nodejs/doc/api/http.markdown

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',
  'connection': '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:

Event: 'request'

function (request, response) { }

Emitted each time there is a request. Note that there may be multiple requests per connection (in the case of keep-alive connections). request is an instance of http.ServerRequest and response is an instance of http.ServerResponse

Event: 'connection'

function (socket) { }

When a new TCP stream is established. socket is an object of type net.Socket. Usually users will not want to access this event. The socket can also be accessed at request.connection.

Event: 'close'

function (errno) { }

Emitted when the server closes.

Event: 'checkContinue'

function (request, response) { }

Emitted each time a request with an http Expect: 100-continue is received. If this event isn't listened for, the server will automatically respond with a 100 Continue as appropriate.

Handling this event involves calling response.writeContinue if the client should continue to send the request body, or generating an appropriate HTTP response (e.g., 400 Bad Request) if the client should not continue to send the request body.

Note that when this event is emitted and handled, the request event will not be emitted.

Event: 'upgrade'

function (request, socket, head) { }

Emitted each time a client requests a http upgrade. If this event isn't listened for, then clients requesting an upgrade will have their connections closed.

• request is the arguments for the http request, as it is in the request event.
• socket is the network socket between the server and client.
• head is an instance of Buffer, the first packet of the upgraded stream, this may be empty.

After this event is emitted, the request's socket will not have a data event listener, meaning you will need to bind to it in order to handle data sent to the server on that socket.

Event: 'clientError'

function (exception) { }

If a client connection emits an 'error' event - it will forwarded here.

http.createServer([requestListener])

Returns a new web server object.

The requestListener is a function which is automatically added to the 'request' event.

server.listen(port, [hostname], [callback])

Begin accepting connections on the specified port and hostname. If the hostname is omitted, the server will accept connections directed to any IPv4 address (INADDR_ANY).

To listen to a unix socket, supply a filename instead of port and hostname.

This function is asynchronous. The last parameter callback will be called when the server has been bound to the port.

server.listen(path, [callback])

Start a UNIX socket server listening for connections on the given path.

This function is asynchronous. The last parameter callback will be called when the server has been bound.

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:

Event: 'data'

function (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.setEncoding().

Event: 'end'

function () { }

Emitted exactly once for each request. After that, no more 'data' events will be emitted on the request.

Event: 'close'

function (err) { }

Indicates that the underlaying connection was terminated before response.end() was called or able to flush.

The err parameter is always present and indicates the reason for the timeout:

err.code === 'timeout' indicates that the underlaying connection timed out. This may happen because all incoming connections have a default timeout of 2 minutes.

err.code === 'aborted' means that the client has closed the underlaying connection prematurely.

Just like 'end', this event occurs only once per request, and no more 'data' events will fire afterwards.

Note: 'close' can fire after 'end', but not vice versa.

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.trailers

Read only; HTTP trailers (if present). Only populated after the 'end' event.

request.httpVersion

The HTTP protocol version as a string. Read only. Examples: '1.1', '1.0'. Also request.httpVersionMajor is the first integer and request.httpVersionMinor is the second.

request.setEncoding(encoding=null)

Set the encoding for the request body. Either 'utf8' or 'binary'. Defaults to null, which means that the 'data' event will emit a Buffer object..

request.pause()

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

request.resume()

Resumes a paused request.

request.connection

The net.Socket object associated with the connection.

With HTTPS support, use request.connection.verifyPeer() and request.connection.getPeerCertificate() to obtain the client's authentication details.

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. It is a Writable Stream.

response.writeContinue()

Sends a HTTP/1.1 100 Continue message to the client, indicating that the request body should be sent. See the checkContinue event on Server.

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.

If you call response.write() or response.end() before calling this, the implicit/mutable headers will be calculated and call this function for you.

Note: that Content-Length is given in bytes not characters. The above example works because the string 'hello world' contains only single byte characters. If the body contains higher coded characters then Buffer.byteLength() should be used to determine the number of bytes in a given encoding. And Node does not check whether Content-Length and the length of the body which has been transmitted are equal or not.

response.statusCode

When using implicit headers (not calling response.writeHead() explicitly), this property controls the status code that will be send to the client when the headers get flushed.

Example:

response.statusCode = 404;

After response header was sent to the client, this property indicates the status code which was sent out.

response.setHeader(name, value)

Sets a single header value for implicit headers. If this header already exists in the to-be-sent headers, its value will be replaced. Use an array of strings here if you need to send multiple headers with the same name.

Example:

response.setHeader("Content-Type", "text/html");

or

response.setHeader("Set-Cookie", ["type=ninja", "language=javascript"]);

response.getHeader(name)

Reads out a header that's already been queued but not sent to the client. Note that the name is case insensitive. This can only be called before headers get implicitly flushed.

Example:

var contentType = response.getHeader('content-type');

response.removeHeader(name)

Removes a header that's queued for implicit sending.

Example:

response.removeHeader("Content-Encoding");

response.write(chunk, encoding='utf8')

If this method is called and response.writeHead() has not been called, it will switch to implicit header mode and flush the implicit headers.

This sends a chunk of the response body. This method may be called multiple times to provide successive parts of the body.

chunk can be a string or a buffer. If chunk is a string, the second parameter specifies how to encode it into a byte stream. By default the encoding is 'utf8'.

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.addTrailers(headers)

This method adds HTTP trailing headers (a header but at the end of the message) to the response.

Trailers will only be emitted if chunked encoding is used for the response; if it is not (e.g., if the request was HTTP/1.0), they will be silently discarded.

Note that HTTP requires the Trailer header to be sent if you intend to emit trailers, with a list of the header fields in its value. E.g.,

response.writeHead(200, { 'Content-Type': 'text/plain',
                          'Trailer': 'TraceInfo' });
response.write(fileData);
response.addTrailers({'Content-MD5': "7895bf4b8828b55ceaf47747b4bca667"});
response.end();

response.end([data], [encoding])

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.

If data is specified, it is equivalent to calling response.write(data, encoding) followed by response.end().

http.request(options, callback)

Node maintains several connections per server to make HTTP requests. This function allows one to transparently issue requests.

Options:

• host: A domain name or IP address of the server to issue the request to.
• port: Port of remote server.
• socketPath: Unix Domain Socket (use one of host:port or socketPath)
• method: A string specifying the HTTP request method. Possible values: 'GET' (default), 'POST', 'PUT', and 'DELETE'.
• path: Request path. Should include query string and fragments if any. E.G. '/index.html?page=12'
• headers: An object containing request headers.
• agent: Controls Agent behavior. When an Agent is used request will default to Connection:keep-alive. Possible values:
• undefined (default): use default Agent for this host and port.
• Agent object: explicitly use the passed in Agent.
• false: opts out of connection pooling with an Agent, defaults request to Connection:close.

http.request() returns an instance of the http.ClientRequest class. The ClientRequest instance is a writable stream. If one needs to upload a file with a POST request, then write to the ClientRequest object.

Example:

var options = {
  host: 'www.google.com',
  port: 80,
  path: '/upload',
  method: 'POST'
};

var req = http.request(options, function(res) {
  console.log('STATUS: ' + res.statusCode);
  console.log('HEADERS: ' + JSON.stringify(res.headers));
  res.setEncoding('utf8');
  res.on('data', function (chunk) {
    console.log('BODY: ' + chunk);
  });
});

req.on('error', function(e) {
  console.log('problem with request: ' + e.message);
});

// write data to request body
req.write('data\n');
req.write('data\n');
req.end();

Note that in the example req.end() was called. With http.request() one must always call req.end() to signify that you're done with the request - even if there is no data being written to the request body.

If any error is encountered during the request (be that with DNS resolution, TCP level errors, or actual HTTP parse errors) an 'error' event is emitted on the returned request object.

There are a few special headers that should be noted.

• Sending a 'Connection: keep-alive' will notify Node that the connection to the server should be persisted until the next request.

• Sending a 'Content-length' header will disable the default chunked encoding.

• Sending an 'Expect' header will immediately send the request headers. Usually, when sending 'Expect: 100-continue', you should both set a timeout and listen for the continue event. See RFC2616 Section 8.2.3 for more information.

http.get(options, callback)

Since most requests are GET requests without bodies, Node provides this convenience method. The only difference between this method and http.request() is that it sets the method to GET and calls req.end() automatically.

Example:

var options = {
  host: 'www.google.com',
  port: 80,
  path: '/index.html'
};

http.get(options, function(res) {
  console.log("Got response: " + res.statusCode);
}).on('error', function(e) {
  console.log("Got error: " + e.message);
});

http.Agent

In node 0.5.3+ there is a new implementation of the HTTP Agent which is used for pooling sockets used in HTTP client requests.

Previously, a single agent instance help the pool for single host+port. The current implementation now holds sockets for any number of hosts.

The current HTTP Agent also defaults client requests to using Connection:keep-alive. If no pending HTTP requests are waiting on a socket to become free the socket is closed. This means that node's pool has the benefit of keep-alive when under load but still does not require developers to manually close the HTTP clients using keep-alive.

Sockets are removed from the agent's pool when the socket emits either a "close" event or a special "agentRemove" event. This means that if you intend to keep one HTTP request open for a long time and don't want it to stay in the pool you can do something along the lines of:

http.get(options, function(res) {
  // Do stuff
}).on("socket", function (socket) {
  socket.emit("agentRemove");
});

Alternatively, you could just opt out of pooling entirely using agent:false:

http.get({host:'localhost', port:80, path:'/', agent:false}, function (res) {
  // Do stuff
})

http.globalAgent

Global instance of Agent which is used as the default for all http client requests.

agent.maxSockets

By default set to 5. Determines how many concurrent sockets the agent can have open per host.

agent.sockets

An object which contains arrays of sockets currently in use by the Agent. Do not modify.

agent.requests

An object which contains queues of requests that have not yet been assigned to sockets. Do not modify.

http.ClientRequest

This object is created internally and returned from http.request(). It represents an in-progress request whose header has already been queued. The header is still mutable using the setHeader(name, value), getHeader(name), removeHeader(name) API. The actual header will be sent along with the first data chunk or when closing the connection.

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.on('response', function (response) {
  response.on('data', function (chunk) {
    console.log('BODY: ' + chunk);
  });
});

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

This is a Writable Stream. Note: Node does not check whether Content-Length and the length of the body which has been transmitted are equal or not.

This is an EventEmitter with the following events:

Event 'response'

function (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.

Options:

• host: A domain name or IP address of the server to issue the request to.
• port: Port of remote server.
• socketPath: Unix Domain Socket (use one of host:port or socketPath)

Event: 'socket'

function (socket) { }

Emitted after a socket is assigned to this request.

Event: 'upgrade'

function (response, socket, head) { }

Emitted each time a server responds to a request with an upgrade. If this event isn't being listened for, clients receiving an upgrade header will have their connections closed.

A client server pair that show you how to listen for the upgrade event using http.getAgent:

var http = require('http');
var net = require('net');

// Create an HTTP server
var srv = http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('okay');
});
srv.on('upgrade', function(req, socket, upgradeHead) {
  socket.write('HTTP/1.1 101 Web Socket Protocol Handshake\r\n' +
               'Upgrade: WebSocket\r\n' +
               'Connection: Upgrade\r\n' +
               '\r\n\r\n');

  socket.ondata = function(data, start, end) {
    socket.write(data.toString('utf8', start, end), 'utf8'); // echo back
  };
});

// now that server is running
srv.listen(1337, '127.0.0.1', function() {

  // make a request
  var options = {
    port: 1337,
    host: '127.0.0.1',
    headers: {
      'Connection': 'Upgrade',
      'Upgrade': 'websocket'
    }
  };

  var req = http.request(options);
  req.end();

  req.on('upgrade', function(res, socket, upgradeHead) {
    console.log('got upgraded!');
    socket.end();
    process.exit(0);
  });
});

Event: 'continue'

function ()

Emitted when the server sends a '100 Continue' HTTP response, usually because the request contained 'Expect: 100-continue'. This is an instruction that the client should send the request body.

request.write(chunk, encoding='utf8')

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.

request.end([data], [encoding])

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'.

If data is specified, it is equivalent to calling request.write(data, encoding) followed by request.end().

request.abort()

Aborts a request. (New since v0.3.8.)

request.setTimeout(timeout, [callback])

Once a socket is assigned to this request and is connected socket.setTimeout(timeout, [callback]) will be called.

request.setNoDelay(noDelay=true)

Once a socket is assigned to this request and is connected socket.setNoDelay(noDelay) will be called.

request.setSocketKeepAlive(enable=false, [initialDelay])

Once a socket is assigned to this request and is connected socket.setKeepAlive(enable, [initialDelay]) will be called.

http.ClientResponse

This object is created when making a request with http.request(). It is passed to the 'response' event of the request object.

The response implements the Readable Stream interface.

Event: 'data'

function (chunk) { }

Emitted when a piece of the message body is received.

Event: 'end'

function () { }

Emitted exactly once for each message. No arguments. After emitted no other events will be emitted on the response.

Event: 'close'

function (err) { }

Indicates that the underlaying connection was terminated before end event was emitted. See http.ServerRequest's 'close' event for more information.

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'. Also response.httpVersionMajor is the first integer and response.httpVersionMinor is the second.

response.headers

The response headers object.

response.trailers

The response trailers object. Only populated after the 'end' event.

response.setEncoding(encoding=null)

Set the encoding for the response body. Either 'utf8', 'ascii', or 'base64'. Defaults to null, which means that the 'data' event will emit a Buffer object..

response.pause()

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

response.resume()

Resumes a paused response.