e.g. to remove listeners.


### emitter.emit(event, arg1, arg2, ...)

Execute each of the listeners in order with the supplied arguments.



## Streams

A stream is an abstract interface implemented by various objects in Node.
For example a request to an HTTP server is a stream, as is stdout. Streams
are readable, writable, or both. All streams are instances of `EventEmitter`.

### Readable Stream

A **readable stream** has the following methods, members, and events.

- Event: **`'data'`** - `callback(data)`:
The `'data'` event emits either a `Buffer` (by default) or a string if
`setEncoding()` was used.

- Event: **`'end'`** - `callback()`:
Emitted when the stream has received an EOF (FIN in TCP terminology).
Indicates that no more `'data'` events will happen. If the stream is also
writable, it may be possible to continue writing.

- Event: **`'error'`** - `callback(exception)`:
Emitted if there was an error receiving data.

- Event: **`'close'`** - `callback()`:
Emitted when the underlying file descriptor has be closed. Not all streams
will emit this.  (For example, an incoming HTTP request will not emit
`'close'`.)

- **`stream.setEncoding(encoding)`**:
Makes the data event emit a string instead of a `Buffer`. `encoding` can be
`'utf8'`, `'ascii'`, or `'binary'`.

- **`stream.pause()`**:
Pauses the incoming `'data'` events.

- **`stream.resume()`**:
Resumes the incoming `'data'` events after a `pause()`.

- **`stream.destroy()`**:
Closes the underlying file descriptor. Stream will not emit any more events.

### Writable Stream

A **writable stream** has the following methods, members, and events.

- Event: **`'drain'`** - `callback()`:
Emitted after a `write()` method was called that returned `false` to
indicate that it is safe to write again.

- Event: **`'error'`** - `callback(exception)`:
Emitted on error with the exception `e`.

- Event **`'close'`** - `callback()`:
Emitted when the underlying file descriptor has been closed.

- **`stream.write(string, encoding)`**:
Writes `string` with the given `encoding` to the stream.  Returns `true` if
the string has been flushed to the kernel buffer.  Returns `false` to
indicate that the kernel buffer is full, and the data will be sent out in
the future. The `'drain'` event will indicate when the kernel buffer is
empty again. The `encoding` defaults to `'utf8'`.


- **`stream.write(buffer)`**:
Same as the above except with a raw buffer.

- **`stream.end()`**:
Terminates the stream with EOF or FIN.

- **`stream.end(string, encoding)`**:
Sends `string` with the given `encoding` and terminates the stream with EOF
or FIN. This is useful to reduce the number of packets sent.

- **`stream.end(buffer)`**:
Same as above but with a `buffer`.

- **`stream.destroy()`**:
Closes the underlying file descriptor. Stream will not emit any more events.


## Global Objects

These object are available in the global scope and can be accessed from anywhere.

- **`global`**: The global namespace object.

- **`process`**: The process object. Most stuff lives in here. See the "process
object" section.

- **`require()`**: See the modules section.

- **`require.paths`**: The search path for absolute path arguments to `require()`.

- **`__filename`**: The filename of the script being executed.

- **`__dirname`**: The dirname of the script being executed.

- **`module`**: A reference to the current module (of type
`process.Module`). In particular `module.exports` is the same as the
`exports` object. See `src/process.js` for more information.


## process

The `process` object is a global object and can be accessed from anywhere.
It is an instance of `EventEmitter` and has the following events:


### Event: 'exit' - callback()

Emitted when the process is about to exit.  This is a good hook to perform
constant time checks of the module's state (like for unit tests).  The main
event loop will no longer be run after the "exit" callback finishes, so
timers may not be scheduled.

Example of listening for `exit`:

    var sys = require('sys');

    process.addListener('exit', function () {
      process.nextTick(function () {
       sys.puts("This will not run");
      });
      sys.puts("About to exit.");
    });

### Event: 'uncaughtException' - callback(err)

Emitted when an exception bubbles all the way back to the event loop. If a
listener is added for this exception, the default action (which is to print
a stack trace and exit) will not occur.

Example of listening for `uncaughtException`:

    var sys = require("sys");

    process.addListener('uncaughtException', function (err) {
      sys.puts("Caught exception: " + err);
    });

    setTimeout(function () {
      sys.puts("This will still run.");
    }, 500);

    // Intentionally cause an exception, but don't catch it.
    nonexistantFunc();
    sys.puts("This will not run.");

Note that `uncaughtException` is a very crude mechanism for exception
handling.  Using try / catch in your program will give you more control over
your program's flow.  Especially for server programs that are designed to
stay running forever, `uncaughtException` can be a useful safety mechanism.


### Event: 'SIGINT' - callback()

Emitted when the processes receives a signal. See sigaction(2) for a list of
standard POSIX signal names such as SIGINT, SIGUSR1, etc.

Example of listening for `SIGINT`:

    var sys = require("sys"),
        stdin = process.openStdin();

    process.addListener('SIGINT', function () {
      sys.puts("Got SIGINT.  Press Control-D to exit.");
    });

An easy way to send the `SIGINT` signal is with `Control-C` in most terminal
programs.

### process.stdout

A writable stream to `stdout`.

Example: the definition of `sys.puts`

    exports.puts = function (d) {
      process.stdout.write(d + '\n');
    };



### process.openStdin()

Opens the standard input stream, returns a readable stream.

Example of opening standard input and listening for both events:

    var stdin = process.openStdin();

    stdin.setEncoding('utf8');

    stdin.addListener('data', function (chunk) {
      process.stdout.write("data: " + chunk);
    });

    stdin.addListener('end', function () {
      process.stdout.write("end");
    });


### process.argv

An array containing the command line arguments.  The first element will be
'node', the second element will be the name of the JavaScript file.  The
next elements will be any additional command line arguments.

    // print process.argv
    var sys = require("sys");

    process.argv.forEach(function (val, index, array) {
      sys.puts(index + ": " + val);
    });

This will generate:

    $ node process-2.js one two=three four
    0: node
    1: /Users/mjr/work/node_docs/data/v0.1.31/examples/process-2.js
    2: one
    3: two=three
    4: four



### process.chdir(directory)

Changes the current working directory of the process or throws an exception if that fails.

    var sys = require('sys');

    sys.puts("Starting directory: " + process.cwd());
    try {
      process.chdir("/tmp");
      sys.puts("New directory: " + process.cwd());
    }
    catch (err) {
      sys.puts("chdir: " + err);
    }


### process.compile(code, filename)

Similar to `eval` except that you can specify a `filename` for better
error reporting and the `code` cannot see the local scope.  The value of `filename`
will be used as a filename if a stack trace is generated by the compiled code.

Example of using `process.compile` and `eval` to run the same code:

    var sys = require("sys"),
        localVar = 123,
        compiled, evaled;

    compiled = process.compile("localVar = 1;", "myfile.js");
    sys.puts("localVar: " + localVar + ", compiled: " + compiled);
    evaled = eval("localVar = 1;");
    sys.puts("localVar: " + localVar + ", evaled: " + evaled);

    // localVar: 123, compiled: 1
    // localVar: 1, evaled: 1

`process.compile` does not have access to the local scope, so `localVar` is unchanged.
`eval` does have access to the local scope, so `localVar` is changed.

See also: `process.evalcx`


### process.cwd()

Returns the current working directory of the process.

    require('sys').puts("Current directory: " + process.cwd());


### process.env

An object containing the user environment. See environ(7).

    // print process.env
    var sys = require("sys");

    Object.getOwnPropertyNames(process.env).forEach(function (val, index, array) {
      sys.puts(index + ": " + val + "=" + process.env[val]);
    });



### process.evalcx(code, sandbox, filename)

Similar to `eval` and `process.compile`.  `process.evalcx` compiles `code` to run in `sandbox`
as if it were loaded from `filename`.  The object `sandbox` will be used as the global object for
`code`.  `sandbox` and `filename` are optional.

    var sys = require("sys"),
        sandbox = {
          animal: "cat",
          count: 2
        };

    process.evalcx('count += 1; name = "kitty"', sandbox, "myfile.js");
    sys.puts(sys.inspect(sandbox));

Note that running untrusted code is a tricky business requiring great care.  To prevent accidental
global variable leakage, `process.evalcx` is quite useful, but to safely run untrusted code, many more steps
must be taken.



### process.exit(code)

Ends the process with the specified `code`.  If omitted, exit uses the 
"success" code `0`.

To exit with a "failure" code:

    process.exit(1);

The shell that executed node should see the exit code as 1.


### process.getgid(), process.setgid(id)

Gets/sets the group identity of the process. (See setgid(2).)  This is the numerical group id, not the group name.

    var sys = require('sys');

    sys.puts("Current gid: " + process.getgid());
    try {
      process.setgid(501);
      sys.puts("New gid: " + process.getgid());
    }
    catch (err) {
      sys.puts("Failed to set gid: " + err);
    }


### process.getuid(), process.setuid(id)

Gets/sets the user identity of the process. (See setuid(2).)  This is the numerical userid, not the username.

    var sys = require('sys');

    sys.puts("Current uid: " + process.getuid());
    try {
      process.setuid(501);
      sys.puts("New uid: " + process.getuid());
    }
    catch (err) {
      sys.puts("Failed to set uid: " + err);
    }


### process.installPrefix

A compiled-in property that exposes `NODE_PREFIX`.

    require("sys").puts("Install prefix: " + process.installPrefix);


### process.kill(pid, signal)

Send a signal to a process. `pid` is the process id and `signal` is the
string describing the signal to send.  Signal names are strings like
"SIGINT" or "SIGUSR1".  If omitted, the signal will be "SIGINT".
See kill(2) for more information.

Note that just because the name of this function is `process.kill`, it is
really just a signal sender, like the `kill` system call.  The signal sent
may do something other than kill the target process.

Example of sending a signal to yourself:

    var sys = require("sys");

    process.addListener('SIGHUP', function () {
      sys.puts("Got SIGHUP signal.");
    });

    setTimeout(function () {
      sys.puts("Exiting.");
      process.exit(0);
    }, 100);

    process.kill(process.pid, "SIGHUP");


### process.pid

The PID of the process.

    require("sys").puts("This process is pid " + process.pid);


### process.platform

What platform you're running on. `"linux2"`, `"darwin"`, etc.

    require("sys").puts("This platform is " + process.platform);


### process.memoryUsage()

Returns an object describing the memory usage of the Node process.

    var sys = require("sys");

    sys.puts(sys.inspect(process.memoryUsage()));

This will generate:

    { rss: 4935680
    , vsize: 41893888
    , heapTotal: 1826816
    , heapUsed: 650472
    }

`heapTotal` and `heapUsed` refer to V8's memory usage.


### process.nextTick(callback)

On the next loop around the event loop call this callback.
This is *not* a simple alias to `setTimeout(fn, 0)`, it's much more
efficient.

    var sys = require("sys");

    process.nextTick(function () {
      sys.puts("nextTick callback");
    });


### process.umask(mask)

Sets or read the process's file mode creation mask. Child processes inherit
the mask from the parent process. Returns the old mask if `mask` argument is
given, otherwise returns the current mask.

    var sys = require('sys'),
        oldmask, newmask = 0644;

    oldmask = process.umask(newmask);
    // these octal numbers don't display right in JavaScript
    sys.puts("Changed umask from: " + oldmask + " to " + newmask);



## sys

These functions are in the module `"sys"`. Use `require("sys")` to access
them.


### puts(string)

Outputs `string` and a trailing new-line to `stdout`.

    require("sys").puts("String with a newline");
    

### print(string)

Like `puts()` but without the trailing new-line.

    require("sys").print("String with no newline");


### debug(string)

A synchronous output function. Will block the process and
output `string` immediately to `stderr`.

    require("sys").debug("message on stderr");


### log(string)

Output with timestamp on `stdout`.

    require("sys").log("Timestmaped message.");


### inspect(object, showHidden, depth)

Return a string representation of `object`, which is useful for debugging.

If `showHidden` is `true`, then the object's non-enumerable properties will be
shown too.

If `depth` is provided, it tells `inspect` how many times to recurse while
formatting the object. This is useful for inspecting large complicated objects.

The default is to only recurse twice.  To make it recurse indefinitely, pass
in `null` for `depth`.

Example of inspecting all properties of the `sys` object:

    var sys = require("sys");

    sys.puts(sys.inspect(sys, true, null));







## Modules

Node uses the CommonJS module system.

Node has a simple module loading system.  In Node, files and modules are in
one-to-one correspondence.  As an example, `foo.js` loads the module
`circle.js` in the same directory.

The contents of `foo.js`:

    var circle = require("./circle"),
    var sys = require("sys");
    sys.puts( "The area of a circle of radius 4 is " 
            + circle.area(4));

The contents of `circle.js`:

    var PI = 3.14;

    exports.area = function (r) {
      return PI * r * r;
    };

    exports.circumference = function (r) {
      return 2 * PI * r;
    };

The module `circle.js` has exported the functions `area()` and
`circumference()`.  To export an object, add to the special `exports`
object.  (Alternatively, one can use `this` instead of `exports`.) Variables
local to the module will be private. In this example the variable `PI` is
private to `circle.js`. The function `puts()` comes from the module `"sys"`,
which is a built-in module. Modules which are not prefixed by `"./"` are
built-in module--more about this later.

A module prefixed with `"./"` is relative to the file calling `require()`.
That is, `circle.js` must be in the same directory as `foo.js` for
`require("./circle")` to find it.

Without the leading `"./"`, like `require("assert")` the module is searched
for in the `require.paths` array. `require.paths` on my system looks like
this: 

`[ "/home/ryan/.node_libraries" ]`

That is, when `require("assert")` is called Node looks for: 

  * 1: `/home/ryan/.node_libraries/assert.js`
  * 2: `/home/ryan/.node_libraries/assert.node`
  * 3: `/home/ryan/.node_libraries/assert/index.js`
  * 4: `/home/ryan/.node_libraries/assert/index.node`

interrupting once a file is found. Files ending in `".node"` are binary Addon
Modules; see the section below about addons. `"index.js"` allows one to
package a module as a directory.

`require.paths` can be modified at runtime by simply unshifting new
paths onto it, or at startup with the `NODE_PATH` environmental
variable (which should be a list of paths, colon separated).

Use `process.mixin()` to include modules into the global namespace.

    process.mixin(GLOBAL, require("./circle"), require("sys"));
    puts("The area of a circle of radius 4 is " + area(4));

## Timers

### setTimeout(callback, delay, [arg, ...])

To schedule execution of `callback` after `delay` milliseconds. Returns a
`timeoutId` for possible use with `clearTimeout()`.

    var sys   = require("sys"),
        start = new Date(),
        timer = setTimeout(function () {
            sys.puts("Timer fired after " + (Date.now() - start) + "ms");
        }, 1000);

    sys.puts("Started timer.");

Optionally, you can pass arguments to the callback.

    var sys   = require("sys"),
        start = new Date(),
        timer = setTimeout(function (start_time, message) {
            sys.puts(message + (Date.now() - start_time) + "ms");
        }, 1000, start, "Timer fired after ");

    sys.puts("Started timer.");

These two examples generate the same output.

### clearTimeout(timeoutId)

Prevents a timeout from triggering.

    var sys    = require("sys"),
        start  = new Date(),
        timer1 = setTimeout(function () {
          sys.puts("Timer fired after " + (Date.now() - start) + "ms");
        }, 5000),
        timer2 = setTimeout(function () {
          sys.puts("This is taking too long.  Stopping timer1.");
          clearTimeout(timer1);
        }, 1000);

    sys.puts("Started timers.");

### setInterval(callback, delay, [arg, ...])

To schedule the repeated execution of `callback` every `delay` milliseconds. Returns a `intervalId` for possible use with `clearInterval()`.

Optionally, you can also pass arguments to the callback.

### clearInterval(intervalId)

Stops a interval from triggering.

    var sys   = require("sys"),
        start = new Date(),
        count = 10,
        timer = setInterval(function () {
          count -= 1;
          sys.puts("Timer fired after " + (Date.now() - start) + "ms " + count + " remaining.");
          if (count === 0) {
            clearInterval(timer);
          }
        }, 100);

    sys.puts("Started timer.");


## Child Processes

Node provides a tri-directional `popen(3)` facility through the `ChildProcess`
class.

It is possible to stream data through the child's `stdin`, `stdout`, and
`stderr` in a fully non-blocking way.

To create a child process use `require("child_process").spawn()`.

Child processes always have three streams associated with them. `child.stdin`,
`child.stdout`, and `child.stderr`.

`ChildProcess` is an EventEmitter with the following events:

 - **`exit`** - `callback(code)`:
   This event is emitted after the child process ends. `code` is the final
   exit code of the process.  After this event is emitted, the `"output"`
   and `"error"` callbacks will no longer be made.


### child_process.spawn(command, args, env)

Launches a new process with the given `command`, command line arguments, and
environment variables.  If omitted, `args` defaults to an empty Array, and `env`
defaults to `process.env`.

Example of running `ls -lh /usr`, capturing `stdout`, `stderr`, and the exit code:

    var sys   = require("sys"),
        spawn = require("child_process").spawn,
        ls    = spawn("ls", ["-lh", "/usr"]);

    ls.stdout.addListener("data", function (data) {
      sys.print("stdout: " + data);
    });

    ls.stderr.addListener("data", function (data) {
      sys.print("stderr: " + data);
    });

    ls.addListener("exit", function (code) {
      sys.puts("child process exited with code " + code);
    });


Example of checking for failed exec:

    var sys   = require("sys"),
        spawn = require("child_process").spawn,
        child = spawn("bad_command");

    child.stderr.addListener("data", function (data) {
      if (/^execvp\(\)/.test(data.asciiSlice(0,data.length))) {
        sys.puts("Failed to start child process.");
      }
    });


See also: `child_process.exec()`


### child.kill(signal)

Send a signal to the child process. If no argument is given, the process will
be sent `"SIGTERM"`. See `signal(7)` for a list of available signals.

    var sys   = require("sys"),
        spawn = require("child_process").spawn,
        grep  = spawn("grep", ["ssh"]);

    grep.addListener("exit", function (code) {
      sys.puts("child process exited with code " + code);
    });

    // send SIGHUP to process
    grep.kill("SIGHUP");

Note that while the function is called `kill`, the signal delivered to the child
process may not actually kill it.  `kill` really just sends a signal to a process.

See `kill(2)`


### child.pid

The PID of the child process.

Example:

    var sys   = require("sys"),
        spawn = require("child_process").spawn,
        grep  = spawn("grep", ["ssh"]);

    sys.puts("Spawned child pid: " + grep.pid);
    grep.stdin.close();


### child.stdin.write(data, encoding)

Write data to the child process's `stdin`. The second argument is optional and
specifies the encoding: possible values are `"utf8"`, `"ascii"`, and
`"binary"`.

Example: A very elaborate way to run "ps ax | grep ssh"

    var sys   = require("sys"),
        spawn = require("child_process").spawn,
        ps    = spawn("ps", ["ax"]),
        grep  = spawn("grep", ["ssh"]);

    ps.stdout.addListener("data", function (data) {
      grep.stdin.write(data);
    });

    ps.stderr.addListener("data", function (data) {
      sys.print("ps stderr: " + data);
    });

    ps.addListener("exit", function (code) {
      if (code !== 0) {
        sys.puts("ps process exited with code " + code);
      }
      grep.stdin.close();
    });

    grep.stdout.addListener("data", function (data) {
      sys.print(data);
    });

    grep.stderr.addListener("data", function (data) {
      sys.print("grep stderr: " + data);
    });

    grep.addListener("exit", function (code) {
      if (code !== 0) {
        sys.puts("grep process exited with code " + code);
      }
    });


### child.stdin.close()

Closes the child process's `stdin` stream.  This often causes the child process to terminate.

Example:

    var sys   = require("sys"),
        spawn = require("child_process").spawn,
        grep  = spawn("grep", ["ssh"]);

    grep.addListener("exit", function (code) {
      sys.puts("child process exited with code " + code);
    });

    grep.stdin.close();


### child_process.exec(command, callback)

High-level way to execute a command as a child process, buffer the
output, and return it all in a callback.

    var sys   = require("sys"),
        exec  = require("child_process").exec,
        child;
    
    child = exec("cat *.js bad_file | wc -l", function (error, stdout, stderr) {
      sys.print("stdout: " + stdout);
      sys.print("stderr: " + stderr);
      if (error !== null) {
        sys.puts("exec error: " + error);
      }
    });

The callback gets the arguments `(error, stdout, stderr)`. On success, `error`
will be `null`.  On error, `error` will be an instance of `Error` and `err.code`
will be the exit code of the child process.



## File System

File I/O is provided by simple wrappers around standard POSIX functions.  To
use this module do `require("fs")`. All the methods have asynchronous and
synchronous forms. 

The asynchronous form always take a completion callback as its last argument.
The arguments passed to the completion callback depend on the method, but the
first argument is always reserved for an exception. If the operation was
completed successfully, then the first argument will be `null` or `undefined`.

Here is an example of the asynchronous version:

    var fs = require("fs"),
        sys = require("sys");

    fs.unlink("/tmp/hello", function (err) {
      if (err) throw err;
      sys.puts("successfully deleted /tmp/hello");
    });

Here is the synchronous version:

    var fs = require("fs"),
        sys = require("sys");

    fs.unlinkSync("/tmp/hello")
    sys.puts("successfully deleted /tmp/hello");

With the asynchronous methods there is no guaranteed ordering. So the
following is prone to error:

    fs.rename("/tmp/hello", "/tmp/world", function (err) {
      if (err) throw err;
      sys.puts("renamed complete");
    });
    fs.stat("/tmp/world", function (err, stats) {
      if (err) throw err;
      sys.puts("stats: " + JSON.stringify(stats));
    });

It could be that `fs.stat` is executed before `fs.rename`.
The correct way to do this is to chain the callbacks.

    fs.rename("/tmp/hello", "/tmp/world", function (err) {
      if (err) throw err;
      fs.stat("/tmp/world", function (err, stats) {
        if (err) throw err;
        sys.puts("stats: " + JSON.stringify(stats));
      });
    });

In busy processes, the programmer is _strongly encouraged_ to use the
asynchronous versions of these calls. The synchronous versions will block
the entire process until they complete--halting all connections.

### fs.rename(path1, path2, callback)

Asynchronous rename(2). No arguments other than a possible exception are given to the completion callback.

### fs.renameSync(path1, path2)

Synchronous rename(2).

### fs.truncate(fd, len, callback)

Asynchronous ftruncate(2). No arguments other than a possible exception are given to the completion callback.

### fs.truncateSync(fd, len)

Synchronous ftruncate(2).

### fs.chmod(path, mode, callback)

Asynchronous chmod(2). No arguments other than a possible exception are given to the completion callback.

### fs.chmodSync(path, mode)

Synchronous chmod(2).
  
### fs.stat(path, callback), fs.lstat(path, callback)

Asynchronous stat(2) or lstat(2). The callback gets two arguments `(err, stats)` where `stats` is a `fs.Stats` object. It looks like this:

    { dev: 2049
    , ino: 305352
    , mode: 16877
    , nlink: 12
    , uid: 1000
    , gid: 1000
    , rdev: 0
    , size: 4096
    , blksize: 4096
    , blocks: 8
    , atime: "2009-06-29T11:11:55Z"
    , mtime: "2009-06-29T11:11:40Z"
    , ctime: "2009-06-29T11:11:40Z" 
    }

See the `fs.Stats` section below for more information.

### fs.statSync(path), fs.lstatSync(path)

Synchronous stat(2) or lstat(2). Returns an instance of `fs.Stats`.

### fs.link(srcpath, dstpath, callback)

Asynchronous link(2). No arguments other than a possible exception are given to the completion callback.

### fs.linkSync(dstpath, srcpath)

Synchronous link(2).

### fs.symlink(linkdata, path, callback)

Asynchronous symlink(2). No arguments other than a possible exception are given to the completion callback.

### fs.symlinkSync(linkdata, path)

Synchronous symlink(2).

### fs.readlink(path, callback)

Asynchronous readlink(2). The callback gets two arguments `(err, resolvedPath)`. 

### fs.readlinkSync(path)

Synchronous readlink(2). Returns the resolved path.

### fs.realpath(path, callback)

Asynchronous realpath(2).  The callback gets two arguments `(err, resolvedPath)`.

### fs.realpathSync(path)

Synchronous realpath(2). Returns the resolved path.

### fs.unlink(path, callback)

Asynchronous unlink(2). No arguments other than a possible exception are given to the completion callback.

### fs.unlinkSync(path)

Synchronous unlink(2).

### fs.rmdir(path, callback)

Asynchronous rmdir(2). No arguments other than a possible exception are given to the completion callback.

### fs.rmdirSync(path)

Synchronous rmdir(2).

### fs.mkdir(path, mode, callback)

Asynchronous mkdir(2). No arguments other than a possible exception are given to the completion callback.

### fs.mkdirSync(path, mode)

Synchronous mkdir(2).

### fs.readdir(path, callback)

Asynchronous readdir(3).  Reads the contents of a directory.
The callback gets two arguments `(err, files)` where `files` is an array of
the names of the files in the directory excluding `"."` and `".."`.

### fs.readdirSync(path)

Synchronous readdir(3). Returns an array of filenames excluding `"."` and
`".."`.

### fs.close(fd, callback)

Asynchronous close(2).  No arguments other than a possible exception are given to the completion callback.

### fs.closeSync(fd)

Synchronous close(2).

### fs.open(path, flags, mode, callback)

Asynchronous file open. See open(2). Flags can be "r", "r+", "w", "w+", "a",
or "a+". The callback gets two arguments `(err, fd)`. 

### fs.openSync(path, flags, mode)

Synchronous open(2). 

### fs.write(fd, data, position, encoding, callback)

Write data to the file specified by `fd`.  `position` refers to the offset
from the beginning of the file where this data should be written. If
`position` is `null`, the data will be written at the current position.
See pwrite(2).

The callback will be given two arguments `(err, written)` where `written`
specifies how many _bytes_ were written.

### fs.writeSync(fd, data, position, encoding)

Synchronous version of `fs.write()`. Returns the number of bytes written.

### fs.read(fd, length, position, encoding, callback)

Read data from the file specified by `fd`.

`length` is an integer specifying the number of bytes to read.

`position` is an integer specifying where to begin reading from in the file.

The callback is given three arguments, `(err, data, bytesRead)` where `data`
is a string--what was read--and `bytesRead` is the number of bytes read.

### fs.readSync(fd, length, position, encoding)

Synchronous version of `fs.read`. Returns an array `[data, bytesRead]`.

### fs.readFile(filename, encoding="utf8", callback)

Asynchronously reads the entire contents of a file. Example:

    fs.readFile("/etc/passwd", function (err, data) {
      if (err) throw err;
      sys.puts(data);
    });

The callback is passed two arguments `(err, data)`, where `data` is the
contents of the file.

### fs.readFileSync(filename, encoding="utf8")

Synchronous version of `fs.readFile`. Returns the contents of the `filename`.

### fs.writeFile(filename, data, encoding="utf8", callback)

Asynchronously writes data to a file. Example:

    fs.writeFile("message.txt", "Hello Node", function (err) {
      if (err) throw err;
      sys.puts("It's saved!");
    });

### fs.writeFileSync(filename, data, encoding="utf8")

The synchronous version of `fs.writeFile`.

### fs.watchFile(filename, [options,] listener)

Watch for changes on `filename`. The callback `listener` will be called each
time the file changes.

The second argument is optional. The `options` if provided should be an object
containing two members a boolean, `persistent`, and `interval`, a polling
value in milliseconds. The default is `{persistent: true, interval: 0}`.

The `listener` gets two arguments the current stat object and the previous
stat object:

    fs.watchFile(f, function (curr, prev) {
      sys.puts("the current mtime is: " + curr.mtime);
      sys.puts("the previous mtime was: " + prev.mtime);
    });

These stat objects are instances of `fs.Stat`. 

### fs.unwatchFile(filename)

Stop watching for changes on `filename`.

### fs.Stats

Objects returned from `fs.stat()` and `fs.lstat()` are of this type.

 - `stats.isFile()`
 - `stats.isDirectory()`
 - `stats.isBlockDevice()`
 - `stats.isCharacterDevice()`
 - `stats.isSymbolicLink()`
 - `stats.isFIFO()`
 - `stats.isSocket()`

### fs.FileReadStream

This is an EventEmitter with the following events.

 - **`"open"`** `callback(fd)` The file descriptor was opened.
 - **`"data"`** `callback(chunk)` A chunk of data was read.
 - **`"error"`** `callback(err)` An error occurred. This stops the stream.
 - **`"end"`** `callback()` The end of the file was reached.
 - **`"close"`** `callback()` The file descriptor was closed.

### fs.createReadStream(path, [options])

Returns a new FileReadStream object.

`options` is an object with the following defaults:

    { "flags": "r"
    , "encoding": "binary"
    , "mode": 0666
    , "bufferSize": 4 * 1024
    }

### readStream.readable

A boolean that is `true` by default, but turns `false` after an `"error"`
occured, the stream came to an "end", or `destroy()` was called.

### readStream.pause()

Stops the stream from reading further data. No `"data"` event will be fired
until the stream is resumed.

### readStream.resume()

Resumes the stream. Together with `pause()` this useful to throttle reading.

### readStream.destroy()

Allows to close the stream before the `"end"` is reached. No more events other
than `"close"` will be fired after this method has been called.

### fs.FileWriteStream

- **`"open"`**`(fd)` The file descriptor was opened.
- **`"drain"`**`()` No more data needs to be written.
- **`"error"`**`(err)` An error occurred. This stops the stream.
- **`"close"`**`()` The file descriptor was closed.

### fs.createWriteStream(path, [options])

Returns a new FileWriteStream object.
`options` is an object with the following defaults:

    { "flags": "w"
    , "encoding": "binary"
    , "mode": 0666
    }

### writeStream.writeable

A boolean that is `true` by default, but turns `false` after an `"error"`
occurred or `end()` / `destroy()` was called.

### writeStream.write(data)

Returns `true` if the data was flushed to the kernel, and `false` if it was
queued up for being written later. A `"drain"` will fire after all queued data
has been written.

You can also specify `callback` to be notified when the data from this write
has been flushed. The first param is `err`, the second is `bytesWritten`.

### writeStream.end()

Closes the stream right after all queued `write()` calls have finished.

### writeStream.destroy()

Allows to close the stream regardless of its current state.

## HTTP

To use the HTTP server and client one must `require("http")`.

The HTTP interfaces in Node are designed to support many features
of the protocol which have been traditionally difficult to use.
In particular, large, possibly chunk-encoded, messages. The interface is
careful to never buffer entire requests or responses--the
user is able to stream data.

HTTP message headers are represented by an object like this:

    { "content-length": "123"
    , "content-type": "text/plain"
    , "stream": "keep-alive"
    , "accept": "*/*"
    }

Keys are lowercased. Values are not modified.

In order to support the full spectrum of possible HTTP applications, Node's
HTTP API is very low-level. It deals with stream handling and message
parsing only. It parses a message into headers and body but it does not
parse the actual headers or the body.


### http.Server

This is an EventEmitter with the following events:

 - **`"request"`** - `callback(request, response)`:
 `request` is an instance of `http.ServerRequest` and `response` is
 an instance of `http.ServerResponse`

 - **`"stream"`** - `callback(stream)`:
 When a new TCP stream is established.
 `stream` is an object of type `http.Connection`. Usually users
 will not want to access this event. The `stream` can also be
 accessed at `request.stream`.

 - **`"close"`** - `callback(errno)`:
 Emitted when the server closes. `errorno` is an integer which indicates what, if any,
 error caused the server to close. If no
 error occured `errorno` will be 0.


### http.createServer(request_listener, [options])

Returns a new web server object.

The `options` argument is optional. The
`options` argument accepts the same values as the
options argument for `net.Server`.

The `request_listener` is a function which is automatically
added to the `"request"` event.

### 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.

This function is asynchronous. `listening` will be emitted when the server
is ready to accept connections.


### server.listen(path)

Start an HTTP UNIX socket server listening for connections on the given `path`.
(Hint: use NGINX to load balance across many Node servers with this.)

This function is asynchronous. `listening` will be emitted when the server
is ready to accept connections.


### server.close()

Stops the server from accepting new connections.


### http.ServerRequest

This object is created internally by a HTTP server--not by
the user--and passed as the first argument to a `"request"` listener.

This is an EventEmitter with the following events:

- **`"data"`** - `callback(chunk)`:
Emitted when a piece of the message body is received.

Example: A chunk of the body is given as the single
argument. The transfer-encoding has been decoded.  The
body chunk is a string.  The body encoding is set with
`request.setBodyEncoding()`.

- **`"end"`** - `callback()`:
Emitted exactly once for each message. No arguments.  After
emitted no other events will be emitted on the request.


### request.method

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


### request.url

Request URL string. This contains only the URL that is
present in the actual HTTP request. If the request is:

    GET /status?name=ryan HTTP/1.1\r\n
    Accept: text/plain\r\n
    \r\n

Then `request.url` will be:

    "/status?name=ryan"

If you would like to parse the URL into its parts, you can use
`require("url").parse(request.url)`.  Example:

    node> require("url").parse("/status?name=ryan")
    { href: '/status?name=ryan'
    , search: '?name=ryan'
    , query: 'name=ryan'
    , pathname: '/status'
    }

If you would like to extract the params from the query string,
you can use the `require("querystring").parse` function, or pass
`true` as the second argument to `require("url").parse`.  Example:

    node> require("url").parse("/status?name=ryan", true)
    { href: '/status?name=ryan'
    , search: '?name=ryan'
    , query: { name: 'ryan' }
    , pathname: '/status'
    }



### request.headers

Read only.

### request.httpVersion

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


### request.setEncoding(encoding="binary")

Set the encoding for the request body. Either `"utf8"` or `"binary"`. Defaults
to `"binary"`.


### request.pause()

Pauses request from emitting events.  Useful to throttle back an upload.


### request.resume()

Resumes a paused request.

### request.stream

The `http.Connection` object.

### http.ServerResponse

This object is created internally by a HTTP server--not by the user. It is
passed as the second parameter to the `"request"` event.

### response.writeHead(statusCode[, reasonPhrase] , headers)

Sends a response header to the request. The status code is a 3-digit HTTP
status code, like `404`. The last argument, `headers`, are the response headers.
Optionally one can give a human-readable `reasonPhrase` as the second
argument.

Example:

    var body = "hello world";
    response.writeHead(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 `response.end()` is called.

### response.write(chunk, encoding="ascii")

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

If `chunk` is a string, the second parameter
specifies how to encode it into a byte stream. By default the
`encoding` is `"ascii"`.

**Note**: This is the raw HTTP body and has nothing to do with
higher-level multi-part body encodings that may be used.

The first time `response.write()` is called, it will send the buffered
header information and the first body to the client. The second time
`response.write()` is called, Node assumes you're going to be streaming
data, and sends that separately. That is, the response is buffered up to the
first chunk of body.


### response.end()

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

### http.Client

An HTTP client is constructed with a server address as its
argument, the returned handle is then used to issue one or more
requests.  Depending on the server connected to, the client might
pipeline the requests or reestablish the stream after each
stream. _Currently the implementation does not pipeline requests._

Example of connecting to `google.com`:

    var sys = require("sys"),
       http = require("http");
    var google = http.createClient(80, "www.google.com");
    var request = google.request("GET", "/", {"host": "www.google.com"});
    request.addListener('response', function (response) {
      sys.puts("STATUS: " + response.statusCode);
      sys.puts("HEADERS: " + JSON.stringify(response.headers));
      response.setEncoding("utf8");
      response.addListener('data', function (chunk) {
        sys.puts("BODY: " + chunk);
      });
    });
    request.end();


### http.createClient(port, host)

Constructs a new HTTP client. `port` and
`host` refer to the server to be connected to. A
stream is not established until a request is issued.

### client.request([method], path, [request_headers])

Issues a request; if necessary establishes stream. Returns a `http.ClientRequest` instance.

`method` is optional and defaults to "GET" if omitted.

`request_headers` is optional.
Additional request headers might be added internally
by Node. Returns a `ClientRequest` object.

Do remember to include the `Content-Length` header if you
plan on sending a body. If you plan on streaming the body, perhaps
set `Transfer-Encoding: chunked`.

*NOTE*: the request is not complete. This method only sends the header of
the request. One needs to call `request.end()` to finalize the request and
retrieve the response.  (This sounds convoluted but it provides a chance for
the user to stream a body to the server with `request.write()`.)



### http.ClientRequest

This object is created internally and returned from the request methods of a
`http.Client`. It represents an _in-progress_ request whose header has
already been sent.

To get the response, add a listener for `'response'` to the request object.
`'response'` will be emitted from the request object when the response
headers have been received.  The `'response'` event is executed with one
argument which is an instance of `http.ClientResponse`.

During the `'response'` event, one can add listeners to the
response object; particularly to listen for the `"data"` event. Note that
the `'response'` event is called before any part of the response body is received,
so there is no need to worry about racing to catch the first part of the
body. As long as a listener for `'data'` is added during the `'response'`
event, the entire body will be caught.


    // Good
    request.addListener('response', function (response) {
      response.addListener('data', function (chunk) {
        sys.puts("BODY: " + chunk);
      });
    });

    // Bad - misses all or part of the body
    request.addListener('response', function (response) {
      setTimeout(function () {
        response.addListener('data', function (chunk) {
          sys.puts("BODY: " + chunk);
        });
      }, 10);
    });

This is an `EventEmitter` with the following events:

- **`"response"`** - `callback(response)`:
Emitted when a response is received to this request. This event is emitted only once. The
`response` argument will be an instance of `http.ClientResponse`.


### request.write(chunk, encoding="ascii")

Sends a chunk of the body.  By calling this method
many times, the user can stream a request body to a
server--in that case it is suggested to use the
`["Transfer-Encoding", "chunked"]` header line when
creating the request.

The `chunk` argument should be an array of integers
or a string.

The `encoding` argument is optional and only
applies when `chunk` is a string. The encoding
argument should be either `"utf8"` or
`"ascii"`. By default the body uses ASCII encoding,
as it is faster.

### request.end()

Finishes sending the request. If any parts of the body are
unsent, it will flush them to the stream. If the request is
chunked, this will send the terminating `"0\r\n\r\n"`.



### http.ClientResponse

This object is created internally and passed to the `"response"` event.

This is an `EventEmitter` with the following events.

- **`"data"`** - `callback(chunk)`:
Emitted when a piece of the message body is received.

    Example: A chunk of the body is given as the single
    argument. The transfer-encoding has been decoded.  The
    body chunk a String.  The body encoding is set with
    `response.setBodyEncoding()`.

- **`"end"`** - `callback()`:
Emitted exactly once for each message. No arguments. After
emitted no other events will be emitted on the response.

### response.statusCode

The 3-digit HTTP response status code. E.G. `404`.

### response.httpVersion

The HTTP version of the connected-to server. Probably either
`"1.1"` or `"1.0"`.

### response.headers

The response headers.

### response.setEncoding(encoding)

Set the encoding for the response body. Either `"utf8"` or `"binary"`.
Defaults to `"binary"`.

### response.pause()

Pauses response from emitting events.  Useful to throttle back a download.

### response.resume()

Resumes a paused response.

### response.client

A reference to the `http.Client` that this response belongs to.


## Networking

Creating UNIX and TCP servers and clients.
To use networking, one must `require("net")`.

### net.Server

Here is an example of a echo server which listens for connections
on port 7000:

    var net = require("net");
    var server = net.createServer(function (stream) {
      stream.setEncoding("utf8");
      stream.addListener('connect', function () {
        stream.write("hello\r\n");
      });
      stream.addListener('data', function (data) {
        stream.write(data);
      });
      stream.addListener('end', function () {
        stream.write("goodbye\r\n");
        stream.end();
      });
    });
    server.listen(7000, "localhost");

This is an EventEmitter with the following events:

- **`"stream"`** - `callback(stream)`:
Emitted when a new stream is made. `stream` is an instance of `net.Stream`.

- **`"close"`** - `callback(errno)`:
Emitted when the server closes. `errorno` is an integer which indicates what, if any, error caused
the server to close. If no error occurred `errorno` will be 0.


### net.createServer(connectionListener)

Creates a new TCP server.

The `connection_listener` argument is automatically set as a listener for
the `"stream"` event.


### server.listen(port, host=null)

Tells the server to listen for TCP connections to `port` and `host`.

`host` is optional. If `host` is not specified the server will accept client
connections on any network address.

This function is asynchronous. The server will emit `'listening'` when it is
safe to connect to it.


### server.close()

Stops the server from accepting new connections. This function is
asynchronous, the server is finally closed when the server emits a `"close"`
event.

### net.Stream

This object is used as a TCP/UNIX client and also as a server-side stream
for `net.Server`.

This is an EventEmitter and duplex stream with the following events:

- **`"connect"`** - `callback()`:
Call once the stream is established after a call to `createConnection()` or
`connect()`.

- **`"data"`** - `callback(data)`:
Called when data is received on the stream.  `data`
will be a string. Encoding of data is set by `stream.setEncoding()`.

- **`"end"`** - `callback()`:
Called when the other end of the stream sends a FIN
packet. After this is emitted the `readyState` will be
`"writeOnly"`. One should probably just call
`stream.end()` when this event is emitted.

- **`"timeout"`** - `callback()`:
Emitted if the stream times out from inactivity. The
`"close"` event will be emitted immediately following this event.

- **`"drain"`** - `callback()`:
Emitted when the write buffer becomes empty. Can be used to throttle uploads.

- **`"close"`** - `callback(had_error)`:
Emitted once the stream is fully closed. The argument `had_error` is a boolean which says if
the stream was closed due to a transmission
error. (TODO: access error codes.)

### net.createConnection(port, host="127.0.0.1")

Creates a new stream object and opens a stream to the specified `port`
and `host`. If the second parameter is omitted, localhost is assumed.

When the stream is established the `"connect"` event will be emitted.

### stream.connect(port, host="127.0.0.1")

Opens a stream to the specified `port` and `host`. `createConnection()`
also opens a stream; normally this method is not needed. Use this only if
a stream is closed and you want to reuse the object to connect to another
server.

This function is asynchronous. When the `"connect"` event is emitted the
stream is established. If there is a problem connecting, the `"connect"`
event will not be emitted, the `"close"` event will be emitted with 
`had_error == true`.

### stream.remoteAddress

The string representation of the remote IP address. For example,
`"74.125.127.100"` or `"2001:4860:a005::68"`.

This member is only present in server-side connections.

### stream.readyState

Either `"closed"`, `"open"`, `"opening"`, `"readOnly"`, or `"writeOnly"`.

### stream.setEncoding(encoding)

Sets the encoding (either `"ascii"`, `"utf8"`, or `"binary"`) for data that is
received.

### stream.write(data, encoding="ascii")

Sends data on the stream. The second parameter specifies the encoding in
the case of a string--it defaults to ASCII because encoding to UTF8 is rather
slow.

Returns `true` if the entire data was flushed successfully to the kernel
buffer. Returns `false` if all or part of the data was queued in user memory.
`'drain'` will be emitted when the buffer is again free.

### stream.end()

Half-closes the stream. I.E., it sends a FIN packet. It is possible the
server will still send some data. After calling this `readyState` will be
`"readOnly"`.

### stream.destroy()

Ensures that no more I/O activity happens on this stream. Only necessary in
case of errors (parse error or so).

### stream.pause()

Pauses the reading of data. That is, `"data"` events will not be emitted.
Useful to throttle back an upload.

### stream.resume()

Resumes reading after a call to `pause()`.

### stream.setTimeout(timeout)

Sets the stream to timeout after `timeout` milliseconds of inactivity on
the stream. By default all `net.Stream` objects have a timeout of 60
seconds (60000 ms).

If `timeout` is 0, then the idle timeout is disabled.

### stream.setNoDelay(noDelay=true)

Disables the Nagle algorithm. By default TCP connections use the Nagle
algorithm, they buffer data before sending it off. Setting `noDelay` will
immediately fire off data each time `stream.write()` is called.


## DNS module

Use `require("dns")` to access this module.

Here is an example which resolves `"www.google.com"` then reverse
resolves the IP addresses which are returned.

    var dns = require("dns"),
        sys = require("sys");

    dns.resolve4("www.google.com", function (err, addresses) {
      if (err) throw err;

      sys.puts("addresses: " + JSON.stringify(addresses));

      for (var i = 0; i < addresses.length; i++) {
        var a = addresses[i];
        dns.reverse(a, function (err, domains) {
          if (err) {
            puts("reverse for " + a + " failed: " + e.message);
          } else {
            sys.puts("reverse for " + a + ": " + JSON.stringify(domains));
          }
        });
      }
    });

### dns.resolve(domain, rrtype = 'A', callback)

Resolves a domain (e.g. `"google.com"`) into an array of the record types
specified by rrtype. Valid rrtypes are `A` (IPV4 addresses), `AAAA` (IPV6
addresses), `MX` (mail exchange records), `TXT` (text records), `SRV` (SRV
records), and `PTR` (used for reverse IP lookups).

The callback has arguments `(err, addresses)`.  The type of each item
in `addresses` is determined by the record type, and described in the
documentation for the corresponding lookup methods below.

On error, `err` would be an instanceof `Error` object, where `err.errno` is
one of the error codes listed below and `err.message` is a string describing
the error in English.


### dns.resolve4(domain, callback)

The same as `dns.resolve()`, but only for IPv4 queries (`A` records). 
`addresses` is an array of IPv4 addresses (e.g.  `["74.125.79.104", "74.125.79.105", "74.125.79.106"]`).

### dns.resolve6(domain, callback)

The same as `dns.resolve4()` except for IPv6 queries (an `AAAA` query).


### dns.resolveMx(domain, callback)

The same as `dns.resolve()`, but only for mail exchange queries (`MX` records).

`addresses` is an array of MX records, each with a priority and an exchange
attribute (e.g. `[{"priority": 10, "exchange": "mx.example.com"},...]`).

### dns.resolveTxt(domain, callback)

The same as `dns.resolve()`, but only for text queries (`TXT` records).
`addresses` is an array of the text records available for `domain` (e.g.,
`["v=spf1 ip4:0.0.0.0 ~all"]`).

### dns.resolveSrv(domain, callback)

The same as `dns.resolve()`, but only for service records (`SRV` records).
`addresses` is an array of the SRV records available for `domain`. Properties
of SRV records are priority, weight, port, and name (e.g., `[{"priority": 10, {"weight": 5, "port": 21223, "name": "service.example.com"}, ...]`).

### dns.reverse(ip, callback)

Reverse resolves an ip address to an array of domain names.

The callback has arguments `(err, domains)`. 

If there an an error, `err` will be non-null and an instanceof the Error
object.

Each DNS query can return an error code.

- `dns.TEMPFAIL`: timeout, SERVFAIL or similar.
- `dns.PROTOCOL`: got garbled reply.
- `dns.NXDOMAIN`: domain does not exists.
- `dns.NODATA`: domain exists but no data of reqd type.
- `dns.NOMEM`: out of memory while processing.
- `dns.BADQUERY`: the query is malformed.


## Assert Module

This module is used for writing unit tests for your applications, you can access it with `require("assert")`.

### assert.fail(actual, expected, message, operator)

Tests if `actual` is equal to `expected` using the operator provided.

### assert.ok(value, message)

Tests if value is a `true` value, it is equivalent to `assert.equal(true, value, message);`

### assert.equal(actual, expected, message)

Tests shallow, coercive equality with the equal comparison operator ( `==` ). 

### assert.notEqual(actual, expected, message)

Tests shallow, coercive non-equality with the not equal comparison operator ( `!=` ).

### assert.deepEqual(actual, expected, message)

Tests for deep equality.

### assert.notDeepEqual(actual, expected, message)

Tests for any deep inequality. 

### assert.strictEqual(actual, expected, message)

Tests strict equality, as determined by the strict equality operator ( `===` ) 

### assert.notStrictEqual(actual, expected, message)

Tests strict non-equality, as determined by the strict not equal operator ( `!==` ) 

### assert.throws(block, error, message)

Expects `block` to throw an error.

### assert.doesNotThrow(block, error, message)

Expects `block` not to throw an error.


## Path Module

This module contains utilities for dealing with file paths.  Use
`require("path")` to use it.  It provides the following methods:

### path.join(/* path1, path2, ... */)

Join all arguments together and resolve the resulting path.  Example:

    node> require("path").join("/foo", "bar", "baz/asdf", "quux", "..")
    "/foo/bar/baz/asdf"

### path.normalizeArray(arr)

Normalize an array of path parts, taking care of `".."` and `"."` parts.  Example:

    path.normalizeArray(["", 
      "foo", "bar", "baz", "asdf", "quux", ".."])
    // returns
    [ '', 'foo', 'bar', 'baz', 'asdf' ]

### path.normalize(p)

Normalize a string path, taking care of `".."` and `"."` parts.  Example:

    path.normalize("/foo/bar/baz/asdf/quux/..")
    // returns
    "/foo/bar/baz/asdf"

### path.dirname(p)

Return the directory name of a path.  Similar to the Unix `dirname` command.  Example:

    path.dirname("/foo/bar/baz/asdf/quux")
    // returns
    "/foo/bar/baz/asdf"

### path.basename(p, ext)

Return the last portion of a path.  Similar to the Unix `basename` command.  Example:

    path.basename("/foo/bar/baz/asdf/quux.html")
    // returns
    "quux.html"

    path.basename("/foo/bar/baz/asdf/quux.html", ".html")
    // returns
    "quux"

### path.extname(p)

Return the extension of the path.  Everything after the last '.', if there
is no '.' then it returns an empty string.  Examples:

    path.extname("index.html")
    // returns 
    ".html"

    path.extname("index")
    // returns
    ""

### path.exists(p, callback)

Test whether or not the given path exists.  Then, call the `callback` argument with either true or false.  Example:

    path.exists("/etc/passwd", function (exists) {
      sys.debug(exists ? "it's there" : "no passwd!");
    });


## URL Module

This module has utilities for URL resolution and parsing.

Parsed URL objects have some or all of the following fields, depending on
whether or not they exist in the URL string. Any parts that are not in the URL
string will not be in the parsed object. Examples are shown for the URL

`"http://user:pass@host.com:8080/p/a/t/h?query=string#hash"`

- `href`

  The full URL that was originally parsed. Example:   
  `"http://user:pass@host.com:8080/p/a/t/h?query=string#hash"`

- `protocol`

  The request protocol.  Example: `"http:"`

- `host`

  The full host portion of the URL, including port and authentication information. Example:
  `"user:pass@host.com:8080"`

- `auth`

  The authentication information portion of a URL.  Example: `"user:pass"`

- `hostname`

  Just the hostname portion of the host.  Example: `"host.com"`

- `port`

  The port number portion of the host.  Example: `"8080"`

- `pathname`

  The path section of the URL, that comes after the host and before the query, including the initial slash if present.  Example: `"/p/a/t/h"`

- `search`

  The "query string" portion of the URL, including the leading question mark. Example: `"?query=string"`

- `query`

  Either the "params" portion of the query string, or a querystring-parsed object. Example:
  `"query=string"` or `{"query":"string"}`

- `hash`

  The "fragment" portion of the URL including the pound-sign. Example: `"#hash"`


The following methods are provided by the URL module:

### url.parse(urlStr, parseQueryString=false)

Take a URL string, and return an object.  Pass `true` as the second argument to also parse
the query string using the `querystring` module.

### url.format(urlObj)

Take a parsed URL object, and return a formatted URL string.

### url.resolve(from, to)

Take a base URL, and a href URL, and resolve them as a browser would for an anchor tag.


## Query String Module

This module provides utilities for dealing with query strings.  It provides the following methods:

### querystring.stringify(obj, sep="&", eq="=")

Serialize an object to a query string.  Optionally override the default separator and assignment characters.
Example:

    querystring.stringify({foo: 'bar'})
    // returns
    "foo=bar"

### querystring.parse(str, sep="&", eq="=")

Deserialize a query string to an object.  Optionally override the default separator and assignment characters.

    querystring.parse('a=b&b=c')
    // returns
    { 'a': 'b'
    , 'b': 'c'
    }

### querystring.escape

The escape function used by `querystring.stringify`, provided so that it could be overridden if necessary.

### querystring.unescape

The unescape function used by `querystring.parse`, provided so that it could be overridden if necessary.

## REPL

A Read-Eval-Print-Loop is available both as a standalone program and easily
includable in other programs. 

The standalone REPL is called `node-repl` and is installed at
`$PREFIX/bin/node-repl`. It's recommended to use it with the program
`rlwrap` for a better user interface. I set 

    alias node-repl="rlwrap node-repl"

in my zsh configuration.

Inside the REPL, Control+D will exit. The special variable `_` (underscore) contains the
result of the last expression.

The library is called `/repl.js` and it can be used like this:

    var sys = require("sys"),
        net = require("net"),
       repl = require("repl");
    nconnections = 0;
    net.createServer(function (c) {
      sys.error("Connection!");
      nconnections += 1;
      c.close();
    }).listen(5000);
    repl.start("simple tcp server> ");

The repl provides access to any variables in the global scope. You can expose a variable 
to the repl explicitly by assigning it to the `repl.scope` object:

    var count = 5;
    repl.start();
    repl.scope.count = count;


## Addons

Addons are dynamically linked shared objects. They can provide glue to C and
C++ libraries. The API (at the moment) is rather complex, involving
knowledge of several libraries:

 - V8 JavaScript, a C++ library. Used for interfacing with JavaScript:
   creating objects, calling functions, etc.  Documented mostly in the
   `v8.h` header file (`deps/v8/include/v8.h` in the Node source tree).

 - libev, C event loop library. Anytime one needs to wait for a file
   descriptor to become readable, wait for a timer, or wait for a signal to
   received one will need to interface with libev.  That is, if you perform
   any I/O, libev will need to be used.  Node uses the `EV_DEFAULT` event
   loop.  Documentation can be found http:/cvs.schmorp.de/libev/ev.html[here].

 - libeio, C thread pool library. Used to execute blocking POSIX system
   calls asynchronously. Mostly wrappers already exist for such calls, in
   `src/file.cc` so you will probably not need to use it. If you do need it,
   look at the header file `deps/libeio/eio.h`.

 - Internal Node libraries. Most importantly is the `node::EventEmitter`
   class which you will likely want to derive from. 

 - Others. Look in `deps/` for what else is available. 

Node statically compiles all its dependencies into the executable. When
compiling your module, you don't need to worry about linking to any of these
libraries. 

To get started let's make a small Addon which does the following except in
C++:

    exports.hello = "world";

To get started we create a file `hello.cc`:

    #include <v8.h>

    using namespace v8;

    extern "C" void
    init (Handle<Object> target) 
    {
      HandleScope scope;
      target->Set(String::New("hello"), String::New("World"));
    }

This source code needs to be built into `hello.node`, the binary Addon. To
do this we create a file called `wscript` which is python code and looks
like this:

    srcdir = "."
    blddir = "build"
    VERSION = "0.0.1"

    def set_options(opt):
      opt.tool_options("compiler_cxx")

    def configure(conf):
      conf.check_tool("compiler_cxx")
      conf.check_tool("node_addon")

    def build(bld):
      obj = bld.new_task_gen("cxx", "shlib", "node_addon")
      obj.target = "hello"
      obj.source = "hello.cc"

Running `node-waf configure build` will create a file
`build/default/hello.node` which is our Addon.

`node-waf` is just http://code.google.com/p/waf/[WAF], the python-based build system. `node-waf` is
provided for the ease of users.

All Node addons must export a function called `init` with this signature:

    extern "C" void init (Handle<Object> target) 

For the moment, that is all the documentation on addons. Please see
<http://github.com/ry/node_postgres[node_postgres]> for a real example.