<?php
/**
 * Handles all HTTP requests using cURL and manages the responses.
 *
 * @version 2012.01.17
 * @copyright 2006-2011 Ryan Parman
 * @copyright 2006-2010 Foleeo Inc.
 * @copyright 2010-2011 Amazon.com, Inc. or its affiliates.
 * @copyright 2008-2011 Contributors
 * @license http://opensource.org/licenses/bsd-license.php Simplified BSD License
 */
class RequestCore
{
	/**
	 * The URL being requested.
	 */
	public $request_url;

	/**
	 * The headers being sent in the request.
	 */
	public $request_headers;

	/**
	 * The body being sent in the request.
	 */
	public $request_body;

	/**
	 * The response returned by the request.
	 */
	public $response;

	/**
	 * The headers returned by the request.
	 */
	public $response_headers;

	/**
	 * The body returned by the request.
	 */
	public $response_body;

	/**
	 * The HTTP status code returned by the request.
	 */
	public $response_code;

	/**
	 * Additional response data.
	 */
	public $response_info;

	/**
	 * The handle for the cURL object.
	 */
	public $curl_handle;

	/**
	 * The method by which the request is being made.
	 */
	public $method;

	/**
	 * Stores the proxy settings to use for the request.
	 */
	public $proxy = null;

	/**
	 * The username to use for the request.
	 */
	public $username = null;

	/**
	 * The password to use for the request.
	 */
	public $password = null;

	/**
	 * Custom CURLOPT settings.
	 */
	public $curlopts = null;

	/**
	 * The state of debug mode.
	 */
	public $debug_mode = false;

	/**
	 * The default class to use for HTTP Requests (defaults to <RequestCore>).
	 */
	public $request_class = 'RequestCore';

	/**
	 * The default class to use for HTTP Responses (defaults to <ResponseCore>).
	 */
	public $response_class = 'ResponseCore';

	/**
	 * Default useragent string to use.
	 */
	public $useragent = 'RequestCore/1.4.4';

	/**
	 * File to read from while streaming up.
	 */
	public $read_file = null;

	/**
	 * The resource to read from while streaming up.
	 */
	public $read_stream = null;

	/**
	 * The size of the stream to read from.
	 */
	public $read_stream_size = null;

	/**
	 * The length already read from the stream.
	 */
	public $read_stream_read = 0;

	/**
	 * File to write to while streaming down.
	 */
	public $write_file = null;

	/**
	 * The resource to write to while streaming down.
	 */
	public $write_stream = null;

	/**
	 * Stores the intended starting seek position.
	 */
	public $seek_position = null;

	/**
	 * The location of the cacert.pem file to use.
	 */
	public $cacert_location = false;

	/**
	 * The state of SSL certificate verification.
	 */
	public $ssl_verification = true;

	/**
	 * The user-defined callback function to call when a stream is read from.
	 */
	public $registered_streaming_read_callback = null;

	/**
	 * The user-defined callback function to call when a stream is written to.
	 */
	public $registered_streaming_write_callback = null;


	/*%******************************************************************************************%*/
	// CONSTANTS

	/**
	 * GET HTTP Method
	 */
	const HTTP_GET = 'GET';

	/**
	 * POST HTTP Method
	 */
	const HTTP_POST = 'POST';

	/**
	 * PUT HTTP Method
	 */
	const HTTP_PUT = 'PUT';

	/**
	 * DELETE HTTP Method
	 */
	const HTTP_DELETE = 'DELETE';

	/**
	 * HEAD HTTP Method
	 */
	const HTTP_HEAD = 'HEAD';


	/*%******************************************************************************************%*/
	// CONSTRUCTOR/DESTRUCTOR

	/**
	 * Constructs a new instance of this class.
	 *
	 * @param string $url (Optional) The URL to request or service endpoint to query.
	 * @param string $proxy (Optional) The faux-url to use for proxy settings. Takes the following format: `proxy://user:pass@hostname:port`
	 * @param array $helpers (Optional) An associative array of classnames to use for request, and response functionality. Gets passed in automatically by the calling class.
	 * @return $this A reference to the current instance.
	 */
	public function __construct($url = null, $proxy = null, $helpers = null)
	{
		// Set some default values.
		$this->request_url = $url;
		$this->method = self::HTTP_GET;
		$this->request_headers = array();
		$this->request_body = '';

		// Set a new Request class if one was set.
		if (isset($helpers['request']) && !empty($helpers['request']))
		{
			$this->request_class = $helpers['request'];
		}

		// Set a new Request class if one was set.
		if (isset($helpers['response']) && !empty($helpers['response']))
		{
			$this->response_class = $helpers['response'];
		}

		if ($proxy)
		{
			$this->set_proxy($proxy);
		}

		return $this;
	}

	/**
	 * Destructs the instance. Closes opened file handles.
	 *
	 * @return $this A reference to the current instance.
	 */
	public function __destruct()
	{
		if (isset($this->read_file) && isset($this->read_stream))
		{
			fclose($this->read_stream);
		}

		if (isset($this->write_file) && isset($this->write_stream))
		{
			fclose($this->write_stream);
		}

		return $this;
	}


	/*%******************************************************************************************%*/
	// REQUEST METHODS

	/**
	 * Sets the credentials to use for authentication.
	 *
	 * @param string $user (Required) The username to authenticate with.
	 * @param string $pass (Required) The password to authenticate with.
	 * @return $this A reference to the current instance.
	 */
	public function set_credentials($user, $pass)
	{
		$this->username = $user;
		$this->password = $pass;
		return $this;
	}

	/**
	 * Adds a custom HTTP header to the cURL request.
	 *
	 * @param string $key (Required) The custom HTTP header to set.
	 * @param mixed $value (Required) The value to assign to the custom HTTP header.
	 * @return $this A reference to the current instance.
	 */
	public function add_header($key, $value)
	{
		$this->request_headers[$key] = $value;
		return $this;
	}

	/**
	 * Removes an HTTP header from the cURL request.
	 *
	 * @param string $key (Required) The custom HTTP header to set.
	 * @return $this A reference to the current instance.
	 */
	public function remove_header($key)
	{
		if (isset($this->request_headers[$key]))
		{
			unset($this->request_headers[$key]);
		}
		return $this;
	}

	/**
	 * Set the method type for the request.
	 *
	 * @param string $method (Required) One of the following constants: <HTTP_GET>, <HTTP_POST>, <HTTP_PUT>, <HTTP_HEAD>, <HTTP_DELETE>.
	 * @return $this A reference to the current instance.
	 */
	public function set_method($method)
	{
		$this->method = strtoupper($method);
		return $this;
	}

	/**
	 * Sets a custom useragent string for the class.
	 *
	 * @param string $ua (Required) The useragent string to use.
	 * @return $this A reference to the current instance.
	 */
	public function set_useragent($ua)
	{
		$this->useragent = $ua;
		return $this;
	}

	/**
	 * Set the body to send in the request.
	 *
	 * @param string $body (Required) The textual content to send along in the body of the request.
	 * @return $this A reference to the current instance.
	 */
	public function set_body($body)
	{
		$this->request_body = $body;
		return $this;
	}

	/**
	 * Set the URL to make the request to.
	 *
	 * @param string $url (Required) The URL to make the request to.
	 * @return $this A reference to the current instance.
	 */
	public function set_request_url($url)
	{
		$this->request_url = $url;
		return $this;
	}

	/**
	 * Set additional CURLOPT settings. These will merge with the default settings, and override if
	 * there is a duplicate.
	 *
	 * @param array $curlopts (Optional) A set of key-value pairs that set `CURLOPT` options. These will merge with the existing CURLOPTs, and ones passed here will override the defaults. Keys should be the `CURLOPT_*` constants, not strings.
	 * @return $this A reference to the current instance.
	 */
	public function set_curlopts($curlopts)
	{
		$this->curlopts = $curlopts;
		return $this;
	}

	/**
	 * Sets the length in bytes to read from the stream while streaming up.
	 *
	 * @param integer $size (Required) The length in bytes to read from the stream.
	 * @return $this A reference to the current instance.
	 */
	public function set_read_stream_size($size)
	{
		$this->read_stream_size = $size;

		return $this;
	}

	/**
	 * Sets the resource to read from while streaming up. Reads the stream from its current position until
	 * EOF or `$size` bytes have been read. If `$size` is not given it will be determined by <php:fstat()> and
	 * <php:ftell()>.
	 *
	 * @param resource $resource (Required) The readable resource to read from.
	 * @param integer $size (Optional) The size of the stream to read.
	 * @return $this A reference to the current instance.
	 */
	public function set_read_stream($resource, $size = null)
	{
		if (!isset($size) || $size < 0)
		{
			$stats = fstat($resource);

			if ($stats && $stats['size'] >= 0)
			{
				$position = ftell($resource);

				if ($position !== false && $position >= 0)
				{
					$size = $stats['size'] - $position;
				}
			}
		}

		$this->read_stream = $resource;

		return $this->set_read_stream_size($size);
	}

	/**
	 * Sets the file to read from while streaming up.
	 *
	 * @param string $location (Required) The readable location to read from.
	 * @return $this A reference to the current instance.
	 */
	public function set_read_file($location)
	{
		$this->read_file = $location;
		$read_file_handle = fopen($location, 'r');

		return $this->set_read_stream($read_file_handle);
	}

	/**
	 * Sets the resource to write to while streaming down.
	 *
	 * @param resource $resource (Required) The writeable resource to write to.
	 * @return $this A reference to the current instance.
	 */
	public function set_write_stream($resource)
	{
		$this->write_stream = $resource;

		return $this;
	}

	/**
	 * Sets the file to write to while streaming down.
	 *
	 * @param string $location (Required) The writeable location to write to.
	 * @return $this A reference to the current instance.
	 */
	public function set_write_file($location)
	{
		$this->write_file = $location;
		$write_file_handle = fopen($location, 'w');

		return $this->set_write_stream($write_file_handle);
	}

	/**
	 * Set the proxy to use for making requests.
	 *
	 * @param string $proxy (Required) The faux-url to use for proxy settings. Takes the following format: `proxy://user:pass@hostname:port`
	 * @return $this A reference to the current instance.
	 */
	public function set_proxy($proxy)
	{
		$proxy = parse_url($proxy);
		$proxy['user'] = isset($proxy['user']) ? $proxy['user'] : null;
		$proxy['pass'] = isset($proxy['pass']) ? $proxy['pass'] : null;
		$proxy['port'] = isset($proxy['port']) ? $proxy['port'] : null;
		$this->proxy = $proxy;
		return $this;
	}

	/**
	 * Set the intended starting seek position.
	 *
	 * @param integer $position (Required) The byte-position of the stream to begin reading from.
	 * @return $this A reference to the current instance.
	 */
	public function set_seek_position($position)
	{
		$this->seek_position = isset($position) ? (integer) $position : null;

		return $this;
	}

	/**
	 * Register a callback function to execute whenever a data stream is read from using
	 * <CFRequest::streaming_read_callback()>.
	 *
	 * The user-defined callback function should accept three arguments:
	 *
	 * <ul>
	 * 	<li><code>$curl_handle</code> - <code>resource</code> - Required - The cURL handle resource that represents the in-progress transfer.</li>
	 * 	<li><code>$file_handle</code> - <code>resource</code> - Required - The file handle resource that represents the file on the local file system.</li>
	 * 	<li><code>$length</code> - <code>integer</code> - Required - The length in kilobytes of the data chunk that was transferred.</li>
	 * </ul>
	 *
	 * @param string|array|function $callback (Required) The callback function is called by <php:call_user_func()>, so you can pass the following values: <ul>
	 * 	<li>The name of a global function to execute, passed as a string.</li>
	 * 	<li>A method to execute, passed as <code>array('ClassName', 'MethodName')</code>.</li>
	 * 	<li>An anonymous function (PHP 5.3+).</li></ul>
	 * @return $this A reference to the current instance.
	 */
	public function register_streaming_read_callback($callback)
	{
		$this->registered_streaming_read_callback = $callback;

		return $this;
	}

	/**
	 * Register a callback function to execute whenever a data stream is written to using
	 * <CFRequest::streaming_write_callback()>.
	 *
	 * The user-defined callback function should accept two arguments:
	 *
	 * <ul>
	 * 	<li><code>$curl_handle</code> - <code>resource</code> - Required - The cURL handle resource that represents the in-progress transfer.</li>
	 * 	<li><code>$length</code> - <code>integer</code> - Required - The length in kilobytes of the data chunk that was transferred.</li>
	 * </ul>
	 *
	 * @param string|array|function $callback (Required) The callback function is called by <php:call_user_func()>, so you can pass the following values: <ul>
	 * 	<li>The name of a global function to execute, passed as a string.</li>
	 * 	<li>A method to execute, passed as <code>array('ClassName', 'MethodName')</code>.</li>
	 * 	<li>An anonymous function (PHP 5.3+).</li></ul>
	 * @return $this A reference to the current instance.
	 */
	public function register_streaming_write_callback($callback)
	{
		$this->registered_streaming_write_callback = $callback;

		return $this;
	}


	/*%******************************************************************************************%*/
	// PREPARE, SEND, AND PROCESS REQUEST

	/**
	 * A callback function that is invoked by cURL for streaming up.
	 *
	 * @param resource $curl_handle (Required) The cURL handle for the request.
	 * @param resource $file_handle (Required) The open file handle resource.
	 * @param integer $length (Required) The maximum number of bytes to read.
	 * @return binary Binary data from a stream.
	 */
	public function streaming_read_callback($curl_handle, $file_handle, $length)
	{
		// Once we've sent as much as we're supposed to send...
		if ($this->read_stream_read >= $this->read_stream_size)
		{
			// Send EOF
			return '';
		}

		// If we're at the beginning of an upload and need to seek...
		if ($this->read_stream_read == 0 && isset($this->seek_position) && $this->seek_position !== ftell($this->read_stream))
		{
			if (fseek($this->read_stream, $this->seek_position) !== 0)
			{
				throw new RequestCore_Exception('The stream does not support seeking and is either not at the requested position or the position is unknown.');
			}
		}

		$read = fread($this->read_stream, min($this->read_stream_size - $this->read_stream_read, $length)); // Remaining upload data or cURL's requested chunk size
		$this->read_stream_read += strlen($read);

		$out = $read === false ? '' : $read;

		// Execute callback function
		if ($this->registered_streaming_read_callback)
		{
			call_user_func($this->registered_streaming_read_callback, $curl_handle, $file_handle, $out);
		}

		return $out;
	}

	/**
	 * A callback function that is invoked by cURL for streaming down.
	 *
	 * @param resource $curl_handle (Required) The cURL handle for the request.
	 * @param binary $data (Required) The data to write.
	 * @return integer The number of bytes written.
	 */
	public function streaming_write_callback($curl_handle, $data)
	{
		$length = strlen($data);
		$written_total = 0;
		$written_last = 0;

		while ($written_total < $length)
		{
			$written_last = fwrite($this->write_stream, substr($data, $written_total));

			if ($written_last === false)
			{
				return $written_total;
			}

			$written_total += $written_last;
		}

		// Execute callback function
		if ($this->registered_streaming_write_callback)
		{
			call_user_func($this->registered_streaming_write_callback, $curl_handle, $written_total);
		}

		return $written_total;
	}

	/**
	 * Prepares and adds the details of the cURL request. This can be passed along to a <php:curl_multi_exec()>
	 * function.
	 *
	 * @return resource The handle for the cURL object.
	 */
	public function prep_request()
	{
		$curl_handle = curl_init();

		// Set default options.
		curl_setopt($curl_handle, CURLOPT_URL, $this->request_url);
		curl_setopt($curl_handle, CURLOPT_FILETIME, true);
		curl_setopt($curl_handle, CURLOPT_FRESH_CONNECT, false);
		curl_setopt($curl_handle, CURLOPT_CLOSEPOLICY, CURLCLOSEPOLICY_LEAST_RECENTLY_USED);
		curl_setopt($curl_handle, CURLOPT_MAXREDIRS, 5);
		curl_setopt($curl_handle, CURLOPT_HEADER, true);
		curl_setopt($curl_handle, CURLOPT_RETURNTRANSFER, true);
		curl_setopt($curl_handle, CURLOPT_TIMEOUT, 5184000);
		curl_setopt($curl_handle, CURLOPT_CONNECTTIMEOUT, 120);
		curl_setopt($curl_handle, CURLOPT_NOSIGNAL, true);
		curl_setopt($curl_handle, CURLOPT_REFERER, $this->request_url);
		curl_setopt($curl_handle, CURLOPT_USERAGENT, $this->useragent);
		curl_setopt($curl_handle, CURLOPT_READFUNCTION, array($this, 'streaming_read_callback'));

		// Verification of the SSL cert
		if ($this->ssl_verification)
		{
			curl_setopt($curl_handle, CURLOPT_SSL_VERIFYPEER, true);
			curl_setopt($curl_handle, CURLOPT_SSL_VERIFYHOST, 2);
		}
		else
		{
			curl_setopt($curl_handle, CURLOPT_SSL_VERIFYPEER, false);
			curl_setopt($curl_handle, CURLOPT_SSL_VERIFYHOST, false);
		}

		// chmod the file as 0755
		if ($this->cacert_location === true)
		{
			curl_setopt($curl_handle, CURLOPT_CAINFO, dirname(__FILE__) . '/cacert.pem');
		}
		elseif (is_string($this->cacert_location))
		{
			curl_setopt($curl_handle, CURLOPT_CAINFO, $this->cacert_location);
		}

		// Debug mode
		if ($this->debug_mode)
		{
			curl_setopt($curl_handle, CURLOPT_VERBOSE, true);
		}

		// Handle open_basedir & safe mode
		if (!ini_get('safe_mode') && !ini_get('open_basedir'))
		{
			curl_setopt($curl_handle, CURLOPT_FOLLOWLOCATION, true);
		}

		// Enable a proxy connection if requested.
		if ($this->proxy)
		{
			curl_setopt($curl_handle, CURLOPT_HTTPPROXYTUNNEL, true);

			$host = $this->proxy['host'];
			$host .= ($this->proxy['port']) ? ':' . $this->proxy['port'] : '';
			curl_setopt($curl_handle, CURLOPT_PROXY, $host);

			if (isset($this->proxy['user']) && isset($this->proxy['pass']))
			{
				curl_setopt($curl_handle, CURLOPT_PROXYUSERPWD, $this->proxy['user'] . ':' . $this->proxy['pass']);
			}
		}

		// Set credentials for HTTP Basic/Digest Authentication.
		if ($this->username && $this->password)
		{
			curl_setopt($curl_handle, CURLOPT_HTTPAUTH, CURLAUTH_ANY);
			curl_setopt($curl_handle, CURLOPT_USERPWD, $this->username . ':' . $this->password);
		}

		// Handle the encoding if we can.
		if (extension_loaded('zlib'))
		{
			curl_setopt($curl_handle, CURLOPT_ENCODING, 'gzip, deflate');
		}

		// Process custom headers
		if (isset($this->request_headers) && count($this->request_headers))
		{
			$temp_headers = array();

			if (!array_key_exists('Expect', $this->request_headers))
			{
				$this->request_headers['Expect'] = '';
			}

			foreach ($this->request_headers as $k => $v)
			{
				$temp_headers[] = $k . ': ' . $v;
			}

			curl_setopt($curl_handle, CURLOPT_HTTPHEADER, $temp_headers);
		}

		switch ($this->method)
		{
			case self::HTTP_PUT:
				curl_setopt($curl_handle, CURLOPT_CUSTOMREQUEST, 'PUT');
				if (isset($this->read_stream))
				{
					if (!isset($this->read_stream_size) || $this->read_stream_size < 0)
					{
						throw new RequestCore_Exception('The stream size for the streaming upload cannot be determined.');
					}

					curl_setopt($curl_handle, CURLOPT_INFILESIZE, $this->read_stream_size);
					curl_setopt($curl_handle, CURLOPT_UPLOAD, true);
				}
				else
				{
					curl_setopt($curl_handle, CURLOPT_POSTFIELDS, $this->request_body);
				}
				break;

			case self::HTTP_POST:
				curl_setopt($curl_handle, CURLOPT_POST, true);
				curl_setopt($curl_handle, CURLOPT_POSTFIELDS, $this->request_body);
				break;

			case self::HTTP_HEAD:
				curl_setopt($curl_handle, CURLOPT_CUSTOMREQUEST, self::HTTP_HEAD);
				curl_setopt($curl_handle, CURLOPT_NOBODY, 1);
				break;

			default: // Assumed GET
				curl_setopt($curl_handle, CURLOPT_CUSTOMREQUEST, $this->method);
				if (isset($this->write_stream))
				{
					curl_setopt($curl_handle, CURLOPT_WRITEFUNCTION, array($this, 'streaming_write_callback'));
					curl_setopt($curl_handle, CURLOPT_HEADER, false);
				}
				else
				{
					curl_setopt($curl_handle, CURLOPT_POSTFIELDS, $this->request_body);
				}
				break;
		}

		// Merge in the CURLOPTs
		if (isset($this->curlopts) && sizeof($this->curlopts) > 0)
		{
			foreach ($this->curlopts as $k => $v)
			{
				curl_setopt($curl_handle, $k, $v);
			}
		}

		return $curl_handle;
	}

	/**
	 * Take the post-processed cURL data and break it down into useful header/body/info chunks. Uses the
	 * data stored in the `curl_handle` and `response` properties unless replacement data is passed in via
	 * parameters.
	 *
	 * @param resource $curl_handle (Optional) The reference to the already executed cURL request.
	 * @param string $response (Optional) The actual response content itself that needs to be parsed.
	 * @return ResponseCore A <ResponseCore> object containing a parsed HTTP response.
	 */
	public function process_response($curl_handle = null, $response = null)
	{
		// Accept a custom one if it's passed.
		if ($curl_handle && $response)
		{
			$this->curl_handle = $curl_handle;
			$this->response = $response;
		}

		// As long as this came back as a valid resource...
		if (is_resource($this->curl_handle))
		{
			// Determine what's what.
			$header_size = curl_getinfo($this->curl_handle, CURLINFO_HEADER_SIZE);
			$this->response_headers = substr($this->response, 0, $header_size);
			$this->response_body = substr($this->response, $header_size);
			$this->response_code = curl_getinfo($this->curl_handle, CURLINFO_HTTP_CODE);
			$this->response_info = curl_getinfo($this->curl_handle);

			// Parse out the headers
			$this->response_headers = explode("\r\n\r\n", trim($this->response_headers));
			$this->response_headers = array_pop($this->response_headers);
			$this->response_headers = explode("\r\n", $this->response_headers);
			array_shift($this->response_headers);

			// Loop through and split up the headers.
			$header_assoc = array();
			foreach ($this->response_headers as $header)
			{
				$kv = explode(': ', $header);
				$header_assoc[strtolower($kv[0])] = $kv[1];
			}

			// Reset the headers to the appropriate property.
			$this->response_headers = $header_assoc;
			$this->response_headers['_info'] = $this->response_info;
			$this->response_headers['_info']['method'] = $this->method;

			if ($curl_handle && $response)
			{
				return new $this->response_class($this->response_headers, $this->response_body, $this->response_code, $this->curl_handle);
			}
		}

		// Return false
		return false;
	}

	/**
	 * Sends the request, calling necessary utility functions to update built-in properties.
	 *
	 * @param boolean $parse (Optional) Whether to parse the response with ResponseCore or not.
	 * @return string The resulting unparsed data from the request.
	 */
	public function send_request($parse = false)
	{
		set_time_limit(0);

		$curl_handle = $this->prep_request();
		$this->response = curl_exec($curl_handle);

		if ($this->response === false)
		{
			throw new cURL_Exception('cURL resource: ' . (string) $curl_handle . '; cURL error: ' . curl_error($curl_handle) . ' (cURL error code ' . curl_errno($curl_handle) . '). See http://curl.haxx.se/libcurl/c/libcurl-errors.html for an explanation of error codes.');
		}

		$parsed_response = $this->process_response($curl_handle, $this->response);

		curl_close($curl_handle);

		if ($parse)
		{
			return $parsed_response;
		}

		return $this->response;
	}

	/**
	 * Sends the request using <php:curl_multi_exec()>, enabling parallel requests. Uses the "rolling" method.
	 *
	 * @param array $handles (Required) An indexed array of cURL handles to process simultaneously.
	 * @param array $opt (Optional) An associative array of parameters that can have the following keys: <ul>
	 * 	<li><code>callback</code> - <code>string|array</code> - Optional - The string name of a function to pass the response data to. If this is a method, pass an array where the <code>[0]</code> index is the class and the <code>[1]</code> index is the method name.</li>
	 * 	<li><code>limit</code> - <code>integer</code> - Optional - The number of simultaneous requests to make. This can be useful for scaling around slow server responses. Defaults to trusting cURLs judgement as to how many to use.</li></ul>
	 * @return array Post-processed cURL responses.
	 */
	public function send_multi_request($handles, $opt = null)
	{
		set_time_limit(0);

		// Skip everything if there are no handles to process.
		if (count($handles) === 0) return array();

		if (!$opt) $opt = array();

		// Initialize any missing options
		$limit = isset($opt['limit']) ? $opt['limit'] : -1;

		// Initialize
		$handle_list = $handles;
		$http = new $this->request_class();
		$multi_handle = curl_multi_init();
		$handles_post = array();
		$added = count($handles);
		$last_handle = null;
		$count = 0;
		$i = 0;

		// Loop through the cURL handles and add as many as it set by the limit parameter.
		while ($i < $added)
		{
			if ($limit > 0 && $i >= $limit) break;
			curl_multi_add_handle($multi_handle, array_shift($handles));
			$i++;
		}

		do
		{
			$active = false;

			// Start executing and wait for a response.
			while (($status = curl_multi_exec($multi_handle, $active)) === CURLM_CALL_MULTI_PERFORM)
			{
				// Start looking for possible responses immediately when we have to add more handles
				if (count($handles) > 0) break;
			}

			// Figure out which requests finished.
			$to_process = array();

			while ($done = curl_multi_info_read($multi_handle))
			{
				// Since curl_errno() isn't reliable for handles that were in multirequests, we check the 'result' of the info read, which contains the curl error number, (listed here http://curl.haxx.se/libcurl/c/libcurl-errors.html )
				if ($done['result'] > 0)
				{
					throw new cURL_Multi_Exception('cURL resource: ' . (string) $done['handle'] . '; cURL error: ' . curl_error($done['handle']) . ' (cURL error code ' . $done['result'] . '). See http://curl.haxx.se/libcurl/c/libcurl-errors.html for an explanation of error codes.');
				}

				// Because curl_multi_info_read() might return more than one message about a request, we check to see if this request is already in our array of completed requests
				elseif (!isset($to_process[(int) $done['handle']]))
				{
					$to_process[(int) $done['handle']] = $done;
				}
			}

			// Actually deal with the request
			foreach ($to_process as $pkey => $done)
			{
				$response = $http->process_response($done['handle'], curl_multi_getcontent($done['handle']));
				$key = array_search($done['handle'], $handle_list, true);
				$handles_post[$key] = $response;

				if (count($handles) > 0)
				{
					curl_multi_add_handle($multi_handle, array_shift($handles));
				}

				curl_multi_remove_handle($multi_handle, $done['handle']);
				curl_close($done['handle']);
			}
		}
		while ($active || count($handles_post) < $added);

		curl_multi_close($multi_handle);

		ksort($handles_post, SORT_NUMERIC);
		return $handles_post;
	}


	/*%******************************************************************************************%*/
	// RESPONSE METHODS

	/**
	 * Get the HTTP response headers from the request.
	 *
	 * @param string $header (Optional) A specific header value to return. Defaults to all headers.
	 * @return string|array All or selected header values.
	 */
	public function get_response_header($header = null)
	{
		if ($header)
		{
			return $this->response_headers[strtolower($header)];
		}
		return $this->response_headers;
	}

	/**
	 * Get the HTTP response body from the request.
	 *
	 * @return string The response body.
	 */
	public function get_response_body()
	{
		return $this->response_body;
	}

	/**
	 * Get the HTTP response code from the request.
	 *
	 * @return string The HTTP response code.
	 */
	public function get_response_code()
	{
		return $this->response_code;
	}
}


/**
 * Container for all response-related methods.
 */
class ResponseCore
{
	/**
	 * Stores the HTTP header information.
	 */
	public $header;

	/**
	 * Stores the SimpleXML response.
	 */
	public $body;

	/**
	 * Stores the HTTP response code.
	 */
	public $status;

	/**
	 * Constructs a new instance of this class.
	 *
	 * @param array $header (Required) Associative array of HTTP headers (typically returned by <RequestCore::get_response_header()>).
	 * @param string $body (Required) XML-formatted response from AWS.
	 * @param integer $status (Optional) HTTP response status code from the request.
	 * @return object Contains an <php:array> `header` property (HTTP headers as an associative array), a <php:SimpleXMLElement> or <php:string> `body` property, and an <php:integer> `status` code.
	 */
	public function __construct($header, $body, $status = null)
	{
		$this->header = $header;
		$this->body = $body;
		$this->status = $status;

		return $this;
	}

	/**
	 * Did we receive the status code we expected?
	 *
	 * @param integer|array $codes (Optional) The status code(s) to expect. Pass an <php:integer> for a single acceptable value, or an <php:array> of integers for multiple acceptable values.
	 * @return boolean Whether we received the expected status code or not.
	 */
	public function isOK($codes = array(200, 201, 204, 206))
	{
		if (is_array($codes))
		{
			return in_array($this->status, $codes);
		}

		return $this->status === $codes;
	}
}

class cURL_Exception extends Exception {}
class cURL_Multi_Exception extends cURL_Exception {}
class RequestCore_Exception extends Exception {}
