@ -48,26 +48,32 @@ list like the following:
added: v0.3.4
-->
The HTTP Agent is used for pooling sockets used in HTTP client
requests.
The 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.js's
pool has the benefit of keep-alive when under load but still does not
require developers to manually close the HTTP clients using
KeepAlive.
If you opt into using HTTP KeepAlive, you can create an Agent object
with that flag set to `true` . (See the [constructor options][].)
Then, the Agent will keep unused sockets in a pool for later use. They
will be explicitly marked so as to not keep the Node.js process running.
However, it is still a good idea to explicitly [`destroy()`][] KeepAlive
agents when they are no longer in use, so that the Sockets will be shut
down.
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
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 ](#http_new_agent_options ).
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's pool when the socket emits either
a `'close'` event or an `'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:
@ -79,7 +85,11 @@ http.get(options, (res) => {
});
```
Alternatively, you could just opt out of pooling entirely using
You may also use an agent 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` :
```js
@ -104,7 +114,7 @@ added: v0.3.4
outstanding requests, so they can be used for future requests without
having to reestablish a TCP connection. Default = `false`
* `keepAliveMsecs` {Integer} When using the `keepAlive` option, specifies
the [initial delay ](net.html #net_socket_setkeepalive_enable_initialdelay
the [initial delay ](#net_socket_setkeepalive_enable_initialdelay )
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
@ -116,7 +126,7 @@ added: v0.3.4
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, you must create your own [`http.Agent`][] object .
To configure any of them, you must create your own [`http.Agent`][] instance .
```js
const http = require('http');
@ -138,7 +148,7 @@ added: 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 A gents may override this method in case greater flexibility is desired.
custom a gents 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` .
@ -153,7 +163,7 @@ added: v0.11.4
Destroy any sockets that are currently in use by the agent.
It is usually not necessary to do this. However, if you are using an
agent with KeepAlive enabled, then it is best to explicitly shut down
agent with `keepAlive`
the agent when you know that it will no longer be used. Otherwise,
sockets may hang open for quite a long time before the server
terminates them.
@ -166,7 +176,7 @@ added: v0.11.4
* {Object}
An object which contains arrays of sockets currently awaiting use by
the Agent when HTTP KeepAlive is us ed. Do not modify.
the agent when `keepAlive` is enabl ed. Do not modify.
### agent.getName(options)
<!-- YAML
@ -181,8 +191,8 @@ added: v0.11.4
* Returns: {String}
Get a unique name for a set of request options, to determine whether a
connection can be reused. In the http agent, this returns
`host:port:localAddress` . In the https agent, the name includes the
connection can be reused. For an HTTP agent, this returns
`host:port:localAddress` . For an HTTPS agent, the name includes the
CA, cert, ciphers, and other HTTPS/TLS-specific options that determine
socket reusability.
@ -193,7 +203,7 @@ added: v0.11.7
* {Number}
By default set to 256. For Agents supporting HTTP KeepAlive , this
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.
@ -226,7 +236,7 @@ added: v0.3.6
* {Object}
An object which contains arrays of sockets currently in use by the
A gent. Do not modify.
a gent. Do not modify.
## Class: http.ClientRequest
<!-- YAML
@ -662,7 +672,7 @@ added: v0.1.0
* `response` {http.ServerResponse}
Emitted each time there is a request. Note that there may be multiple requests
per connection (in the case of keep-a live connections).
per connection (in the case of HTTP Keep-A live connections).
### Event: 'upgrade'
<!-- YAML
@ -1510,7 +1520,7 @@ added: v0.5.9
* {http.Agent}
Global instance of Agent which is used as the default for all HTTP client
Global instance of ` Agent`
requests.
## http.request(options[, callback])
@ -1540,15 +1550,13 @@ added: v0.3.6
* `headers` {Object} An object containing request headers.
* `auth` {String} Basic authentication i.e. `'user:password'` to compute an
Authorization header.
* `agent` {http.Agent|Boolean} Controls [`Agent`][] behavior. When an Agent
is used request will default to `Connection: keep-alive` . Possible values:
* `agent` {http.Agent|Boolean} Controls [`Agent`][] behavior. Possible values:
* `undefined` (default): use [`http.globalAgent`][] 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` .
* `false` : causes a new `Agent` with default values to be used.
* `createConnection` {Function} A function that produces a socket/stream to
use for the request when the `agent` option is not used. This can be used to
avoid creating a custom Agent class just to override the default
avoid creating a custom ` Agent`
`createConnection` function. See [`agent.createConnection()`][] for more
details.
* `timeout` {Integer}: A number specifying the socket timeout in milliseconds.
@ -1669,3 +1677,4 @@ There are a few special headers that should be noted.
[constructor options]: #http_new_agent_options
[Readable Stream]: stream.html#stream_class_stream_readable
[Writable Stream]: stream.html#stream_class_stream_writable
[socket.unref()]: net.html#net_socket_unref
Lance Ball
8 years ago
Myles Borins