# NODE(1)

Ryan Dahl
`<ry@tinyclouds.org>`
version 0.1.13, 2009.09.30

## NAME

node - evented I/O for V8 javascript

## SYNOPSIS

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

    include("/utils.js");
    include("/http.js");
    createServer(function (request, response) {
      response.sendHeader(200, {"Content-Type": "text/plain"});
      response.sendBody("Hello World\n");
      response.finish();
    }).listen(8000);
    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/

## API

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. Both are relatively fast—use them if you can. `"utf8"` is slower and should be avoided when possible.

Unless otherwise noted, functions are all asynchronous and do not block execution.

### Helpers

These objects are available to all programs.

`node.cwd()`

  Returns the current working directory of the process.

`node.compile(source, scriptOrigin)`

  Just like `eval()` except that you can specify a `scriptOrigin` for better error reporting.

`__filename`

  The filename of the script being executed.

`require(path)`
`include(path)`

  See the modules section.

`node.libraryPaths`

  The search path for absolute path arguments to `require()` and `include()`.

### The `process` Object

`process` is the equivalent of `window` in browser-side javascript. It is the global scope. `process` is an instance of `node.EventEmitter`.

Event | Parameters | Notes
--- | --- | ---
`"exit"` | `code` | Made when the process exits. A listener on this event should not try to perform I/O since the process will forcibly exit in less than microsecond. However, it is a good hook to perform constant time checks of the module’s state (like for unit tests). The parameter `code` is the integer exit code passed to `process.exit()`.

`process.exit(code=0)`

  Ends the process with the specified code. By default it exits with the success code 0.

`process.ARGV`

  An array containing the command line arguments.

`process.ENV`

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

### Utilities

These function are in `"/utils.js"`. Use `require("/utils.js")` to access them.

`puts(string)`

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

`print(string)`

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

`debug(string)`

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

`inspect(object)`

  Return a string representation of the `object`. (For debugging.)

`exec(command)`

  Executes the command as a child process, buffers the output and returns it in a promise callback.

      include("/utils.js");
      exec("ls /").addCallback(function (stdout, stderr) {
        puts(stdout);
      });

  - on success: stdout buffer, stderr buffer

  - on error: exit code, stdout buffer, stderr buffer

### Events

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

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

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

Some asynchronous file operations return an `EventEmitter` called a promise. A promise emits just a single event when the operation is complete.

#### `node.EventEmitter`

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

Event | Parameters | Notes
--- | --- | ---
`"newListener"` | `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("connection", function (socket) {
        puts("someone connected!");
      });

`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.

#### `node.Promise`

`node.Promise` inherits from `node.eventEmitter`. A promise emits one of two events: `"success"` or `"error"`. After emitting its event, it will not emit anymore events.

Event | Parameters | Notes
--- | --- | ---
`"success"` | (depends) |
`"error"` | (depends) |

`promise.addCallback(listener)`

  Adds a listener for the `"success"` event. Returns the same promise object.

`promise.addErrback(listener)`

  Adds a listener for the `"error"` event. Returns the same promise object.

`promise.emitSuccess(arg1, arg2, …)`

  If you created the promise (by doing `new node.Promise()`) then call `emitSuccess` to emit the `"success"` event with the given arguments.

  (`promise.emit("success", arg1, arg2, …)` should also work, but doesn’t at the moment due to a bug; use `emitSuccess` instead.)

`promise.emitError(arg1, arg2, …)`

  Emits the `"error"` event.

`promise.wait()`

  Blocks futher execution until the promise emits a success or error event. Events setup before the call to `promise.wait()` was made may still be emitted and executed while `promise.wait()` is blocking.

  If there was a single argument to the `"success"` event then it is returned. If there were multiple arguments to `"success"` then they are returned as an array.

  If `"error"` was emitted instead, `wait()` throws an error.

  IMPORTANT `promise.wait()` is not a true fiber/coroutine. If any other promises are created and made to wait while the first promise waits, the first promise’s wait will not return until all others return. The benefit of this is a simple implementation and the event loop does not get blocked. Disadvantage is the possibility of situations where the promise stack grows infinitely large because promises keep getting created and keep being told to wait(). Use `promise.wait()` sparingly—probably best used only during program setup, not during busy server activity.

### Standard I/O

Standard I/O is handled through a special object `node.stdio`. stdout and stdin are fully non-blocking (even when piping to files). stderr is synchronous.

Event | Parameters | Notes
--- | --- | ---
`"data"` | `data` | Made when stdin has received a chunk of data. Depending on the encoding that stdin was opened with, `data` will be a string. This event will only be emited after `node.stdio.open()` has been called.
`"close"` |  | Made when stdin has been closed.

`node.stdio.open(encoding="utf8")`

  Open stdin. The program will not exit until `node.stdio.close()` has been called or the `"close"` event has been emitted.

`node.stdio.write(data)`

  Write data to stdout.

`node.stdio.writeError(data)`

  Write data to stderr. Synchronous.

`node.stdio.close()`

  Close stdin.

### Modules

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`.

The contents of `foo.js`:

    var circle = require("circle.js");
    include("/utils.js");
    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 `"/utils.js"`. Because `include("/utils.js")` was called, `puts()` is in the global namespace.

The module path is relative to the file calling `require()`. That is, `circle.js` must be in the same directory as `foo.js` for `require()` to find it.

Like `require()` the function `include()` also loads a module. Instead of returning a namespace object, `include()` will add the module’s exports into the global namespace. For example:

    include("circle.js");
    include("/utils.js");
    puts("The area of a cirlce of radius 4 is " + area(4));

When an absolute path is given to `require()` or `include()`, like `require("/mjsunit.js")` the module is searched for in the `node.libraryPaths` array. `node.libraryPaths` on my system looks like this:

    [ "/home/ryan/.node_libraries"
    , "/home/ryan/local/node/lib/node_libraries"
    , "/"
    ]

That is, first Node looks for `"/home/ryan/.node_libraries/mjsunit.js"` and then for `"/home/ryan/local/node/lib/node_libraries/mjsunit.js"`. If not found, it finally looks for `"/mjsunit.js"` (in the root directory).

`node.libraryPaths` can be modified at runtime by simply unshifting new paths on to it and at startup with the `NODE_LIBRARY_PATHS` environmental variable (which should be a list of paths, colon separated).

Node comes with several libraries which are installed when `"make install"` is run. These are currently undocumented, but do look them up in your system.

### Timers

`setTimeout(callback, delay)`

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

`clearTimeout(timeoutId)`

  Prevents said timeout from triggering.

`setInterval(callback, delay)`

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

`clearInterval(intervalId)`

  Stops a interval from triggering.

### Child Processes

Node provides a tridirectional `popen(3)` facility through the class `node.ChildProcess`. It is possible to stream data through the child’s `stdin`, `stdout`, and `stderr` in a fully non-blocking way.

#### `node.ChildProcess`

Event | Parameters | Notes
--- | --- | ---
`"output"` | `data` | Each time the child process sends data to its `stdout`, this event is emitted. `data` is a string. + If the child process closes its `stdout` stream (a common thing to do on exit), this event will be emitted with `data === null`.
`"error"` | `data` | Identical to the `"output"` event except for `stderr` instead of `stdout`.
`"exit"` | `code` | This event is emitted after the child process ends. `code` is the final exit code of the process. One can be assured that after this event is emitted that the `"output"` and `"error"` callbacks will no longer be made.

`node.createChildProcess(command)`

  Launches a new process with the given `command`. For example:

      var ls = node.createChildProcess("ls -lh /usr");
      ls.addListener("output", function (data) {
        puts(data);
      });

`child.pid`

  The PID of the child process.

`child.write(data, encoding="ascii")`

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

`child.close()`

  Closes the process’s `stdin` stream.

`child.kill(signal=node.SIGTERM)`

  Send a single to the child process. If no argument is given, the process will be sent `node.SIGTERM`. The standard POSIX signals are defined under the `node` namespace (`node.SIGINT`, `node.SIGUSR1`, …).

### File I/O

File I/O is provided by simple wrappers around standard POSIX functions. All POSIX wrappers have a similar form. They return a promise (`node.Promise`). Example:

    var promise = node.fs.unlink("/tmp/hello");
    promise.addCallback(function () {
      puts("successfully deleted /tmp/hello");
    });

There is no guaranteed ordering to the POSIX wrappers. The following is very much prone to error

    node.fs.rename("/tmp/hello", "/tmp/world");
    node.fs.stat("/tmp/world").addCallback(function (stats) {
      puts("stats: " + JSON.stringify(stats));
    });

It could be that `stat()` is executed before the `rename()`. The correct way to do this is to chain the promises.

    node.fs.rename("/tmp/hello", "/tmp/world").addCallback(function () {
      node.fs.stat("/tmp/world").addCallback(function (stats) {
        puts("stats: " + JSON.stringify(stats));
      });
    });

Or use the `promise.wait()` functionality:

    node.fs.rename("/tmp/hello", "/tmp/world").wait();
    node.fs.stat("/tmp/world").addCallback(function (stats) {
      puts("stats: " + JSON.stringify(stats));
    });

`node.fs.rename(path1, path2)`

  See rename(2).

  - on success: no parameters.

  - on error: no parameters.

`node.fs.stat(path)`

  See stat(2).

  - on success: Returns `node.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 `node.fs.Stats` section below for more information.

  - on error: no parameters.

`node.fs.unlink(path)`

  See unlink(2)

  - on success: no parameters.

  - on error: no parameters.

`node.fs.rmdir(path)`

  See rmdir(2)

  - on success: no parameters.

  - on error: no parameters.

`node.fs.mkdir(path, mode)`

  See mkdir(2)

  - on success: no parameters.

  - on error: no parameters.

`node.fs.readdir(path)`

  Reads the contents of a directory.

  - on success: One argument, an array containing the names (strings) of the files in the directory (excluding "." and "..").

  - on error: no parameters.

`node.fs.close(fd)`

  See close(2)

  - on success: no parameters.

  - on error: no parameters.

`node.fs.open(path, flags, mode)`

  See open(2). The constants like `O_CREAT` are defined at `node.O_CREAT`.

  - on success: `fd` is given as the parameter.

  - on error: no parameters.

`node.fs.write(fd, data, position, encoding)`

  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).

  - on success: returns an integer `written` which specifies how many bytes were written.

  - on error: no parameters.

`node.fs.read(fd, length, position, encoding)`

  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.

  - on success: returns `data, bytes_read`, what was read from the file.

  - on error: no parameters.

`node.fs.cat(filename, encoding="utf8")`

  Outputs the entire contents of a file. Example:

      node.fs.cat("/etc/passwd").addCallback(function (content) {
        puts(content);
      });

  - on success: returns `data`, what was read from the file.

  - on error: no parameters.

#### `node.fs.Stats`

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

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

  …

### HTTP

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

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"
    , "Connection": "keep-alive"
    , "Accept": "*/*"
    }

In order to support the full spectrum of possible HTTP applications, Node’s HTTP API is very low-level. It deals with connection 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`

Event | Parameters | Notes
--- | --- | ---
`"request"` | `request, response` | `request` is an instance of `http.ServerRequest` `response` is an instance of `http.ServerResponse`
`"connection"` | `connection` | When a new TCP connection is established. `connection` is an object of type `http.Connection`. Usually users will not want to access this event. The `connection` can also be accessed at `request.connection`.
`"close"` | `errorno` | 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 `tcp.Server` does.

  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 synchronous.

`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.

Event | Parameters | Notes
--- | --- | ---
`"body"` | `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()`.
`"complete"` | (none) | 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.uri`

  Request URI Object. This contains only the parameters that are present in the actual HTTP request. That is, if the request is

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

  Then `request.uri` will be

      { path: "/status",
        file: "status",
        directory: "/",
        params: { "name" : "ryan" }
      }

  In particular, note that `request.uri.protocol` is `undefined`. This is because there was no URI protocol given in the actual HTTP Request.

  Here is what’s available: `request.uri.anchor`, `request.uri.query`, `request.uri.file`, `request.uri.directory`, `request.uri.path`, `request.uri.relative`, `request.uri.port`, `request.uri.host`, `request.uri.password`, `request.uri.user`, `request.uri.authority`, `request.uri.protocol`, `request.uri.params`, `request.uri.toString()`, `request.uri.source`

`request.headers`

  Read only.

`request.httpVersion`

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

`request.setBodyEncoding(encoding)`

  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.connection`

  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.sendHeader(statusCode, headers)`

  Sends a response header to the request. The status code is a 3-digit HTTP status code, like `404`. The second argument, `headers` are the response headers.

  Example:

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

`response.sendBody(chunk, encoding="ascii")`

  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.

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

`response.finish()`

  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.finish()`, 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 connection after each connection. Currently the implementation does not pipeline requests.

Example of connecting to `google.com`

    var google = http.createClient(80, "google.com");
    var request = google.get("/");
    request.finish(function (response) {
      puts("STATUS: " + response.statusCode);
      puts("HEADERS: " + JSON.stringify(response.headers));
      response.setBodyEncoding("utf8");
      response.addListener("body", function (chunk) {
        puts("BODY: " + chunk);
      });
    });

`http.createClient(port, host)`

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

`client.get(path, request_headers)`, `client.head(path, request_headers)`, `client.post(path, request_headers)`, `client.del(path, request_headers)`, `client.put(path, request_headers)`

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

  `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.finish()` 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.sendBody()`.)

#### `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.

Event | Parameters | Notes
--- | --- | ---
`"response"` | `response` | Emitted when a response is received to this request. Typically the user will set a listener to this via the `request.finish()` method. This event is emitted only once. The `response` argument will be an instance of `http.ClientResponse`.

`request.sendBody(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.finish(responseListener)`

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

  The parameter `responseListener` is a callback which will be executed when the response headers have been received. The `responseListener` callback is executed with one argument which is an instance of `http.ClientResponse`.

  In the `responseListener` callback, one can add more listeners to the response, in particular listening for the `"body"` event. Note that the `responseListener` is called before any part of the body is receieved, so there is no need to worry about racing to catch the first part of the body. As long as a listener for `"body"` is added during the `responseListener` callback, the entire body will be caught.

      // Good
      request.finish(function (response) {
        response.addListener("body", function (chunk) {
          puts("BODY: " + chunk);
        });
      });

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

#### `http.ClientResponse`

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

Event | Parameters | Notes
--- | --- | ---
`"body"` | `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()`.
`"complete"` |  | 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.setBodyEncoding(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.

### TCP

To use the TCP server and client one must `require("/tcp.js")` or `include("/tcp.js")`.

#### `tcp.Server`

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

    include("/tcp.js");
    var server = createServer(function (socket) {
      socket.setEncoding("utf8");
      socket.addListener("connect", function () {
        socket.send("hello\r\n");
      });
      socket.addListener("receive", function (data) {
        socket.send(data);
      });
      socket.addListener("eof", function () {
        socket.send("goodbye\r\n");
        socket.close();
      });
    });
    server.listen(7000, "localhost");

Event | Parameters | Notes
--- | --- | ---
`"connection"` | `connection` | Emitted when a new connection is made. `connection` is an instance of `tcp.Connection`.
`"close"` | `errorno` | 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.

`tcp.createServer(connection_listener);`

  Creates a new TCP server.

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

`server.listen(port, host=null, backlog=128)`

  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.

  The third argument, `backlog`, is also optional and defaults to 128. The `backlog` argument defines the maximum length to which the queue of pending connections for the server may grow.

  This function is synchronous.

`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.

#### `tcp.Connection`

This object is used as a TCP client and also as a server-side socket for `tcp.Server`.

Event | Parameters | Notes
--- | --- | ---
`"connect"` |  | Call once the connection is established after a call to `createConnection()` or `connect()`.
`"receive"` | `data` | Called when data is received on the connection. `data` will be a string. Encoding of data is set by `connection.setEncoding()`.
`"eof"` |  | Called when the other end of the connection sends a FIN packet. After this is emitted the `readyState` will be `"writeOnly"`. One should probably just call `connection.close()` when this event is emitted.
`"timeout"` |  | Emitted if the connection times out from inactivity. The `"close"` event will be emitted immediately following this event.
`"close"` | `had_error` | Emitted once the connection is fully closed. The argument `had_error` is a boolean which says if the connection was closed due to a transmission error. (TODO: access error codes.)

`tcp.createConnection(port, host="127.0.0.1")`

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

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

`connection.connect(port, host="127.0.0.1")`

  Opens a connection to the specified `port` and `host`. `createConnection()` also opens a connection; normally this method is not needed. Use this only if a connection 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 connection 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`.

`connection.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.

`connection.readyState`

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

`connection.setEncoding(encoding)`

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

`connection.send(data, encoding="ascii")`

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

`connection.close()`

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

`connection.forceClose()`

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

`connection.readPause()`

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

`connection.readResume()`

  Resumes reading if reading was paused by `readPause()`.

`connection.setTimeout(timeout)`

  Sets the connection to timeout after `timeout` milliseconds of inactivity on the connection. By default all `tcp.Connection` objects have a timeout of 60 seconds (60000 ms).

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

`connection.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 `connection.send()` is called.

### DNS

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

    var resolution = node.dns.resolve4("www.google.com");

    resolution.addCallback(function (addresses, ttl, cname) {
      puts("addresses: " + JSON.stringify(addresses));
      puts("ttl: " + JSON.stringify(ttl));
      puts("cname: " + JSON.stringify(cname));

      for (var i = 0; i < addresses.length; i++) {
        var a = addresses[i];
        var reversing = node.dns.reverse(a);
        reversing.addCallback( function (domains, ttl, cname) {
          puts("reverse for " + a + ": " + JSON.stringify(domains));
        });
        reversing.addErrback( function (code, msg) {
          puts("reverse for " + a + " failed: " + msg);
        });
      }
    });

    resolution.addErrback(function (code, msg) {
      puts("error: " + msg);
    });

`node.dns.resolve4(domain)`

  Resolves a domain (e.g. `"google.com"`) into an array of IPv4 addresses (e.g. `["74.125.79.104", "74.125.79.105", "74.125.79.106"]`). This function returns a promise.

  - on success: returns `addresses, ttl, cname`. `ttl` (time-to-live) is an integer specifying the number of seconds this result is valid for. `cname` is the canonical name for the query.

  - on error: returns `code, msg`. `code` is one of the error codes listed below and `msg` is a string describing the error in English.

`node.dns.resolve6(domain)`

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

`node.dns.reverse(ip)`

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

  - on success: returns `domains, ttl, cname`. `ttl` (time-to-live) is an integer specifying the number of seconds this result is valid for. `cname` is the canonical name for the query. `domains` is an array of domains.

  - on error: returns `code, msg`. `code` is one of the error codes listed below and `msg` is a string describing the error in English.

Each DNS query can return an error code.

- `node.dns.TEMPFAIL`: timeout, SERVFAIL or similar.

- `node.dns.PROTOCOL`: got garbled reply.

- `node.dns.NXDOMAIN`: domain does not exists.

- `node.dns.NODATA`: domain exists but no data of reqd type.

- `node.dns.NOMEM`: out of memory while processing.

- `node.dns.BADQUERY`: the query is malformed.

## 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:

    include("/utils.js");
    include("/tcp.js");
    nconnections = 0;
    createServer(function (c) {
      error("Connection!");
      nconnections += 1;
      c.close();
    }).listen(5000);
    require("/repl.js").start("simple tcp server> ");

## Extension API

External modules can be compiled and dynamically linked into Node. Node is more or less glue between several C and C++ 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 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.

Here is a sample Makefile taken from node_postgres:

    binding.node: binding.o Makefile
            gcc -shared -o binding.node  binding.o \
                    -L`pg_config --libdir` -lpq

    binding.o: binding.cc Makefile
            gcc `node --cflags` -I`pg_config --includedir` \
                    binding.cc -c -o binding.o

    clean:
            rm -f binding.o binding.node
    .PHONY: clean

As you can see, the only thing your module needs to know about Node is the CFLAGS that node was compiled with which are gotten from `node --cflags` If you want to make a debug build, then use `node_g --cflags`. (`node_g` is the debug build of node, which can built with `configure --debug; make; make install`.)

Node extension modules are dynamically linked libraries with a `.node` extension. Node opens this file and looks for a function called `init()` which must be of the form:

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

In this function you can create new javascript objects and attach them to `target`. Here is a very simple module:

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

Further documentation will come soon. For now see the source code of node_postgres.