Uniformize spam-checker API, part 4: port other spam-checker callbacks to return `Union[Allow, Codes]`. (#12857)

Co-authored-by: Brendan Abolivier <babolivier@matrix.org>

8 files changed, 258 insertions, 121 deletions

diff --git a/synapse/events/spamcheck.py b/synapse/events/spamcheck.py
index d2e06c754e..32712d2042 100644
--- a/synapse/events/spamcheck.py
+++ b/synapse/events/spamcheck.py
@@ -28,7 +28,10 @@ from typing import (
     Union,
 )
 
-from synapse.api.errors import Codes
+# `Literal` appears with Python 3.8.
+from typing_extensions import Literal
+
+import synapse
 from synapse.rest.media.v1._base import FileInfo
 from synapse.rest.media.v1.media_storage import ReadableFileWrapper
 from synapse.spam_checker_api import RegistrationBehaviour
@@ -47,12 +50,12 @@ CHECK_EVENT_FOR_SPAM_CALLBACK = Callable[
     Awaitable[
         Union[
             str,
-            Codes,
+            "synapse.api.errors.Codes",
             # Highly experimental, not officially part of the spamchecker API, may
             # disappear without warning depending on the results of ongoing
             # experiments.
             # Use this to return additional information as part of an error.
-            Tuple[Codes, Dict],
+            Tuple["synapse.api.errors.Codes", Dict],
             # Deprecated
             bool,
         ]
@@ -62,12 +65,72 @@ SHOULD_DROP_FEDERATED_EVENT_CALLBACK = Callable[
     ["synapse.events.EventBase"],
     Awaitable[Union[bool, str]],
 ]
-USER_MAY_JOIN_ROOM_CALLBACK = Callable[[str, str, bool], Awaitable[bool]]
-USER_MAY_INVITE_CALLBACK = Callable[[str, str, str], Awaitable[bool]]
-USER_MAY_SEND_3PID_INVITE_CALLBACK = Callable[[str, str, str, str], Awaitable[bool]]
-USER_MAY_CREATE_ROOM_CALLBACK = Callable[[str], Awaitable[bool]]
-USER_MAY_CREATE_ROOM_ALIAS_CALLBACK = Callable[[str, RoomAlias], Awaitable[bool]]
-USER_MAY_PUBLISH_ROOM_CALLBACK = Callable[[str, str], Awaitable[bool]]
+USER_MAY_JOIN_ROOM_CALLBACK = Callable[
+    [str, str, bool],
+    Awaitable[
+        Union[
+            Literal["NOT_SPAM"],
+            "synapse.api.errors.Codes",
+            # Deprecated
+            bool,
+        ]
+    ],
+]
+USER_MAY_INVITE_CALLBACK = Callable[
+    [str, str, str],
+    Awaitable[
+        Union[
+            Literal["NOT_SPAM"],
+            "synapse.api.errors.Codes",
+            # Deprecated
+            bool,
+        ]
+    ],
+]
+USER_MAY_SEND_3PID_INVITE_CALLBACK = Callable[
+    [str, str, str, str],
+    Awaitable[
+        Union[
+            Literal["NOT_SPAM"],
+            "synapse.api.errors.Codes",
+            # Deprecated
+            bool,
+        ]
+    ],
+]
+USER_MAY_CREATE_ROOM_CALLBACK = Callable[
+    [str],
+    Awaitable[
+        Union[
+            Literal["NOT_SPAM"],
+            "synapse.api.errors.Codes",
+            # Deprecated
+            bool,
+        ]
+    ],
+]
+USER_MAY_CREATE_ROOM_ALIAS_CALLBACK = Callable[
+    [str, RoomAlias],
+    Awaitable[
+        Union[
+            Literal["NOT_SPAM"],
+            "synapse.api.errors.Codes",
+            # Deprecated
+            bool,
+        ]
+    ],
+]
+USER_MAY_PUBLISH_ROOM_CALLBACK = Callable[
+    [str, str],
+    Awaitable[
+        Union[
+            Literal["NOT_SPAM"],
+            "synapse.api.errors.Codes",
+            # Deprecated
+            bool,
+        ]
+    ],
+]
 CHECK_USERNAME_FOR_SPAM_CALLBACK = Callable[[UserProfile], Awaitable[bool]]
 LEGACY_CHECK_REGISTRATION_FOR_SPAM_CALLBACK = Callable[
     [
@@ -88,7 +151,14 @@ CHECK_REGISTRATION_FOR_SPAM_CALLBACK = Callable[
 ]
 CHECK_MEDIA_FILE_FOR_SPAM_CALLBACK = Callable[
     [ReadableFileWrapper, FileInfo],
-    Awaitable[bool],
+    Awaitable[
+        Union[
+            Literal["NOT_SPAM"],
+            "synapse.api.errors.Codes",
+            # Deprecated
+            bool,
+        ]
+    ],
 ]
 
 
@@ -181,7 +251,7 @@ def load_legacy_spam_checkers(hs: "synapse.server.HomeServer") -> None:
 
 
 class SpamChecker:
-    NOT_SPAM = "NOT_SPAM"
+    NOT_SPAM: Literal["NOT_SPAM"] = "NOT_SPAM"
 
     def __init__(self, hs: "synapse.server.HomeServer") -> None:
         self.hs = hs
@@ -275,7 +345,7 @@ class SpamChecker:
 
     async def check_event_for_spam(
         self, event: "synapse.events.EventBase"
-    ) -> Union[Tuple[Codes, Dict], str]:
+    ) -> Union[Tuple["synapse.api.errors.Codes", Dict], str]:
         """Checks if a given event is considered "spammy" by this server.
 
         If the server considers an event spammy, then it will be rejected if
@@ -306,7 +376,7 @@ class SpamChecker:
                 elif res is True:
                     # This spam-checker rejects the event with deprecated
                     # return value `True`
-                    return Codes.FORBIDDEN
+                    return (synapse.api.errors.Codes.FORBIDDEN, {})
                 elif not isinstance(res, str):
                     # mypy complains that we can't reach this code because of the
                     # return type in CHECK_EVENT_FOR_SPAM_CALLBACK, but we don't know
@@ -352,7 +422,7 @@ class SpamChecker:
 
     async def user_may_join_room(
         self, user_id: str, room_id: str, is_invited: bool
-    ) -> bool:
+    ) -> Union["synapse.api.errors.Codes", Literal["NOT_SPAM"]]:
         """Checks if a given users is allowed to join a room.
         Not called when a user creates a room.
 
@@ -362,54 +432,70 @@ class SpamChecker:
             is_invited: Whether the user is invited into the room
 
         Returns:
-            Whether the user may join the room
+            NOT_SPAM if the operation is permitted, Codes otherwise.
         """
         for callback in self._user_may_join_room_callbacks:
             with Measure(
                 self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
             ):
-                may_join_room = await delay_cancellation(
-                    callback(user_id, room_id, is_invited)
-                )
-            if may_join_room is False:
-                return False
+                res = await delay_cancellation(callback(user_id, room_id, is_invited))
+                # Normalize return values to `Codes` or `"NOT_SPAM"`.
+                if res is True or res is self.NOT_SPAM:
+                    continue
+                elif res is False:
+                    return synapse.api.errors.Codes.FORBIDDEN
+                elif isinstance(res, synapse.api.errors.Codes):
+                    return res
+                else:
+                    logger.warning(
+                        "Module returned invalid value, rejecting join as spam"
+                    )
+                    return synapse.api.errors.Codes.FORBIDDEN
 
-        return True
+        # No spam-checker has rejected the request, let it pass.
+        return self.NOT_SPAM
 
     async def user_may_invite(
         self, inviter_userid: str, invitee_userid: str, room_id: str
-    ) -> bool:
+    ) -> Union["synapse.api.errors.Codes", Literal["NOT_SPAM"]]:
         """Checks if a given user may send an invite
 
-        If this method returns false, the invite will be rejected.
-
         Args:
             inviter_userid: The user ID of the sender of the invitation
             invitee_userid: The user ID targeted in the invitation
             room_id: The room ID
 
         Returns:
-            True if the user may send an invite, otherwise False
+            NOT_SPAM if the operation is permitted, Codes otherwise.
         """
         for callback in self._user_may_invite_callbacks:
             with Measure(
                 self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
             ):
-                may_invite = await delay_cancellation(
+                res = await delay_cancellation(
                     callback(inviter_userid, invitee_userid, room_id)
                 )
-            if may_invite is False:
-                return False
+                # Normalize return values to `Codes` or `"NOT_SPAM"`.
+                if res is True or res is self.NOT_SPAM:
+                    continue
+                elif res is False:
+                    return synapse.api.errors.Codes.FORBIDDEN
+                elif isinstance(res, synapse.api.errors.Codes):
+                    return res
+                else:
+                    logger.warning(
+                        "Module returned invalid value, rejecting invite as spam"
+                    )
+                    return synapse.api.errors.Codes.FORBIDDEN
 
-        return True
+        # No spam-checker has rejected the request, let it pass.
+        return self.NOT_SPAM
 
     async def user_may_send_3pid_invite(
         self, inviter_userid: str, medium: str, address: str, room_id: str
-    ) -> bool:
+    ) -> Union["synapse.api.errors.Codes", Literal["NOT_SPAM"]]:
         """Checks if a given user may invite a given threepid into the room
 
-        If this method returns false, the threepid invite will be rejected.
-
         Note that if the threepid is already associated with a Matrix user ID, Synapse
         will call user_may_invite with said user ID instead.
 
@@ -420,88 +506,113 @@ class SpamChecker:
             room_id: The room ID
 
         Returns:
-            True if the user may send the invite, otherwise False
+            NOT_SPAM if the operation is permitted, Codes otherwise.
         """
         for callback in self._user_may_send_3pid_invite_callbacks:
             with Measure(
                 self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
             ):
-                may_send_3pid_invite = await delay_cancellation(
+                res = await delay_cancellation(
                     callback(inviter_userid, medium, address, room_id)
                 )
-            if may_send_3pid_invite is False:
-                return False
+                # Normalize return values to `Codes` or `"NOT_SPAM"`.
+                if res is True or res is self.NOT_SPAM:
+                    continue
+                elif res is False:
+                    return synapse.api.errors.Codes.FORBIDDEN
+                elif isinstance(res, synapse.api.errors.Codes):
+                    return res
+                else:
+                    logger.warning(
+                        "Module returned invalid value, rejecting 3pid invite as spam"
+                    )
+                    return synapse.api.errors.Codes.FORBIDDEN
 
-        return True
+        return self.NOT_SPAM
 
-    async def user_may_create_room(self, userid: str) -> bool:
+    async def user_may_create_room(
+        self, userid: str
+    ) -> Union["synapse.api.errors.Codes", Literal["NOT_SPAM"]]:
         """Checks if a given user may create a room
 
-        If this method returns false, the creation request will be rejected.
-
         Args:
             userid: The ID of the user attempting to create a room
-
-        Returns:
-            True if the user may create a room, otherwise False
         """
         for callback in self._user_may_create_room_callbacks:
             with Measure(
                 self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
             ):
-                may_create_room = await delay_cancellation(callback(userid))
-            if may_create_room is False:
-                return False
+                res = await delay_cancellation(callback(userid))
+                if res is True or res is self.NOT_SPAM:
+                    continue
+                elif res is False:
+                    return synapse.api.errors.Codes.FORBIDDEN
+                elif isinstance(res, synapse.api.errors.Codes):
+                    return res
+                else:
+                    logger.warning(
+                        "Module returned invalid value, rejecting room creation as spam"
+                    )
+                    return synapse.api.errors.Codes.FORBIDDEN
 
-        return True
+        return self.NOT_SPAM
 
     async def user_may_create_room_alias(
         self, userid: str, room_alias: RoomAlias
-    ) -> bool:
+    ) -> Union["synapse.api.errors.Codes", Literal["NOT_SPAM"]]:
         """Checks if a given user may create a room alias
 
-        If this method returns false, the association request will be rejected.
-
         Args:
             userid: The ID of the user attempting to create a room alias
             room_alias: The alias to be created
 
-        Returns:
-            True if the user may create a room alias, otherwise False
         """
         for callback in self._user_may_create_room_alias_callbacks:
             with Measure(
                 self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
             ):
-                may_create_room_alias = await delay_cancellation(
-                    callback(userid, room_alias)
-                )
-            if may_create_room_alias is False:
-                return False
+                res = await delay_cancellation(callback(userid, room_alias))
+                if res is True or res is self.NOT_SPAM:
+                    continue
+                elif res is False:
+                    return synapse.api.errors.Codes.FORBIDDEN
+                elif isinstance(res, synapse.api.errors.Codes):
+                    return res
+                else:
+                    logger.warning(
+                        "Module returned invalid value, rejecting room create as spam"
+                    )
+                    return synapse.api.errors.Codes.FORBIDDEN
 
-        return True
+        return self.NOT_SPAM
 
-    async def user_may_publish_room(self, userid: str, room_id: str) -> bool:
+    async def user_may_publish_room(
+        self, userid: str, room_id: str
+    ) -> Union["synapse.api.errors.Codes", Literal["NOT_SPAM"]]:
         """Checks if a given user may publish a room to the directory
 
-        If this method returns false, the publish request will be rejected.
-
         Args:
             userid: The user ID attempting to publish the room
             room_id: The ID of the room that would be published
-
-        Returns:
-            True if the user may publish the room, otherwise False
         """
         for callback in self._user_may_publish_room_callbacks:
             with Measure(
                 self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
             ):
-                may_publish_room = await delay_cancellation(callback(userid, room_id))
-            if may_publish_room is False:
-                return False
+                res = await delay_cancellation(callback(userid, room_id))
+                if res is True or res is self.NOT_SPAM:
+                    continue
+                elif res is False:
+                    return synapse.api.errors.Codes.FORBIDDEN
+                elif isinstance(res, synapse.api.errors.Codes):
+                    return res
+                else:
+                    logger.warning(
+                        "Module returned invalid value, rejecting room publication as spam"
+                    )
+                    return synapse.api.errors.Codes.FORBIDDEN
 
-        return True
+        return self.NOT_SPAM
 
     async def check_username_for_spam(self, user_profile: UserProfile) -> bool:
         """Checks if a user ID or display name are considered "spammy" by this server.
@@ -567,7 +678,7 @@ class SpamChecker:
 
     async def check_media_file_for_spam(
         self, file_wrapper: ReadableFileWrapper, file_info: FileInfo
-    ) -> bool:
+    ) -> Union["synapse.api.errors.Codes", Literal["NOT_SPAM"]]:
         """Checks if a piece of newly uploaded media should be blocked.
 
         This will be called for local uploads, downloads of remote media, each
@@ -580,31 +691,37 @@ class SpamChecker:
 
             async def check_media_file_for_spam(
                 self, file: ReadableFileWrapper, file_info: FileInfo
-            ) -> bool:
+            ) -> Union[Codes, Literal["NOT_SPAM"]]:
                 buffer = BytesIO()
                 await file.write_chunks_to(buffer.write)
 
                 if buffer.getvalue() == b"Hello World":
-                    return True
+                    return synapse.module_api.NOT_SPAM
 
-                return False
+                return Codes.FORBIDDEN
 
 
         Args:
             file: An object that allows reading the contents of the media.
             file_info: Metadata about the file.
-
-        Returns:
-            True if the media should be blocked or False if it should be
-            allowed.
         """
 
         for callback in self._check_media_file_for_spam_callbacks:
             with Measure(
                 self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
             ):
-                spam = await delay_cancellation(callback(file_wrapper, file_info))
-            if spam:
-                return True
+                res = await delay_cancellation(callback(file_wrapper, file_info))
+                # Normalize return values to `Codes` or `"NOT_SPAM"`.
+                if res is False or res is self.NOT_SPAM:
+                    continue
+                elif res is True:
+                    return synapse.api.errors.Codes.FORBIDDEN
+                elif isinstance(res, synapse.api.errors.Codes):
+                    return res
+                else:
+                    logger.warning(
+                        "Module returned invalid value, rejecting media file as spam"
+                    )
+                    return synapse.api.errors.Codes.FORBIDDEN
 
-        return False
+        return self.NOT_SPAM
diff --git a/synapse/handlers/directory.py b/synapse/handlers/directory.py
index 1459a046de..8b0f16f965 100644
--- a/synapse/handlers/directory.py
+++ b/synapse/handlers/directory.py
@@ -28,6 +28,7 @@ from synapse.api.errors import (
     SynapseError,
 )
 from synapse.appservice import ApplicationService
+from synapse.module_api import NOT_SPAM
 from synapse.storage.databases.main.directory import RoomAliasMapping
 from synapse.types import JsonDict, Requester, RoomAlias, UserID, get_domain_from_id
 
@@ -141,10 +142,15 @@ class DirectoryHandler:
                         403, "You must be in the room to create an alias for it"
                     )
 
-            if not await self.spam_checker.user_may_create_room_alias(
+            spam_check = await self.spam_checker.user_may_create_room_alias(
                 user_id, room_alias
-            ):
-                raise AuthError(403, "This user is not permitted to create this alias")
+            )
+            if spam_check != self.spam_checker.NOT_SPAM:
+                raise AuthError(
+                    403,
+                    "This user is not permitted to create this alias",
+                    spam_check,
+                )
 
             if not self.config.roomdirectory.is_alias_creation_allowed(
                 user_id, room_id, room_alias_str
@@ -430,9 +436,12 @@ class DirectoryHandler:
         """
         user_id = requester.user.to_string()
 
-        if not await self.spam_checker.user_may_publish_room(user_id, room_id):
+        spam_check = await self.spam_checker.user_may_publish_room(user_id, room_id)
+        if spam_check != NOT_SPAM:
             raise AuthError(
-                403, "This user is not permitted to publish rooms to the room list"
+                403,
+                "This user is not permitted to publish rooms to the room list",
+                spam_check,
             )
 
         if requester.is_guest:
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 1e5694244a..34cc5ecd11 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -59,6 +59,7 @@ from synapse.federation.federation_client import InvalidResponseError
 from synapse.http.servlet import assert_params_in_dict
 from synapse.logging.context import nested_logging_context
 from synapse.metrics.background_process_metrics import run_as_background_process
+from synapse.module_api import NOT_SPAM
 from synapse.replication.http.federation import (
     ReplicationCleanRoomRestServlet,
     ReplicationStoreRoomOnOutlierMembershipRestServlet,
@@ -820,11 +821,14 @@ class FederationHandler:
         if self.hs.config.server.block_non_admin_invites:
             raise SynapseError(403, "This server does not accept room invites")
 
-        if not await self.spam_checker.user_may_invite(
+        spam_check = await self.spam_checker.user_may_invite(
             event.sender, event.state_key, event.room_id
-        ):
+        )
+        if spam_check != NOT_SPAM:
             raise SynapseError(
-                403, "This user is not permitted to send invites to this server/user"
+                403,
+                "This user is not permitted to send invites to this server/user",
+                spam_check,
             )
 
         membership = event.content.get("membership")
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 9b17939163..ad87c41782 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -954,14 +954,12 @@ class EventCreationHandler:
                             "Spam-check module returned invalid error value. Expecting [code, dict], got %s",
                             spam_check_result,
                         )
-                        spam_check_result = Codes.FORBIDDEN
 
-                if isinstance(spam_check_result, Codes):
-                    raise SynapseError(
-                        403,
-                        "This message has been rejected as probable spam",
-                        spam_check_result,
-                    )
+                        raise SynapseError(
+                            403,
+                            "This message has been rejected as probable spam",
+                            Codes.FORBIDDEN,
+                        )
 
                 # Backwards compatibility: if the return value is not an error code, it
                 # means the module returned an error message to be included in the
diff --git a/synapse/handlers/room.py b/synapse/handlers/room.py
index d8918ee1aa..42aae4a215 100644
--- a/synapse/handlers/room.py
+++ b/synapse/handlers/room.py
@@ -62,6 +62,7 @@ from synapse.events.utils import copy_and_fixup_power_levels_contents
 from synapse.federation.federation_client import InvalidResponseError
 from synapse.handlers.federation import get_domains_from_state
 from synapse.handlers.relations import BundledAggregations
+from synapse.module_api import NOT_SPAM
 from synapse.rest.admin._base import assert_user_is_admin
 from synapse.storage.state import StateFilter
 from synapse.streams import EventSource
@@ -436,10 +437,9 @@ class RoomCreationHandler:
         """
         user_id = requester.user.to_string()
 
-        if not await self.spam_checker.user_may_create_room(user_id):
-            raise SynapseError(
-                403, "You are not permitted to create rooms", Codes.FORBIDDEN
-            )
+        spam_check = await self.spam_checker.user_may_create_room(user_id)
+        if spam_check != NOT_SPAM:
+            raise SynapseError(403, "You are not permitted to create rooms", spam_check)
 
         creation_content: JsonDict = {
             "room_version": new_room_version.identifier,
@@ -726,12 +726,12 @@ class RoomCreationHandler:
         invite_3pid_list = config.get("invite_3pid", [])
         invite_list = config.get("invite", [])
 
-        if not is_requester_admin and not (
-            await self.spam_checker.user_may_create_room(user_id)
-        ):
-            raise SynapseError(
-                403, "You are not permitted to create rooms", Codes.FORBIDDEN
-            )
+        if not is_requester_admin:
+            spam_check = await self.spam_checker.user_may_create_room(user_id)
+            if spam_check != NOT_SPAM:
+                raise SynapseError(
+                    403, "You are not permitted to create rooms", spam_check
+                )
 
         if ratelimit:
             await self.request_ratelimiter.ratelimit(requester)
diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py
index d1199a0644..e89b7441ad 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -38,6 +38,7 @@ from synapse.event_auth import get_named_level, get_power_level_event
 from synapse.events import EventBase
 from synapse.events.snapshot import EventContext
 from synapse.handlers.profile import MAX_AVATAR_URL_LEN, MAX_DISPLAYNAME_LEN
+from synapse.module_api import NOT_SPAM
 from synapse.storage.state import StateFilter
 from synapse.types import (
     JsonDict,
@@ -683,7 +684,7 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):
             if target_id == self._server_notices_mxid:
                 raise SynapseError(HTTPStatus.FORBIDDEN, "Cannot invite this user")
 
-            block_invite = False
+            block_invite_code = None
 
             if (
                 self._server_notices_mxid is not None
@@ -701,16 +702,19 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):
                         "Blocking invite: user is not admin and non-admin "
                         "invites disabled"
                     )
-                    block_invite = True
+                    block_invite_code = Codes.FORBIDDEN
 
-                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 != NOT_SPAM:
                     logger.info("Blocking invite due to spam checker")
-                    block_invite = True
+                    block_invite_code = spam_check
 
-            if block_invite:
-                raise SynapseError(403, "Invites have been disabled on this server")
+            if block_invite_code is not None:
+                raise SynapseError(
+                    403, "Invites have been disabled on this server", block_invite_code
+                )
 
         # An empty prev_events list is allowed as long as the auth_event_ids are present
         if prev_event_ids is not None:
@@ -818,11 +822,12 @@ 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 != NOT_SPAM:
+                    raise SynapseError(403, "Not allowed to join this room", spam_check)
 
             # Check if a remote join should be performed.
             remote_join, remote_room_hosts = await self._should_perform_remote_join(
@@ -1369,13 +1374,14 @@ 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 != NOT_SPAM:
+                raise SynapseError(403, "Cannot send threepid invite", spam_check)
 
             stream_id = await self._make_and_store_3pid_invite(
                 requester,
diff --git a/synapse/module_api/__init__.py b/synapse/module_api/__init__.py
index 30b2aeffdd..6191c2dc96 100644
--- a/synapse/module_api/__init__.py
+++ b/synapse/module_api/__init__.py
@@ -115,6 +115,7 @@ from synapse.types import (
     JsonDict,
     JsonMapping,
     Requester,
+    RoomAlias,
     StateMap,
     UserID,
     UserInfo,
@@ -163,6 +164,7 @@ __all__ = [
     "EventBase",
     "StateMap",
     "ProfileInfo",
+    "RoomAlias",
     "UserProfile",
 ]
 
diff --git a/synapse/rest/media/v1/media_storage.py b/synapse/rest/media/v1/media_storage.py
index 604f18bf52..9137417342 100644
--- a/synapse/rest/media/v1/media_storage.py
+++ b/synapse/rest/media/v1/media_storage.py
@@ -36,6 +36,7 @@ from twisted.internet.defer import Deferred
 from twisted.internet.interfaces import IConsumer
 from twisted.protocols.basic import FileSender
 
+import synapse
 from synapse.api.errors import NotFoundError
 from synapse.logging.context import defer_to_thread, make_deferred_yieldable
 from synapse.util import Clock
@@ -145,15 +146,15 @@ class MediaStorage:
                     f.flush()
                     f.close()
 
-                    spam = await self.spam_checker.check_media_file_for_spam(
+                    spam_check = await self.spam_checker.check_media_file_for_spam(
                         ReadableFileWrapper(self.clock, fname), file_info
                     )
-                    if spam:
+                    if spam_check != synapse.module_api.NOT_SPAM:
                         logger.info("Blocking media due to spam checker")
                         # Note that we'll delete the stored media, due to the
                         # try/except below. The media also won't be stored in
                         # the DB.
-                        raise SpamMediaException()
+                        raise SpamMediaException(errcode=spam_check)
 
                     for provider in self.storage_providers:
                         await provider.store_file(path, file_info)