How to do a 302 redirect in grpc-gateway

Question

I use grpc-gateway to host an HTTP server out of my proto definitions. It works great overall.

However, for one special endpoint, instead of returning a value back, I want to do a 302 redirect to an image hosted in an s3.

If you want to return an error via grpc-gateway, you can return it like

nil, status.Error(codes.Unauthenticated, "Nope")

I wonder if there is something similar to do a 302 redirect?

As far as I get from this page it seems unlikely. I hope I overlooked something.

Answer 1

you could also use WithForwardResponseOption method which allows you to modify your response and response headers.

here is what I did to set Location header in response.

1. Set Location header in your GRPC method using metadata. this adds Grpc-Metadata-Location header to your response.

func (s *Server) CreatePayment(ctx context.Context, in *proto.Request) (*proto.Response, error) {
    header := metadata.Pairs("Location", url)
    grpc.SendHeader(ctx, header)
    
    return &proto.Response{}, nil
}

2. If Grpc-Metadata-Location header exists in your GRPC response headers, Set HTTP Location header and status code as well.

func responseHeaderMatcher(ctx context.Context, w http.ResponseWriter, resp proto.Message) error {
    headers := w.Header()
    if location, ok := headers["Grpc-Metadata-Location"]; ok {
        w.Header().Set("Location", location[0])
        w.WriteHeader(http.StatusFound)
    }

    return nil
}

3. Set this func as an Option in NewServeMux:

grpcGatewayMux := runtime.NewServeMux(
    runtime.WithForwardResponseOption(responseHeaderMatcher),
)