Controllers should never echo data! Echoing data can lead to all kinds of problems, from the data not being recognized in the test environment, to headers not being able to be sent, and even data being cut off.
Doing it that way was already wrong in CakePHP 2.x, even though it might have worked in some, maybe even most situations. With the introduction of the new HTTP stack, CakePHP now explicitly checks for sent headers before echoing the response, and will trigger an error accordingly.
The proper way to send custom output was to configure and return the response object, or to use serialized views, and it’s still the same in 3.x.
Quote from the docs:
Controller actions generally use
Controller::set()to create a context that View uses to render the view layer. Because of the conventions that CakePHP uses, you don’t need to create and render the view manually. Instead, once a controller action has completed, CakePHP will handle rendering and delivering the View.If for some reason you’d like to skip the default behavior, you can return a
Cake\Network\Responseobject from the action with the fully created response.
* As of 3.4 that would be \Cake\Http\Response
Cookbook > Controllers > Controller Actions
Configure the response
Using the PSR-7 compliant interface
$content = json_encode(['method' => __METHOD__, 'class' => get_called_class()]);
$this->response = $this->response->withStringBody($content);
$this->response = $this->response->withType('json');
// ...
return $this->response;
The PSR-7 compliant interface uses immutable methods, hence the utilization of the return value of withStringBody() and withType(). In CakePHP < 3.4.3, withStringBody() is not available, and you can instead directly write to the body stream, which will not change the state of the response object:
$this->response->getBody()->write($content);
Using the deprecated interface
$content = json_encode(['method' => __METHOD__, 'class' => get_called_class()]);
$this->response->body($content);
$this->response->type('json');
// ...
return $this->response;
Use a serialized view
$content = ['method' => __METHOD__, 'class' => get_called_class()];
$this->set('content', $content);
$this->set('_serialize', 'content');
This requires to also use the request handler component, and to enable extensing parsing and using correponsing URLs with .json appended, or to send a proper request with a application/json accept header.