Unmarshall intercepted grpc

[vovean]

Hi everyone!
I have a mobile apllication which communicates with server using gRPC. I have all the api proto files and golang genrated code from this files.
Now I'm trying to test the application. First thing I want to be able to view requests and response bodies as json. What i've tried is saving response body to file (pressing key 'b' in flowview mode), then reading it with golang code and unmarshalling the body as if it was a common protobuf data. Also I tried using data from flow.requests.raw_content and flow.requests.data.content.
However, that doesn't work. An error occures "cannot parse invalid wire-format data". Also, I know that the data if perfectly fine, since both the client mobile app was able to read it and process and mitmproxy shows it as grpc view.

Some internet research makes me think that the response body is somehow extended beyound common protobuf message but I do not understand how do i gen from here to protobuf message.

Please, help