# Spam checker callbacks Spam checker callbacks allow module developers to implement spam mitigation actions for Synapse instances. Spam checker callbacks can be registered using the module API's `register_spam_checker_callbacks` method. ## Callbacks The available spam checker callbacks are: ### `check_event_for_spam` _First introduced in Synapse v1.37.0_ _Changed in Synapse v1.60.0: `synapse.module_api.NOT_SPAM` and `synapse.module_api.errors.Codes` can be returned by this callback. Returning a boolean or a string is now deprecated._ ```python async def check_event_for_spam(event: "synapse.module_api.EventBase") -> Union["synapse.module_api.NOT_SPAM", "synapse.module_api.errors.Codes", str, bool] ``` Called when receiving an event from a client or via federation. The callback must return one of: - `synapse.module_api.NOT_SPAM`, to allow the operation. Other callbacks may still decide to reject it. - `synapse.module_api.errors.Codes` to reject the operation with an error code. In case of doubt, `synapse.module_api.errors.Codes.FORBIDDEN` is a good error code. - (deprecated) a non-`Codes` `str` to reject the operation and specify an error message. Note that clients typically will not localize the error message to the user's preferred locale. - (deprecated) `False`, which is the same as returning `synapse.module_api.NOT_SPAM`. - (deprecated) `True`, which is the same as returning `synapse.module_api.errors.Codes.FORBIDDEN`. If multiple modules implement this callback, they will be considered in order. If a callback returns `synapse.module_api.NOT_SPAM`, Synapse falls through to the next one. The value of the first callback that does not return `synapse.module_api.NOT_SPAM` will be used. If this happens, Synapse will not call any of the subsequent implementations of this callback. ### `user_may_join_room` _First introduced in Synapse v1.37.0_ _Changed in Synapse v1.61.0: `synapse.module_api.NOT_SPAM` and `synapse.module_api.errors.Codes` can be returned by this callback. Returning a boolean is now deprecated._ ```python async def user_may_join_room(user: str, room: str, is_invited: bool) -> Union["synapse.module_api.NOT_SPAM", "synapse.module_api.errors.Codes", bool] ``` Called when a user is trying to join a room. The user is represented by their Matrix user ID (e.g. `@alice:example.com`) and the room is represented by its Matrix ID (e.g. `!room:example.com`). The module is also given a boolean to indicate whether the user currently has a pending invite in the room. This callback isn't called if the join is performed by a server administrator, or in the context of a room creation. The callback must return one of: - `synapse.module_api.NOT_SPAM`, to allow the operation. Other callbacks may still decide to reject it. - `synapse.module_api.errors.Codes` to reject the operation with an error code. In case of doubt, `synapse.module_api.errors.Codes.FORBIDDEN` is a good error code. - (deprecated) `False`, which is the same as returning `synapse.module_api.NOT_SPAM`. - (deprecated) `True`, which is the same as returning `synapse.module_api.errors.Codes.FORBIDDEN`. If multiple modules implement this callback, they will be considered in order. If a callback returns `synapse.module_api.NOT_SPAM`, Synapse falls through to the next one. The value of the first callback that does not return `synapse.module_api.NOT_SPAM` will be used. If this happens, Synapse will not call any of the subsequent implementations of this callback. ### `user_may_invite` _First introduced in Synapse v1.37.0_ _Changed in Synapse v1.62.0: `synapse.module_api.NOT_SPAM` and `synapse.module_api.errors.Codes` can be returned by this callback. Returning a boolean is now deprecated._ ```python async def user_may_invite(inviter: str, invitee: str, room_id: str) -> Union["synapse.module_api.NOT_SPAM", "synapse.module_api.errors.Codes", bool] ``` Called when processing an invitation, both when one is created locally or when receiving an invite over federation. Both inviter and invitee are represented by their Matrix user ID (e.g. `@alice:example.com`). The callback must return one of: - `synapse.module_api.NOT_SPAM`, to allow the operation. Other callbacks may still decide to reject it. - `synapse.module_api.errors.Codes` to reject the operation with an error code. In case of doubt, `synapse.module_api.errors.Codes.FORBIDDEN` is a good error code. - (deprecated) `False`, which is the same as returning `synapse.module_api.NOT_SPAM`. - (deprecated) `True`, which is the same as returning `synapse.module_api.errors.Codes.FORBIDDEN`. If multiple modules implement this callback, they will be considered in order. If a callback returns `synapse.module_api.NOT_SPAM`, Synapse falls through to the next one. The value of the first callback that does not return `synapse.module_api.NOT_SPAM` will be used. If this happens, Synapse will not call any of the subsequent implementations of this callback. ### `user_may_send_3pid_invite` _First introduced in Synapse v1.45.0_ _Changed in Synapse v1.62.0: `synapse.module_api.NOT_SPAM` and `synapse.module_api.errors.Codes` can be returned by this callback. Returning a boolean is now deprecated._ ```python async def user_may_send_3pid_invite( inviter: str, medium: str, address: str, room_id: str, ) -> Union["synapse.module_api.NOT_SPAM", "synapse.module_api.errors.Codes", bool] ``` Called when processing an invitation using a third-party identifier (also called a 3PID, e.g. an email address or a phone number). It is only called when a 3PID invite is created locally - not when one is received in a room over federation. If the 3PID is already associated with a Matrix ID, the spam check will go through the `user_may_invite` callback instead. The inviter is represented by their Matrix user ID (e.g. `@alice:example.com`), and the invitee is represented by its medium (e.g. "email") and its address (e.g. `alice@example.com`). See [the Matrix specification](https://matrix.org/docs/spec/appendices#pid-types) for more information regarding third-party identifiers. For example, a call to this callback to send an invitation to the email address `alice@example.com` would look like this: ```python await user_may_send_3pid_invite( "@bob:example.com", # The inviter's user ID "email", # The medium of the 3PID to invite "alice@example.com", # The address of the 3PID to invite "!some_room:example.com", # The ID of the room to send the invite into ) ``` **Note**: If the third-party identifier is already associated with a matrix user ID, [`user_may_invite`](#user_may_invite) will be used instead. The callback must return one of: - `synapse.module_api.NOT_SPAM`, to allow the operation. Other callbacks may still decide to reject it. - `synapse.module_api.errors.Codes` to reject the operation with an error code. In case of doubt, `synapse.module_api.errors.Codes.FORBIDDEN` is a good error code. - (deprecated) `False`, which is the same as returning `synapse.module_api.NOT_SPAM`. - (deprecated) `True`, which is the same as returning `synapse.module_api.errors.Codes.FORBIDDEN`. If multiple modules implement this callback, they will be considered in order. If a callback returns `synapse.module_api.NOT_SPAM`, Synapse falls through to the next one. The value of the first callback that does not return `synapse.module_api.NOT_SPAM` will be used. If this happens, Synapse will not call any of the subsequent implementations of this callback. ### `user_may_create_room` _First introduced in Synapse v1.37.0_ _Changed in Synapse v1.62.0: `synapse.module_api.NOT_SPAM` and `synapse.module_api.errors.Codes` can be returned by this callback. Returning a boolean is now deprecated._ ```python async def user_may_create_room(user_id: str) -> Union["synapse.module_api.NOT_SPAM", "synapse.module_api.errors.Codes", bool] ``` Called when processing a room creation request. The callback must return one of: - `synapse.module_api.NOT_SPAM`, to allow the operation. Other callbacks may still decide to reject it. - `synapse.module_api.errors.Codes` to reject the operation with an error code. In case of doubt, `synapse.module_api.errors.Codes.FORBIDDEN` is a good error code. - (deprecated) `False`, which is the same as returning `synapse.module_api.NOT_SPAM`. - (deprecated) `True`, which is the same as returning `synapse.module_api.errors.Codes.FORBIDDEN`. If multiple modules implement this callback, they will be considered in order. If a callback returns `synapse.module_api.NOT_SPAM`, Synapse falls through to the next one. The value of the first callback that does not return `synapse.module_api.NOT_SPAM` will be used. If this happens, Synapse will not call any of the subsequent implementations of this callback. ### `user_may_create_room_alias` _First introduced in Synapse v1.37.0_ _Changed in Synapse v1.62.0: `synapse.module_api.NOT_SPAM` and `synapse.module_api.errors.Codes` can be returned by this callback. Returning a boolean is now deprecated._ ```python async def user_may_create_room_alias(user_id: str, room_alias: "synapse.module_api.RoomAlias") -> Union["synapse.module_api.NOT_SPAM", "synapse.module_api.errors.Codes", bool] ``` Called when trying to associate an alias with an existing room. The callback must return one of: - `synapse.module_api.NOT_SPAM`, to allow the operation. Other callbacks may still decide to reject it. - `synapse.module_api.errors.Codes` to reject the operation with an error code. In case of doubt, `synapse.module_api.errors.Codes.FORBIDDEN` is a good error code. - (deprecated) `False`, which is the same as returning `synapse.module_api.NOT_SPAM`. - (deprecated) `True`, which is the same as returning `synapse.module_api.errors.Codes.FORBIDDEN`. If multiple modules implement this callback, they will be considered in order. If a callback returns `synapse.module_api.NOT_SPAM`, Synapse falls through to the next one. The value of the first callback that does not return `synapse.module_api.NOT_SPAM` will be used. If this happens, Synapse will not call any of the subsequent implementations of this callback. ### `user_may_publish_room` _First introduced in Synapse v1.37.0_ _Changed in Synapse v1.62.0: `synapse.module_api.NOT_SPAM` and `synapse.module_api.errors.Codes` can be returned by this callback. Returning a boolean is now deprecated._ ```python async def user_may_publish_room(user_id: str, room_id: str) -> Union["synapse.module_api.NOT_SPAM", "synapse.module_api.errors.Codes", bool] ``` Called when trying to publish a room to the homeserver's public rooms directory. The callback must return one of: - `synapse.module_api.NOT_SPAM`, to allow the operation. Other callbacks may still decide to reject it. - `synapse.module_api.errors.Codes` to reject the operation with an error code. In case of doubt, `synapse.module_api.errors.Codes.FORBIDDEN` is a good error code. - (deprecated) `False`, which is the same as returning `synapse.module_api.NOT_SPAM`. - (deprecated) `True`, which is the same as returning `synapse.module_api.errors.Codes.FORBIDDEN`. If multiple modules implement this callback, they will be considered in order. If a callback returns `synapse.module_api.NOT_SPAM`, Synapse falls through to the next one. The value of the first callback that does not return `synapse.module_api.NOT_SPAM` will be used. If this happens, Synapse will not call any of the subsequent implementations of this callback. ### `check_username_for_spam` _First introduced in Synapse v1.37.0_ ```python async def check_username_for_spam(user_profile: synapse.module_api.UserProfile, requester_id: str) -> bool ``` Called when computing search results in the user directory. The module must return a `bool` indicating whether the given user should be excluded from user directory searches. Return `True` to indicate that the user is spammy and exclude them from search results; otherwise return `False`. The profile is represented as a dictionary with the following keys: * `user_id: str`. The Matrix ID for this user. * `display_name: Optional[str]`. The user's display name, or `None` if this user has not set a display name. * `avatar_url: Optional[str]`. The `mxc://` URL to the user's avatar, or `None` if this user has not set an avatar. The module is given a copy of the original dictionary, so modifying it from within the module cannot modify a user's profile when included in user directory search results. The requester_id parameter is the ID of the user that called the user directory API. If multiple modules implement this callback, they will be considered in order. If a callback returns `False`, Synapse falls through to the next one. The value of the first callback that does not return `False` will be used. If this happens, Synapse will not call any of the subsequent implementations of this callback. ### `check_registration_for_spam` _First introduced in Synapse v1.37.0_ ```python async def check_registration_for_spam( email_threepid: Optional[dict], username: Optional[str], request_info: Collection[Tuple[str, str]], auth_provider_id: Optional[str] = None, ) -> "synapse.spam_checker_api.RegistrationBehaviour" ``` Called when registering a new user. The module must return a `RegistrationBehaviour` indicating whether the registration can go through or must be denied, or whether the user may be allowed to register but will be shadow banned. The arguments passed to this callback are: * `email_threepid`: The email address used for registering, if any. * `username`: The username the user would like to register. Can be `None`, meaning that Synapse will generate one later. * `request_info`: A collection of tuples, which first item is a user agent, and which second item is an IP address. These user agents and IP addresses are the ones that were used during the registration process. * `auth_provider_id`: The identifier of the SSO authentication provider, if any. If multiple modules implement this callback, they will be considered in order. If a callback returns `RegistrationBehaviour.ALLOW`, Synapse falls through to the next one. The value of the first callback that does not return `RegistrationBehaviour.ALLOW` will be used. If this happens, Synapse will not call any of the subsequent implementations of this callback. ### `check_media_file_for_spam` _First introduced in Synapse v1.37.0_ _Changed in Synapse v1.62.0: `synapse.module_api.NOT_SPAM` and `synapse.module_api.errors.Codes` can be returned by this callback. Returning a boolean is now deprecated._ ```python async def check_media_file_for_spam( file_wrapper: "synapse.media.media_storage.ReadableFileWrapper", file_info: "synapse.media._base.FileInfo", ) -> Union["synapse.module_api.NOT_SPAM", "synapse.module_api.errors.Codes", bool] ``` Called when storing a local or remote file. The callback must return one of: - `synapse.module_api.NOT_SPAM`, to allow the operation. Other callbacks may still decide to reject it. - `synapse.module_api.errors.Codes` to reject the operation with an error code. In case of doubt, `synapse.module_api.errors.Codes.FORBIDDEN` is a good error code. - (deprecated) `False`, which is the same as returning `synapse.module_api.NOT_SPAM`. - (deprecated) `True`, which is the same as returning `synapse.module_api.errors.Codes.FORBIDDEN`. If multiple modules implement this callback, they will be considered in order. If a callback returns `synapse.module_api.NOT_SPAM`, Synapse falls through to the next one. The value of the first callback that does not return `synapse.module_api.NOT_SPAM` will be used. If this happens, Synapse will not call any of the subsequent implementations of this callback. ### `should_drop_federated_event` _First introduced in Synapse v1.60.0_ ```python async def should_drop_federated_event(event: "synapse.events.EventBase") -> bool ``` Called when checking whether a remote server can federate an event with us. **Returning `True` from this function will silently drop a federated event and split-brain our view of a room's DAG, and thus you shouldn't use this callback unless you know what you are doing.** If multiple modules implement this callback, they will be considered in order. If a callback returns `False`, Synapse falls through to the next one. The value of the first callback that does not return `False` will be used. If this happens, Synapse will not call any of the subsequent implementations of this callback. ### `check_login_for_spam` _First introduced in Synapse v1.87.0_ ```python async def check_login_for_spam( user_id: str, device_id: Optional[str], initial_display_name: Optional[str], request_info: Collection[Tuple[Optional[str], str]], auth_provider_id: Optional[str] = None, ) -> Union["synapse.module_api.NOT_SPAM", "synapse.module_api.errors.Codes"] ``` Called when a user logs in. The arguments passed to this callback are: * `user_id`: The user ID the user is logging in with * `device_id`: The device ID the user is re-logging into. * `initial_display_name`: The device display name, if any. * `request_info`: A collection of tuples, which first item is a user agent, and which second item is an IP address. These user agents and IP addresses are the ones that were used during the login process. * `auth_provider_id`: The identifier of the SSO authentication provider, if any. If multiple modules implement this callback, they will be considered in order. If a callback returns `synapse.module_api.NOT_SPAM`, Synapse falls through to the next one. The value of the first callback that does not return `synapse.module_api.NOT_SPAM` will be used. If this happens, Synapse will not call any of the subsequent implementations of this callback. *Note:* This will not be called when a user registers. ## Example The example below is a module that implements the spam checker callback `check_event_for_spam` to deny any message sent by users whose Matrix user IDs are mentioned in a configured list, and registers a web resource to the path `/_synapse/client/list_spam_checker/is_evil` that returns a JSON object indicating whether the provided user appears in that list. ```python import json from typing import Union from twisted.web.resource import Resource from twisted.web.server import Request from synapse.module_api import ModuleApi class IsUserEvilResource(Resource): def __init__(self, config): super(IsUserEvilResource, self).__init__() self.evil_users = config.get("evil_users") or [] def render_GET(self, request: Request): user = request.args.get(b"user")[0].decode() request.setHeader(b"Content-Type", b"application/json") return json.dumps({"evil": user in self.evil_users}).encode() class ListSpamChecker: def __init__(self, config: dict, api: ModuleApi): self.api = api self.evil_users = config.get("evil_users") or [] self.api.register_spam_checker_callbacks( check_event_for_spam=self.check_event_for_spam, ) self.api.register_web_resource( path="/_synapse/client/list_spam_checker/is_evil", resource=IsUserEvilResource(config), ) async def check_event_for_spam(self, event: "synapse.events.EventBase") -> Union[Literal["NOT_SPAM"], Codes]: if event.sender in self.evil_users: return Codes.FORBIDDEN else: return synapse.module_api.NOT_SPAM ```