Add dns prefetch functionality

DorsetDigital · Jun 12, 2018 · 0f341ae · 0f341ae
1 parent 303a1f5
commit 0f341ae
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diff --git a/README.md b/README.md
@@ -34,6 +34,7 @@ DorsetDigital\CDNRewrite\CDNMiddleware:
   add_debug_headers: true
   enable_in_dev: true
   subdirectory: ''
+  add_prefetch: true
 ```
 
 The options are hopefully fairly self explanatory:
@@ -45,6 +46,7 @@ The options are hopefully fairly self explanatory:
 * `add_debug_headers` - if enabled, adds extra HTML headers to show the various operations being applied (default false)
 * `enable_in_dev` - enable the CDN in dev mode (default false)
 * `subdirectory` - set this if your site is in a subdirectory (eg. for http://www.example.com/silverstripe - set this to 'silverstripe')
+* `add_prefetch` - set this to true if you want the module to automatically add a `<link rel="dns-prefetch">` tag to your html head to improve performance
 
 # Notes
 

diff --git a/src/CDNMiddleware.php b/src/CDNMiddleware.php
@@ -7,6 +7,7 @@
 use SilverStripe\Core\Injector\Injectable;
 use SilverStripe\Control\Director;
 use SilverStripe\Admin\AdminRootController;
+use SilverStripe\View\HTML;
 
 class CDNMiddleware implements HTTPMiddleware
 {
@@ -70,6 +71,15 @@ class CDNMiddleware implements HTTPMiddleware
   */
  private static $subdirectory = '';
 
+ /**
+  * @config
+  * 
+  * Add dns-prefetch links to the html head
+  * @var boolean
+  */
+ private static $add_prefetch = false;
+
+
  /**
   * Process the request
   * @param HTTPRequest $request
@@ -135,6 +145,14 @@ private function updateBody(&$body, &$response)
    if ($this->config()->get('add_debug_headers') == true) {
     $response->addHeader('X-CDN-Assets', 'Enabled');
    }
+
+   if ($this->config()->get('add_prefetch') === true) {
+     $prefetchTag = $this->getPrefetchTag();
+     $body = str_replace('<head>', "<head>".$prefetchTag, $body);
+     if ($this->config()->get('add_debug_headers') == true) {
+       $response->addHeader('X-CDN-Prefetch', 'Enabled');
+     }       
+   }
   }
 
   if ($this->config()->get('rewrite_resources') === true) {
@@ -169,6 +187,17 @@ private function getSubdirectory()
   }
   return $subDir;
  }
+
+ private function getPrefetchTag() 
+ {
+   $atts = [
+     'rel' => 'dns-prefetch',
+     'href' => $this->config()->get('cdn_domain')
+   ];
+   $pfTag = "\n" . HTML::createTag('link', $atts);
+
+   return $pfTag;
+ }
 
  /**
   * Determine whether the website is being viewed from an admin protected area or not