用php实现文件上载支持断点

            ob_start();            $size = filesize($file_dir . $file_name);            // 输入文件标签            Header("Content-type: application/octet-stream");            Header("Cache-Control: must-revalidate, post-check=0, pre-check=0");                        Header("Content-length: " . $size);                        $encoded_filename = urlencode($down_name);            $encoded_filename = str_replace("+", "%20", $encoded_filename);            $ua = $_SERVER["HTTP_USER_AGENT"];            // 处理下载的时候的文件名            if (preg_match("/MSIE/", $ua)) {                header('Content-Disposition: attachment; filename="' . $encoded_filename . '"');            } else if (preg_match("/Firefox/", $ua)) {                header('Content-Disposition: attachment; filename*="utf8\'\'' . $down_name . '"');            } else {                header('Content-Disposition: attachment; filename="' . $down_name . '"');            }            $fp = fopen($file_dir . $file_name, "r"); // 打开文件            if (isset($_SERVER['HTTP_RANGE']) && ($_SERVER['HTTP_RANGE'] != "") && preg_match("/^bytes=([0-9]+)-/i", $_SERVER['HTTP_RANGE'], $match) && ($match[1] < $size)) {                $range = $match[1];                                fseek($fp, $range);                header("HTTP/1.1 206 Partial Content");                //header("Date: " . gmdate("D, d M Y H:i:s") . " GMT");                header("Last-Modified: " . gmdate("D, d M Y H:i:s", filemtime($file_dir . $file_name)) . " GMT");                header("Accept-Ranges: bytes");                $rangesize = ($size - $range) > 0 ? ($size - $range) : 0;                header("Content-Length:" . $rangesize);                header("Content-Range: bytes " . $range . '-' . ($size - 1) . "/" . $size);                // header("Connection: close" . "\n\n" );                //header("Connection: close"." ");            } else {                                header("Content-Length: " . (string) ($size));                header("Accept-Ranges: bytes");                $range = 0;                header("Content-Range: bytes " . $range . '-' . ($size - 1) . "/" . $size);            }            fpassthru($fp);            ob_end_flush();            fclose($fp);            exit;