php resume capability or download in chunks - php

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;
}
?>