When output buffering is on, using the gzhandler, then ob_get_length() returns the uncompressed content length in stead of the actual (compressed) payload.

This is fatal if a Content-Length HTTP-header is sent and the browser implements HTTP keep-alive. The result is a web-site which appears to be down or with extremely slow responses.

Example PHP code:

<?php

ob_start('ob_gzhandler');

print "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"; // 30 a's
print "bbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"; // 30 b's
print "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"; // 30 a's

header('Content-Length: '.ob_get_length());
ob_end_flush();

?>

If this is saved as http://localhost/ob.php then try the following wget command:

wget --header="Accept-Encoding: gzip" --header="Connection: close" -S http://localhost/ob.php
Notice that wget displays the following error message continuously:
Connection closed at byte 36. Retrying.

Also notice that the web-server told wget to expect 90 bytes (the uncompressed payload).