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add support for modifying the cache content before sending to azure - #18

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add support for modifying the cache content before sending to azure#18
tsdexter wants to merge 1 commit into
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tsdexter:master

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@tsdexter tsdexter commented Dec 10, 2019

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We have a WordPress setup that requires us to modify the wordpress output buffer right before sending to the browser, this is accomplished with the below mu-plugin and a final_output filter in our theme - this happens too late for the PN Blob Cache to pick up and cache the changes:

ob_start();

add_action('shutdown', function () {
  $final = '';

  // We'll need to get the number of ob levels we're in, so that we can iterate over each, collecting
  // that buffer's output into the final output.
  $levels = ob_get_level();

  for ($i = 0; $i < $levels; $i++) {
    $final .= ob_get_clean();
  }

  // Apply any filters to the final output
  echo apply_filters('final_output', $final);
}, 0);

This PR adds support for users to modify the content that is sent to the Azure blob storage. It can be used by adding a filter on pn_cached_content to your theme or plugin. For example:

add_filter('pn_cached_content', function ($content, $url, $key) {
  // say you wanted to add the cache URL and/or key to your HTML for debugging purposes
  $modified_content = str_replace("<head>", "<head>\n<meta name=\"CACHEURL\" content=\"{$url}\">\n<meta name=\"CACHEKEY\" content=\"{$key}\">", $content);
  
  // or you had some other modification to the final output of wordpress
  $modified_content = YourThemesContentModificationFunction($content);

  return $modified_content;
}, 1, 3);

We are currently running this successfully in production on a site with ~1.5M pageviews/month.

@tsdexter tsdexter mentioned this pull request Jan 6, 2020
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