Uniformize spam-checker API: github/ts/spam-errors ts/spam-errors

- Some callbacks should return `True` to allow, `False` to deny, while others should return `True` to deny and `False` to allow. With this PR, all callbacks return `ALLOW` to allow or a `Codes` (typically `Codes.FORBIDDEN`) to deny.
- Similarly, some methods returned `True` to allow, `False` to deny, while others returned `True` to deny and `False` to allow. They now all return `ALLOW` to allow or a `Codes` to deny.
- Spam-checker implementations may now return an explicit code, e.g. to differentiate between "User account has been suspended" (which is in practice required by law in some countries, including UK) and "This message looks like spam".

1 files changed, 20 insertions, 15 deletions

diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py
index 802e57c4d0..d3ef6a05ca 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -18,6 +18,7 @@ import random
 from http import HTTPStatus
 from typing import TYPE_CHECKING, Iterable, List, Optional, Set, Tuple
 
+import synapse
 from synapse import types
 from synapse.api.constants import (
     AccountDataTypes,
@@ -679,8 +680,6 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):
             if target_id == self._server_notices_mxid:
                 raise SynapseError(HTTPStatus.FORBIDDEN, "Cannot invite this user")
 
-            block_invite = False
-
             if (
                 self._server_notices_mxid is not None
                 and requester.user.to_string() == self._server_notices_mxid
@@ -697,16 +696,18 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):
                         "Blocking invite: user is not admin and non-admin "
                         "invites disabled"
                     )
-                    block_invite = True
+                    raise SynapseError(403, "Invites have been disabled on this server")
 
-                if not await self.spam_checker.user_may_invite(
+                spam_check = await self.spam_checker.user_may_invite(
                     requester.user.to_string(), target_id, room_id
-                ):
+                )
+                if spam_check is not synapse.spam_checker_api.ALLOW:
                     logger.info("Blocking invite due to spam checker")
-                    block_invite = True
-
-            if block_invite:
-                raise SynapseError(403, "Invites have been disabled on this server")
+                    raise SynapseError(
+                        403,
+                        "This invite has been rejected as probable spam",
+                        spam_check,
+                    )
 
         # An empty prev_events list is allowed as long as the auth_event_ids are present
         if prev_event_ids is not None:
@@ -814,11 +815,14 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):
                 # We assume that if the spam checker allowed the user to create
                 # a room then they're allowed to join it.
                 and not new_room
-                and not await self.spam_checker.user_may_join_room(
+            ):
+                spam_check = await self.spam_checker.user_may_join_room(
                     target.to_string(), room_id, is_invited=inviter is not None
                 )
-            ):
-                raise SynapseError(403, "Not allowed to join this room")
+                if spam_check is not synapse.spam_checker_api.ALLOW:
+                    raise SynapseError(
+                        403, "This request to join room has been rejected", spam_check
+                    )
 
             # Check if a remote join should be performed.
             remote_join, remote_room_hosts = await self._should_perform_remote_join(
@@ -1372,13 +1376,14 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):
             )
         else:
             # Check if the spamchecker(s) allow this invite to go through.
-            if not await self.spam_checker.user_may_send_3pid_invite(
+            spam_check = await self.spam_checker.user_may_send_3pid_invite(
                 inviter_userid=requester.user.to_string(),
                 medium=medium,
                 address=address,
                 room_id=room_id,
-            ):
-                raise SynapseError(403, "Cannot send threepid invite")
+            )
+            if spam_check is not synapse.spam_checker_api.ALLOW:
+                raise SynapseError(403, "Cannot send threepid invite", spam_check)
 
             stream_id = await self._make_and_store_3pid_invite(
                 requester,