How to best implement gRPC metrics?

[2xic]

Hello,

I want to have a metric to track the gRPC status code and the associated method. Looking around most people recommend implement it using tracing, but then I only get the grpc-status. Looking at how this is implement under the hood https://github.com/tower-rs/tower-http/blob/33645694bda18105decc54be33d659c82ff07435/tower-http/src/trace/body.rs#L29 seems to be very complicated for what I'm trying to achieve.

Is there a more straightforward way ?

For context, this is how I implemented it with using the traces, but here I am missing the method as mentioned

fn record_grpc_status(header_map: &http::HeaderMap, span: &tracing::Span) {
    let status_str = header_map
        .get("grpc-status")
        .and_then(|status| status.to_str().ok())
        .map(|s| s.to_owned());

    if let Some(status_str) = status_str {
        // NOTE: I also want to know which method failed here 
        span.record("grpc.status", &status_str);
        counter!("grpc.status.total", &[("status", status_str)]).increment(1);
    }
}


/*
tower_http::trace::TraceLayer::new_for_grpc()
                .make_span_with(make_span_with_w3c_parent_context)
                .on_response(GrpcStatusMetric)
                .on_eos(GrpcStatusMetric)
*/
#[derive(Clone)]
pub struct GrpcStatusMetric;

impl OnEos for GrpcStatusMetric {
    fn on_eos(
        self,
        trailers: Option<&http::HeaderMap>,
        _stream_duration: std::time::Duration,
        span: &tracing::Span,
    ) {
        if let Some(header_map) = trailers {
            record_grpc_status(header_map, span);
        }
    }
}

impl<B> OnResponse<B> for GrpcStatusMetric {
    fn on_response(
        self,
        response: &http::Response<B>,
        _stream_duration: std::time::Duration,
        span: &tracing::Span,
    ) {
        record_grpc_status(response.headers(), span);
    }
}