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
});
options
in socket.connect()
are also supported.
To configure any of them, a custom {@link Agent} instance must be created.
const http = require('node:http');
const keepAliveAgent = new http.Agent({ keepAlive: true });
options.agent = keepAliveAgent;
http.request(options, onResponseCallback)
Since
v0.3.4
Inheritors
Properties
An object which contains arrays of sockets currently awaiting use by the agent when keepAlive
is enabled. Do not modify.
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.
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()
.
By default set to Infinity
. Determines how many concurrent sockets the agent can have open. Unlike maxSockets
, this parameter applies across all origins.
An object which contains queues of requests that have not yet been assigned to sockets. Do not modify.
An object which contains arrays of sockets currently in use by the agent. Do not modify.
Functions
Returns an array listing the events for which the emitter has registered listeners. The values in the array are strings or Symbol
s.
Returns the current max listener value for the EventEmitter
which is either set by emitter.setMaxListeners(n)
or defaults to {@link defaultMaxListeners}.
By default EventEmitter
s will print a warning if more than 10
listeners are added for a particular event. This is a useful default that helps finding memory leaks. The emitter.setMaxListeners()
method allows the limit to be modified for this specific EventEmitter
instance. The value can be set to Infinity
(or 0
) to indicate an unlimited number of listeners.