Provide Content-length header for cached pages

It looks like drupal_page_cache_header() already does that for the Etag part. The Content-Length might help, thou.

Could you please elaborate how the Content-Legth field can help with performance ? if you can give some URLs it would be nice !. Thanks.

Sorry I mistakenly changed the title of the thread.

I have found problems applying this patch on my site.

Specifically, I have found incomplete load of our home page when it is served from the cache on Internet Explorer 6, we use a lot of jquery and ajax calls on the web page, and the problem dissapears if I remove the Content-Length header and truncate cache_page.

Revised patch that adds the content-length to drupal_page_cache_header, instead of adding the headers really late in page_set_cache.

Revision to title because this patch no longer adds the etag header, since the drupal_page_cache_header function already does that. The patch in #5 also moves some header() calls around so that they can be done together.

I am watching the patch and it seems not right to me. After adding the header Content-Lenght, there is a condition that uncompress cache->data if the browser does not support compression, that would make the value previously set invalid, wouldn't it?

No, it sends that header only after $cache->data has been prepared.

Ok, I didn't apply the patch and I was looking at my source code, which is D5:

function drupal_page_cache_header($cache) {
  // Set default values:
  $last_modified = gmdate('D, d M Y H:i:s', $cache->created) .' GMT';
  $etag = '"'.md5($last_modified).'"';

  // See if the client has provided the required HTTP headers:
  // *** Added preg_replace; some browsers append a "; length=..." entity to the header
  $if_modified_since = isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) ? preg_replace('/;.*$/','',stripslashes($_SERVER['HTTP_IF_MODIFIED_SINCE'])) : FALSE;
  $if_none_match = isset($_SERVER['HTTP_IF_NONE_MATCH']) ? stripslashes($_SERVER['HTTP_IF_NONE_MATCH']) : FALSE;

  // *** Added:
  // ***IE6 does not support Entity Tags, so depend on the if_modified_since to guide us.
  if (preg_match('/MSIE\s6\.\d+/i',$_SERVER['HTTP_USER_AGENT']) && $if_modified_since!==false)
        $if_none_match = '"'.md5($if_modified_since).'"';

  if ($if_modified_since && $if_none_match
      && $if_none_match == $etag // etag must match
      && $if_modified_since == $last_modified) {  // if-modified-since must match
    header('HTTP/1.1 304 Not Modified');
    // All 304 responses must send an etag if the 200 response for the same object contained an etag
    header("Etag: $etag");
    exit();
  }

  // Send appropriate response:
  header("Last-Modified: $last_modified");
  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");

  // 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');
  }

Obvisouly to apply this patch on this code, the header('Content-Length') should be set AFTER the line:

    $cache->data = gzinflate(substr(substr($cache->data, 10), 0, -8));

because this line modifies the length.
That was what I was saying. Sorry for the confusion.

Patch attached according to #9. Add also a comment (from http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html ) :

// Send size of the entity-body, in decimal number of octets:

Ok seriously, the patch in #5, sends that header after all the $cache->data manipulation has been done. You need to try the patch. According to the description, "The patch in #5 also moves some header() calls around so that they can be done together." (for clarity).

  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 appropriate response:
+  header("Last-Modified: $last_modified");
+  header("ETag: $etag");
+  header('Content-Length: ' . strlen($cache->data));
+
+  // The following headers force validation of cache:
+  header("Expires: Sun, 19 Nov 1978 05:00:00 GMT");
+  header("Cache-Control: must-revalidate");
+

I'm all for the additional comment in #10, but for readability sake, let's please base off the patch in #5.

So ...

Dave Reid is absolutely right, his patch applies correctly.

Is it not possible to delete my previous post (#10) ?

I see that I can edit it, but I am a bit ashamed so I would like to remove it...
(you can consider me as a kind of drupal.org newbie :)

Note that setting Content-Length explicitly causes problems with PHPs zlib.output_compression feature, so I suggest not adding the header if this feature is enabled:
http://www.php.net/manual/en/ref.zlib.php#43181

Could you give some examples of situations where this would improve performance?

Failed due to #74645: modify file_scan_directory to include a regex for the nomask.. Setting back to code needs review.

Add tag.

What's the status of this? Is it safe to add the Content-Length header even for gzipped pages?