Test reverse proxies for full ETag support.

etagtest.php

<?php
$etag = date('s') < 30 ? 'one' : 'two';

header('Cache-Control: public, must-revalidate, max-age=60');
header('X-Foo: '.$etag);
header('Vary: X-Foo');
header('ETag: W/"X'.$etag.'X"');

if (isset($_SERVER['HTTP_IF_NONE_MATCH'])) {
  $ifNoneMatch = $_SERVER['HTTP_IF_NONE_MATCH'];
  file_put_contents('./etagtest.log', "HIT: $ifNoneMatch\n", FILE_APPEND);
  if (preg_match('|(?:W/)?"X'.$etag.'X"|', $ifNoneMatch)) {
    header(':', true, 304);
    exit;
  }
}

file_put_contents('./etagtest.log', "MISS\n", FILE_APPEND);
header('Expires: '.gmdate('D, d M Y H:i:s', time() + 600).' GMT');
echo '<h1>'.date('r').'</h1>';
foreach ($_SERVER as $key => $value) {
  if (strpos($key, 'HTTP_') === 0) {
    echo "$key: $value<br/>";
  }
}