validator.py: Create a validator for login email.

This validator raises JsonableError exception.

Fixes: #2748

zerver/lib/validator.py

@@ -27,8 +27,12 @@ for any particular type of object.
 '''
 from __future__ import absolute_import
 from django.utils.translation import ugettext as _
+from django.core.exceptions import ValidationError
+from django.core.validators import validate_email
 import six
-from typing import Any, Callable, Iterable, Optional, Tuple, TypeVar
+from typing import Any, Callable, Iterable, Optional, Tuple, TypeVar, Text
+
+from zerver.lib.request import JsonableError
 
 Validator = Callable[[str, Any], Optional[str]]
 
@@ -144,3 +148,10 @@ def equals(expected_val):
                      'value': val})
         return None
     return f
+
+def validate_login_email(email):
+    # type: (Text) -> None
+    try:
+        validate_email(email)
+    except ValidationError as err:
+        raise JsonableError(str(err.message))

zerver/tests/test_auth_backends.py

@@ -22,6 +22,8 @@ from zerver.lib.actions import (
     do_reactivate_user,
     do_set_realm_authentication_methods,
 )
+from zerver.lib.validator import validate_login_email
+from zerver.lib.request import JsonableError
 from zerver.lib.initial_password import initial_password
 from zerver.lib.sessions import get_session_dict_user
 from zerver.lib.test_classes import (
@@ -1834,3 +1836,13 @@ class TestAdminSetBackends(ZulipTestCase):
         self.assertFalse(github_auth_enabled(realm))
         self.assertTrue(dev_auth_enabled(realm))
         self.assertFalse(password_auth_enabled(realm))
+
+class LoginEmailValidatorTestCase(TestCase):
+    def test_valid_email(self):
+        # type: () -> None
+        validate_login_email(u'hamlet@zulip.com')
+
+    def test_invalid_email(self):
+        # type: () -> None
+        with self.assertRaises(JsonableError):
+            validate_login_email(u'hamlet')