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This is an extracted copy of Node 0.12's keep-alive Agent implementation with some small changes intended to make it work with older versions of Node. It also has one extra feature, which I needed.

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'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 below.) 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 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 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:

http.get(options, function(res) {
  // Do stuff
}).on("socket", function (socket) {
  socket.emit("agentRemove");
});

• options {Object} Set of configurable options to set on the agent. Can have the following fields:
  • keepAlive {Boolean} Keep sockets around in a pool to be used by other requests in the future. Default = false
  • keepAliveMsecs {Integer} When using HTTP KeepAlive, how often to send TCP KeepAlive packets over sockets being kept alive. Default = 1000. Only relevant if keepAlive is set to true.
  • ADDED keepAliveTimeoutMsecs {Integer} When using HTTP KeepAlive, how long to keep the socket connected without activity before it gets reaped.
  • maxSockets {Number} Maximum number of sockets to allow per host. 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.

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 Agent object.

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

By default set to Infinity. Determines how many concurrent sockets the agent can have open per origin. Origin is either a 'host:port' or 'host:port:localAddress' combination.

By default set to 256. For Agents supporting HTTP KeepAlive, this sets the maximum number of sockets that will be left open in the free state.

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

An object which contains arrays of sockets currently awaiting use by the Agent when HTTP KeepAlive is used. Do not modify.

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

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 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.

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 CA, cert, ciphers, and other HTTPS/TLS-specific options that determine socket reusability.

An Agent object for HTTPS similar to Agent.

options is an object. All options from Agent are valid.

The following options from [tls.connect()][] can also be used.

• pfx: Certificate, Private key and CA certificates to use for SSL. Default null.
• key: Private key to use for SSL. Default null.
• passphrase: A string of passphrase for the private key or pfx. Default null.
• cert: Public x509 certificate to use. Default null.
• ca: An authority certificate or array of authority certificates to check the remote host against.
• ciphers: A string describing the ciphers to use or exclude. Consult http://www.openssl.org/docs/apps/ciphers.html#CIPHER_LIST_FORMAT for details on the format.
• rejectUnauthorized: If true, the server certificate is verified against the list of supplied CAs. An 'error' event is emitted if verification fails. Verification happens at the connection level, before the HTTP request is sent. Default true.
• secureProtocol: The SSL method to use, e.g. SSLv3_method to force SSL version 3. The possible values depend on your installation of OpenSSL and are defined in the constant [SSL_METHODS][].

Example:

var SSLAgent = require('yakaa').SSL;

var options = {
  hostname: 'encrypted.google.com',
  port: 443,
  path: '/',
  method: 'GET',
  key: fs.readFileSync('test/fixtures/keys/agent2-key.pem'),
  cert: fs.readFileSync('test/fixtures/keys/agent2-cert.pem')
};
options.agent = new SSLAgent(options);

See LICENSE in this distribution. As code derived from Node's source, it's governed by the same license as Node itself.