drupal_page_cache_header

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• Drupal 6
• Drupal 7

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Definition

drupal_page_cache_header($cache)
includes/bootstrap.inc, line 731

Description

Set HTTP headers in preparation for a cached page response.

The general approach here is that anonymous users can keep a local cache of the page, but must revalidate it on every request. Then, they are given a '304 Not Modified' response as long as they stay logged out and the page has not been modified.

Code

<?php
function drupal_page_cache_header($cache) {
  // Create entity tag based on cache update time.
  $etag = '"' . md5($cache->created) . '"';

  // See if the client has provided the required HTTP headers.
  $if_modified_since = isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) ? strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']) : FALSE;
  $if_none_match = isset($_SERVER['HTTP_IF_NONE_MATCH']) ? stripslashes($_SERVER['HTTP_IF_NONE_MATCH']) : FALSE;

  if ($if_modified_since && $if_none_match
      && $if_none_match == $etag // etag must match
      && $if_modified_since == $cache->created) {  // if-modified-since must match
    header($_SERVER['SERVER_PROTOCOL'] . ' 304 Not Modified');
    // All 304 responses must send an etag if the 200 response for the same object contained an etag
    header("Etag: $etag");
    return;
  }

  // Send appropriate response:
  header("Last-Modified: " . gmdate(DATE_RFC1123, $cache->created));
  header("ETag: $etag");

  // The following headers force validation of cache:
  header("Expires: Sun, 19 Nov 1978 05:00:00 GMT");
  header("Cache-Control: must-revalidate");

  if (variable_get('page_compression', TRUE)) {
    // Determine if the browser accepts gzipped data.
    if (@strpos($_SERVER['HTTP_ACCEPT_ENCODING'], 'gzip') === FALSE && function_exists('gzencode')) {
      // Strip the gzip header and run uncompress.
      $cache->data = gzinflate(substr(substr($cache->data, 10), 0, -8));
    }
    elseif (function_exists('gzencode')) {
      header('Content-Encoding: gzip');
    }
  }

  // Send the original request's headers. We send them one after
  // another so PHP's header() function can deal with duplicate
  // headers.
  $headers = explode("\n", $cache->headers);
  foreach ($headers as $header) {
    header($header);
  }

  print $cache->data;
}
?>