From aa44b992ebbd6fd0239b352afbd69fbafee1359a Mon Sep 17 00:00:00 2001
From: "M. Vugteveen" <it-can@users.noreply.github.com>
Date: Mon, 16 May 2022 14:11:08 +0200
Subject: [PATCH] Add option to output cache age header (#385)

* Add option to output cache age header

* fix config

* extract method

* update readme
---
 README.md                         | 21 +++++++++++++++++----
 config/responsecache.php          | 14 ++++++++++++++
 src/Middlewares/CacheResponse.php | 14 ++++++++++++++
 tests/IntegrationTest.php         | 18 ++++++++++++++++++
 4 files changed, 63 insertions(+), 4 deletions(-)

diff --git a/README.md b/README.md
index 267ffc0..3f6dd12 100644
--- a/README.md
+++ b/README.md
@@ -79,6 +79,20 @@ return [
      */
     'cache_time_header_name' => env('RESPONSE_CACHE_HEADER_NAME', 'laravel-responsecache'),
 
+    /*
+     * This setting determines if a http header named with the cache age
+     * should be added to a cached response. This can be handy when
+     * debugging.
+     * ONLY works when "add_cache_time_header" is also active!
+     */
+    'add_cache_age_header' => env('RESPONSE_CACHE_AGE_HEADER', false),
+
+    /*
+     * This setting determines the name of the http header that contains
+     * the age of cache
+     */
+    'cache_age_header_name' => env('RESPONSE_CACHE_AGE_HEADER_NAME', 'laravel-responsecache-age'),
+
     /*
      * Here you may define the cache store that should be used to store
      * requests. This can be the name of any store that is
@@ -105,15 +119,14 @@ return [
 
     /*
      * This class is responsible for generating a hash for a request. This hash
-     * is used as a key to look up a cached response.
+     * is used to look up an cached response.
      */
     'hasher' => \Spatie\ResponseCache\Hasher\DefaultHasher::class,
 
     /*
-     * This class serializes cache data and expands it.
-     * Serialization can save the data to be returned in an appropriate form.
+     * This class is responsible for serializing responses.
      */
-    'serializer' => \Spatie\ResponseCache\Serializer\DefaultSerializer::class,
+    'serializer' => \Spatie\ResponseCache\Serializers\DefaultSerializer::class,
 ];
 ```
 
diff --git a/config/responsecache.php b/config/responsecache.php
index d90896e..36df8e2 100644
--- a/config/responsecache.php
+++ b/config/responsecache.php
@@ -34,6 +34,20 @@
      */
     'cache_time_header_name' => env('RESPONSE_CACHE_HEADER_NAME', 'laravel-responsecache'),
 
+    /*
+     * This setting determines if a http header named with the cache age
+     * should be added to a cached response. This can be handy when
+     * debugging.
+     * ONLY works when "add_cache_time_header" is also active!
+     */
+    'add_cache_age_header' => env('RESPONSE_CACHE_AGE_HEADER', false),
+
+    /*
+     * This setting determines the name of the http header that contains
+     * the age of cache
+     */
+    'cache_age_header_name' => env('RESPONSE_CACHE_AGE_HEADER_NAME', 'laravel-responsecache-age'),
+
     /*
      * Here you may define the cache store that should be used to store
      * requests. This can be the name of any store that is
diff --git a/src/Middlewares/CacheResponse.php b/src/Middlewares/CacheResponse.php
index 1813370..3ad8b57 100644
--- a/src/Middlewares/CacheResponse.php
+++ b/src/Middlewares/CacheResponse.php
@@ -2,6 +2,7 @@
 
 namespace Spatie\ResponseCache\Middlewares;
 
+use Carbon\Carbon;
 use Closure;
 use Illuminate\Http\Request;
 use Illuminate\Support\Collection;
@@ -31,6 +32,8 @@ public function handle(Request $request, Closure $next, ...$args): Response
 
                 $response = $this->responseCache->getCachedResponseFor($request, $tags);
 
+                $response = $this->addCacheAgeHeader($response);
+
                 $this->getReplacers()->each(function (Replacer $replacer) use ($response) {
                     $replacer->replaceInCachedResponse($response);
                 });
@@ -90,4 +93,15 @@ protected function getTags(array $args): array
 
         return array_filter($tags);
     }
+
+    public function addCacheAgeHeader(Response $response): Response
+    {
+        if (config('responsecache.add_cache_age_header') and $time = $response->headers->get(config('responsecache.cache_time_header_name'))) {
+            $ageInSeconds = Carbon::parse($time)->diffInSeconds(Carbon::now());
+
+            $response->headers->set(config('responsecache.cache_age_header_name'), $ageInSeconds);
+        }
+
+        return $response;
+    }
 }
diff --git a/tests/IntegrationTest.php b/tests/IntegrationTest.php
index a0f6280..4c27342 100644
--- a/tests/IntegrationTest.php
+++ b/tests/IntegrationTest.php
@@ -257,4 +257,22 @@ public function it_can_add_a_cache_time_header()
 
         $this->assertSameResponse($firstResponse, $secondResponse);
     }
+
+    /** @test */
+    public function it_can_add_a_cache_age_header()
+    {
+        $this->app['config']->set('responsecache.add_cache_time_header', true);
+        $this->app['config']->set('responsecache.add_cache_age_header', true);
+        $this->app['config']->set('responsecache.cache_age_header_name', 'X-Cached-Age');
+
+        $firstResponse = $this->get('/random');
+        $secondResponse = $this->get('/random');
+
+        $this->assertFalse($firstResponse->headers->has('X-Cached-Age'));
+        $this->assertTrue($secondResponse->headers->has('X-Cached-Age'));
+
+        $this->assertIsNumeric($secondResponse->headers->get('X-Cached-Age'));
+
+        $this->assertSameResponse($firstResponse, $secondResponse);
+    }
 }