Handle immutable responses better.

Wait until the afterDispatch event to grab the controller response
property. Event listeners in the shutdown or afterDispatch events may
have replaced the controller's response.

src/Controller/Controller.php

@@ -622,9 +622,9 @@ class Controller implements EventListenerInterface, EventDispatcherInterface
 
         $this->View = $this->createView();
         $contents = $this->View->render($view, $layout);
-        $this->response = $this->View->response;
+        $this->response = $this->View->response->withStringBody($contents);
 
-        return $this->response->withStringBody($contents);
+        return $this->response;
     }
 
     /**

src/Http/ActionDispatcher.php

@@ -122,15 +122,16 @@ class ActionDispatcher
         }
 
         if (!$response && $controller->autoRender) {
-            $response = $controller->render();
-        } elseif (!$response) {
-            $response = $controller->response;
+            $controller->render();
         }
 
         $result = $controller->shutdownProcess();
         if ($result instanceof Response) {
             return $result;
         }
+        if (!$response) {
+            $response = $controller->response;
+        }
 
         return $response;
     }

tests/TestCase/Routing/DispatcherFactoryTest.php

@@ -121,12 +121,16 @@ class DispatcherFactoryTest extends TestCase
         $response = $this->getMockBuilder('Cake\Http\Response')
             ->setMethods(['send'])
             ->getMock();
+
+        $response->expects($this->once())
+            ->method('send')
+            ->will($this->returnSelf());
+
         DispatcherFactory::add('ControllerFactory');
         DispatcherFactory::add('Append');
 
         $dispatcher = DispatcherFactory::create();
         $result = $dispatcher->dispatch($url, $response);
-        $this->assertNull($result);
-        $this->assertEquals('posts index appended content', $response->body());
+        $this->assertEquals('posts index appended content', $result->body());
     }
 }

tests/TestCase/Routing/DispatcherTest.php

@@ -160,7 +160,9 @@ class DispatcherTest extends TestCase
                 'pass' => ['extract'],
             ]
         ]);
-        $response = $this->getMockBuilder('Cake\Http\Response')->getMock();
+        $response = $this->getMockBuilder('Cake\Http\Response')
+            ->setMethods(['send'])
+            ->getMock();
         $response->expects($this->once())
             ->method('send');
 

tests/test_app/TestApp/Template/Posts/header.ctp

@@ -0,0 +1,4 @@
+<?php
+$this->response = $this->response->withHeader('X-view-template', 'yes');
+?>
+header template