Additional fix to #4728.

docs/guide/caching-http.md

@@ -107,12 +107,10 @@ Expensive ETag generation may defeat the purpose of using `HttpCache` and introd
 since they need to be re-evaluated on every request. Try to find a simple expression that invalidates
 the cache if the page content has been modified.
 
-
-> Note: In compliance to [RFC 7232, section 2.4](http://tools.ietf.org/html/rfc7232#section-2.4),
+> Note: In compliance to [RFC 7232](http://tools.ietf.org/html/rfc7232#section-2.4),
   `HttpCache` will send out both `ETag` and `Last-Modified` headers if they are both configured.
-  However, in order to satisfy [section 3.3](http://tools.ietf.org/html/rfc7232#section-3.3) the
-  `If-None-Match` client header will always take precedence over `If-Modified-Since` during validation; meaning
-  latter one is going to be ignored if a `If-None-Match` header is present in the request.
+  And if the client sends both of the `If-None-Match` header and the `If-Modified-Since` header, only the former
+  will be respected.
 
 
 ## `Cache-Control` Header <a name="cache-control"></a>

framework/filters/HttpCache.php

@@ -130,7 +130,6 @@ class HttpCache extends ActionFilter
 
         if ($this->validateCache($lastModified, $etag)) {
             $response->setStatusCode(304);
-
             return false;
         }
 
@@ -150,10 +149,14 @@ class HttpCache extends ActionFilter
      */
     protected function validateCache($lastModified, $etag)
     {
-        if($etag !== null && in_array($etag, Yii::$app->request->getEtags(), true)) {
-            return true;
+        if (isset($_SERVER['HTTP_IF_NONE_MATCH'])) {
+            // HTTP_IF_NONE_MATCH takes precedence over HTTP_IF_MODIFIED_SINCE
+            // http://tools.ietf.org/html/rfc7232#section-3.3
+            return $etag === null || in_array($etag, Yii::$app->request->getEtags(), true);
+        } elseif (isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])) {
+            return $lastModified === null || @strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']) >= $lastModified;
         } else {
-            return $lastModified !== null && isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) && @strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']) >= $lastModified;
+            return $etag === null && $lastModified === null;
         }
     }
 

tests/unit/framework/filters/HttpCacheTest.php

@@ -37,7 +37,10 @@ class HttpCacheTest extends \yiiunit\TestCase
         $method = new \ReflectionMethod($httpCache, 'validateCache');
         $method->setAccessible(true);
 
-        $this->assertFalse($method->invoke($httpCache, null, null));
+        unset($_SERVER['HTTP_IF_MODIFIED_SINCE'], $_SERVER['HTTP_IF_NONE_MATCH']);
+        $this->assertTrue($method->invoke($httpCache, null, null));
+        $this->assertFalse($method->invoke($httpCache, 0, null));
+        $this->assertFalse($method->invoke($httpCache, 0, '"foo"'));
 
         $_SERVER['HTTP_IF_MODIFIED_SINCE'] = 'Thu, 01 Jan 1970 00:00:00 GMT';
         $this->assertTrue($method->invoke($httpCache, 0, null));
@@ -45,8 +48,10 @@ class HttpCacheTest extends \yiiunit\TestCase
 
         $_SERVER['HTTP_IF_NONE_MATCH'] = '"foo"';
         $this->assertTrue($method->invoke($httpCache, 0, '"foo"'));
+        $this->assertFalse($method->invoke($httpCache, 0, '"foos"'));
         $this->assertTrue($method->invoke($httpCache, 1, '"foo"'));
-        $this->assertFalse($method->invoke($httpCache, null, null));
+        $this->assertFalse($method->invoke($httpCache, 1, '"foos"'));
+        $this->assertTrue($method->invoke($httpCache, null, null));
     }
 
     /**