VAPID header caching (#208)

* Implemented VAPID header caching

As @ozgurhangisi suggested in #195

* Implemented VAPID header caching

As @ozgurhangisi suggested in #195

* Docs updated

Author: javiermarinros

README.md

@@ -156,6 +156,14 @@ serviceWorkerRegistration.pushManager.subscribe({
 })
 ```
 
+#### Reusing VAPID headers
+
+VAPID headers make use of a JSON Web Token (JWT) to verify your identity. That token payload includes the protocol and hostname of the endpoint included in the subscription and an expiration timestamp (usually between 12-24h), and it's signed using your public and private key. Given that, two notifications sent to the same push service will use the same token, so you can reuse them for the same flush session to boost performance using:
+
+```php
+$webPush->setReuseVAPIDHeaders(true);
+```
+
 ### Notifications and default options
 Each notification can have a specific Time To Live, urgency, and topic.
 You can change the default options with `setDefaultOptions()` or in the constructor:

src/WebPush.php

@@ -49,6 +49,16 @@ class WebPush
      */
     private $automaticPadding = Encryption::MAX_COMPATIBILITY_PAYLOAD_LENGTH;
 
+    /**
+     * @var bool Reuse VAPID headers in the same flush session to improve performance
+     */
+    private $reuseVAPIDHeaders = false;
+
+    /**
+     * @var array Dictionary for VAPID headers cache
+     */
+    private $vapidHeaders = [];
+
     /**
      * WebPush constructor.
      *
@@ -173,6 +183,10 @@ public function flush(?int $batchSize = null) : iterable
 		        yield $result;
 	        }
         }
+
+        if ($this->reuseVAPIDHeaders) {
+            $this->vapidHeaders = [];
+        }
     }
 
     /**
@@ -256,11 +270,26 @@ private function prepare(array $notifications): array
                     throw new \ErrorException('Audience "'.$audience.'"" could not be generated.');
                 }
 
-                if (!$contentEncoding) {
-                    throw new \ErrorException('Subscription should have a content encoding');
+                $vapidHeaders = null;
+                $cache_key = null;
+                if ($this->reuseVAPIDHeaders) {
+                    $cache_key = implode('#', [$audience, $contentEncoding, crc32(serialize($vapid))]);
+                    if (array_key_exists($cache_key, $this->vapidHeaders)) {
+                        $vapidHeaders = $this->vapidHeaders[$cache_key];
+                    }
                 }
 
-                $vapidHeaders = VAPID::getVapidHeaders($audience, $vapid['subject'], $vapid['publicKey'], $vapid['privateKey'], $contentEncoding);
+                if (!$vapidHeaders) {
+                    if (!$contentEncoding) {
+                        throw new \ErrorException('Subscription should have a content encoding');
+                    }
+
+                    $vapidHeaders = VAPID::getVapidHeaders($audience, $vapid['subject'], $vapid['publicKey'], $vapid['privateKey'], $contentEncoding);
+                }
+
+                if ($this->reuseVAPIDHeaders) {
+                    $this->vapidHeaders[$cache_key] = $vapidHeaders;
+                }
 
                 $headers['Authorization'] = $vapidHeaders['Authorization'];
 
@@ -321,6 +350,22 @@ public function setAutomaticPadding($automaticPadding): WebPush
         return $this;
     }
 
+    /**
+     * @return bool
+     */
+    public function getReuseVAPIDHeaders()
+    {
+        return $this->reuseVAPIDHeaders;
+    }
+
+    /**
+     * Reuse VAPID headers in the same flush session to improve performance
+     */
+    public function setReuseVAPIDHeaders($enabled)
+    {
+        $this->reuseVAPIDHeaders = $enabled;
+    }
+
     /**
      * @return array
      */