Hostname should support Internationalized domain name (IDN) TLDs

[candita]

Hostname RegEx should support a TLD that exists in the IANA list of TLDs at http://data.iana.org/TLD/tlds-alpha-by-domain.txt,
e.g. XN--11B4C3D, or कॉम.

Currently it disallows numbers and hyphen in the last label of the Hostname (TLD):
^([a-zA-Z0-9\p{S}\p{L}]((-?[a-zA-Z0-9\p{S}\p{L}]{0,62})?)|([a-zA-Z0-9\p{S}\p{L}](([a-zA-Z0-9-\p{S}\p{L}]{0,61}[a-zA-Z0-9\p{S}\p{L}])?)(\.)){1,}([a-zA-Z\p{L}]){2,63})$

Can I change it to allow digits and hyphens in the TLD, or create a new format called HostnameIDN?
^([a-zA-Z0-9\p{S}\p{L}]((-?[a-zA-Z0-9\p{S}\p{L}]{0,62})?)|([a-zA-Z0-9\p{S}\p{L}](([a-zA-Z0-9-\p{S}\p{L}]{0,61}[a-zA-Z0-9\p{S}\p{L}])?)(\.)){1,}([a-zA-Z0-9-\p{L}]){2,63})$

[casualjim]

Yeah, but maybe we should just go with https://pkg.go.dev/golang.org/x/net/idna ?

[candita]

You would make the Hostname RegEx obsolete?

[casualjim]

Yeah, we did the same for email addresses because regex'es are always a bit wonky for these things.
https://github.com/go-openapi/strfmt/blob/master/default.go#L122-L126

[fredbi]

@candita I've pushed a PR that goes the regexp way, but with a very localized use of the idna package.
The problem with the idna package is that it covers only partially the set of validation rules.

Also I've hit an issue with the devanagari example that you supplied: these rune do not classify as unicode letters, so my PR doesn't cover these. I am not aware of any regexp trick to easily cover such runes.

Cheers

Fred

[fredbi]

New PR now addresses the above concerns