gzcompress

While looking into a strange issue on a multisite WordPress installation which optimized the pages of the main but not of the sub-blogs, I needed code to check whether a string was gzipped or not. I found this like-a-boss code-snippet on StackOverflow which worked for gzencoded strings:

$is_gzip = 0 === mb_strpos($mystery_string , "\x1f" . "\x8b" . "\x08");

But this does not work for strings compressed with gzcompress or gzdeflate, which don’t have the GZIP header data, so in the end I came up with this less funky function which somewhat brutally simply tries to gzuncompress and gzinflate the string:

function isGzipped($in) {
  if (mb_strpos($in , "\x1f" . "\x8b" . "\x08")===0) {
    return true;
  } else if (@gzuncompress($in)!==false) {
    return true;
  } else if (@gzinflate($in)!==false) {
    return true;
  } else {
    return false;
  }
}

Klunky, but it works. Now if only this would confirm my “educated guess” that the original problem was due to a compressed string.