How to send error trailers for grpc server streams

[cwanda]

I want to send some trailers for grpc server streams when an error occurs mid-stream after status 200 and some data has been proxied to the client.

I do the following in the grpc server function

if err != nil {
    grpc.SetTrailer(out.Context(), metadata.Pairs("grpc-status", "13"))
    grpc.SetTrailer(out.Context(), metadata.Pairs("stream-error", "true"))
    return err
}

I do not see trailers returned in the http response ( The request has header "TE: trailers" set). I see that FowardResponseMessage () adds trailers for unary grpc, but I do not see that ForwardResponseStream() for streaming rpc adds trailers.

How do we configure grpc-gateway so grpc servers streams error trailers are sent? I considered using: WithStreamErrorHandler to customize a handler but the handler which gets called in handleForwardResponseStreamError() does not have access to the response writer and handleForwardReponseStreamError() doesn't add trailers

[johanbrandhorst]

I believe it is impossible to set headers after the body has first been written to, which makes it impossible for us to set trailers on streaming responses. You will have to use an envelope message in your response stream that you can return with an error type, e.g.

rpc MyStream(StreamRequest) returns (stream StreamResponse);

message StreamResponse {
  MyMessage message = 1
  Error error = 2
}

Does that help?