Allow ThirdPartyRules modules to replace event content

Support returning a new event dict from `check_event_allowed`.
This commit is contained in:
Richard van der Hoff 2020-10-13 18:53:56 +01:00
parent 123711ed19
commit 617e8a4653
3 changed files with 75 additions and 9 deletions

View file

@ -12,7 +12,8 @@
# 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.
from typing import Callable
from typing import Callable, Union
from synapse.events import EventBase
from synapse.events.snapshot import EventContext
@ -44,15 +45,20 @@ class ThirdPartyEventRules:
async def check_event_allowed(
self, event: EventBase, context: EventContext
) -> bool:
) -> Union[bool, 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.
* a dict: replacement event data.
Args:
event: The event to be checked.
context: The context of the event.
Returns:
True if the event should be allowed, False if not.
The result from the ThirdPartyRules module, as above
"""
if self.third_party_rules is None:
return True

View file

@ -795,16 +795,22 @@ class EventCreationHandler:
if requester:
context.app_service = requester.app_service
event_allowed = await self.third_party_event_rules.check_event_allowed(
third_party_result = await self.third_party_event_rules.check_event_allowed(
event, context
)
if not event_allowed:
if not third_party_result:
logger.info(
"Event %s forbidden by third-party rules", event,
)
raise SynapseError(
403, "This event is not allowed in this context", Codes.FORBIDDEN
)
elif isinstance(third_party_result, dict):
# the third-party rules want to replace the event. We'll need to build a new
# event.
event, context = await self._rebuild_event_after_third_party_rules(
third_party_result, event
)
self.validator.validate_new(event, self.config)
@ -1294,3 +1300,57 @@ class EventCreationHandler:
room_id,
)
del self._rooms_to_exclude_from_dummy_event_insertion[room_id]
async def _rebuild_event_after_third_party_rules(
self, third_party_result: dict, original_event: EventBase
) -> Tuple[EventBase, EventContext]:
# the third_party_event_rules want to replace the event.
# we do some basic checks, and then return the replacement event and context.
# Construct a new EventBuilder and validate it, which helps with the
# rest of these checks.
try:
builder = self.event_builder_factory.for_room_version(
original_event.room_version, third_party_result
)
self.validator.validate_builder(builder)
except SynapseError as e:
raise Exception(
"Third party rules module created an invalid event: " + e.msg,
)
immutable_fields = [
# changing the room is going to break things: we've already checked that the
# room exists, and are holding a concurrency limiter token for that room.
# Also, we might need to use a different room version.
"room_id",
# changing the type or state key might work, but we'd need to check that the
# calling functions aren't making assumptions about them.
"type",
"state_key",
]
for k in immutable_fields:
if getattr(builder, k, None) != original_event.get(k):
raise Exception(
"Third party rules module created an invalid event: "
"cannot change field " + k
)
# check that the new sender belongs to this HS
if not self.hs.is_mine_id(builder.sender):
raise Exception(
"Third party rules module created an invalid event: "
"invalid sender " + builder.sender
)
# copy over the original internal metadata
for k, v in original_event.internal_metadata.get_dict().items():
setattr(builder.internal_metadata, k, v)
event = await builder.build(prev_event_ids=original_event.prev_event_ids())
# we rebuild the event context, to be on the safe side. If nothing else,
# delta_ids might need an update.
context = await self.state.compute_event_context(event)
return event, context

View file

@ -115,12 +115,12 @@ class ThirdPartyRulesTestCase(unittest.HomeserverTestCase):
self.assertEquals(channel.result["code"], b"403", channel.result)
def test_modify_event(self):
"""Tests that the module can successfully tweak an event before it is persisted.
"""
"""The module can return a modified version of the event"""
# first patch the event checker so that it will modify the event
async def check(ev: EventBase, state):
ev.content = {"x": "y"}
return True
d = ev.get_dict()
d["content"] = {"x": "y"}
return d
current_rules_module().check_event_allowed = check