Move Spam Checker callbacks to a dedicated file (#15453)

3 files changed, 847 insertions, 18 deletions

diff --git a/synapse/module_api/__init__.py b/synapse/module_api/__init__.py
index 595c23e78d..eeafea74d1 100644
--- a/synapse/module_api/__init__.py
+++ b/synapse/module_api/__init__.py
@@ -44,20 +44,6 @@ from synapse.events.presence_router import (
     GET_USERS_FOR_STATES_CALLBACK,
     PresenceRouter,
 )
-from synapse.events.spamcheck import (
-    CHECK_EVENT_FOR_SPAM_CALLBACK,
-    CHECK_MEDIA_FILE_FOR_SPAM_CALLBACK,
-    CHECK_REGISTRATION_FOR_SPAM_CALLBACK,
-    CHECK_USERNAME_FOR_SPAM_CALLBACK,
-    SHOULD_DROP_FEDERATED_EVENT_CALLBACK,
-    USER_MAY_CREATE_ROOM_ALIAS_CALLBACK,
-    USER_MAY_CREATE_ROOM_CALLBACK,
-    USER_MAY_INVITE_CALLBACK,
-    USER_MAY_JOIN_ROOM_CALLBACK,
-    USER_MAY_PUBLISH_ROOM_CALLBACK,
-    USER_MAY_SEND_3PID_INVITE_CALLBACK,
-    SpamChecker,
-)
 from synapse.events.third_party_rules import (
     CHECK_CAN_DEACTIVATE_USER_CALLBACK,
     CHECK_CAN_SHUTDOWN_ROOM_CALLBACK,
@@ -105,6 +91,20 @@ from synapse.module_api.callbacks.account_validity_callbacks import (
     ON_LEGACY_SEND_MAIL_CALLBACK,
     ON_USER_REGISTRATION_CALLBACK,
 )
+from synapse.module_api.callbacks.spamchecker_callbacks import (
+    CHECK_EVENT_FOR_SPAM_CALLBACK,
+    CHECK_MEDIA_FILE_FOR_SPAM_CALLBACK,
+    CHECK_REGISTRATION_FOR_SPAM_CALLBACK,
+    CHECK_USERNAME_FOR_SPAM_CALLBACK,
+    SHOULD_DROP_FEDERATED_EVENT_CALLBACK,
+    USER_MAY_CREATE_ROOM_ALIAS_CALLBACK,
+    USER_MAY_CREATE_ROOM_CALLBACK,
+    USER_MAY_INVITE_CALLBACK,
+    USER_MAY_JOIN_ROOM_CALLBACK,
+    USER_MAY_PUBLISH_ROOM_CALLBACK,
+    USER_MAY_SEND_3PID_INVITE_CALLBACK,
+    SpamCheckerModuleApiCallbacks,
+)
 from synapse.rest.client.login import LoginResponse
 from synapse.storage import DataStore
 from synapse.storage.background_updates import (
@@ -147,7 +147,7 @@ are loaded into Synapse.
 """
 
 PRESENCE_ALL_USERS = PresenceRouter.ALL_USERS
-NOT_SPAM = SpamChecker.NOT_SPAM
+NOT_SPAM = SpamCheckerModuleApiCallbacks.NOT_SPAM
 
 __all__ = [
     "errors",
@@ -271,7 +271,6 @@ class ModuleApi:
         self._public_room_list_manager = PublicRoomListManager(hs)
         self._account_data_manager = AccountDataManager(hs)
 
-        self._spam_checker = hs.get_spam_checker()
         self._third_party_event_rules = hs.get_third_party_event_rules()
         self._password_auth_provider = hs.get_password_auth_provider()
         self._presence_router = hs.get_presence_router()
@@ -305,7 +304,7 @@ class ModuleApi:
 
         Added in Synapse v1.37.0.
         """
-        return self._spam_checker.register_callbacks(
+        return self._callbacks.spam_checker.register_callbacks(
             check_event_for_spam=check_event_for_spam,
             should_drop_federated_event=should_drop_federated_event,
             user_may_join_room=user_may_join_room,
diff --git a/synapse/module_api/callbacks/__init__.py b/synapse/module_api/callbacks/__init__.py
index 3d977bf655..5cdb2c003a 100644
--- a/synapse/module_api/callbacks/__init__.py
+++ b/synapse/module_api/callbacks/__init__.py
@@ -12,11 +12,20 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from synapse.server import HomeServer
+
 from synapse.module_api.callbacks.account_validity_callbacks import (
     AccountValidityModuleApiCallbacks,
 )
+from synapse.module_api.callbacks.spamchecker_callbacks import (
+    SpamCheckerModuleApiCallbacks,
+)
 
 
 class ModuleApiCallbacks:
-    def __init__(self) -> None:
+    def __init__(self, hs: "HomeServer") -> None:
         self.account_validity = AccountValidityModuleApiCallbacks()
+        self.spam_checker = SpamCheckerModuleApiCallbacks(hs)
diff --git a/synapse/module_api/callbacks/spamchecker_callbacks.py b/synapse/module_api/callbacks/spamchecker_callbacks.py
new file mode 100644
index 0000000000..4456d1b81e
--- /dev/null
+++ b/synapse/module_api/callbacks/spamchecker_callbacks.py
@@ -0,0 +1,821 @@
+# Copyright 2017 New Vector Ltd
+# Copyright 2019 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import inspect
+import logging
+from typing import (
+    TYPE_CHECKING,
+    Any,
+    Awaitable,
+    Callable,
+    Collection,
+    List,
+    Optional,
+    Tuple,
+    Union,
+)
+
+# `Literal` appears with Python 3.8.
+from typing_extensions import Literal
+
+import synapse
+from synapse.api.errors import Codes
+from synapse.logging.opentracing import trace
+from synapse.media._base import FileInfo
+from synapse.media.media_storage import ReadableFileWrapper
+from synapse.spam_checker_api import RegistrationBehaviour
+from synapse.types import JsonDict, RoomAlias, UserProfile
+from synapse.util.async_helpers import delay_cancellation, maybe_awaitable
+from synapse.util.metrics import Measure
+
+if TYPE_CHECKING:
+    import synapse.events
+    import synapse.server
+
+logger = logging.getLogger(__name__)
+
+CHECK_EVENT_FOR_SPAM_CALLBACK = Callable[
+    ["synapse.events.EventBase"],
+    Awaitable[
+        Union[
+            str,
+            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, JsonDict],
+            # Deprecated
+            bool,
+        ]
+    ],
+]
+SHOULD_DROP_FEDERATED_EVENT_CALLBACK = Callable[
+    ["synapse.events.EventBase"],
+    Awaitable[Union[bool, str]],
+]
+USER_MAY_JOIN_ROOM_CALLBACK = Callable[
+    [str, str, bool],
+    Awaitable[
+        Union[
+            Literal["NOT_SPAM"],
+            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, JsonDict],
+            # Deprecated
+            bool,
+        ]
+    ],
+]
+USER_MAY_INVITE_CALLBACK = Callable[
+    [str, str, str],
+    Awaitable[
+        Union[
+            Literal["NOT_SPAM"],
+            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, JsonDict],
+            # Deprecated
+            bool,
+        ]
+    ],
+]
+USER_MAY_SEND_3PID_INVITE_CALLBACK = Callable[
+    [str, str, str, str],
+    Awaitable[
+        Union[
+            Literal["NOT_SPAM"],
+            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, JsonDict],
+            # Deprecated
+            bool,
+        ]
+    ],
+]
+USER_MAY_CREATE_ROOM_CALLBACK = Callable[
+    [str],
+    Awaitable[
+        Union[
+            Literal["NOT_SPAM"],
+            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, JsonDict],
+            # Deprecated
+            bool,
+        ]
+    ],
+]
+USER_MAY_CREATE_ROOM_ALIAS_CALLBACK = Callable[
+    [str, RoomAlias],
+    Awaitable[
+        Union[
+            Literal["NOT_SPAM"],
+            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, JsonDict],
+            # Deprecated
+            bool,
+        ]
+    ],
+]
+USER_MAY_PUBLISH_ROOM_CALLBACK = Callable[
+    [str, str],
+    Awaitable[
+        Union[
+            Literal["NOT_SPAM"],
+            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, JsonDict],
+            # Deprecated
+            bool,
+        ]
+    ],
+]
+CHECK_USERNAME_FOR_SPAM_CALLBACK = Callable[[UserProfile], Awaitable[bool]]
+LEGACY_CHECK_REGISTRATION_FOR_SPAM_CALLBACK = Callable[
+    [
+        Optional[dict],
+        Optional[str],
+        Collection[Tuple[str, str]],
+    ],
+    Awaitable[RegistrationBehaviour],
+]
+CHECK_REGISTRATION_FOR_SPAM_CALLBACK = Callable[
+    [
+        Optional[dict],
+        Optional[str],
+        Collection[Tuple[str, str]],
+        Optional[str],
+    ],
+    Awaitable[RegistrationBehaviour],
+]
+CHECK_MEDIA_FILE_FOR_SPAM_CALLBACK = Callable[
+    [ReadableFileWrapper, FileInfo],
+    Awaitable[
+        Union[
+            Literal["NOT_SPAM"],
+            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, JsonDict],
+            # Deprecated
+            bool,
+        ]
+    ],
+]
+
+
+def load_legacy_spam_checkers(hs: "synapse.server.HomeServer") -> None:
+    """Wrapper that loads spam checkers configured using the old configuration, and
+    registers the spam checker hooks they implement.
+    """
+    spam_checkers: List[Any] = []
+    api = hs.get_module_api()
+    for module, config in hs.config.spamchecker.spam_checkers:
+        # Older spam checkers don't accept the `api` argument, so we
+        # try and detect support.
+        spam_args = inspect.getfullargspec(module)
+        if "api" in spam_args.args:
+            spam_checkers.append(module(config=config, api=api))
+        else:
+            spam_checkers.append(module(config=config))
+
+    # The known spam checker hooks. If a spam checker module implements a method
+    # which name appears in this set, we'll want to register it.
+    spam_checker_methods = {
+        "check_event_for_spam",
+        "user_may_invite",
+        "user_may_create_room",
+        "user_may_create_room_alias",
+        "user_may_publish_room",
+        "check_username_for_spam",
+        "check_registration_for_spam",
+        "check_media_file_for_spam",
+    }
+
+    for spam_checker in spam_checkers:
+        # Methods on legacy spam checkers might not be async, so we wrap them around a
+        # wrapper that will call maybe_awaitable on the result.
+        def async_wrapper(f: Optional[Callable]) -> Optional[Callable[..., Awaitable]]:
+            # f might be None if the callback isn't implemented by the module. In this
+            # case we don't want to register a callback at all so we return None.
+            if f is None:
+                return None
+
+            wrapped_func = f
+
+            if f.__name__ == "check_registration_for_spam":
+                checker_args = inspect.signature(f)
+                if len(checker_args.parameters) == 3:
+                    # Backwards compatibility; some modules might implement a hook that
+                    # doesn't expect a 4th argument. In this case, wrap it in a function
+                    # that gives it only 3 arguments and drops the auth_provider_id on
+                    # the floor.
+                    def wrapper(
+                        email_threepid: Optional[dict],
+                        username: Optional[str],
+                        request_info: Collection[Tuple[str, str]],
+                        auth_provider_id: Optional[str],
+                    ) -> Union[Awaitable[RegistrationBehaviour], RegistrationBehaviour]:
+                        # Assertion required because mypy can't prove we won't
+                        # change `f` back to `None`. See
+                        # https://mypy.readthedocs.io/en/latest/common_issues.html#narrowing-and-inner-functions
+                        assert f is not None
+
+                        return f(
+                            email_threepid,
+                            username,
+                            request_info,
+                        )
+
+                    wrapped_func = wrapper
+                elif len(checker_args.parameters) != 4:
+                    raise RuntimeError(
+                        "Bad signature for callback check_registration_for_spam",
+                    )
+
+            def run(*args: Any, **kwargs: Any) -> Awaitable:
+                # Assertion required because mypy can't prove we won't change `f`
+                # back to `None`. See
+                # https://mypy.readthedocs.io/en/latest/common_issues.html#narrowing-and-inner-functions
+                assert wrapped_func is not None
+
+                return maybe_awaitable(wrapped_func(*args, **kwargs))
+
+            return run
+
+        # Register the hooks through the module API.
+        hooks = {
+            hook: async_wrapper(getattr(spam_checker, hook, None))
+            for hook in spam_checker_methods
+        }
+
+        api.register_spam_checker_callbacks(**hooks)
+
+
+class SpamCheckerModuleApiCallbacks:
+    NOT_SPAM: Literal["NOT_SPAM"] = "NOT_SPAM"
+
+    def __init__(self, hs: "synapse.server.HomeServer") -> None:
+        self.clock = hs.get_clock()
+
+        self._check_event_for_spam_callbacks: List[CHECK_EVENT_FOR_SPAM_CALLBACK] = []
+        self._should_drop_federated_event_callbacks: List[
+            SHOULD_DROP_FEDERATED_EVENT_CALLBACK
+        ] = []
+        self._user_may_join_room_callbacks: List[USER_MAY_JOIN_ROOM_CALLBACK] = []
+        self._user_may_invite_callbacks: List[USER_MAY_INVITE_CALLBACK] = []
+        self._user_may_send_3pid_invite_callbacks: List[
+            USER_MAY_SEND_3PID_INVITE_CALLBACK
+        ] = []
+        self._user_may_create_room_callbacks: List[USER_MAY_CREATE_ROOM_CALLBACK] = []
+        self._user_may_create_room_alias_callbacks: List[
+            USER_MAY_CREATE_ROOM_ALIAS_CALLBACK
+        ] = []
+        self._user_may_publish_room_callbacks: List[USER_MAY_PUBLISH_ROOM_CALLBACK] = []
+        self._check_username_for_spam_callbacks: List[
+            CHECK_USERNAME_FOR_SPAM_CALLBACK
+        ] = []
+        self._check_registration_for_spam_callbacks: List[
+            CHECK_REGISTRATION_FOR_SPAM_CALLBACK
+        ] = []
+        self._check_media_file_for_spam_callbacks: List[
+            CHECK_MEDIA_FILE_FOR_SPAM_CALLBACK
+        ] = []
+
+    def register_callbacks(
+        self,
+        check_event_for_spam: Optional[CHECK_EVENT_FOR_SPAM_CALLBACK] = None,
+        should_drop_federated_event: Optional[
+            SHOULD_DROP_FEDERATED_EVENT_CALLBACK
+        ] = None,
+        user_may_join_room: Optional[USER_MAY_JOIN_ROOM_CALLBACK] = None,
+        user_may_invite: Optional[USER_MAY_INVITE_CALLBACK] = None,
+        user_may_send_3pid_invite: Optional[USER_MAY_SEND_3PID_INVITE_CALLBACK] = None,
+        user_may_create_room: Optional[USER_MAY_CREATE_ROOM_CALLBACK] = None,
+        user_may_create_room_alias: Optional[
+            USER_MAY_CREATE_ROOM_ALIAS_CALLBACK
+        ] = None,
+        user_may_publish_room: Optional[USER_MAY_PUBLISH_ROOM_CALLBACK] = None,
+        check_username_for_spam: Optional[CHECK_USERNAME_FOR_SPAM_CALLBACK] = None,
+        check_registration_for_spam: Optional[
+            CHECK_REGISTRATION_FOR_SPAM_CALLBACK
+        ] = None,
+        check_media_file_for_spam: Optional[CHECK_MEDIA_FILE_FOR_SPAM_CALLBACK] = None,
+    ) -> None:
+        """Register callbacks from module for each hook."""
+        if check_event_for_spam is not None:
+            self._check_event_for_spam_callbacks.append(check_event_for_spam)
+
+        if should_drop_federated_event is not None:
+            self._should_drop_federated_event_callbacks.append(
+                should_drop_federated_event
+            )
+
+        if user_may_join_room is not None:
+            self._user_may_join_room_callbacks.append(user_may_join_room)
+
+        if user_may_invite is not None:
+            self._user_may_invite_callbacks.append(user_may_invite)
+
+        if user_may_send_3pid_invite is not None:
+            self._user_may_send_3pid_invite_callbacks.append(
+                user_may_send_3pid_invite,
+            )
+
+        if user_may_create_room is not None:
+            self._user_may_create_room_callbacks.append(user_may_create_room)
+
+        if user_may_create_room_alias is not None:
+            self._user_may_create_room_alias_callbacks.append(
+                user_may_create_room_alias,
+            )
+
+        if user_may_publish_room is not None:
+            self._user_may_publish_room_callbacks.append(user_may_publish_room)
+
+        if check_username_for_spam is not None:
+            self._check_username_for_spam_callbacks.append(check_username_for_spam)
+
+        if check_registration_for_spam is not None:
+            self._check_registration_for_spam_callbacks.append(
+                check_registration_for_spam,
+            )
+
+        if check_media_file_for_spam is not None:
+            self._check_media_file_for_spam_callbacks.append(check_media_file_for_spam)
+
+    @trace
+    async def check_event_for_spam(
+        self, event: "synapse.events.EventBase"
+    ) -> Union[Tuple[Codes, JsonDict], 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
+        sent by a local user. If it is sent by a user on another server, the
+        event is soft-failed.
+
+        Args:
+            event: the event to be checked
+
+        Returns:
+            - `NOT_SPAM` if the event is considered good (non-spammy) and should be let
+                through. Other spamcheck filters may still reject it.
+            - A `Code` if the event is considered spammy and is rejected with a specific
+                error message/code.
+            - A string that isn't `NOT_SPAM` if the event is considered spammy and the
+                string should be used as the client-facing error message. This usage is
+                generally discouraged as it doesn't support internationalization.
+        """
+        for callback in self._check_event_for_spam_callbacks:
+            with Measure(
+                self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
+            ):
+                res = await delay_cancellation(callback(event))
+                if res is False or res == self.NOT_SPAM:
+                    # This spam-checker accepts the event.
+                    # Other spam-checkers may reject it, though.
+                    continue
+                elif res is True:
+                    # This spam-checker rejects the event with deprecated
+                    # return value `True`
+                    return synapse.api.errors.Codes.FORBIDDEN, {}
+                elif (
+                    isinstance(res, tuple)
+                    and len(res) == 2
+                    and isinstance(res[0], synapse.api.errors.Codes)
+                    and isinstance(res[1], dict)
+                ):
+                    return res
+                elif isinstance(res, synapse.api.errors.Codes):
+                    return res, {}
+                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
+                    # for sure that the module actually returns it.
+                    logger.warning(
+                        "Module returned invalid value, rejecting message as spam"
+                    )
+                    res = "This message has been rejected as probable spam"
+                else:
+                    # The module rejected the event either with a `Codes`
+                    # or some other `str`. In either case, we stop here.
+                    pass
+
+                return res
+
+        # No spam-checker has rejected the event, let it pass.
+        return self.NOT_SPAM
+
+    async def should_drop_federated_event(
+        self, event: "synapse.events.EventBase"
+    ) -> Union[bool, str]:
+        """Checks if a given federated event is considered "spammy" by this
+        server.
+
+        If the server considers an event spammy, it will be silently dropped,
+        and in doing so will split-brain our view of the room's DAG.
+
+        Args:
+            event: the event to be checked
+
+        Returns:
+            True if the event should be silently dropped
+        """
+        for callback in self._should_drop_federated_event_callbacks:
+            with Measure(
+                self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
+            ):
+                res: Union[bool, str] = await delay_cancellation(callback(event))
+            if res:
+                return res
+
+        return False
+
+    async def user_may_join_room(
+        self, user_id: str, room_id: str, is_invited: bool
+    ) -> Union[Tuple[Codes, JsonDict], Literal["NOT_SPAM"]]:
+        """Checks if a given users is allowed to join a room.
+        Not called when a user creates a room.
+
+        Args:
+            userid: The ID of the user wanting to join the room
+            room_id: The ID of the room the user wants to join
+            is_invited: Whether the user is invited into the room
+
+        Returns:
+            NOT_SPAM if the operation is permitted, [Codes, Dict] otherwise.
+        """
+        for callback in self._user_may_join_room_callbacks:
+            with Measure(
+                self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
+            ):
+                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, {}
+                elif (
+                    isinstance(res, tuple)
+                    and len(res) == 2
+                    and isinstance(res[0], synapse.api.errors.Codes)
+                    and isinstance(res[1], dict)
+                ):
+                    return res
+                else:
+                    logger.warning(
+                        "Module returned invalid value, rejecting join as spam"
+                    )
+                    return synapse.api.errors.Codes.FORBIDDEN, {}
+
+        # 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
+    ) -> Union[Tuple[Codes, dict], Literal["NOT_SPAM"]]:
+        """Checks if a given user may send an invite
+
+        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:
+            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__)
+            ):
+                res = await delay_cancellation(
+                    callback(inviter_userid, invitee_userid, room_id)
+                )
+                # 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, {}
+                elif (
+                    isinstance(res, tuple)
+                    and len(res) == 2
+                    and isinstance(res[0], synapse.api.errors.Codes)
+                    and isinstance(res[1], dict)
+                ):
+                    return res
+                else:
+                    logger.warning(
+                        "Module returned invalid value, rejecting invite as spam"
+                    )
+                    return synapse.api.errors.Codes.FORBIDDEN, {}
+
+        # 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
+    ) -> Union[Tuple[Codes, dict], Literal["NOT_SPAM"]]:
+        """Checks if a given user may invite a given threepid into the room
+
+        Note that if the threepid is already associated with a Matrix user ID, Synapse
+        will call user_may_invite with said user ID instead.
+
+        Args:
+            inviter_userid: The user ID of the sender of the invitation
+            medium: The 3PID's medium (e.g. "email")
+            address: The 3PID's address (e.g. "alice@example.com")
+            room_id: The room ID
+
+        Returns:
+            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__)
+            ):
+                res = await delay_cancellation(
+                    callback(inviter_userid, medium, address, room_id)
+                )
+                # 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, {}
+                elif (
+                    isinstance(res, tuple)
+                    and len(res) == 2
+                    and isinstance(res[0], synapse.api.errors.Codes)
+                    and isinstance(res[1], dict)
+                ):
+                    return res
+                else:
+                    logger.warning(
+                        "Module returned invalid value, rejecting 3pid invite as spam"
+                    )
+                    return synapse.api.errors.Codes.FORBIDDEN, {}
+
+        return self.NOT_SPAM
+
+    async def user_may_create_room(
+        self, userid: str
+    ) -> Union[Tuple[Codes, dict], Literal["NOT_SPAM"]]:
+        """Checks if a given user may create a room
+
+        Args:
+            userid: The ID of the user attempting to create a room
+        """
+        for callback in self._user_may_create_room_callbacks:
+            with Measure(
+                self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
+            ):
+                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, {}
+                elif (
+                    isinstance(res, tuple)
+                    and len(res) == 2
+                    and isinstance(res[0], synapse.api.errors.Codes)
+                    and isinstance(res[1], dict)
+                ):
+                    return res
+                else:
+                    logger.warning(
+                        "Module returned invalid value, rejecting room creation as spam"
+                    )
+                    return synapse.api.errors.Codes.FORBIDDEN, {}
+
+        return self.NOT_SPAM
+
+    async def user_may_create_room_alias(
+        self, userid: str, room_alias: RoomAlias
+    ) -> Union[Tuple[Codes, dict], Literal["NOT_SPAM"]]:
+        """Checks if a given user may create a room alias
+
+        Args:
+            userid: The ID of the user attempting to create a room alias
+            room_alias: The alias to be created
+
+        """
+        for callback in self._user_may_create_room_alias_callbacks:
+            with Measure(
+                self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
+            ):
+                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, {}
+                elif (
+                    isinstance(res, tuple)
+                    and len(res) == 2
+                    and isinstance(res[0], synapse.api.errors.Codes)
+                    and isinstance(res[1], dict)
+                ):
+                    return res
+                else:
+                    logger.warning(
+                        "Module returned invalid value, rejecting room create as spam"
+                    )
+                    return synapse.api.errors.Codes.FORBIDDEN, {}
+
+        return self.NOT_SPAM
+
+    async def user_may_publish_room(
+        self, userid: str, room_id: str
+    ) -> Union[Tuple[Codes, dict], Literal["NOT_SPAM"]]:
+        """Checks if a given user may publish a room to the directory
+
+        Args:
+            userid: The user ID attempting to publish the room
+            room_id: The ID of the room that would be published
+        """
+        for callback in self._user_may_publish_room_callbacks:
+            with Measure(
+                self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
+            ):
+                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, {}
+                elif (
+                    isinstance(res, tuple)
+                    and len(res) == 2
+                    and isinstance(res[0], synapse.api.errors.Codes)
+                    and isinstance(res[1], dict)
+                ):
+                    return res
+                else:
+                    logger.warning(
+                        "Module returned invalid value, rejecting room publication as spam"
+                    )
+                    return synapse.api.errors.Codes.FORBIDDEN, {}
+
+        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.
+
+        If the server considers a username spammy, then it will not be included in
+        user directory results.
+
+        Args:
+            user_profile: The user information to check, it contains the keys:
+                * user_id
+                * display_name
+                * avatar_url
+
+        Returns:
+            True if the user is spammy.
+        """
+        for callback in self._check_username_for_spam_callbacks:
+            with Measure(
+                self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
+            ):
+                # Make a copy of the user profile object to ensure the spam checker cannot
+                # modify it.
+                res = await delay_cancellation(callback(user_profile.copy()))
+            if res:
+                return True
+
+        return False
+
+    async def check_registration_for_spam(
+        self,
+        email_threepid: Optional[dict],
+        username: Optional[str],
+        request_info: Collection[Tuple[str, str]],
+        auth_provider_id: Optional[str] = None,
+    ) -> RegistrationBehaviour:
+        """Checks if we should allow the given registration request.
+
+        Args:
+            email_threepid: The email threepid used for registering, if any
+            username: The request user name, if any
+            request_info: List of tuples of user agent and IP that
+                were used during the registration process.
+            auth_provider_id: The SSO IdP the user used, e.g "oidc", "saml",
+                "cas". If any. Note this does not include users registered
+                via a password provider.
+
+        Returns:
+            Enum for how the request should be handled
+        """
+
+        for callback in self._check_registration_for_spam_callbacks:
+            with Measure(
+                self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
+            ):
+                behaviour = await delay_cancellation(
+                    callback(email_threepid, username, request_info, auth_provider_id)
+                )
+            assert isinstance(behaviour, RegistrationBehaviour)
+            if behaviour != RegistrationBehaviour.ALLOW:
+                return behaviour
+
+        return RegistrationBehaviour.ALLOW
+
+    async def check_media_file_for_spam(
+        self, file_wrapper: ReadableFileWrapper, file_info: FileInfo
+    ) -> Union[Tuple[Codes, dict], 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
+        thumbnail generated for those, and web pages/images used for URL
+        previews.
+
+        Note that care should be taken to not do blocking IO operations in the
+        main thread. For example, to get the contents of a file a module
+        should do::
+
+            async def check_media_file_for_spam(
+                self, file: ReadableFileWrapper, file_info: FileInfo
+            ) -> Union[Codes, Literal["NOT_SPAM"]]:
+                buffer = BytesIO()
+                await file.write_chunks_to(buffer.write)
+
+                if buffer.getvalue() == b"Hello World":
+                    return synapse.module_api.NOT_SPAM
+
+                return Codes.FORBIDDEN
+
+
+        Args:
+            file: An object that allows reading the contents of the media.
+            file_info: Metadata about the file.
+        """
+
+        for callback in self._check_media_file_for_spam_callbacks:
+            with Measure(
+                self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
+            ):
+                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, {}
+                elif (
+                    isinstance(res, tuple)
+                    and len(res) == 2
+                    and isinstance(res[0], synapse.api.errors.Codes)
+                    and isinstance(res[1], dict)
+                ):
+                    return res
+                else:
+                    logger.warning(
+                        "Module returned invalid value, rejecting media file as spam"
+                    )
+                    return synapse.api.errors.Codes.FORBIDDEN, {}
+
+        return self.NOT_SPAM