add DomainNameField model Field type to validate and store Internet Domain Names

[michele]

In django models you can store an URL, but not a domain name. This patch adds a DomainNameField class to address that.

DomainNameField accepts:

• traditional domain names in ASCII form
• Internationalized Domain Names in IDNA form (ASCII encoded)
• Internationalized Domain Names in UTF form

DomainNameField always stores values in ASCII format by encoding and decoding UTF IDNs as needed.

Implementation notes:

• based on CharField and DomainNameValidator (see #18119)
• an implicit max_length=255 is added to CharField to propagate the Domain constraint down to the db schema
• naming: accept_idna might be renamed to "accept_idn" or simply "idn" for Internationalized Domain Name

This passes successfully a buch of tests:

class Zone(models.Model):
    name = models.DomainNameField()

plain_domain = 'foo.com'
idn_domain_good = 'xn--1lq90ic7fzpc.xn--fiqs8s'.decode('idna')   # a IDN domain in UTF format
idn_domain_bad = idn_domain + '#'

Zone(name=plain_domain).full_clean()
# ok!
Zone(name=idn_domain_good).full_clean()
# ok!
Zone(name=idn_domain_bad).full_clean()
# raises ValidationError ok!
Zone(name=idn_domain).save()
# selecting from db yields:
xn--1lq90ic7fzpc.xn--fiqs8s
# ok!

class Zone(models.Model):
    name = models.DomainNameField(accept_idna=False)

Zone(name=idn_domain_good).full_clean()
# raises ValidationError ok!

I'll implement these in a suitable test module if django.db will start one.

Work for this and DomainNameValidator was sponsored by ​BuddyNS.

[michele]

Two notes:

1. the test mentioned above has idn_domain_good = 'xn--1lq90ic7fzpc.xn--fiqs8s'.encode('idna') instead of decode
2. please review and comment about to_python() being called on both raw and python data (see comment in patch)

[michele]

ensure python string is always UTF

[michele]

Please refer to attachment:models_domainnamefield_2.txt​ , obsoletes the previous patch.

[Claude Paroz]

I think the DomainNameValidator (#18119) is a useful addition to Django. However, a specific DomainName field seems far too specialized to be maintained into Django. It is probably much more adequate for an external package.