transport.go

// transport.go

r.Methods("GET").Handle("/users/{id}", httptransport.NewServer(
    endpoints.GetUserEndpoint,
    decodeGetUserRequest,
    encodeResponse,
    options...,
))

type errorer interface {
    GetError() *example.Error
}

func encodeResponse(ctx context.Context, w http.ResponseWriter, response interface{}) error {
    if e, ok := response.(errorer); ok {
        if err := e.GetError(); err != nil {
            w.WriteHeader(int(err.Code))
        }
    }
    w.Header().Set("Content-Type", "application/json; charset=utf-8")
    return json.NewEncoder(w).Encode(response)
}