php恢复功能或以块的形式下载

Question

PHP $_SERVER does not return HTTP_range key and without that key how can I perform a "resume download" or download in chunks?

   if (isset($_SERVER['HTTP_RANGE'])) {
    echo "find";
   } else{
    echo "not find";
   }

i can't get $_SERVER['HTTP_RANGE'] from server .......

There is no key HTTP_RANGE when i print $_SERVER

===================================================

<?php

    // get the file request, throw error if nothing supplied

    // hide notices
    @ini_set('error_reporting', E_ALL & ~ E_NOTICE);

    //- turn off compression on the server
    @apache_setenv('no-gzip', 1);
    @ini_set('zlib.output_compression', 'Off');

    if(!isset($_REQUEST['file']) || empty($_REQUEST['file'])) 
    {
        header("HTTP/1.0 400 Bad Request");
        exit;
    }

    // sanitize the file request, keep just the name and extension
    // also, replaces the file location with a preset one ('./myfiles/' in this example)
    $file_path  = $_REQUEST['file'];
    $path_parts = pathinfo($file_path);
    $file_name  = $path_parts['basename'];
    $file_ext   = $path_parts['extension'];
    $file_path  = './myfiles/' . $file_name;

    // allow a file to be streamed instead of sent as an attachment
    $is_attachment = isset($_REQUEST['stream']) ? false : true;

    // make sure the file exists
    if (is_file($file_path))
    {
        $file_size  = filesize($file_path);
        $file = @fopen($file_path,"rb");
        if ($file)
        {
            // set the headers, prevent caching
            header("Pragma: public");
            header("Expires: -1");
            header("Cache-Control: public, must-revalidate, post-check=0, pre-check=0");
            header("Content-Disposition: attachment; filename=\"$file_name\"");

            // set appropriate headers for attachment or streamed file
            if ($is_attachment) {
                    header("Content-Disposition: attachment; filename=\"$file_name\"");
            }
            else {
                    header('Content-Disposition: inline;');
                    header('Content-Transfer-Encoding: binary');
            }

            // set the mime type based on extension, add yours if needed.
            $ctype_default = "application/octet-stream";
            $content_types = array(
                    "exe" => "application/octet-stream",
                    "zip" => "application/zip",
                    "mp3" => "audio/mpeg",
                    "mpg" => "video/mpeg",
                    "avi" => "video/x-msvideo",
            );
            $ctype = isset($content_types[$file_ext]) ? $content_types[$file_ext] : $ctype_default;
            header("Content-Type: " . $ctype);

            //check if http_range is sent by browser (or download manager)
            if(isset($_SERVER['HTTP_RANGE']))
            {
                list($size_unit, $range_orig) = explode('=', $_SERVER['HTTP_RANGE'], 2);
                if ($size_unit == 'bytes')
                {
                    //multiple ranges could be specified at the same time, but for simplicity only serve the first range
                    //http://tools.ietf.org/id/draft-ietf-http-range-retrieval-00.txt
                    list($range, $extra_ranges) = explode(',', $range_orig, 2);
                }
                else
                {
                    $range = '';
                    header('HTTP/1.1 416 Requested Range Not Satisfiable');
                    exit;
                }
            }
            else
            {
                $range = '';
            }

            //figure out download piece from range (if set)
            list($seek_start, $seek_end) = explode('-', $range, 2);

            //set start and end based on range (if set), else set defaults
            //also check for invalid ranges.
            $seek_end   = (empty($seek_end)) ? ($file_size - 1) : min(abs(intval($seek_end)),($file_size - 1));
            $seek_start = (empty($seek_start) || $seek_end < abs(intval($seek_start))) ? 0 : max(abs(intval($seek_start)),0);

            //Only send partial content header if downloading a piece of the file (IE workaround)
            if ($seek_start > 0 || $seek_end < ($file_size - 1))
            {
                header('HTTP/1.1 206 Partial Content');
                header('Content-Range: bytes '.$seek_start.'-'.$seek_end.'/'.$file_size);
                header('Content-Length: '.($seek_end - $seek_start + 1));
            }
            else
              header("Content-Length: $file_size");

            header('Accept-Ranges: bytes');

            set_time_limit(0);
            fseek($file, $seek_start);

            while(!feof($file)) 
            {
                print(@fread($file, 1024*8));
                ob_flush();
                flush();
                if (connection_status()!=0) 
                {
                    @fclose($file);
                    exit;
                }           
            }

            // file save was a success
            @fclose($file);
            exit;
        }
        else 
        {
            // file couldn't be opened
            header("HTTP/1.0 500 Internal Server Error");
            exit;
        }
    }
    else
    {
        // file does not exist
        header("HTTP/1.0 404 Not Found");
        exit;
    }
    ?>