Introduced "Cacheable Response" feature

Author: Geolim4

README.md

@@ -62,6 +62,23 @@ Or in your template:
     {% endcache %}
 </div>
 ```
+#### :bulb: Introducing Cacheable Responses (V3 only)
+As of the V3 there's a new, easier and cleaner way to setup HTTP cache to decrease your server bandwidth along your CPU load: Cacheable Responses.
+And it's pretty easy to implement:
+```php
+    /**
+     * @Route("/cached", name="cached")
+     */
+    public function cachedAction(Phpfastcache $phpfastcache, Request $request): Response
+    {
+        return (new CacheableResponse($phpfastcache->get('filecache'), $request))->getResponse('cache_key', 3600, function () {
+            return new Response('Random bytes: ' . \random_bytes(255));
+        });
+    }
+``` 
+`CacheableResponse` is provided by `\Phpfastcache\Bundle\Response\CacheableResponse`.
+This class will handle responses headers (cache-control, etag, etc...) and http status (304 Not modified).
+
 #### :boom: phpFastCache Bundle support
 Found an issue or had an idea ? Come here [here](https://github.com/PHPSocialNetwork/phpfastcache-bundle/issues) and let us know !
 

src/Response/CacheableResponse.php

@@ -0,0 +1,81 @@
+<?php
+/**
+ * Created by PhpStorm.
+ * User: Geolim4
+ * Date: 12/05/2018
+ * Time: 02:18
+ */
+
+namespace Phpfastcache\Bundle\Response;
+
+use Phpfastcache\Core\Pool\ExtendedCacheItemPoolInterface;
+use Phpfastcache\Exceptions\PhpfastcacheLogicException;
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpFoundation\Response;
+
+class CacheableResponse
+{
+    const RESPONSE_PREFIX = '__CACH_RESP__';
+
+    /**
+     * @var ExtendedCacheItemPoolInterface
+     */
+    protected $request;
+
+    /**
+     * @var ExtendedCacheItemPoolInterface
+     */
+    protected $cacheInstance;
+
+    /**
+     * CachePromise constructor.
+     * @param ExtendedCacheItemPoolInterface $cacheInstance
+     */
+    public function __construct(ExtendedCacheItemPoolInterface $cacheInstance, Request $request)
+    {
+        $this->cacheInstance = $cacheInstance;
+        $this->request = $request;
+    }
+
+    /**
+     * @param string $cacheKey
+     * @param int|\DateInterval $expiresAfter
+     * @param callable $callback
+     * @return mixed
+     * @throws PhpfastcacheLogicException
+     */
+    public function getResponse(string $cacheKey, $expiresAfter = null, callable $callback): Response
+    {
+        $cacheKey = self::RESPONSE_PREFIX . $cacheKey;
+        $cacheItem = $this->cacheInstance->getItem($cacheKey);
+        $cacheResponse = $cacheItem->get();
+
+        /**
+         * No isHit() test here as we directly
+         * test if the cached response object
+         * is effectively a "Response" object
+         */
+        if (!($cacheResponse instanceof Response)) {
+            $response = $callback();
+            if($response instanceof Response){
+                $cacheItem->expiresAfter($expiresAfter);
+
+                $response->setExpires($cacheItem->getExpirationDate());
+                $response->setSharedMaxAge($cacheItem->getTtl());
+                $response->headers->addCacheControlDirective('must-revalidate', true);
+                $response->setEtag(md5($response->getContent()));
+                $response->setPublic();
+
+                $cacheItem->set($response);
+                $this->cacheInstance->save($cacheItem);
+                $cacheResponse = $response;
+            }else{
+               throw new PhpfastcacheLogicException('Your callback response MUST return a valid Symfony HTTP Foundation Response object');
+            }
+        }else{
+            $cacheResponse->isNotModified($this->request);
+        }
+
+        return $cacheResponse;
+    }
+}