Added urlsafe token field

AUTHORS.rst

@@ -99,3 +99,4 @@
 | zyegfryed <zyegfryed@gmail.com>
 | Éric Araujo <merwok@netwok.org>
 | Őry Máté <ory.mate@cloud.bme.hu>
+| Nafees Anwar <h.nafees.anwar@gmail.com>

CHANGES.rst

@@ -6,6 +6,8 @@ Unreleased
 - Add support for `Django 3.2`
 - Drop support for `Django 3.0`
 
+- Added urlsafe token field.
+
 4.1.1 (2020-12-01)
 ------------------
 - Applied `isort` to codebase (Refs GH-#402)

docs/fields.rst

@@ -180,3 +180,46 @@ or any other ModelForm, default is False.
     class MyAppModel(models.Model):
         uuid = UUIDField(primary_key=True, version=4, editable=False)
 
+
+UrlsafeTokenField
+-----------------
+
+A ``CharField`` subclass that provides random token generating using
+python's ``secrets.token_urlsafe`` as default value.
+
+If ``editable`` is set to false the field will not be displayed in the admin
+or any other ModelForm, default is False.
+
+``max_length`` specifies the maximum length of the token. The default value is 128.
+
+
+.. code-block:: python
+
+    from django.db import models
+    from model_utils.fields import UrlsafeTokenField
+
+
+    class MyAppModel(models.Model):
+        uuid = UrlsafeTokenField(editable=False, max_length=128)
+
+
+You can provide your custom token generator using the ``factory`` argument.
+``factory`` should be callable. It will raise ``TypeError`` if it is not callable.
+``factory`` is called with ``max_length`` argument to generate the token, and should
+return a string of specified maximum length.
+
+
+.. code-block:: python
+
+    import uuid
+
+    from django.db import models
+    from model_utils.fields import UrlsafeTokenField
+
+
+    def _token_factory(max_length):
+        return uuid.uuid4().hex
+
+
+    class MyAppModel(models.Model):
+        uuid = UrlsafeTokenField(max_length=32, factory=_token_factory)

model_utils/fields.py

@@ -1,4 +1,6 @@
+import secrets
 import uuid
+from collections import Callable
 
 from django.conf import settings
 from django.core.exceptions import ValidationError
@@ -309,3 +311,41 @@ def __init__(self, primary_key=True, version=4, editable=False, *args, **kwargs)
         kwargs.setdefault('editable', editable)
         kwargs.setdefault('default', default)
         super().__init__(*args, **kwargs)
+
+
+class UrlsafeTokenField(models.CharField):
+    """
+    A field for storing a unique token in database.
+    """
+
+    def __init__(self, editable=False, max_length=128, factory=None, **kwargs):
+        """
+        Parameters
+        ----------
+        editable: bool
+            If true token is editable.
+        max_length: int
+            Maximum length of the token.
+        factory: callable
+            If provided, called with max_length of the field instance to generate token.
+
+        Raises
+        ------
+        TypeError
+            non-callable value for factory is not supported.
+        """
+
+        if factory is not None and not isinstance(factory, Callable):
+            raise TypeError("'factory' should either be a callable not 'None'")
+        self._factory = factory
+
+        kwargs.pop('default', None)  # passing default value has not effect.
+
+        super().__init__(editable=editable, max_length=max_length, **kwargs)
+
+    def get_default(self):
+        if self._factory is not None:
+            return self._factory(self.max_length)
+        # generate a token of length x1.33 approx. trim up to max length
+        token = secrets.token_urlsafe(self.max_length)[:self.max_length]
+        return token

tests/test_fields/test_urlsafe_token_field.py

@@ -0,0 +1,55 @@
+from unittest.mock import Mock
+
+from django.db.models import NOT_PROVIDED
+from django.test import TestCase
+
+from model_utils.fields import UrlsafeTokenField
+
+
+class UrlsaftTokenFieldTests(TestCase):
+    def test_editable_default(self):
+        field = UrlsafeTokenField()
+        self.assertFalse(field.editable)
+
+    def test_editable(self):
+        field = UrlsafeTokenField(editable=True)
+        self.assertTrue(field.editable)
+
+    def test_max_length_default(self):
+        field = UrlsafeTokenField()
+        self.assertEqual(field.max_length, 128)
+
+    def test_max_length(self):
+        field = UrlsafeTokenField(max_length=256)
+        self.assertEqual(field.max_length, 256)
+
+    def test_factory_default(self):
+        field = UrlsafeTokenField()
+        self.assertIsNone(field._factory)
+
+    def test_factory_not_callable(self):
+        with self.assertRaises(TypeError):
+            UrlsafeTokenField(factory='INVALID')
+
+    def test_get_default(self):
+        field = UrlsafeTokenField()
+        value = field.get_default()
+        self.assertEqual(len(value), field.max_length)
+
+    def test_get_default_with_non_default_max_length(self):
+        field = UrlsafeTokenField(max_length=64)
+        value = field.get_default()
+        self.assertEqual(len(value), 64)
+
+    def test_get_default_with_factory(self):
+        token = 'SAMPLE_TOKEN'
+        factory = Mock(return_value=token)
+        field = UrlsafeTokenField(factory=factory)
+        value = field.get_default()
+
+        self.assertEqual(value, token)
+        factory.assert_called_once_with(field.max_length)
+
+    def test_no_default_param(self):
+        field = UrlsafeTokenField(default='DEFAULT')
+        self.assertIs(field.default, NOT_PROVIDED)