Responses
The role of a response is to send it's contents to the client.
The contents of a response can either be set through the constructor or by setting the properties on the response object.
All responses have a statusCode and headers properties.
The default statusCode for all responses is 200 ( OK ),
while each response has it's own default headers.
Built-in Response Classes
StringResponse will send a string as the response body.
RenderResponse will render the element before sending it.
JsonResponse will use JSON.stringify to serialize the response before sending it.
EmptyResponse will only send the provided headers without a body.
RedirectResponse will send a 303 response with the location header and no body.
The client will access this location using a GET request.
Usually used by form controllers which handle data, but don't display a page.
EventStreamResponse is a special case where we can write the messages (events) into the response body.
If a controller sends messages before returning this response the messages will be queued.