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<?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($curl_handle, CURLOPT_SSL_VERIFYHOST, true);
                }
                else
                {
                        curl_setopt($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();

                        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 {}