Event Loop Dreaming.php

<?php

/**
 * What an async proxy server might look like in PHP with a PSR for event loops
 */

use EventLoopImplementation\EventLoop;
use HttpClientImplementation\HttpClient;
use HttpServerImplementation\HttpServer;
use PromiseImplementation\Promise;
use Psr\Http\Message\ResponseInterface;
use Psr\Http\Message\ServerRequestInterface;

/**
 * The HttpServer and HttpClient both depend on the EventLoop. They will add their non-blocking read
 * and write streams to this event loop.
 */
$loop   = new EventLoop;
$server = new HttpServer('localhost:8000', $loop);
$client = new HttpClient($loop);

$proxyDomain = 'http://domain-to-proxy.com/';

$server->on('request', function (ServerRequestInterface $request) use ($client, $proxyDomain) {
    $responsePromise = new Promise;

    /**
     * HttpClient::get() immediately returns a promise which will later be fulfilled with a PSR-7
     * response from the server or an error.
     */
    $client
        ->get($proxyDomain . $request->getRequestTarget())
        ->then(
            function (ResponseInterface $response) use ($responsePromise) {
                $responsePromise->resolve($response);
            },
            function ($error) {
                $responsePromise->reject($error);
            }
        );

    return $responsePromise;
});

$loop->run();

/**
 * This is the same as the code below, but real world use cases are unlikely to be this simple.
 */
$server->on('request', function (ServerRequestInterface $request) use ($client, $proxyDomain) {
    return $client->get($proxyDomain . $request->getRequestTarget());
});