invites: Validation error instead of DB exception on overflowed SMALLINT.

If `invite_as` is passed as a number outside the range of a PostgreSQL
`SMALLINT` field, the database throws an exception. Move this exception
to the glass as a validation error to allow better client-side error
handling and reduce database round-trips.

zerver/tests/test_signup.py

@@ -3220,6 +3220,17 @@ class MultiuseInviteTest(ZulipTestCase):
         )
         self.assert_json_error(result, "Invalid stream ID 54321. No invites were sent.")
 
+    def test_create_multiuse_link_invalid_invite_as_api_call(self) -> None:
+        self.login("iago")
+        result = self.client_post(
+            "/json/invites/multiuse",
+            {
+                "invite_as": orjson.dumps(PreregistrationUser.INVITE_AS["GUEST_USER"] + 1).decode(),
+                "invite_expires_in_minutes": 2 * 24 * 60,
+            },
+        )
+        self.assert_json_error(result, "Invalid invite_as")
+
 
 class EmailUnsubscribeTests(ZulipTestCase):
     def test_error_unsubscribe(self) -> None:

zerver/views/invite.py

@@ -19,7 +19,7 @@ from zerver.lib.exceptions import JsonableError, OrganizationOwnerRequiredError
 from zerver.lib.request import REQ, has_request_variables
 from zerver.lib.response import json_success
 from zerver.lib.streams import access_stream_by_id
-from zerver.lib.validator import check_int, check_list, check_none_or
+from zerver.lib.validator import check_int, check_int_in, check_list, check_none_or
 from zerver.models import MultiuseInvite, PreregistrationUser, Stream, UserProfile
 
 # Convert INVITATION_LINK_VALIDITY_DAYS into minutes.
@@ -190,7 +190,12 @@ def generate_multiuse_invite_backend(
     invite_expires_in_minutes: Optional[int] = REQ(
         json_validator=check_none_or(check_int), default=INVITATION_LINK_VALIDITY_MINUTES
     ),
-    invite_as: int = REQ(json_validator=check_int, default=PreregistrationUser.INVITE_AS["MEMBER"]),
+    invite_as: int = REQ(
+        json_validator=check_int_in(
+            list(PreregistrationUser.INVITE_AS.values()),
+        ),
+        default=PreregistrationUser.INVITE_AS["MEMBER"],
+    ),
     stream_ids: Sequence[int] = REQ(json_validator=check_list(check_int), default=[]),
 ) -> HttpResponse:
     check_if_owner_required(invite_as, user_profile)