Question

I want to make an etag that matches what Apache produces. How does apache create it’s etags?

Answer 1

Apache uses the standard format of inode-filesize-mtime. The only caveat to this is that the mtime must be epoch time and padded with zeros so it is 16 digits. Here is how to do it in PHP:

$fs = stat($file); header('Etag: '.sprintf(''%x-%x-%s'', $fs['ino'], $fs['size'],base_convert(str_pad($fs['mtime'],16,'0'),10,16)));