download - Downloading large files reliably in PHP

Question

I have a php script on a server to send files to recipents: they get a unique link and then they can download large files. Sometimes there is a problem with the transfer and the file is corrupted or never finishes. I am wondering if there is a better way to send large files

Code:

$f = fopen(DOWNLOAD_DIR.$database[$_REQUEST['fid']]['filePath'], 'r');
while(!feof($f)){
    print fgets($f, 1024);
}
fclose($f);

I have seen functions such as

http_send_file
http_send_data

But I am not sure if they will work.

What is the best way to solve this problem?

Regards
erwing

Answer 1

Chunking files is the fastest / simplest method in PHP, if you can't or don't want to make use of something a bit more professional like cURL, mod-xsendfile on Apache or some dedicated script.

$filename = $filePath.$filename;

$chunksize = 5 * (1024 * 1024); //5 MB (= 5 242 880 bytes) per one chunk of file.

if(file_exists($filename))
{
    set_time_limit(300);

    $size = intval(sprintf("%u", filesize($filename)));

    header('Content-Type: application/octet-stream');
    header('Content-Transfer-Encoding: binary');
    header('Content-Length: '.$size);
    header('Content-Disposition: attachment;filename="'.basename($filename).'"');

    if($size > $chunksize)
    { 
        $handle = fopen($filename, 'rb'); 

        while (!feof($handle))
        { 
          print(@fread($handle, $chunksize));

          ob_flush();
          flush();
        } 

        fclose($handle); 
    }
    else readfile($path);

    exit;
}
else echo 'File "'.$filename.'" does not exist!';

Ported from richnetapps.com / NeedBee. Tested on 200 MB files, on which readfile() died, even with maximum allowed memory limit set to 1G, that is five times more than downloaded file size.

BTW: I tested this also on files >2GB, but PHP only managed to write first 2GB of file and then broke the connection. File-related functions (fopen, fread, fseek) uses INT, so you ultimately hit the limit of 2GB. Above mentioned solutions (i.e. mod-xsendfile) seems to be the only option in this case.

EDIT: Make yourself 100% that your file is saved in utf-8. If you omit that, downloaded files will be corrupted. This is, because this solutions uses print to push chunk of a file to a browser.