用PHP实现 HTTP断点续传、分块下载文件（Socket）

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<?php /**  * 支持断点下载的类  */ class downloader {       /**      * download file to local path      *      * @param       $url      * @param       $save_file      * @param int   $speed      * @param array $headers      * @param int   $timeout      * @return bool      * @throws Exception      */     static function get($url, $save_file, $speed = 10240, $headers = array(), $timeout = 10) {         $url_info = self::parse_url($url);         if (!$url_info['host']) {             throw new Exception('Url is Invalid');         }           // default header         $def_headers = array(             'Accept'          => '*/*',             'User-Agent'      => 'Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0)',             'Accept-Encoding' => 'gzip, deflate',             'Host'            => $url_info['host'],             'Connection'      => 'Close',             'Accept-Language' => 'zh-cn',         );           // merge heade         $headers = array_merge($def_headers, $headers);         // get content length         $content_length = self::get_content_size($url_info['host'], $url_info['port'], $url_info['request'], $headers, $timeout);           // content length not exist         if (!$content_length) {             throw new Exception('Content-Length is Not Exists');         }         // get exists length         $exists_length = is_file($save_file) ? filesize($save_file) : 0;         // get tmp data file         $data_file = $save_file . '.data';         // get tmp data         $exists_data = is_file($data_file) ? json_decode(file_get_contents($data_file), 1) : array();         // check file is valid         if ($exists_length == $content_length) {             $exists_data && @unlink($data_file);             return true;         }         // check file is expire         if ($exists_data['length'] != $content_length || $exists_length > $content_length) {             $exists_data = array(                 'length' => $content_length,             );         }         // write exists data         file_put_contents($data_file, json_encode($exists_data));           try {             $download_status = self::download_content($url_info['host'], $url_info['port'], $url_info['request'], $save_file, $content_length, $exists_length, $speed, $headers, $timeout);             if ($download_status) {                 @unlink($data_file);             }         } catch (Exception $e) {             throw new Exception($e->getMessage());         }         return true;     }       /**      * parse url      *      * @param $url      * @return bool|mixed      */     static function parse_url($url) {         $url_info = parse_url($url);         if (!$url_info['host']) {             return false;         }         $url_info['port']    = $url_info['port'] ? $url_info['host'] : 80;         $url_info['request'] = $url_info['path'] . ($url_info['query'] ? '?' . $url_info['query'] : '');         return $url_info;     }       /**      * download content by chunk      *      * @param $host      * @param $port      * @param $url_path      * @param $headers      * @param $timeout      */     static function download_content($host, $port, $url_path, $save_file, $content_length, $range_start, $speed, &$headers, $timeout) {         $request = self::build_header('GET', $url_path, $headers, $range_start);         $fsocket = @fsockopen($host, $port, $errno, $errstr, $timeout);         stream_set_blocking($fsocket, TRUE);         stream_set_timeout($fsocket, $timeout);         fwrite($fsocket, $request);         $status = stream_get_meta_data($fsocket);         if ($status['timed_out']) {             throw new Exception('Socket Connect Timeout');         }         $is_header_end = 0;         $total_size    = $range_start;         $file_fp       = fopen($save_file, 'a+');         while (!feof($fsocket)) {             if (!$is_header_end) {                 $line = @fgets($fsocket);                 if (in_array($line, array("\n", "\r\n"))) {                     $is_header_end = 1;                 }                 continue;             }             $resp        = fread($fsocket, $speed);             $read_length = strlen($resp);             if ($resp === false || $content_length < $total_size + $read_length) {                 fclose($fsocket);                 fclose($file_fp);                 throw new Exception('Socket I/O Error Or File Was Changed');             }             $total_size += $read_length;             fputs($file_fp, $resp);             // check file end             if ($content_length == $total_size) {                 break;             }             sleep(1);             // for test             //break;         }         fclose($fsocket);         fclose($file_fp);         return true;       }       /**      * get content length      *      * @param $host      * @param $port      * @param $url_path      * @param $headers      * @param $timeout      * @return int      */     static function get_content_size($host, $port, $url_path, &$headers, $timeout) {         $request = self::build_header('HEAD', $url_path, $headers);         $fsocket = @fsockopen($host, $port, $errno, $errstr, $timeout);         stream_set_blocking($fsocket, TRUE);         stream_set_timeout($fsocket, $timeout);         fwrite($fsocket, $request);         $status = stream_get_meta_data($fsocket);         $length = 0;         if ($status['timed_out']) {             return 0;         }         while (!feof($fsocket)) {             $line = @fgets($fsocket);             if (in_array($line, array("\n", "\r\n"))) {                 break;             }             $line = strtolower($line);             // get location             if (substr($line, 0, 9) == 'location:') {                 $location = trim(substr($line, 9));                 $url_info = self::parse_url($location);                 if (!$url_info['host']) {                     return 0;                 }                 fclose($fsocket);                 return self::get_content_size($url_info['host'], $url_info['port'], $url_info['request'], $headers, $timeout);             }             // get content length             if (strpos($line, 'content-length:') !== false) {                 list(, $length) = explode('content-length:', $line);                 $length = (int)trim($length);             }         }         fclose($fsocket);         return $length;       }       /**      * build header for socket      *      * @param     $action      * @param     $url_path      * @param     $headers      * @param int $range_start      * @return string      */     static function build_header($action, $url_path, &$headers, $range_start = -1) {         $out = $action . " {$url_path} HTTP/1.0\r\n";         foreach ($headers as $hkey => $hval) {             $out .= $hkey . ': ' . $hval . "\r\n";         }         if ($range_start > -1) {             $out .= "Accept-Ranges: bytes\r\n";             $out .= "Range: bytes={$range_start}-\r\n";         }         $out .= "\r\n";           return $out;     } }   ?>