Future<ServiceExtensionResponse> ServiceExtensionHandler(String method, Map<String, String> parameters)

A service protocol extension handler. Registered with registerExtension.

Must complete to a ServiceExtensionResponse.

method - the method name of the service protocol request. parameters - A map holding the parameters to the service protocol request.

NOTE: All parameter names and values are encoded as strings.

Source 

typedef Future<ServiceExtensionResponse>
    ServiceExtensionHandler(String method, Map<String, String> parameters);