header('Content-type: application/octet-stream') cause 0 byte files

Question

I'm using database query in PHP to retrieve a binary file. But when I'm trying to force download it, the header('Content-type: application/octet-stream') line cause 0 byte files. Without that line I can download the file with full content. It's a binary file that's for sure so I just can't understand why that line causes the problem. The code:

$result = mysql_query("SELECT data FROM stored_file WHERE file_name = '$q'");

while($row = mysql_fetch_array($result))
{
    $file = $row['data'];
}


    header('Content-disposition: attachment; filename='.$q);
    header('Content-type: application/octet-stream');
    header('Content-Length: '.filesize($file));
    header("Pragma: no-cache");
    header("Expires: 0");
    echo $file;

Any idea? Thanks.

Answer 1

filesize() won't return a meaningful value.

You have binary data in $file, not an actual filename as required as first parameter. Hence you would get an error. (Enable error_reporting! Not seeing errors, and not having them are two different things.)

So what you want to use there is strlen($file), not filesize().

Btw, application/octet-stream or other fill-ins have no use for forcing downloads. It's the Content-Disposition: header which is most crucial to that effect. You're still allowed to send the correct MIME type.

Answer 2

From looking at the query I guess that in $row['data'] is the binary data stored. To set the correct Content-Length header you should use mb_strlen($row['data']);. If no multibyte support (the mb_ functions) is activated on your machine, use strlen(). But be aware, this may result in akward results because the binary data could actually contain the EOF byte sequence and return a too short length. With the mb_strlen function you are on the save side.