Fixed #18119 -- Added a DomainNameValidator validator.

Override __init__ function to add accept IDNA.

Updates to DomainNameValidator to add logic around accept_idna flag

Remove outdated details from docs.

Made changes to domain name validation and tests.

Reused regex in URLValidator.

Added more changes to the DomainNameValidator so all  tests pass.

Removed rogue space.

Blacken.

Update documentation for DomainNameValidator.

Remove unused text.

Tidy docs.

Update docs - fix underline.

Update docs/ref/validators.txt

Remove unnecessary blank lines.

Co-authored-by: Mariusz Felisiak <felisiak.mariusz@gmail.com>

Update docs/releases/5.1.txt

Co-authored-by: Mariusz Felisiak <felisiak.mariusz@gmail.com>

Changes to docs for DomainNameValidator.

Change name of the parameter.

Co-authored-by: Sarah Boyce <42296566+sarahboyce@users.noreply.github.com>

Update docs for new naming.

Co-authored-by: Sarah Boyce <42296566+sarahboyce@users.noreply.github.com>

Update django/core/validators.py

Co-authored-by: Sarah Boyce <42296566+sarahboyce@users.noreply.github.com>

Update comments for validators.

Reorder docs to have DomainNameValidator next to URLNameValidator.

blacken

django/core/validators.py

@@ -66,22 +66,16 @@ def __eq__(self, other):
 
 
 @deconstructible
-class URLValidator(RegexValidator):
+class DomainNameValidator(RegexValidator):
+    message = _("Enter a valid domain name.")
     ul = "\u00a1-\uffff"  # Unicode letters range (must not be a raw string).
-
-    # IP patterns
-    ipv4_re = (
-        r"(?:0|25[0-5]|2[0-4][0-9]|1[0-9]?[0-9]?|[1-9][0-9]?)"
-        r"(?:\.(?:0|25[0-5]|2[0-4][0-9]|1[0-9]?[0-9]?|[1-9][0-9]?)){3}"
-    )
-    ipv6_re = r"\[[0-9a-f:.]+\]"  # (simple regex, validated later)
-
-    # Host patterns
+    # Host patterns.
     hostname_re = (
         r"[a-z" + ul + r"0-9](?:[a-z" + ul + r"0-9-]{0,61}[a-z" + ul + r"0-9])?"
     )
-    # Max length for domain name labels is 63 characters per RFC 1034 sec. 3.1
+    # Max length for domain name labels is 63 characters per RFC 1034 sec. 3.1.
     domain_re = r"(?:\.(?!-)[a-z" + ul + r"0-9-]{1,63}(?<!-))*"
+    # Top-level domain.
     tld_re = (
         r"\."  # dot
         r"(?!-)"  # can't start with a dash
@@ -90,6 +84,60 @@ class URLValidator(RegexValidator):
         r"(?<!-)"  # can't end with a dash
         r"\.?"  # may have a trailing dot
     )
+    ascii_only_hostname_re = r"[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?"
+    ascii_only_domain_re = r"(?:\.(?!-)[a-zA-Z0-9-]{1,63}(?<!-))*"
+    ascii_only_tld_re = (
+        r"\."  # dot
+        r"(?!-)"  # can't start with a dash
+        r"(?:[a-zA-Z0-9-]{2,63})"  # domain label
+        r"(?<!-)"  # can't end with a dash
+        r"\.?"  # may have a trailing dot
+    )
+
+    max_length = 255
+
+    def __init__(self, **kwargs):
+        self.accept_idna = kwargs.pop("accept_idna", True)
+
+        if self.accept_idna:
+            self.regex = _lazy_re_compile(
+                self.hostname_re + self.domain_re + self.tld_re, re.IGNORECASE
+            )
+        else:
+            self.regex = _lazy_re_compile(
+                self.ascii_only_hostname_re
+                + self.ascii_only_domain_re
+                + self.ascii_only_tld_re,
+                re.IGNORECASE,
+            )
+        super().__init__(**kwargs)
+
+    def __call__(self, value):
+        if not isinstance(value, str) or len(value) > self.max_length:
+            raise ValidationError(self.message, code=self.code, params={"value": value})
+        if not self.accept_idna and not value.isascii():
+            raise ValidationError(self.message, code=self.code, params={"value": value})
+        super().__call__(value)
+
+
+validate_domain_name = DomainNameValidator()
+
+
+@deconstructible
+class URLValidator(RegexValidator):
+    ul = "\u00a1-\uffff"  # Unicode letters range (must not be a raw string).
+
+    # IP patterns
+    ipv4_re = (
+        r"(?:0|25[0-5]|2[0-4][0-9]|1[0-9]?[0-9]?|[1-9][0-9]?)"
+        r"(?:\.(?:0|25[0-5]|2[0-4][0-9]|1[0-9]?[0-9]?|[1-9][0-9]?)){3}"
+    )
+    ipv6_re = r"\[[0-9a-f:.]+\]"  # (simple regex, validated later)
+
+    hostname_re = DomainNameValidator.hostname_re
+    domain_re = DomainNameValidator.domain_re
+    tld_re = DomainNameValidator.tld_re
+
     host_re = "(" + hostname_re + domain_re + tld_re + "|localhost)"
 
     regex = _lazy_re_compile(

docs/ref/validators.txt

@@ -159,6 +159,31 @@ to, or in lieu of custom ``field.clean()`` methods.
         validation, so you'd need to add them to the ``allowlist`` as
         necessary.
 
+``DomainNameValidator``
+-----------------------
+
+.. versionadded:: 5.1
+
+.. class:: DomainNameValidator(schemes=None, regex=None, message=None, code=None, accept_idna=True)
+
+    A :class:`RegexValidator` subclass that ensures a value looks like a domain name. Values longer than
+    255 characters are always considered invalid.
+
+    In addition to the optional arguments of its parent :class:`RegexValidator`
+    class, ``DomainNameValidator`` accepts an extra optional attribute:
+
+
+    .. attribute:: accept_idna
+        This determines whether or not to accept internationalized domain name, that is,
+        domain names that contain non-ASCII characters. Default value is true.
+
+``validate_domain_name``
+------------------------
+
+.. data:: validate_domain_name
+
+    An :class:`DomainNameValidator` instance without any customizations.
+
 ``URLValidator``
 ----------------
 

docs/releases/5.1.txt

@@ -354,7 +354,8 @@ Utilities
 Validators
 ~~~~~~~~~~
 
-* ...
+* The new :class:`~django.core.validators.DomainNameValidator` validates domain
+  names, including internationalized domain names.
 
 .. _backwards-incompatible-5.1:
 

tests/validators/tests.py

@@ -9,6 +9,7 @@
 from django.core.validators import (
     BaseValidator,
     DecimalValidator,
+    DomainNameValidator,
     EmailValidator,
     FileExtensionValidator,
     MaxLengthValidator,
@@ -21,6 +22,7 @@
     URLValidator,
     int_list_validator,
     validate_comma_separated_integer_list,
+    validate_domain_name,
     validate_email,
     validate_image_file_extension,
     validate_integer,
@@ -618,6 +620,35 @@
     (ProhibitNullCharactersValidator(), "\x00something", ValidationError),
     (ProhibitNullCharactersValidator(), "something", None),
     (ProhibitNullCharactersValidator(), None, None),
+    (validate_domain_name, "000000.org", None),
+    (validate_domain_name, "python.org", None),
+    (validate_domain_name, "python.co.uk", None),
+    (validate_domain_name, "python.tk", None),
+    (validate_domain_name, "domain.with.idn.tld.उदाहरण.परीक्ष", None),
+    (validate_domain_name, "ıçğü.com", None),
+    (validate_domain_name, "xn--7ca6byfyc.com", None),
+    (validate_domain_name, "hg.python.org", None),
+    (validate_domain_name, "python.xyz", None),
+    (validate_domain_name, "djangoproject.com", None),
+    (validate_domain_name, "DJANGOPROJECT.COM", None),
+    (validate_domain_name, "spam.eggs", None),
+    (validate_domain_name, "python-python.com", None),
+    (validate_domain_name, "python.name.uk", None),
+    (validate_domain_name, "python.tips", None),
+    (validate_domain_name, "http://例子.测试", None),
+    (validate_domain_name, "http://dashinpunytld.xn---c", None),
+    (validate_domain_name, "python..org", ValidationError),
+    (validate_domain_name, "python-.org", ValidationError),
+    (validate_domain_name, "too-long-name." * 20 + "com", ValidationError),
+    (validate_domain_name, "stupid-name试", ValidationError),
+    (DomainNameValidator(accept_idna=False), "non-idna-domain-name-passes.com", None),
+    (
+        DomainNameValidator(accept_idna=False),
+        "domain.with.idn.tld.उदाहरण.परीक्ष",
+        ValidationError,
+    ),
+    (DomainNameValidator(accept_idna=False), "ıçğü.com", ValidationError),
+    (DomainNameValidator(accept_idna=False), "not-domain-name", ValidationError),
 ]
 
 # Add valid and invalid URL tests.
@@ -847,3 +878,25 @@ def test_prohibit_null_characters_validator_equality(self):
             ProhibitNullCharactersValidator(message="message", code="code1"),
             ProhibitNullCharactersValidator(message="message", code="code2"),
         )
+
+    def test_domain_name_equality(self):
+        self.assertEqual(
+            DomainNameValidator(),
+            DomainNameValidator(),
+        )
+        self.assertNotEqual(
+            DomainNameValidator(),
+            EmailValidator(),
+        )
+        self.assertNotEqual(
+            DomainNameValidator(),
+            DomainNameValidator(code="custom_code"),
+        )
+        self.assertEqual(
+            DomainNameValidator(message="custom error message"),
+            DomainNameValidator(message="custom error message"),
+        )
+        self.assertNotEqual(
+            DomainNameValidator(message="custom error message"),
+            DomainNameValidator(message="custom error message", code="custom_code"),
+        )