# agent-base

### Turn a function into an [`http.Agent`](https://nodejs.org/api/http.html#http_class_http_agent) instance

This module is a thin wrapper around the base `http.Agent` class.

It provides an abstract class that must define a `connect()` function, which is responsible for creating the underlying socket that the HTTP client requests will use.

The `connect()` function may return an arbitrary `Duplex` stream, or another `http.Agent` instance to delegate the request to, and may be asynchronous (by defining an `async` function).

Instances of this agent can be used with the `http` and `https` modules. To differentiate, the options parameter in the `connect()` function includes a `secureEndpoint` property, which can be checked to determine what type of socket should be returned.

#### Some subclasses:

Here are some more interesting uses of `agent-base`. Send a pull request to list yours!

* [`http-proxy-agent`](https://github.com/usemanusai/JAEGIS/blob/main/http-proxy-agent/README.md): An HTTP(s) proxy `http.Agent` implementation for HTTP endpoints
* [`https-proxy-agent`](https://github.com/usemanusai/JAEGIS/blob/main/https-proxy-agent/README.md): An HTTP(s) proxy `http.Agent` implementation for HTTPS endpoints
* [`pac-proxy-agent`](https://github.com/usemanusai/JAEGIS/blob/main/pac-proxy-agent/README.md): A PAC file proxy `http.Agent` implementation for HTTP and HTTPS
* [`socks-proxy-agent`](https://github.com/usemanusai/JAEGIS/blob/main/socks-proxy-agent/README.md): A SOCKS proxy `http.Agent` implementation for HTTP and HTTPS

## Example

Here's a minimal example that creates a new `net.Socket` or `tls.Socket` based on the `secureEndpoint` property. This agent can be used with both the `http` and `https` modules.

```ts
import * as net from 'net';
import * as tls from 'tls';
import * as http from 'http';
import { Agent } from 'agent-base';

class MyAgent extends Agent {
  connect(req, opts) {
    // `secureEndpoint` is true when using the "https" module
    if (opts.secureEndpoint) {
      return tls.connect(opts);
    } else {
      return net.connect(opts);
    }
  }
});

// Keep alive enabled means that `connect()` will only be
// invoked when a new connection needs to be created
const agent = new MyAgent({ keepAlive: true });

// Pass the `agent` option when creating the HTTP request
http.get('http://nodejs.org/api/', { agent }, (res) => {
  console.log('"response" event!', res.headers);
  res.pipe(process.stdout);
});
```