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diff --git a/docs/presence_router_module.md b/docs/presence_router_module.md new file mode 100644 index 0000000000..d6566d978d --- /dev/null +++ b/docs/presence_router_module.md @@ -0,0 +1,235 @@ +# Presence Router Module + +Synapse supports configuring a module that can specify additional users +(local or remote) to should receive certain presence updates from local +users. + +Note that routing presence via Application Service transactions is not +currently supported. + +The presence routing module is implemented as a Python class, which will +be imported by the running Synapse. + +## Python Presence Router Class + +The Python class is instantiated with two objects: + +* A configuration object of some type (see below). +* An instance of `synapse.module_api.ModuleApi`. + +It then implements methods related to presence routing. + +Note that one method of `ModuleApi` that may be useful is: + +```python +async def ModuleApi.send_local_online_presence_to(users: Iterable[str]) -> None +``` + +which can be given a list of local or remote MXIDs to broadcast known, online user +presence to (for those users that the receiving user is considered interested in). +It does not include state for users who are currently offline, and it can only be +called on workers that support sending federation. + +### Module structure + +Below is a list of possible methods that can be implemented, and whether they are +required. + +#### `parse_config` + +```python +def parse_config(config_dict: dict) -> Any +``` + +**Required.** A static method that is passed a dictionary of config options, and + should return a validated config object. This method is described further in + [Configuration](#configuration). + +#### `get_users_for_states` + +```python +async def get_users_for_states( + self, + state_updates: Iterable[UserPresenceState], +) -> Dict[str, Set[UserPresenceState]]: +``` + +**Required.** An asynchronous method that is passed an iterable of user presence +state. This method can determine whether a given presence update should be sent to certain +users. It does this by returning a dictionary with keys representing local or remote +Matrix User IDs, and values being a python set +of `synapse.handlers.presence.UserPresenceState` instances. + +Synapse will then attempt to send the specified presence updates to each user when +possible. + +#### `get_interested_users` + +```python +async def get_interested_users(self, user_id: str) -> Union[Set[str], str] +``` + +**Required.** An asynchronous method that is passed a single Matrix User ID. This +method is expected to return the users that the passed in user may be interested in the +presence of. Returned users may be local or remote. The presence routed as a result of +what this method returns is sent in addition to the updates already sent between users +that share a room together. Presence updates are deduplicated. + +This method should return a python set of Matrix User IDs, or the object +`synapse.events.presence_router.PresenceRouter.ALL_USERS` to indicate that the passed +user should receive presence information for *all* known users. + +For clarity, if the user `@alice:example.org` is passed to this method, and the Set +`{"@bob:example.com", "@charlie:somewhere.org"}` is returned, this signifies that Alice +should receive presence updates sent by Bob and Charlie, regardless of whether these +users share a room. + +### Example + +Below is an example implementation of a presence router class. + +```python +from typing import Dict, Iterable, Set, Union +from synapse.events.presence_router import PresenceRouter +from synapse.handlers.presence import UserPresenceState +from synapse.module_api import ModuleApi + +class PresenceRouterConfig: + def __init__(self): + # Config options with their defaults + # A list of users to always send all user presence updates to + self.always_send_to_users = [] # type: List[str] + + # A list of users to ignore presence updates for. Does not affect + # shared-room presence relationships + self.blacklisted_users = [] # type: List[str] + +class ExamplePresenceRouter: + """An example implementation of synapse.presence_router.PresenceRouter. + Supports routing all presence to a configured set of users, or a subset + of presence from certain users to members of certain rooms. + + Args: + config: A configuration object. + module_api: An instance of Synapse's ModuleApi. + """ + def __init__(self, config: PresenceRouterConfig, module_api: ModuleApi): + self._config = config + self._module_api = module_api + + @staticmethod + def parse_config(config_dict: dict) -> PresenceRouterConfig: + """Parse a configuration dictionary from the homeserver config, do + some validation and return a typed PresenceRouterConfig. + + Args: + config_dict: The configuration dictionary. + + Returns: + A validated config object. + """ + # Initialise a typed config object + config = PresenceRouterConfig() + always_send_to_users = config_dict.get("always_send_to_users") + blacklisted_users = config_dict.get("blacklisted_users") + + # Do some validation of config options... otherwise raise a + # synapse.config.ConfigError. + config.always_send_to_users = always_send_to_users + config.blacklisted_users = blacklisted_users + + return config + + async def get_users_for_states( + self, + state_updates: Iterable[UserPresenceState], + ) -> Dict[str, Set[UserPresenceState]]: + """Given an iterable of user presence updates, determine where each one + needs to go. Returned results will not affect presence updates that are + sent between users who share a room. + + Args: + state_updates: An iterable of user presence state updates. + + Returns: + A dictionary of user_id -> set of UserPresenceState that the user should + receive. + """ + destination_users = {} # type: Dict[str, Set[UserPresenceState] + + # Ignore any updates for blacklisted users + desired_updates = set() + for update in state_updates: + if update.state_key not in self._config.blacklisted_users: + desired_updates.add(update) + + # Send all presence updates to specific users + for user_id in self._config.always_send_to_users: + destination_users[user_id] = desired_updates + + return destination_users + + async def get_interested_users( + self, + user_id: str, + ) -> Union[Set[str], PresenceRouter.ALL_USERS]: + """ + Retrieve a list of users that `user_id` is interested in receiving the + presence of. This will be in addition to those they share a room with. + Optionally, the object PresenceRouter.ALL_USERS can be returned to indicate + that this user should receive all incoming local and remote presence updates. + + Note that this method will only be called for local users. + + Args: + user_id: A user requesting presence updates. + + Returns: + A set of user IDs to return additional presence updates for, or + PresenceRouter.ALL_USERS to return presence updates for all other users. + """ + if user_id in self._config.always_send_to_users: + return PresenceRouter.ALL_USERS + + return set() +``` + +#### A note on `get_users_for_states` and `get_interested_users` + +Both of these methods are effectively two different sides of the same coin. The logic +regarding which users should receive updates for other users should be the same +between them. + +`get_users_for_states` is called when presence updates come in from either federation +or local users, and is used to either direct local presence to remote users, or to +wake up the sync streams of local users to collect remote presence. + +In contrast, `get_interested_users` is used to determine the users that presence should +be fetched for when a local user is syncing. This presence is then retrieved, before +being fed through `get_users_for_states` once again, with only the syncing user's +routing information pulled from the resulting dictionary. + +Their routing logic should thus line up, else you may run into unintended behaviour. + +## Configuration + +Once you've crafted your module and installed it into the same Python environment as +Synapse, amend your homeserver config file with the following. + +```yaml +presence: + routing_module: + module: my_module.ExamplePresenceRouter + config: + # Any configuration options for your module. The below is an example. + # of setting options for ExamplePresenceRouter. + always_send_to_users: ["@presence_gobbler:example.org"] + blacklisted_users: + - "@alice:example.com" + - "@bob:example.com" + ... +``` + +The contents of `config` will be passed as a Python dictionary to the static +`parse_config` method of your class. The object returned by this method will +then be passed to the `__init__` method of your module as `config`. |