Table of Contents

• HTTP

  • Class: http.Agent

    • new Agent([options])
    • agent.createConnection(options[, callback])
    • agent.keepSocketAlive(socket)
    • agent.reuseSocket(socket, request)
    • agent.destroy()
    • agent.freeSockets
    • agent.getName(options)
    • agent.maxFreeSockets
    • agent.maxSockets
    • agent.requests
    • agent.sockets

  • Class: http.ClientRequest

    • Event: 'abort'
    • Event: 'connect'
    • Event: 'continue'
    • Event: 'information'
    • Event: 'response'
    • Event: 'socket'
    • Event: 'timeout'
    • Event: 'upgrade'
    • request.abort()
    • request.aborted
    • request.connection
    • request.end([data[, encoding]][, callback])
    • request.finished
    • request.flushHeaders()
    • request.getHeader(name)
    • request.maxHeadersCount
    • request.path
    • request.removeHeader(name)
    • request.setHeader(name, value)
    • request.setNoDelay([noDelay])
    • request.setSocketKeepAlive([enable][, initialDelay])
    • request.setTimeout(timeout[, callback])
    • request.socket
    • request.write(chunk[, encoding][, callback])

  • Class: http.Server

    • Event: 'checkContinue'
    • Event: 'checkExpectation'
    • Event: 'clientError'
    • Event: 'close'
    • Event: 'connect'
    • Event: 'connection'
    • Event: 'request'
    • Event: 'upgrade'
    • server.close([callback])
    • server.headersTimeout
    • server.listen()
    • server.listening
    • server.maxHeadersCount
    • server.setTimeout([msecs][, callback])
    • server.timeout
    • server.keepAliveTimeout

  • Class: http.ServerResponse

    • Event: 'close'
    • Event: 'finish'
    • response.addTrailers(headers)
    • response.connection
    • response.end([data][, encoding][, callback])
    • response.finished
    • response.getHeader(name)
    • response.getHeaderNames()
    • response.getHeaders()
    • response.hasHeader(name)
    • response.headersSent
    • response.removeHeader(name)
    • response.sendDate
    • response.setHeader(name, value)
    • response.setTimeout(msecs[, callback])
    • response.socket
    • response.statusCode
    • response.statusMessage
    • response.write(chunk[, encoding][, callback])
    • response.writeContinue()
    • response.writeHead(statusCode[, statusMessage][, headers])
    • response.writeProcessing()

  • Class: http.IncomingMessage

    • Event: 'aborted'
    • Event: 'close'
    • message.aborted
    • message.complete
    • message.destroy([error])
    • message.headers
    • message.httpVersion
    • message.method
    • message.rawHeaders
    • message.rawTrailers
    • message.setTimeout(msecs, callback)
    • message.socket
    • message.statusCode
    • message.statusMessage
    • message.trailers
    • message.url
  • http.METHODS
  • http.STATUS_CODES
  • http.createServer([options][, requestListener])
  • http.get(options[, callback])
  • http.get(url[, options][, callback])
  • http.globalAgent
  • http.maxHeaderSize
  • http.request(options[, callback])
  • http.request(url[, options][, callback])

HTTP#

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

The HTTP interfaces in Node.js 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',
  'host': 'mysite.com',
  'accept': '*/*' }

Keys are lowercased. Values are not modified.

In order to support the full spectrum of possible HTTP applications, Node.js'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.

See message.headers for details on how duplicate headers are handled.

The raw headers as they were received are retained in the rawHeaders property, which is an array of [key, value, key2, value2, ...]. For example, the previous message header object might have a rawHeaders list like the following:

[ 'ConTent-Length', '123456',
  'content-LENGTH', '123',
  'content-type', 'text/plain',
  'CONNECTION', 'keep-alive',
  'Host', 'mysite.com',
  'accepT', '*/*' ]

Class: http.Agent#

An Agent is responsible for managing connection persistence and reuse for HTTP clients. It maintains a queue of pending requests for a given host and port, reusing a single socket connection for each until the queue is empty, at which time the socket is either destroyed or put into a pool where it is kept to be used again for requests to the same host and port. Whether it is destroyed or pooled depends on the keepAlive option.

Pooled connections have TCP Keep-Alive enabled for them, but servers may still close idle connections, in which case they will be removed from the pool and a new connection will be made when a new HTTP request is made for that host and port. Servers may also refuse to allow multiple requests over the same connection, in which case the connection will have to be remade for every request and cannot be pooled. The Agent will still make the requests to that server, but each one will occur over a new connection.

When a connection is closed by the client or the server, it is removed from the pool. Any unused sockets in the pool will be unrefed so as not to keep the Node.js process running when there are no outstanding requests. (see socket.unref()).

It is good practice, to destroy() an Agent instance when it is no longer in use, because unused sockets consume OS resources.

Sockets are removed from an agent when the socket emits either a 'close' event or an 'agentRemove' event. When intending to keep one HTTP request open for a long time without keeping it in the agent, something like the following may be done:

http.get(options, (res) => {
  // Do stuff
}).on('socket', (socket) => {
  socket.emit('agentRemove');
});

An agent may also be used for an individual request. By providing {agent: false} as an option to the http.get() or http.request() functions, a one-time use Agent with default options will be used for the client connection.

agent:false:

http.get({
  hostname: 'localhost',
  port: 80,
  path: '/',
  agent: false  // Create a new agent just for this one request
}, (res) => {
  // Do stuff with response
});

new Agent([options])#

• options <Object> Set of configurable options to set on the agent. Can have the following fields:

  • keepAlive <boolean> Keep sockets around even when there are no outstanding requests, so they can be used for future requests without having to reestablish a TCP connection. Not to be confused with the keep-alive value of the Connection header. The Connection: keep-alive header is always sent when using an agent except when the Connection header is explicitly specified or when the keepAlive and maxSockets options are respectively set to false and Infinity, in which case Connection: close will be used. Default: false.
  • keepAliveMsecs <number> When using the keepAlive option, specifies the initial delay for TCP Keep-Alive packets. Ignored when the keepAlive option is false or undefined. Default: 1000.
  • maxSockets <number> Maximum number of sockets to allow per host. Each request will use a new socket until the maximum is reached. Default: Infinity.
  • maxFreeSockets <number> Maximum number of sockets to leave open in a free state. Only relevant if keepAlive is set to true. Default: 256.
  • timeout <number> Socket timeout in milliseconds. This will set the timeout when the socket is created.

options in socket.connect() are also supported.

The default http.globalAgent that is used by http.request() has all of these values set to their respective defaults.

To configure any of them, a custom http.Agent instance must be created.

const http = require('http');
const keepAliveAgent = new http.Agent({ keepAlive: true });
options.agent = keepAliveAgent;
http.request(options, onResponseCallback);

agent.createConnection(options[, callback])[src]#

• options <Object> Options containing connection details. Check net.createConnection() for the format of the options
• callback <Function> Callback function that receives the created socket
• Returns: <net.Socket>

Produces a socket/stream to be used for HTTP requests.

By default, this function is the same as net.createConnection(). However, custom agents may override this method in case greater flexibility is desired.

A socket/stream can be supplied in one of two ways: by returning the socket/stream from this function, or by passing the socket/stream to callback.

callback has a signature of (err, stream).

agent.keepSocketAlive(socket)[src]#

• socket <net.Socket>

Called when socket is detached from a request and could be persisted by the Agent. Default behavior is to:

socket.setKeepAlive(true, this.keepAliveMsecs);
socket.unref();
return true;

This method can be overridden by a particular Agent subclass. If this method returns a falsy value, the socket will be destroyed instead of persisting it for use with the next request.

agent.reuseSocket(socket, request)[src]#

• socket <net.Socket>
• request <http.ClientRequest>

Called when socket is attached to request after being persisted because of the keep-alive options. Default behavior is to:

socket.ref();

This method can be overridden by a particular Agent subclass.

agent.destroy()[src]#

Destroy any sockets that are currently in use by the agent.

It is usually not necessary to do this. However, if using an agent with keepAlive enabled, then it is best to explicitly shut down the agent when it will no longer be used. Otherwise, sockets may hang open for quite a long time before the server terminates them.

agent.freeSockets#

• <Object>

An object which contains arrays of sockets currently awaiting use by the agent when keepAlive is enabled. Do not modify.

agent.getName(options)[src]#

• options <Object> A set of options providing information for name generation

  • host <string> A domain name or IP address of the server to issue the request to
  • port <number> Port of remote server
  • localAddress <string> Local interface to bind for network connections when issuing the request
  • family <integer> Must be 4 or 6 if this doesn't equal undefined.
• Returns: <string>

Get a unique name for a set of request options, to determine whether a connection can be reused. For an HTTP agent, this returns host:port:localAddress or host:port:localAddress:family. For an HTTPS agent, the name includes the CA, cert, ciphers, and other HTTPS/TLS-specific options that determine socket reusability.

agent.maxFreeSockets#

• <number>

By default set to 256. For agents with keepAlive enabled, this sets the maximum number of sockets that will be left open in the free state.

agent.maxSockets#

• <number>

By default set to Infinity. Determines how many concurrent sockets the agent can have open per origin. Origin is the returned value of agent.getName().

agent.requests#

• <Object>

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

agent.sockets#

• <Object>

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

Class: 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 calling request.end().

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.IncomingMessage.

During the 'response' event, one can add listeners to the response object; particularly to listen for the 'data' event.

If no 'response' handler is added, then the response will be entirely discarded. However, if a 'response' event handler is added, then the data from the response object must be consumed, either by calling response.read() whenever there is a 'readable' event, or by adding a 'data' handler, or by calling the .resume() method. Until the data is consumed, the 'end' event will not fire. Also, until the data is read it will consume memory that can eventually lead to a 'process out of memory' error.

Node.js does not check whether Content-Length and the length of the body which has been transmitted are equal or not.

The request inherits from Stream, and additionally implements the following:

Event: 'abort'#

Emitted when the request has been aborted by the client. This event is only emitted on the first call to abort().

Event: 'connect'#

• response <http.IncomingMessage>
• socket <net.Socket>
• head <Buffer>

Emitted each time a server responds to a request with a CONNECT method. If this event is not being listened for, clients receiving a CONNECT method will have their connections closed.

A client and server pair demonstrating how to listen for the 'connect' event:

const http = require('http');
const net = require('net');
const url = require('url');

// Create an HTTP tunneling proxy
const proxy = http.createServer((req, res) => {
  res.writeHead(200, { 'Content-Type': 'text/plain' });
  res.end('okay');
});
proxy.on('connect', (req, cltSocket, head) => {
  // connect to an origin server
  const srvUrl = url.parse(`http://${req.url}`);
  const srvSocket = net.connect(srvUrl.port, srvUrl.hostname, () => {
    cltSocket.write('HTTP/1.1 200 Connection Established\r\n' +
                    'Proxy-agent: Node.js-Proxy\r\n' +
                    '\r\n');
    srvSocket.write(head);
    srvSocket.pipe(cltSocket);
    cltSocket.pipe(srvSocket);
  });
});

// now that proxy is running
proxy.listen(1337, '127.0.0.1', () => {

  // Make a request to a tunneling proxy
  const options = {
    port: 1337,
    host: '127.0.0.1',
    method: 'CONNECT',
    path: 'www.google.com:80'
  };

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

  req.on('connect', (res, socket, head) => {
    console.log('got connected!');

    // Make a request over an HTTP tunnel
    socket.write('GET / HTTP/1.1\r\n' +
                 'Host: www.google.com:80\r\n' +
                 'Connection: close\r\n' +
                 '\r\n');
    socket.on('data', (chunk) => {
      console.log(chunk.toString());
    });
    socket.on('end', () => {
      proxy.close();
    });
  });
});

Event: 'continue'#

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.

Event: 'information'#

• info <Object>

  • statusCode <integer>

Emitted when the server sends a 1xx response (excluding 101 Upgrade). The listeners of this event will receive an object containing the status code.

const http = require('http');

const options = {
  host: '127.0.0.1',
  port: 8080,
  path: '/length_request'
};

// Make a request
const req = http.request(options);
req.end();

req.on('information', (info) => {
  console.log(`Got information prior to main response: ${info.statusCode}`);
});

101 Upgrade statuses do not fire this event due to their break from the traditional HTTP request/response chain, such as web sockets, in-place TLS upgrades, or HTTP 2.0. To be notified of 101 Upgrade notices, listen for the 'upgrade' event instead.

Event: 'response'#

• response <http.IncomingMessage>

Emitted when a response is received to this request. This event is emitted only once.

Event: 'socket'#

• socket <net.Socket>

Emitted after a socket is assigned to this request.

Event: 'timeout'#

Emitted when the underlying socket times out from inactivity. This only notifies that the socket has been idle. The request must be aborted manually.

See also: request.setTimeout().

Event: 'upgrade'#

• response <http.IncomingMessage>
• socket <net.Socket>
• head <Buffer>

Emitted each time a server responds to a request with an upgrade. If this event is not being listened for and the response status code is 101 Switching Protocols, clients receiving an upgrade header will have their connections closed.

A client server pair demonstrating how to listen for the 'upgrade' event.

const http = require('http');

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

  socket.pipe(socket); // echo back
});

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

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

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

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

request.abort()#

Marks the request as aborting. Calling this will cause remaining data in the response to be dropped and the socket to be destroyed.

request.aborted#

• <boolean>

The request.aborted property will be true if the request has been aborted.

request.connection#

• <net.Socket>

See request.socket.

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

• data <string> | <Buffer>
• encoding <string>
• callback <Function>
• Returns: <this>

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(callback).

If callback is specified, it will be called when the request stream is finished.

request.finished#

• <boolean>

The request.finished property will be true if request.end() has been called. request.end() will automatically be called if the request was initiated via http.get().

request.flushHeaders()#

Flush the request headers.

For efficiency reasons, Node.js normally buffers the request headers until request.end() is called or the first chunk of request data is written. It then tries to pack the request headers and data into a single TCP packet.

That's usually desired (it saves a TCP round-trip), but not when the first data is not sent until possibly much later. request.flushHeaders() bypasses the optimization and kickstarts the request.

request.getHeader(name)#

• name <string>
• Returns: <any>

Reads out a header on the request. Note that the name is case insensitive. The type of the return value depends on the arguments provided to request.setHeader().

request.setHeader('content-type', 'text/html');
request.setHeader('Content-Length', Buffer.byteLength(body));
request.setHeader('Cookie', ['type=ninja', 'language=javascript']);
const contentType = request.getHeader('Content-Type');
// contentType is 'text/html'
const contentLength = request.getHeader('Content-Length');
// contentLength is of type number
const cookie = request.getHeader('Cookie');
// cookie is of type string[]

request.maxHeadersCount#

• <number> Default: 2000

Limits maximum response headers count. If set to 0, no limit will be applied.

request.path#

• <string> The request path.

request.removeHeader(name)#

• name <string>

Removes a header that's already defined into headers object.

request.removeHeader('Content-Type');

request.setHeader(name, value)#

• name <string>
• value <any>

Sets a single header value for headers object. If this header already exists in the to-be-sent headers, its value will be replaced. Use an array of strings here to send multiple headers with the same name. Non-string values will be stored without modification. Therefore, request.getHeader() may return non-string values. However, the non-string values will be converted to strings for network transmission.

request.setHeader('Content-Type', 'application/json');

or

request.setHeader('Cookie', ['type=ninja', 'language=javascript']);

request.setNoDelay([noDelay])#

• noDelay <boolean>

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

request.setSocketKeepAlive([enable][, initialdelay])#

• enable <boolean>
• initialDelay <number>

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

request.setTimeout(timeout[, callback])#

• timeout <number> Milliseconds before a request times out.
• callback <Function> Optional function to be called when a timeout occurs. Same as binding to the 'timeout' event.
• Returns: <http.ClientRequest>