Set correct Content-Type header for ajax responses in the Magento_UI module.

Author: hostep

app/code/Magento/Ui/Controller/Adminhtml/Index/Render.php

@@ -9,6 +9,7 @@
 use Magento\Ui\Controller\Adminhtml\AbstractAction;
 use Magento\Framework\View\Element\UiComponentFactory;
 use Magento\Framework\View\Element\UiComponentInterface;
+use Magento\Framework\View\Element\UiComponent\ContentType;
 
 /**
  * Class Render
@@ -30,6 +31,7 @@ public function execute()
         $component = $this->factory->create($this->_request->getParam('namespace'));
         $this->prepareComponent($component);
         $this->_response->appendBody((string) $component->render());
+        $this->setResponseContentTypeHeader($component);
     }
 
     /**
@@ -45,4 +47,26 @@ protected function prepareComponent(UiComponentInterface $component)
         }
         $component->prepare();
     }
+
+    /**
+     * Set the response 'Content-Type' header based on the component's render engine
+     *
+     * @param UiComponentInterface $component
+     * @return void
+     */
+    private function setResponseContentTypeHeader(UiComponentInterface $component)
+    {
+        $contentType = 'text/html';
+
+        if ($component->getContext()) {
+            $renderEngine = $component->getContext()->getRenderEngine();
+            if ($renderEngine instanceof ContentType\Json) {
+                $contentType = 'application/json';
+            } elseif ($renderEngine instanceof ContentType\Xml) {
+                $contentType = 'application/xml';
+            }
+        }
+
+        $this->_response->setHeader('Content-Type', $contentType, true);
+    }
 }