Apache/PHP large file download (>2Gb) failing

Question

I'm using a PHP script to control access to download files. This works fine for anything under 2Gb but fails for larger files.

• Apache and PHP are both 64bit
• Apache will allow the file to be downloaded if accessed directly (which I can't allow)

The guts of the PHP (ignoring the access control):

if (ob_get_level())  ob_end_clean();

error_log('FILETEST: '.$path.' : '.filesize($path));
header('Content-Description: File Transfer');
header('Content-Type: application/octet-stream');
header('Content-Disposition: attachment; filename='.basename($path));
header('Expires: 0');
header('Cache-Control: must-revalidate');
header('Pragma: public');
header('Content-Length: ' . filesize($path));
readfile($path);
exit;

The error log shows the file size fine

[Tue Apr 08 11:01:16 2014] [error] [client *.*.*.*] FILETEST: /downloads/file.name : 2251373807, referer: http://myurl/files/

But the access log has a negative size:

 *.*.*.* - - [08/Apr/2014:11:01:16 +0100] "GET /files/file.name HTTP/1.1" 200 -2043593489 "http://myurl/files/" "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 Firefox/24.0"

And so browsers refuse to download the file. In fact, using wget, it's not sending anything:

$ wget -S -O - http://myurl/files/file.name
--2014-04-08 11:33:38--  http://myurl/files/file.name
HTTP request sent, awaiting response... No data received.
Retrying.

Answer 1

Try to read the file in chunks and expose them to the browser instead of filling your local memory with 2GB and flushing all at once.

Replace readfile($path); by:

@ob_end_flush();
flush();

$fileDescriptor = fopen($file, 'rb');

while ($chunk = fread($fileDescriptor, 8192)) {
    echo $chunk;
    @ob_end_flush();
    flush();
}

fclose($fileDescriptor);
exit;

8192 bytes is a critical point in some cases, refere to php.net/fread.

Adding some microtime variables (and comparing with the pointer position of the file descriptor) will also allow you to controll the maximum speed of the download.

*(Flushing the output buffer also slightly depends on the webserver, use those commands to be sure it at least tries to flush as much as possible.)