JFeedReader concept.

reader.php

<?php
/**
 * @package     Joomla.Platform
 * @subpackage  Feed
 *
 * @copyright   Copyright (C) 2005 - 2011 Open Source Matters, Inc. All rights reserved.
 * @license     GNU General Public License version 2 or later; see LICENSE
 */

defined('JPATH_PLATFORM') or die();

jimport('joomla.utilities.xmlelement');

/**
 * Feed Reader class.
 *
 * @package     Joomla.Platform
 * @subpackage  Feed
 * @since       11.4
 */
class JFeedReader
{
	/**
	 * @var    integer
	 * @since  11.4
	 */
	const RSS = 1;

	/**
	 * @var    integer
	 * @since  11.4
	 */
	const ATOM = 2;

	/**
	 * @var    JHttp  The HTTP client object for requesting feeds.
	 * @since  11.4
	 */
	protected $http;

	/**
	 * @var    DOMDocument
	 * @since  11.4
	 */
	protected $node;

	/**
	 * @var    XMLReader
	 * @since  11.4
	 */
	protected $reader;

	/**
	 * @var    integer  The feed format.
	 * @since  11.4
	 */
	protected $format;

	/**
	 * @var    string  The feed format version.
	 * @since  11.4
	 */
	protected $version;

	/**
	 * Constructor.
	 *
	 * @param   JHttp  $http  The HTTP client object.
	 *
	 * @since   11.4
	 */
	public function __construct(JHttp $http = null)
	{
		$this->http   = isset($http) ? $http : new JHttp;
		$this->node   = new DOMDocument;
		$this->reader = new XMLReader;
	}

	/**
	 * Method to open a file as a feed.
	 *
	 * @param   string  $uri  The URI of the feed to open.
	 *
	 * @return  JFeed
	 *
	 * @since   11.4
	 */
	public function loadFile($uri)
	{
		// Make sure the file exists.
		if (!file_exists($uri))
		{
			throw new InvalidArgumentException('The file ' . $uri . ' does not exist.');
		}

		// Open the URI within the stream reader.
		if (!$this->reader->open($uri))
		{
			throw new RuntimeException('Unable to open the feed.');
		}

		// Read the root node from the feed.
		if (!$this->reader->read())
		{
			throw new RuntimeException('Unable to read the root node of the feed.');
		}

		return $this;
	}

	/**
	 * Method to detect the feed type and version.
	 *
	 * @return  void
	 *
	 * @since   11.4
	 */
	protected function detectFormat()
	{
		if (strtolower($this->reader->name) == 'rss')
		{
			$this->format = self::RSS;
			$this->version = $this->reader->getAttribute('version');
		}
		elseif (strtolower($this->reader->name) == 'feed')
		{
			$this->format = self::ATOM;
			$this->version = ($this->reader->getAttribute('version') == '0.3') ? '0.3' : '1.0';
		}
	}

	/**
	 * Method to expand the current reader node into a SimpleXML node for more detailed reading
	 * and manipulation.
	 *
	 * @return  SimpleXMLElement
	 *
	 * @since   11.4
	 */
	protected function expandToSimpleXml()
	{
		$el = simplexml_import_dom($this->node->importNode($this->reader->expand(), true), 'JXMLElement');

		if (!($el instanceof JXMLElement))
		{
			throw new RuntimeException('Unable to expand node to SimpleXML element.');
		}

		return $el;
	}
}