HTTP#

Stability: 2 - Stable

Source Code: lib/http.js

This module, containing both a client and server, can be imported via require('node:http') (CommonJS) or import * as http from 'node:http' (ES module).

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, so 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": "example.com",
  "accept": "*/*" }

Keys are lowercased. Values are not modified.

In order to support the full spectrum of possible HTTP applications, the Node.js 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', 'example.com',
  'accepT', '*/*' ]

Class: http.Agent#

Added in: v0.3.4

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])#

History
VersionChanges
v24.7.0

Add support for agentKeepAliveTimeoutBuffer.

v24.5.0

Add support for proxyEnv.

v24.5.0

Add support for defaultPort and protocol.

v15.6.0, v14.17.0

Change the default scheduling from 'fifo' to 'lifo'.

v14.5.0, v12.20.0

Add scheduling option to specify the free socket scheduling strategy.

v14.5.0, v12.19.0

Add maxTotalSockets option to agent constructor.

v0.3.4

Added in: v0.3.4

  • 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.
    • agentKeepAliveTimeoutBuffer <number> Milliseconds to subtract from the server-provided keep-alive: timeout=... hint when determining socket expiration time. This buffer helps ensure the agent closes the socket slightly before the server does, reducing the chance of sending a request on a socket that’s about to be closed by the server. Default: 1000.
    • maxSockets <number> Maximum number of sockets to allow per host. If the same host opens multiple concurrent connections, each request will use new socket until the maxSockets value is reached. If the host attempts to open more connections than maxSockets, the additional requests will enter into a pending request queue, and will enter active connection state when an existing connection terminates. This makes sure there are at most maxSockets active connections at any point in time, from a given host. Default: Infinity.
    • maxTotalSockets <number> Maximum number of sockets allowed for all hosts in total. Each request will use a new socket until the maximum is reached. Default: Infinity.
    • maxFreeSockets <number> Maximum number of sockets per host to leave open in a free state. Only relevant if keepAlive is set to true. Default: 256.
    • scheduling <string> Scheduling strategy to apply when picking the next free socket to use. It can be 'fifo' or 'lifo'. The main difference between the two scheduling strategies is that 'lifo' selects the most recently used socket, while 'fifo' selects the least recently used socket. In case of a low rate of request per second, the 'lifo' scheduling will lower the risk of picking a socket that might have been closed by the server due to inactivity. In case of a high rate of request per second, the 'fifo' scheduling will maximize the number of open sockets, while the 'lifo' scheduling will keep it as low as possible. Default: 'lifo'.
    • timeout <number> Socket timeout in milliseconds. This will set the timeout when the socket is created.
    • proxyEnv <Object> | <undefined> Environment variables for proxy configuration. See Built-in Proxy Support for details. Default: undefined
      • HTTP_PROXY <string> | <undefined> URL for the proxy server that HTTP requests should use. If undefined, no proxy is used for HTTP requests.
      • HTTPS_PROXY <string> | <undefined> URL for the proxy server that HTTPS requests should use. If undefined, no proxy is used for HTTPS requests.
      • NO_PROXY <string> | <undefined> Patterns specifying the endpoints that should not be routed through a proxy.
      • http_proxy <string> | <undefined> Same as HTTP_PROXY. If both are set, http_proxy takes precedence.
      • https_proxy <string> | <undefined> Same as HTTPS_PROXY. If both are set, https_proxy takes precedence.
      • no_proxy <string> | <undefined> Same as NO_PROXY. If both are set, no_proxy takes precedence.
    • defaultPort <number> Default port to use when the port is not specified in requests. Default: 80.
    • protocol <string> The protocol to use for the agent. Default: 'http:'.

options in socket.connect() are also supported.

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

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

agent.createConnection(options[, callback])#

Added in: v0.11.4

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.

This method is guaranteed to return an instance of the <net.Socket> class, a subclass of <stream.Duplex>, unless the user specifies a socket type other than <net.Socket>.

callback has a signature of (err, stream).

agent.keepSocketAlive(socket)#

Added in: v8.1.0
  • socket