fix(iroh-net): do not log as error if client disconnects from relay (#…

…2259)

## Description

In the relay server, we currently log all connection failures with
`error` severity. This means that whenever a node disconnects while
still in the TLS handshaking phase, we get an error log.:

```
2024-05-02T09:00:38.443215Z ERROR relay server{me=svfacrfjgmv7fjeu}:relay-http-serve:conn{peer=127.0.0.1:33596}: iroh_net::relay::http::server: [HTTPS] relay: failed to handl
e connection: TLS[manual] accept
```

This however is a perfectly fine thing, a node may decide to abort the
connection to a relay whenever it pleases. Especially in tests we often
shutdown while still in the process of connecting to a relay. This is
annoying, because the `error` severity indicates things being wrong
(especially with the stack traces we print on error logs in the CI).

This PR checks if the error is a EOF and if so only prints it as a debug
log.

## Breaking Changes

<!-- Optional, if there are any breaking changes document them,
including how to migrate older code. -->

## Notes & open questions

<!-- Any notes, remarks or open questions you have to make about the PR.
-->

## Change checklist

- [x] Self-review.

iroh-net/src/relay/http/server.rs

@@ -299,11 +299,18 @@ impl ServerState {
                             let service = self.service.clone();
                             // spawn a task to handle the connection
                             set.spawn(async move {
-                                if let Err(e) = service
+                                if let Err(error) = service
                                     .handle_connection(stream, tls_config)
                                     .await
                                 {
-                                    error!("[{http_str}] relay: failed to handle connection: {e}");
+                                    match error.downcast_ref::<std::io::Error>() {
+                                        Some(io_error) if io_error.kind() == std::io::ErrorKind::UnexpectedEof => {
+                                            debug!(reason=?error, "[{http_str}] relay: peer disconnected");
+                                        },
+                                        _ => {
+                                            error!(?error, "[{http_str}] relay: failed to handle connection");
+                                        }
+                                    }
                                 }
                             }.instrument(info_span!("conn", peer = %peer_addr)));
                         }