Improve error message for getaddrinfo failure

[rdp]

…s may be connected to DNS #8262
See discussion in #8262
I wasn't sure if the hint were appropriate or not but maybe useful to someone? :)

[straight-shoota]

Runtime error messages should be concise and describe the problem only as much as necessary. This seems to extensive.
How to deal with such an error is a different thing. There may be many reasons why address resolution fails. It shouldn't be Crystals job to provide general troubleshooting advice in an error message.

The only useful improvement IMO is to add context information to all errors, not just for EAI_NONAME. When address resolution fails, it's essential to know which address was tried.

[straight-shoota]

BTW I tried this in several programming languages and most simply just pass the error message from getaddrinfo with no context information.

The only good message I found was in Golang:

lookup badhostname on 192.168.1.1:53: no such host

It's great to show which DNS server was used.

[rdp]

Whoa, golang doing their own DNS resolution, nice.
How about this instead: "getaddrinfo: for badhostname:80 over IP when attempting domain name resolution" ?

[straight-shoota]

I'd go with a very concise message: Hostname lookup for badhostname failed: #{errno_message}.

• We can skip getaddrinfo: at the beginning. This API call is only useful when the errno message is directly passed. Here, we have a customized message anyway.
• protocol and socket are usually not very helpful. I'd omit them unless the error is EAI_SOCKTYPE or EAI_SERVICE, respectively. Similarly, the address family could be shown for EAI_ADDRFAMILY. In all other cases, lookup failed generally and these details don't matter.

[rdp]

OK I didn't see EAI_ADDRFAMILY defined so didn't include that but did some for the rest, please review, thank you!

[rdp]

Looks like this breaks some other specs, I'll check those out.

[rdp]

OK ready for review, thank you.

[straight-shoota]

Thank you @rdp ❤️

[rdp]

Thanks!

…

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