Try other resolved addresses if the first one fails

[vvv]

Problem: metrics-observer cannot connect to raspberrypi.local:8000 -- "error while connecting".

Analysis:

"raspberrypi.local:8000" gets resolved on my machine to

• [fe80::da3a:ddff:fe3c:8772%15]:8000
• 192.168.0.100:8000

The IPv6 SocketAddr -- the first item returned by the iterator -- cannot be connected to. The IPv4 address would work, but metrics-observer never tries it.

Solution: if the first item, returned by to_socket_addrs, cannot be connected to, try the next one. Try them all, if necessary.

[vvv]

Alternatively, we could limit the results to IPv4 address(es).

                    let Ok(mut addrs) = self.addr.to_socket_addrs() else {
                        let mut state = self.client_state.lock().unwrap();
                        *state = ClientState::Disconnected(Some(
                            "failed to resolve specified host".to_string(),
                        ));
                        break;
                    };
                    let Some(addr) = addrs.find(|addr| addr.is_ipv4()) else {
                        let mut state = self.client_state.lock().unwrap();
                        *state = ClientState::Disconnected(Some(
                            "failed to resolve specified host as IPv4".to_string(),
                        ));
                        break;
                    };
                    match TcpStream::connect_timeout(&addr, Duration::from_secs(3)) {
                        Ok(stream) => RunnerState::Connected(stream),
                        Err(_) => RunnerState::ErrorBackoff(
                            "error while connecting",
                            Duration::from_secs(3),
                        ),
                    }

[tobz]

Nice, this is a good improvement. 👍🏻

[tobz]

Released as metrics-observer@v0.3.0.

Thanks again for your contribution. ❤️