# HTTP Caching Slim 3 uses the optional standalone [slimphp/Slim-HttpCache](https://github.com/slimphp/Slim-HttpCache) PHP component for HTTP caching. You can use this component to create and return responses that contain `Cache`,`Expires`, `ETag`, and `Last-Modified` headers that control when and how long application output is retained by client-side caches. ## Installation Execute this bash command from your project’s root directory: ~~~ composer require slim/http-cache ~~~ ## Usage The `slimphp/Slim-HttpCache` component contains a service provider and an application middleware. You should add both to your application like this: ~~~ // Register service provider with the container $container = new \Slim\Container; $container['cache'] = function () { new \Slim\HttpCache\CacheProvider(); }; // Add middleware to the application $app = new \Slim\App($container); $app->add(new \Slim\HttpCache\Cache('public', 86400)); // Create your application routes... // Run application $app->run(); ~~~ ## ETag Use the service provider’s `withEtag()` method to create a Response object with the desired`ETag` header. This method accepts a PSR7 response object, and it returns a cloned PSR7 response with the new HTTP header. ~~~ $app->get('/foo', function ($req, $res, $args) { $resWithEtag = $this->cache->withEtag($res, 'abc'); return $resWithEtag; }); ~~~ ## Expires Use the service provider’s `withExpires()` method to create a Response object with the desired `Expires` header. This method accepts a PSR7 response object, and it returns a cloned PSR7 response with the new HTTP header. ~~~ $app->get('/bar',function ($req, $res, $args) { $resWithExpires = $this->cache->withExpires($res, time() + 3600); return $resWithExpires; }); ~~~ ## Last-Modified Use the service provider’s `withLastModified()` method to create a Response object with the desired `Last-Modified` header. This method accepts a PSR7 response object, and it returns a cloned PSR7 response with the new HTTP header. ~~~ //Example route with LastModified $app->get('/foobar',function ($req, $res, $args) { $resWithLastMod = $this->cache->withLastModified($res, time() - 3600); return $resWithLastMod; }); ~~~