synapse-product/synapse/events/third_party_rules.py

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# 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 logging
from typing import TYPE_CHECKING, Awaitable, Callable, List, Optional, Tuple
from synapse.api.errors import SynapseError
from synapse.events import EventBase
from synapse.events.snapshot import EventContext
from synapse.types import Requester, StateMap
from synapse.util.async_helpers import maybe_awaitable
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if TYPE_CHECKING:
from synapse.server import HomeServer
logger = logging.getLogger(__name__)
CHECK_EVENT_ALLOWED_CALLBACK = Callable[
[EventBase, StateMap[EventBase]], Awaitable[Tuple[bool, Optional[dict]]]
]
ON_CREATE_ROOM_CALLBACK = Callable[[Requester, dict, bool], Awaitable]
CHECK_THREEPID_CAN_BE_INVITED_CALLBACK = Callable[
[str, str, StateMap[EventBase]], Awaitable[bool]
]
CHECK_VISIBILITY_CAN_BE_MODIFIED_CALLBACK = Callable[
[str, StateMap[EventBase], str], Awaitable[bool]
]
def load_legacy_third_party_event_rules(hs: "HomeServer"):
"""Wrapper that loads a third party event rules module configured using the old
configuration, and registers the hooks they implement.
"""
if hs.config.third_party_event_rules is None:
return
module, config = hs.config.third_party_event_rules
api = hs.get_module_api()
third_party_rules = module(config=config, module_api=api)
# The known hooks. If a module implements a method which name appears in this set,
# we'll want to register it.
third_party_event_rules_methods = {
"check_event_allowed",
"on_create_room",
"check_threepid_can_be_invited",
"check_visibility_can_be_modified",
}
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
# We return a separate wrapper for these methods because, in order to wrap them
# correctly, we need to await its result. Therefore it doesn't make a lot of
# sense to make it go through the run() wrapper.
if f.__name__ == "check_event_allowed":
# We need to wrap check_event_allowed because its old form would return either
# a boolean or a dict, but now we want to return the dict separately from the
# boolean.
async def wrap_check_event_allowed(
event: EventBase,
state_events: StateMap[EventBase],
) -> Tuple[bool, Optional[dict]]:
# We've already made sure f is not None above, but mypy doesn't do well
# across function boundaries so we need to tell it f is definitely not
# None.
assert f is not None
res = await f(event, state_events)
if isinstance(res, dict):
return True, res
else:
return res, None
return wrap_check_event_allowed
if f.__name__ == "on_create_room":
# We need to wrap on_create_room because its old form would return a boolean
# if the room creation is denied, but now we just want it to raise an
# exception.
async def wrap_on_create_room(
requester: Requester, config: dict, is_requester_admin: bool
) -> None:
# We've already made sure f is not None above, but mypy doesn't do well
# across function boundaries so we need to tell it f is definitely not
# None.
assert f is not None
res = await f(requester, config, is_requester_admin)
if res is False:
raise SynapseError(
403,
"Room creation forbidden with these parameters",
)
return wrap_on_create_room
def run(*args, **kwargs):
# mypy doesn't do well across function boundaries so we need to tell it
# f is definitely not None.
assert f is not None
return maybe_awaitable(f(*args, **kwargs))
return run
# Register the hooks through the module API.
hooks = {
hook: async_wrapper(getattr(third_party_rules, hook, None))
for hook in third_party_event_rules_methods
}
api.register_third_party_rules_callbacks(**hooks)
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class ThirdPartyEventRules:
"""Allows server admins to provide a Python module implementing an extra
set of rules to apply when processing events.
This is designed to help admins of closed federations with enforcing custom
behaviours.
"""
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def __init__(self, hs: "HomeServer"):
self.third_party_rules = None
self.store = hs.get_datastore()
self._check_event_allowed_callbacks: List[CHECK_EVENT_ALLOWED_CALLBACK] = []
self._on_create_room_callbacks: List[ON_CREATE_ROOM_CALLBACK] = []
self._check_threepid_can_be_invited_callbacks: List[
CHECK_THREEPID_CAN_BE_INVITED_CALLBACK
] = []
self._check_visibility_can_be_modified_callbacks: List[
CHECK_VISIBILITY_CAN_BE_MODIFIED_CALLBACK
] = []
def register_third_party_rules_callbacks(
self,
check_event_allowed: Optional[CHECK_EVENT_ALLOWED_CALLBACK] = None,
on_create_room: Optional[ON_CREATE_ROOM_CALLBACK] = None,
check_threepid_can_be_invited: Optional[
CHECK_THREEPID_CAN_BE_INVITED_CALLBACK
] = None,
check_visibility_can_be_modified: Optional[
CHECK_VISIBILITY_CAN_BE_MODIFIED_CALLBACK
] = None,
):
"""Register callbacks from modules for each hook."""
if check_event_allowed is not None:
self._check_event_allowed_callbacks.append(check_event_allowed)
if on_create_room is not None:
self._on_create_room_callbacks.append(on_create_room)
if check_threepid_can_be_invited is not None:
self._check_threepid_can_be_invited_callbacks.append(
check_threepid_can_be_invited,
)
if check_visibility_can_be_modified is not None:
self._check_visibility_can_be_modified_callbacks.append(
check_visibility_can_be_modified,
)
async def check_event_allowed(
self, event: EventBase, context: EventContext
) -> Tuple[bool, Optional[dict]]:
"""Check if a provided event should be allowed in the given context.
The module can return:
* True: the event is allowed.
* False: the event is not allowed, and should be rejected with M_FORBIDDEN.
If the event is allowed, the module can also return a dictionary to use as a
replacement for the event.
Args:
event: The event to be checked.
context: The context of the event.
Returns:
The result from the ThirdPartyRules module, as above.
"""
# Bail out early without hitting the store if we don't have any callbacks to run.
if len(self._check_event_allowed_callbacks) == 0:
return True, None
prev_state_ids = await context.get_prev_state_ids()
# Retrieve the state events from the database.
events = await self.store.get_events(prev_state_ids.values())
state_events = {(ev.type, ev.state_key): ev for ev in events.values()}
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# Ensure that the event is frozen, to make sure that the module is not tempted
# to try to modify it. Any attempt to modify it at this point will invalidate
# the hashes and signatures.
event.freeze()
for callback in self._check_event_allowed_callbacks:
try:
res, replacement_data = await callback(event, state_events)
except Exception as e:
logger.warning("Failed to run module API callback %s: %s", callback, e)
continue
# Return if the event shouldn't be allowed or if the module came up with a
# replacement dict for the event.
if res is False:
return res, None
elif isinstance(replacement_data, dict):
return True, replacement_data
return True, None
async def on_create_room(
self, requester: Requester, config: dict, is_requester_admin: bool
) -> None:
"""Intercept requests to create room to maybe deny it (via an exception) or
update the request config.
Args:
requester
config: The creation config from the client.
is_requester_admin: If the requester is an admin
"""
for callback in self._on_create_room_callbacks:
try:
await callback(requester, config, is_requester_admin)
except Exception as e:
# Don't silence the errors raised by this callback since we expect it to
# raise an exception to deny the creation of the room; instead make sure
# it's a SynapseError we can send to clients.
if not isinstance(e, SynapseError):
e = SynapseError(
403, "Room creation forbidden with these parameters"
)
raise e
async def check_threepid_can_be_invited(
self, medium: str, address: str, room_id: str
) -> bool:
"""Check if a provided 3PID can be invited in the given room.
Args:
medium: The 3PID's medium.
address: The 3PID's address.
room_id: The room we want to invite the threepid to.
Returns:
True if the 3PID can be invited, False if not.
"""
# Bail out early without hitting the store if we don't have any callbacks to run.
if len(self._check_threepid_can_be_invited_callbacks) == 0:
return True
state_events = await self._get_state_map_for_room(room_id)
for callback in self._check_threepid_can_be_invited_callbacks:
try:
if await callback(medium, address, state_events) is False:
return False
except Exception as e:
logger.warning("Failed to run module API callback %s: %s", callback, e)
return True
async def check_visibility_can_be_modified(
self, room_id: str, new_visibility: str
) -> bool:
"""Check if a room is allowed to be published to, or removed from, the public room
list.
Args:
room_id: The ID of the room.
new_visibility: The new visibility state. Either "public" or "private".
Returns:
True if the room's visibility can be modified, False if not.
"""
# Bail out early without hitting the store if we don't have any callback
if len(self._check_visibility_can_be_modified_callbacks) == 0:
return True
state_events = await self._get_state_map_for_room(room_id)
for callback in self._check_visibility_can_be_modified_callbacks:
try:
if await callback(room_id, state_events, new_visibility) is False:
return False
except Exception as e:
logger.warning("Failed to run module API callback %s: %s", callback, e)
return True
async def _get_state_map_for_room(self, room_id: str) -> StateMap[EventBase]:
"""Given a room ID, return the state events of that room.
Args:
room_id: The ID of the room.
Returns:
A dict mapping (event type, state key) to state event.
"""
state_ids = await self.store.get_filtered_current_state_ids(room_id)
room_state_events = await self.store.get_events(state_ids.values())
state_events = {}
for key, event_id in state_ids.items():
state_events[key] = room_state_events[event_id]
return state_events