abstract fun closeHandler(handler: Handler<Void>): HttpServerResponse
Set a close handler for the response, this is called when the underlying connection is closed and the response was still using the connection.
For HTTP/1.x it is called when the connection is closed before end() is called, therefore it is not guaranteed to be called.
For HTTP/2 it is called when the related stream is closed, and therefore it will be always be called.
Return
a reference to this, so the API can be used fluently