add DomainNameValidator to validate Internet Domain Names

[michele]

Internet Domain Names are very present throughout, e.g. in URLs and e-mail addresses.

This patch adds django.core.validators.DomainNameValidator to check Internet Domain Names.

DomainNameValidator supports IDNA (utf) domain names, but it can reject them if optional accept_idna=False is passed to the constructor (defaults to accept).

DomainNameValidator is implemented as follows:

• derives RegexValidator
• uses the same RegEx of URLValidator (with the additional constrain to accept only 127 labels / 255 chars, as per RFC)
• if plain validation fails, converts UTF -> ASCII with IDNA encoding and attempts to validate again (unless accept_idna=False)

Based on this Validator, I will submit separate patches to add DomainNameField support for models.

[Claude Paroz]

I think it is a good idea to centralize domain name validation. I detected at least three points where we could use this validator (django/core/mail/message.py, django/core/validators.py (URLValidator), django/utils/html.py).

For DRY reasons, the domain regex part should be shared with URLValidator. In __init__, just use self.accept_idna = kwargs.pop('accept_idna', True)

[michele]

DomainNameValidator patch #2 - remove validator-own attributes before super()

[michele]

In attachment:domainnamevalidator_2.txt​ :

• fix the constructor argument as per claudep suggestion
• return a specific error message based on IDNA being accepted or not

[Berker Peksag]

​https://github.com/django/django/pull/3477

[Tim Graham]

This is blocked on #20003. Patch will need to be updated after that change.

[Thomas Güttler]

would be nice to have

[Berker Peksag]

Updated ​PR.