Why does gateway use ServerMetadata?

[tamalsaha]

gateway generated code uses something called ServerMetadata . The trailers from this metadata are returned from gateway response (not the original trailer from grpc response). This seems like a way for grpc server implementation to return some extra metadata. This seems unnecessary.

Below is an example of generated code that shows how ServerMetadata is used.

func request_Artifacts_Search_0(ctx context.Context, marshaler runtime.Marshaler, client ArtifactsClient, req *http.Request, pathParams map[string]string) (proto.Message, runtime.ServerMetadata, error) {
	var protoReq ArtifactSearchRequest
	var metadata runtime.ServerMetadata

	if err := runtime.PopulateQueryParameters(&protoReq, req.URL.Query(), filter_Artifacts_Search_0); err != nil {
		return nil, metadata, status.Errorf(codes.InvalidArgument, "%v", err)
	}

	msg, err := client.Search(ctx, &protoReq, grpc.Header(&metadata.HeaderMD), grpc.Trailer(&metadata.TrailerMD))
	return msg, metadata, err

}

[tamalsaha]

Actually I see how this is used.