add and use public_ip as fallback

[shalzz]

Fixes #244

[CLAassistant]

All committers have signed the CLA.

[vorot93]

Any way to get and print specific error, not None?

[shalzz]

We can, however the crate tries various resolvers to try and get the external IP address on a best effort basis. The error would be resolver specific and in worst case would be a collection of errors of all resolvers tried (connection/networking errors).

[shalzz]

It would look something like this

                                let mut errors = vec![];
                                let ip = public_ip::resolve(public_ip::ALL, public_ip::Version::Any)
                                    .filter_map(|result| std::future::ready( result.map_err(|e| errors.push(e)).ok() ))
                                    .next()
                                    .await
                                    .map(|(addr, _)| addr);

                                if let Some(v) = ip {
                                    debug!("Discovered public IP: {}", v);
                                    node_endpoint.write().address = Ip(v);
                                } else {
                                    debug!("Failed to get public IP via DNS/HTTP resolvers: {:?}", errors);
                                }

[vorot93]

Thanks for the PR!