Serving large files with PHP

The best way to send big files with php is the X-Sendfile header. It allows the webserver to serve files much faster through zero-copy mechanisms like sendfile(2). It is supported by lighttpd and apache with a plugin.

Example:

$file = "/absolute/path/to/file"; // can be protected by .htaccess
header('X-Sendfile: '.$file);
header('Content-type: application/octet-stream');
header('Content-Disposition: attachment; filename="'.basename($file).'"');
// other headers ...
exit;

The server reads the X-Sendfile header and sends out the file.

You don't need to read the whole thing - just enter a loop reading it in, say, 32Kb chunks and sending it as output. Better yet, use fpassthru which does much the same thing for you....

$name = 'mybigfile.zip';
$fp = fopen($name, 'rb');

// send the right headers
header("Content-Type: application/zip");
header("Content-Length: " . filesize($name));

// dump the file and stop the script
fpassthru($fp);
exit;

even less lines if you use readfile, which doesn't need the fopen call...

$name = 'mybigfile.zip';

// send the right headers
header("Content-Type: application/zip");
header("Content-Length: " . filesize($name));

// dump the file and stop the script
readfile($name);
exit;

If you want to get even cuter, you can support the Content-Range header which lets clients request a particular byte range of your file. This is particularly useful for serving PDF files to Adobe Acrobat, which just requests the chunks of the file it needs to render the current page. It's a bit involved, but see this for an example.

While fpassthru() has been my first choice in the past, the PHP manual actually recommends* using readfile() instead, if you are just dumping the file as-is to the client.

* "If you just want to dump the contents of a file to the output buffer, without first modifying it or seeking to a particular offset, you may want to use the readfile(), which saves you the fopen() call." —PHP manual