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Say you want a PHP script that will make the browser to download a file instead of opening it. This is useful for common filetypes that would normally be displayed in a browser, like .html, images, PDFs and .doc files.

You can find a lot of scripts that do this on the web but one thing most of them don’t handle is download resuming and multi-thread downloading. If you don’t need that feature, feel free to use a simpler script. Personally I’ve found that a function that handles download resuming works more reliably across various browsers (what actually happened : a simpler script didn’t work with Opera + my weird Internet connection, so I found another script and decided to make broad generalizations about download resuming :p).

Note – most of the code below isn’t mine. I found it somewhere on the web and adjusted it for my needs; unfortunately I’ve lost the URL of the original page. If you know where it came from, let me know and I’ll add a link to this post.

function output_file($file, $name, $mime_type=”)
{
/*
This function takes a path to a file to output ($file),
the filename that the browser will see ($name) and
the MIME type of the file ($mime_type, optional).

If you want to do something on download abort/finish,
register_shutdown_function(‘function_name’);
*/
if(!is_readable($file)) die(‘File not found or inaccessible!’);

$size = filesize($file);
$name = rawurldecode($name);

/* Figure out the MIME type (if not specified) */
$known_mime_types=array(
“pdf” => “application/pdf”,
“txt” => “text/plain”,
“html” => “text/html”,
“htm” => “text/html”,
“exe” => “application/octet-stream”,
“zip” => “application/zip”,
“doc” => “application/msword”,
“xls” => “application/vnd.ms-excel”,
“ppt” => “application/vnd.ms-powerpoint”,
“gif” => “image/gif”,
“png” => “image/png”,
“jpeg”=> “image/jpg”,
“jpg” => “image/jpg”,
“php” => “text/plain”
);

if($mime_type==”){
$file_extension = strtolower(substr(strrchr($file,”.”),1));
if(array_key_exists($file_extension, $known_mime_types)){
$mime_type=$known_mime_types[$file_extension];
} else {
$mime_type=”application/force-download”;
};
};

@ob_end_clean(); //turn off output buffering to decrease cpu usage

// required for IE, otherwise Content-Disposition may be ignored
if(ini_get(‘zlib.output_compression’))
ini_set(‘zlib.output_compression’, ‘Off’);

header(‘Content-Type: ‘ . $mime_type);
header(‘Content-Disposition: attachment; filename=”‘.$name.'”‘);
header(“Content-Transfer-Encoding: binary”);
header(‘Accept-Ranges: bytes’);

/* The three lines below basically make the
download non-cacheable */
header(“Cache-control: private”);
header(‘Pragma: private’);
header(“Expires: Mon, 26 Jul 1997 05:00:00 GMT”);

// multipart-download and download resuming support
if(isset($_SERVER[‘HTTP_RANGE’]))
{
list($a, $range) = explode(“=”,$_SERVER[‘HTTP_RANGE’],2);
list($range) = explode(“,”,$range,2);
list($range, $range_end) = explode(“-“, $range);
$range=intval($range);
if(!$range_end) {
$range_end=$size-1;
} else {
$range_end=intval($range_end);
}

$new_length = $range_end-$range+1;
header(“HTTP/1.1 206 Partial Content”);
header(“Content-Length: $new_length”);
header(“Content-Range: bytes $range-$range_end/$size”);
} else {
$new_length=$size;
header(“Content-Length: “.$size);
}

/* output the file itself */
$chunksize = 1*(1024*1024); //you may want to change this
$bytes_send = 0;
if ($file = fopen($file, ‘r’))
{
if(isset($_SERVER[‘HTTP_RANGE’]))
fseek($file, $range);

while(!feof($file) &&
(!connection_aborted()) &&
($bytes_send<$new_length) ) { $buffer = fread($file, $chunksize); print($buffer); //echo($buffer); // is also possible flush(); $bytes_send += strlen($buffer); } fclose($file); } else die('Error - can not open file.'); die(); } /********************************************* Example of use **********************************************/ /* Make sure script execution doesn't time out. Set maximum execution time in seconds (0 means no limit). */ set_time_limit(0); $file_path='that_one_file.txt'; output_file($file_path, 'some file.txt', 'text/plain'); [/sourcecode] Related info
Determining MIME type of a file automatically
Common MIME types
HTTP, caching and other stuff