node.js

# Node API

Conventions: Callbacks are object members which are prefixed with `on`. All methods and members are camel cased. Constructors always have a capital first letter.

Node supports 3 byte-string encodings: ASCII (`"ascii"`), UTF-8 (`"utf8"`), and raw binary (`"raw"`). It uses strings to represent ASCII and UTF-8 encoded data. For the moment, arrays of integers are used to represent raw binary data—this representation is rather inefficient. This will change in the future, when V8 supports Blob objects .

The following are global functions:

`puts(string, callback)`
  Alias for `stdout.puts()`. Outputs the `string` and a trailing new-line to `stdout`.

  The `callback` argument is optional and mostly useless: it will notify the user when the operation has completed. Everything in node is asynchronous; `puts()` is no exception. This might seem ridiculous but, if for example, one is piping `stdout` into an NFS file, `printf()` will block from network latency. There is an internal queue for `puts()` output, so you can be assured that output will be displayed in the order it was called.

`print(string, callback)`
  Like `puts()` but without the trailing new-line.
`node.debug(string)`
  A synchronous output function. Will block the process and output the string immediately to stdout. Use with care.
`node.exit(code)`
  Immediately ends the process with the specified code.

## 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.

## `node.fs`

File I/O is tricky because there are not simple non-blocking ways to do it. Node handles file I/O by employing an internal thread pool to execute file system calls.

This part of the API is split into two parts: simple wrappers around standard POSIX file I/O functions and a user-friendly `File` object.

### POSIX Wrappers

All POSIX wrappers have a similar form. They return `undefined` and have a callback called `on_completion` as their last argument. The `on_completion` callback may be passed many parameters, but the first parameter is always an integer indicating the error status. If the status integer is zero, then the call was successful. Example:

    node.fs.unlink("/tmp/hello", function (status) {
      if (status == 0)
        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", function (status, stats) {
      puts("stats: " + JSON.stringify(stats));
    });

because it could be that `stat()` is executed before the `rename()`. The correct way to do this, is use the `on_completion` callback for `rename()`

    node.fs.rename("/tmp/hello", "/tmp/world", function (status) {
      if (status != 0) return;
      node.fs.stat("/tmp/world", function (status, stats) {
        puts("stats: " + JSON.stringify(stats));
      });
    });

`node.fs.rename(path1, path2, on_completion(status))`
  rename(2)
`node.fs.stat(path, on_completion(status, stats))`
  stat(2)
`node.fs.unlink(path, on_completion(status))`
  unlink(2)
`node.fs.rmdir(path, on_completion(status))`
  rmdir(2)
`node.fs.close(fd, on_completion(status))`
  close(2)
`node.fs.open(path, flags, mode, on_completion(status, fd))`
  open(2)

  The constants like `O_CREAT` are defined at `node.O_CREAT`.

`node.fs.write(fd, data, position, on_completion(status, written))`
  Write data to the file specified by `fd`.

  `data` is either an array of integer (for raw data) or a string for UTF-8 encoded characters.

  `position` refers to the offset from the beginning of the file where this data should be written. If `null`, the data will be written at the current position.

  See also pwrite(2)

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

  `encoding` is either `node.UTF8` or `node.RAW`.

### `node.fs.File`

Easy buffered file object.

Internal request queues exist for each file object so that multiple commands can be issued at once without worry that they will be executed out-of-order. Thus the following is safe:

    var file = new node.fs.File();
    file.open("/tmp/blah", "w+");
    file.write("hello");
    file.write("world");
    file.close();

Request queues are local to a single file. If one does

    fileA.write("hello");
    fileB.write("world");

it could be that `fileB` gets written to before `fileA` is written to. If a certain operation order is needed involving multiple files, use the completion callbacks:

    fileA.write("hello", function () {
      fileB.write("world");
    });

`new node.fs.File(options={})`
  Creates a new file object.

  The `options` argument is optional. It can contain the following fields

  - `fd` — a file descriptor for the file.
  - `encoding` — how `file.read()` should return data. Either `"raw"` or `"utf8"`. Defaults to raw.
`file.onError = function (method, errno, msg) { }`
  Callback. This is called internally anytime an error occurs with this file. There are three arguments: the method name, the POSIX errno, and a string describing the error.

  Example

      var path = "/some/path/that/doesnt/exist";
      var file = new node.fs.File();
      file.onError = function (method, errno, msg) {
        stderr.puts("An error occurred calling " + method);
        stderr.puts(msg);
        node.exit(1);
      }
      file.open(path, "w+")

`file.open(path, mode, on_completion())`
  Opens the file at `path`.

  `mode` is a string: `"r"` open for reading and writing. `"r+"` open for only reading. `"w"` create a new file for reading and writing; if it already exists truncate it. `"w+"` create a new file for writing only; if it already exists truncate it. `"a"` create a new file for writing and reading. Writes append to the end of the file. `"a+"`

  The `on_completion` is a callback that is made without arguments when the operation completes. It is optional. If an error occurred the `on_completion` callback will not be called, but the `file.onError` will be called.

`file.read(length, position, on_completion(data))`
`file.write(data, position, on_completion(written))`
`file.close(on_completion())`

## `node.tcp`

### `node.tcp.Server`

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

    function Echo (socket) {
      socket.setEncoding("utf8");
      socket.onConnect = function () {
        socket.send("hello\r\n");
      };
      socket.onReceive = function (data) {
        socket.send(data);
      };
      socket.onEOF = function () {
        socket.send("goodbye\r\n");
        socket.close();
      };
    }
    var server = new node.tcp.Server(Echo, {backlog: 1024});
    server.listen(7000, "localhost");

`new node.tcp.Server(connection_handler(socket), options={});`
  Creates a new TCP server.

  `connection_handler` is a callback which is called on each connection. It is given one argument: an instance of `node.tcp.Connection`.

  `options` for now only supports one option: `backlog` which should be an integer and describes how large of a connection backlog the operating system should maintain for this server. The `backlog` defaults to 1024.

`server.listen(port, host=null)`
  Tells the server to listen for TCP connections to `port` and `host`. Note, `host` is optional. If `host` is not specified the server will accept connections to any IP address on the specified port.
`server.close()`
  Stops the server from accepting new connections.

### `node.tcp.Connection`

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

`new node.tcp.Connection()`
  Creates a new connection object.
`connection.connect(port, host="127.0.0.1")`
  Opens a connection to the specified `port` and `host`. If the second parameter is omitted, localhost is assumed.
`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 `"utf8"` or `"raw"`) for data that is received.
`connection.send(data, encoding="ascii")`
  Sends data on the connection. The data should be eithre an array of integers (for raw binary) or a string (for utf8 or ascii). 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. sends a FIN packet. It is possible the server will still send some data. After calling this `readyState` will be `"readOnly"`.
`connection.fullClose()`
  Close both ends of the connection. Data that is received after this call is responded to with RST packets. If you don't know about this, just use `close()`.
`connection.forceClose()`
  Ensures that no more I/O activity happens on this socket. Only necessary in case of errors (parse error or so).
`connection.onConnect = function () { };`
  Call once the connection is established.
`connection.onReceive = function (data) { };`
  Called when data is received on the connection. Encoding of data is set by `connection.setEncoding()`. `data` will either be a string, in the case of utf8, or an array of integer in the case of raw encoding.
`connection.onEOF = function () { };`
  Called when the other end of the connection sends a FIN packet. `onReceive` will not be called after this. After receiving this `readyState` will be `"writeOnly"`. You should probably just call `connection.close()` in this callback.
`connection.onDisconnect = function (had_error) { };`
  Called once the connection is fully disconnected.

  The callback is passed one boolean argument `had_error`. This lets one know if the connect was closed due to an error. (TODO: look up error codes.)

`connection.onError = function () { };`
  Called on an error.

## `node.http`

The HTTP interfaces here are designed to support many features of the protocol which have been traditionally difficult to handle. In particular, large, possibly chunked, 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 array of 2-element arrays like this

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

Dictionary-like objects are popularly used to represent HTTP headers but they are an incorrect abstraction. It is rare, but possible, to have multiple header lines with the same field. Setting multiple cookies in a single response, for example, can only be done with multiple `Cookie` lines.

### `node.http.Server`

`new node.http.Server(request_handler, options);`

  Creates a new web server.

  The `options` argument is optional. The `options` argument accepts the same values as the options argument for `node.tcp.Server` does.

  The `request_handler` is a callback which is made on each request with a `ServerRequest` and `ServerResponse` arguments.

`server.listen(port, hostname)`

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

`server.close()`

  Stops the server from accepting new connections.

### `node.http.ServerRequest`

This object is created internally by a HTTP server—not by the user. It is passed to the user as the first argument to the `request_handler` callback.

`req.method`
  The request method as a string. Read only. Example: `"GET"`, `"DELETE"`.
`req.uri`
  Request URI. (Object.)
`req.uri.anchor`
`req.uri.query`
`req.uri.file`
`req.uri.directory`
`req.uri.path`
`req.uri.relative`
`req.uri.port`
`req.uri.host`
`req.uri.password`
`req.uri.user`
`req.uri.authority`
`req.uri.protocol`
`req.uri.params`
`req.uri.toString()`, `req.uri.source`
  The original URI found in the status line.
`req.headers`
  The request headers expressed as an array of 2-element arrays. Read only.
`req.httpVersion`
  The HTTP protocol version as a string. Read only. Examples: `"1.1"`, `"1.0"`
`req.onBody = function (chunk) { };`
  Callback. Should be set by the user to be informed of when a piece of the message body is received. Example:

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

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

  The body chunk is either a String in the case of UTF-8 encoding or an array of numbers in the case of raw encoding. The body encoding is set with `req.setBodyEncoding()`.

`req.onBodyComplete = function () { };`
  Callback. Made exactly once for each message. No arguments. After `onBodyComplete` is executed `onBody` will no longer be called.
`req.setBodyEncoding(encoding)`
  Set the encoding for the request body. Either `"utf8"` or `"raw"`. Defaults to raw.
`req.interrupt()`
  Interrupt the request. You will not receive anymore callbacks. This is useful if, for example someone is streaming up a file but it is too large and neesd to be stopped. The connection to the client will be closed immediately.

### `node.http.ServerResponse`

This object is created internally by a HTTP server—not by the user. It is passed to the user as the second argument to the `request_handler` callback.

`res.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`, should be an array of 2-element arrays, representing the response headers.

  Example:

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

`res.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"`.

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

### `node.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 = new node.http.Client(80, "google.com");
    var req = google.get("/");
    req.finish(function (res) {
      puts("STATUS: " + res.statusCode);
      puts("HEADERS: " + JSON.stringify(res.headers));
      res.setBodyEncoding("utf8");
      res.onBody = function (chunk) {
        puts("BODY: " + chunk);
      };
    });

`new node.http.Client(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.

  `request_headers` is optional. `request_headers` should be an array of 2-element arrays. 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`.

  Important: the request is not complete. This method only sends the header of the request. One needs to call `req.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 `req.sendBody()`.)

  `GET` and `HEAD` requests normally are without bodies but HTTP does not forbid it, so neither do we.

### `node.http.ClientRequest`

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

`req.sendBody(chunk, encoding="ascii")`
  Sends a sucessive peice 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.

`req.finish(response_handler)`
  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 `response_handler` is a user-supplied callback which will be executed exactly once when the server response headers have been received. The `response_handler` callback is executed with one argument: a `ClientResponse` object.

### `node.http.ClientResponse`

This object is created internally and passed to the `response_handler` callback (is given to the client in `req.finish` function). The response object appears exactly as the header is completely received but before any part of the response body has been read.

`res.statusCode`
  The 3-digit HTTP response status code. E.G. `404`.
`res.httpVersion`
  The HTTP version of the connected-to server. Probably either `"1.1"` or `"1.0"`.
`res.headers`
  The response headers. An Array of 2-element arrays.
`res.onBody`
  Callback. Should be set by the user to be informed of when a piece of the response body is received. A chunk of the body is given as the single argument. The transfer-encoding has been removed.

  The body chunk is either a `String` in the case of UTF-8 encoding or an array of numbers in the case of raw encoding. The body encoding is set with `res.setBodyEncoding()`.

`res.onBodyComplete`
  Callback. Made exactly once for each message. No arguments. After `onBodyComplete` is executed `onBody` will no longer be called.
`res.setBodyEncoding(encoding)`
  Set the encoding for the response body. Either `"utf8"` or `"raw"`. Defaults to raw.

## 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 `mjsunit.js`.

The contents of `foo.js`:

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

The contents of `mjsunit.js`:

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

The module `mjsunit.js` has exported a function `assertEquals()`. `mjsunit.js` must be in the same directory as `foo.js` for `include()` to find it. The module path is relative to the file calling `include()`.

`include()` inserts the exported objects from the specified module into the global namespace.

Because file loading does not happen instantaneously, and because Node has a policy of never blocking, the callback `onLoad` can be set and will notify the user when the included modules are loaded. Each file/module can have an `onLoad` callback.

To export an object, add to the special `exports` object. The functions `fail` and `deepEquals` are not exported and remain private to the module.

`require()` is like `include()` except does not polute the global namespace. It returns a namespace object. The exported objects can only be guaranteed to exist after the `onLoad()` callback is made. For example:

    var mjsunit = require("mjsunit.js");
    function onLoad () {
      mjsunit.assertEquals(1, 2);
    }

`include()` and `require()` cannot be used after `onLoad()` is called. So put them at the beginning of your file.

Additionally when `node.exit()` is called or when a program exits naturally, the function `onExit()` will be called for each module (children first). The `onExit()` callback cannot perform I/O as the process is going to forcably exit in several microseconds, however it is a good hook to perform some constant time checks of the module's state. It's useful for unit tests.

Just to reiterate: `onExit()`, is not the place to close files or shutdown servers. The process will exit before they get performed.