How to get message value in gRPC stream interceptor

Question

I have implement a gRPC stream interceptor in Server like this:

// Service define:
// rpc searchProducts(google.protobuf.StringValue) returns (stream Product);

func (w *wrappedStream) RecvMsg(m interface{}) error {
    log.Printf("%T, %v", m, m)
    return w.ServerStream.RecvMsg(m)
}

// Log print:
// *wrapperspb.StringValue, 

It can print the message type using %T correctly, but the message value printing by %v is just a blank.

I'm sure that Server received the right message, because it replied Client the right thing.

The interceptor wrapper RecvMsg is not working in Client too.

Answer 1

w.ServerStream.RecvMsg(m) will unmarshall data into m, just move print after RecvMsg() call.

func (w *wrappedStream) RecvMsg(m interface{}) error {
    err := w.ServerStream.RecvMsg(m)
    log.Printf("%T, %v", m, m)
    return err
}