A Guzzle Plugin for streaming files. Maybe someday a real Guzzle Plugin with Composer package...

guzzle_streamer.php

<?php
/**
 * Direct streamer for guzzle.
 * Makes a HEAD request to fetch content length first.
 * Uses GET request to stream read data directly to the browser.
 *
 * @author Julius Beckmann
 */

include('guzzle.phar');


use Guzzle\Http\Client;
use Guzzle\Common\Event;


class StreamPlugin implements Symfony\Component\EventDispatcher\EventSubscriberInterface
{
  private $head_request = null;
  
  public static function getSubscribedEvents() {
    return array(
      'curl.callback.write' => 'onCurlCallbackWrite',
      'request.before_send' => 'configureRequest',
    );
  }

  public function configureRequest($event) {
    $request = $event->offsetGet('request');
    $request->getParams()->set('curl.emit_io', true);
  }
  
  public function onCurlCallbackWrite(Guzzle\Common\Event $event){
    // Maybe sue ob_flush() here.
    echo $event->offsetGet('write');
  }
}


class GuzzleStreamer {

  private $client;
  private $plugin;

  public function __construct(Guzzle\Http\Client $client) {
    $this->client = $client;
    $this->plugin = new StreamPlugin();
    $client->addSubscriber($this->plugin);
  }

  public function stream($url) {
    // Fetch Content-Length via HEAD request.
    $response = $this->client->head($url)->send();
    $content_length = (string)$response->getHeader('Content-Length');
    if($content_length) {
      header('Content-Length: '.$content_length);
    }
    
    // Request and output directly.
    $this->client->get($url)->send();
  }

}

$client = new Client('http://example.com');
$streamer = new GuzzleStreamer($client);
$streamer->stream('/file');