lib/actions: Add helper recipient_for_user_ids().

This function is equivalent to recipient_for_emails, but fetches
user_profiles by IDs, not by emails.

This commit is a part of our efforts surrounding #9474, but is
more primarily geared towards adding support for sending typing
notifications by user IDs.

zerver/lib/actions.py

@@ -97,7 +97,7 @@ from zerver.models import Realm, RealmEmoji, Stream, UserProfile, UserActivity,
     UserGroup, UserGroupMembership, get_default_stream_groups, \
     get_bot_services, get_bot_dicts_in_realm, DomainNotAllowedForRealmError, \
     DisposableEmailError, EmailContainsPlusError, \
-    get_user_including_cross_realm
+    get_user_including_cross_realm, get_user_by_id_in_realm_including_cross_realm
 
 from zerver.lib.alert_words import alert_words_in_realm
 from zerver.lib.avatar import avatar_url, avatar_url_from_dict
@@ -1785,6 +1785,23 @@ def recipient_for_emails(emails: Iterable[str], not_forged_mirror_message: bool,
         sender=sender
     )
 
+def recipient_for_user_ids(user_ids: Iterable[int], sender: UserProfile) -> Recipient:
+    user_profiles = []  # type: List[UserProfile]
+    for user_id in user_ids:
+        try:
+            user_profile = get_user_by_id_in_realm_including_cross_realm(
+                user_id, sender.realm)
+        except UserProfile.DoesNotExist:
+            raise ValidationError(_("Invalid user ID {}".format(user_id)))
+        user_profiles.append(user_profile)
+
+    return recipient_for_user_profiles(
+        user_profiles=user_profiles,
+        not_forged_mirror_message=False,
+        forwarder_user_profile=None,
+        sender=sender
+    )
+
 def recipient_for_user_profiles(user_profiles: List[UserProfile], not_forged_mirror_message: bool,
                                 forwarder_user_profile: Optional[UserProfile],
                                 sender: UserProfile) -> Recipient:

zerver/tests/test_typing.py

@@ -3,11 +3,14 @@
 import ujson
 from typing import Any, Mapping, List
 
+from django.core.exceptions import ValidationError
+
+from zerver.lib.actions import recipient_for_user_ids
 from zerver.lib.test_helpers import tornado_redirected_to_list, get_display_recipient
 from zerver.lib.test_classes import (
     ZulipTestCase,
 )
-from zerver.models import get_realm, get_user
+from zerver.models import get_realm, get_user, get_display_recipient
 
 class TypingNotificationOperatorTest(ZulipTestCase):
     def test_missing_parameter(self) -> None:
@@ -222,3 +225,27 @@ class StoppedTypingNotificationTest(ZulipTestCase):
         self.assertEqual(event['sender']['email'], sender.email)
         self.assertEqual(event['type'], 'typing')
         self.assertEqual(event['op'], 'stop')
+
+class TypingValidationHelpersTest(ZulipTestCase):
+    def test_recipient_for_user_ids(self) -> None:
+        hamlet = self.example_user('hamlet')
+        othello = self.example_user('othello')
+        cross_realm_bot = self.example_user('welcome_bot')
+        sender = self.example_user('iago')
+        recipient_user_ids = [hamlet.id, othello.id, cross_realm_bot.id]
+
+        result = recipient_for_user_ids(recipient_user_ids, sender)
+        recipient = get_display_recipient(result)
+        recipient_ids = [recipient[0]['id'], recipient[1]['id'],  # type: ignore
+                         recipient[2]['id'], recipient[3]['id']]  # type: ignore
+
+        expected_recipient_ids = [hamlet.id, othello.id,
+                                  sender.id, cross_realm_bot.id]
+        self.assertEqual(set(recipient_ids), set(expected_recipient_ids))
+
+    def test_recipient_for_user_ids_non_existent_id(self) -> None:
+        sender = self.example_user('iago')
+        recipient_user_ids = [999]
+
+        with self.assertRaisesRegex(ValidationError, 'Invalid user ID '):
+            recipient_for_user_ids(recipient_user_ids, sender)