================= cargo build error
error[E0271]: type mismatch resolving `<MetricServer as hyper::client::Service>::Error == hyper::Error`
  --> metrics/src/lib.rs:30:38
   |
30 |         let mut server = Http::new().bind(&addr, || Ok(MetricServer)).unwrap();
   |                                      ^^^^ expected struct `failure::Error`, found enum `hyper::Error`
   |
   = note: expected type `failure::Error`
              found type `hyper::Error`

error: aborting due to previous error

error: Could not compile `metrics`.

================= relevant code snippet:
fn init() {
    thread::spawn(|| {
        let addr = "127.0.0.1:9898".parse().unwrap();
        let mut server = Http::new().bind(&addr, || Ok(MetricServer)).unwrap();  <-- error here
    });
}

impl MetricServer {
    fn metric_response(&self, req: Request) -> std::result::Result<Response, failure::Error> {
      ...
    }
}

impl Service for MetricServer {
    type Request = Request;
    type Response = Response;
    type Error = failure::Error;
    type Future = FutureResult<Response, failure::Error>;
    fn call(&self, req: Request) -> Self::Future {
        futures::future::result(self.metric_response(req))
    }
}