我在网上找到了这个功能：
function download_file($file,$ctype, $is_resume=TRUE)
{
//First, see if the file exists
if (!is_file($file))
{
die("<b>404 File not found!</b>");
}
//Gather relevent info about file
$size = filesize($file);
$fileinfo = pathinfo($file);
//workaround for IE filename bug with multiple periods / multiple dots in filename
//that adds square brackets to filename - eg. setup.abc.exe becomes setup[1].abc.exe
$filename = (strstr($_SERVER['HTTP_USER_AGENT'], 'MSIE')) ?
preg_replace('/\./', '%2e', $fileinfo['basename'], substr_count($fileinfo['basename'], '.') - 1) :
$fileinfo['basename'];
//check if http_range is sent by browser (or download manager)
if($is_resume && 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 = '';
}
}
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)) ? ($size - 1) : min(abs(intval($seek_end)),($size - 1));
$seek_start = (empty($seek_start) || $seek_end < abs(intval($seek_start))) ? 0 : max(abs(intval($seek_start)),0);
//add headers if resumable
if ($is_resume)
{
//Only send partial content header if downloading a piece of the file (IE workaround)
if ($seek_start > 0 || $seek_end < ($size - 1))
{
header('HTTP/1.1 206 Partial Content');
}
header('Accept-Ranges: bytes');
header('Content-Range: bytes '.$seek_start.'-'.$seek_end.'/'.$size);
}
//headers for IE Bugs (is this necessary?)
//header("Cache-Control: cache, must-revalidate");
//header("Pragma: public");
header('Content-Type: ' . $ctype);
header('Content-Disposition: attachment; filename="' . $filename . '"');
header('Content-Length: '.($seek_end - $seek_start + 1));
//open the file
$fp = fopen($file, 'rb');
//seek to start of missing part
fseek($fp, $seek_start);
//start buffered download
while(!feof($fp))
{
//reset time limit for big files
set_time_limit(0);
print(fread($fp, 1024*8));
flush();
ob_flush();
}
fclose($fp);
exit;
}
下载正在运行，但是当我使用下载管理器（IDM 等）并且我想暂停下载以便稍后继续下载时，我不能。这个函数应该允许这样做（查看Content-Range标题），但由于某种原因，它不起作用。
有谁知道为什么？我该如何解决？
我已经尝试了很多我在互联网上找到的功能，但没有一个能正常工作。