[5.x] Add cache-control header to cached content

config/static_caching.php

@@ -45,6 +45,23 @@
 
     ],
 
+    /*
+    |--------------------------------------------------------------------------
+    | Cache Control
+    |--------------------------------------------------------------------------
+    |
+    | Here you may choose what information gets sent in the cache-control
+    | header when cache gets hit in PHP.
+    | Ages are in seconds.
+    |
+    | Note that when using the "full" strategy you must also set this in
+    | Your webserver, e.g.: max-age=60, public, s-maxage=60, stale-while-revalidate=60
+    */
+
+    'max_age' => 120, // The amount of time the browser may cache this response for.
+    'shared_max_age' => null, // The amount of time a Proxy/CDN may cache this response for. null will use max_age.
+    'stale_while_revalidate' => 120, // How long may a stale cache be used while fetching fresh content in the background.
+
     /*
     |--------------------------------------------------------------------------
     | Exclusions

src/StaticCaching/Middleware/Cache.php

@@ -20,6 +20,7 @@
 use Statamic\StaticCaching\NoCache\Session;
 use Statamic\StaticCaching\Replacer;
 use Statamic\StaticCaching\ResponseStatus;
+use Statamic\StaticCaching\UrlExcluder;
 
 class Cache
 {
@@ -83,6 +84,10 @@ private function handleRequest($request, Closure $next)
             $this->makeReplacementsAndCacheResponse($request, $response);
 
             $this->nocache->write();
+
+            if(!app(UrlExcluder::class)->isExcluded($request->normalizedFullUrl())) {
+                $response->makeCacheControlCacheable();
+            }
         } elseif (! $response->isRedirect()) {
             $this->makeReplacements($response);
         }
@@ -125,6 +130,7 @@ private function attemptToGetCachedResponse($request)
             $this->makeReplacements($response);
 
             $response->setStaticCacheResponseStatus(ResponseStatus::HIT);
+            $response->makeCacheControlCacheable();
 
             return $response;
         }

src/StaticCaching/ServiceProvider.php

@@ -91,6 +91,14 @@ public function boot()
             return app(Cacher::class)->getUrl($this);
         });
 
+        Response::macro('makeCacheControlCacheable', function () {
+            $this
+                ->setMaxAge(config('statamic.static_caching.max_age', 60))
+                ->setSharedMaxAge(config('statamic.static_caching.shared_max_age', config('statamic.static_caching.max_age', 60)))
+                ->setStaleWhileRevalidate(config('statamic.static_caching.stale_while_revalidate', 60))
+                ->setEtag(md5($this->getContent() ?: ''));
+        });
+
         Request::macro('fakeStaticCacheStatus', function (int $status) {
             $url = '/__shared-errors/'.$status;
             $this->pathInfo = $url;