Allow bypassing content negotiation during API responses.

system/API/ResponseTrait.php

@@ -56,7 +56,6 @@
  */
 trait ResponseTrait
 {
-
 	/**
 	 * Allows child classes to override the
 	 * status code that is used in their API.
@@ -95,8 +94,11 @@ trait ResponseTrait
 	];
 
 	/**
+	 * How to format the response data.
+	 * Either 'json' or 'xml'. If blank will be
+	 * determine through content negotiation.
 	 *
-	 * @var string the representation format to return resource data in (json/xml)
+	 * @var string
 	 */
 	protected $format = 'json';
 
@@ -384,17 +386,14 @@ protected function format($data = null)
 			return $data;
 		}
 
-		// Determine correct response type through content negotiation
 		$config = new Format();
+		$format = "application/$this->format";
 
-		if (! in_array($this->format, ['json', 'xml']))
+		// Determine correct response type through content negotiation if not explicitly declared
+		if (empty($this->format) || ! in_array($this->format, ['json', 'xml']))
 		{
 			$format = $this->request->negotiate('media', $config->supportedResponseFormats, false);
 		}
-		else
-		{
-			$format = "application/$this->format";
-		}
 
 		$this->response->setContentType($format);
 
@@ -415,4 +414,17 @@ protected function format($data = null)
 		return $this->formatter->format($data);
 	}
 
+	/**
+	 * Sets the format the response should be in.
+	 *
+	 * @param string $format
+	 *
+	 * @return $this
+	 */
+	public function setResponseFormat(string $format = null)
+	{
+		$this->format = strtolower($format);
+
+		return $this;
+	}
 }

tests/system/API/ResponseTraitTest.php

@@ -502,4 +502,19 @@ public function __construct(&$request, &$response)
 		$this->assertStringStartsWith(config('Format')->supportedResponseFormats[0], $response->getHeaderLine('Content-Type'));
 	}
 
+	public function testResponseFormat()
+	{
+		$data = ['foo' => 'something'];
+
+		$controller = $this->makeController();
+		$controller->setResponseFormat('json');
+		$controller->respond($data, 201);
+
+		$this->assertStringStartsWith('application/json', $this->response->getHeaderLine('Content-Type'));
+
+		$controller->setResponseFormat('xml');
+		$controller->respond($data, 201);
+
+		$this->assertStringStartsWith('application/xml', $this->response->getHeaderLine('Content-Type'));
+	}
 }

user_guide_src/source/outgoing/api_responses.rst

@@ -73,7 +73,8 @@ When you pass your data in any of these methods, they will determine the data ty
 the following criteria:
 
 * If $data is a string, it will be treated as HTML to send back to the client.
-* If $data is an array, it will try to negotiate the content type with what the client asked for, defaulting to JSON
+* If $data is an array, it will be formatted according to the controller's ``$this->format`` value. If that is empty
+    it will try to negotiate the content type with what the client asked for, defaulting to JSON
     if nothing else has been specified within Config\API.php, the ``$supportedResponseFormats`` property.
 
 To define the formatter that is used, edit **Config/Format.php**. The ``$supportedResponseFormats`` contains a list of
@@ -104,6 +105,17 @@ JSON data will be sent back to the client.
 
 Class Reference
 ***************
+.. php:method:: setResponseFormat($format)
+
+    :param string $format The type of response to return, either ``json`` or ``xml``
+
+    This defines the format to be used when formatting arrays in responses. If you provide a ``null`` value for
+    ``$format``, it will be automatically determined through content negotiation.
+
+::
+
+    return $this->setResponseFormat('json')->respond(['error' => false]);
+
 
 .. php:method:: respond($data[, $statusCode=200[, $message='']])
 
@@ -186,13 +198,13 @@ Class Reference
     :param string $message: A custom "reason" message to return.
     :returns: The value of the Response object's send() method.
 
-    Sets the appropriate status code to use when a command was successfully executed by the server but there is no 
+    Sets the appropriate status code to use when a command was successfully executed by the server but there is no
     meaningful reply to send back to the client, typically 204.
 
     ::
 
 	    sleep(1);
-	    return $this->respondNoContent();        
+	    return $this->respondNoContent();
 
 .. php:method:: failUnauthorized(string $description = 'Unauthorized'[, string $code=null[, string $message = '']])