Node.js v22.19.0 documentation

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. 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.

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);copy

agent.createConnection(options[, callback])#

• 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: <stream.Duplex>

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)#

• socket <stream.Duplex>

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; copy

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.

The socket argument can be an instance of <net.Socket>, a subclass of <stream.Duplex>.

agent.reuseSocket(socket, request)#

• socket <stream.Duplex>
• 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(); copy

This method can be overridden by a particular Agent subclass.

The socket argument can be an instance of <net.Socket>, a subclass of <stream.Duplex>.

agent.destroy()#

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 is no longer needed. Otherwise, sockets might stay open for quite a long time before the server terminates them.

agent.freeSockets#

• Type: <Object>

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

Sockets in the freeSockets list will be automatically destroyed and removed from the array on 'timeout'.

agent.getName([options])#

• 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#

• Type: <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#

• Type: <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.maxTotalSockets#

• Type: <number>

By default set to Infinity. Determines how many concurrent sockets the agent can have open. Unlike maxSockets, this parameter applies across all origins.

agent.requests#

• Type: <Object>

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

agent.sockets#

• Type: <Object>

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