Improve Cache-Control header handling

Author: codeguy

src/Cache.php

@@ -48,11 +48,13 @@ public function __invoke(RequestInterface $request, ResponseInterface $response,
         $response = $next($request, $response);
 
         // Cache-Control header
-        $response = $response->withHeader('Cache-Control', sprintf(
-            '%s, max-age=%s',
-            $this->type,
-            $this->maxAge
-        ));
+        if (!$response->hasHeader('Cache-Control')) {
+            $response = $response->withHeader('Cache-Control', sprintf(
+                '%s, max-age=%s',
+                $this->type,
+                $this->maxAge
+            ));
+        }
 
         // Last-Modified header and conditional GET check
         $lastModified = $response->getHeader('Last-Modified');

src/CacheProvider.php

@@ -17,6 +17,43 @@ public function register(Container $container)
         $container['cache'] = $this;
     }
 
+    /**
+     * Enable client-side HTTP caching
+     *
+     * @param  ResponseInterface $response PSR7 response object
+     * @param  string            $type     Cache-Control type: "private" or "public"
+     * @param  null|int|string   $maxAge   Maximum cache age (integer timestamp or datetime string)
+     *
+     * @return ResponseInterface           A new PSR7 response object with `Cache-Control` header
+     */
+    public function allowCache(ResponseInterface $response, $type = 'private', $maxAge = null)
+    {
+        if (!in_array($type, ['private', 'public'])) {
+            throw new \InvalidArgumentException('Invalid Cache-Control type. Must be "public" or "private".');
+        }
+        $headerValue = $type;
+        if ($maxAge) {
+            if (!is_integer($maxAge)) {
+                $maxAge = strtotime($maxAge);
+            }
+            $headerValue = $headerValue . ', max-age=' . $maxAge;
+        }
+
+        return $response->withHeader('Cache-Control', $headerValue);
+    }
+
+    /**
+     * Disable client-side HTTP caching
+     *
+     * @param  ResponseInterface $response PSR7 response object
+     *
+     * @return ResponseInterface           A new PSR7 response object with `Cache-Control` header
+     */
+    public function denyCache(ResponseInterface $response)
+    {
+        return $response->withHeader('Cache-Control', 'no-store,no-cache');
+    }
+
     /**
      * Add `Expires` header to PSR7 response object
      *

tests/CacheProviderTest.php

@@ -6,6 +6,22 @@
 
 class CacheProviderTest extends \PHPUnit_Framework_TestCase
 {
+    public function testAllowCache()
+    {
+        $cacheProvider = new CacheProvider();
+        $res = $cacheProvider->allowCache(new Response(), 'private', 43200);
+
+        $this->assertEquals('private, max-age=43200', $res->getHeader('Cache-Control'));
+    }
+
+    public function testDenyCache()
+    {
+        $cacheProvider = new CacheProvider();
+        $res = $cacheProvider->denyCache(new Response());
+
+        $this->assertEquals('no-store,no-cache', $res->getHeader('Cache-Control'));
+    }
+
     public function testWithExpires()
     {
         $now = time();

tests/CacheTest.php

@@ -35,6 +35,19 @@ public function testCacheControlHeader()
         $this->assertEquals('public, max-age=86400', $res->getHeader('Cache-Control'));
     }
 
+    public function testCacheControlHeaderDoesNotOverrideExistingHeader()
+    {
+        $cache = new Cache('public', 86400);
+        $req = $this->requestFactory();
+        $res = new Response();
+        $next = function (Request $req, Response $res) {
+            return $res->withHeader('Cache-Control', 'no-cache,no-store');
+        };
+        $res = $cache($req, $res, $next);
+
+        $this->assertEquals('no-cache,no-store', $res->getHeader('Cache-Control'));
+    }
+
     public function testLastModifiedWithCacheHit()
     {
         $now = time();