Allow modules to create and send events into rooms (#8479)

This PR allows Synapse modules making use of the `ModuleApi` to create and send non-membership events into a room. This can useful to have modules send messages, or change power levels in a room etc. Note that they must send event through a user that's already in the room.

The non-membership event limitation is currently arbitrary, as it's another chunk of work and not necessary at the moment.

5 files changed, 157 insertions, 8 deletions

diff --git a/changelog.d/8479.feature b/changelog.d/8479.feature
new file mode 100644
index 0000000000..11adeec8a9
--- /dev/null
+++ b/changelog.d/8479.feature
@@ -0,0 +1 @@
+Add the ability to send non-membership events into a room via the `ModuleApi`.
\ No newline at end of file
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 33d133a4b2..ad0b7bd868 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -59,6 +59,7 @@ from synapse.visibility import filter_events_for_client
 from ._base import BaseHandler
 
 if TYPE_CHECKING:
+    from synapse.events.third_party_rules import ThirdPartyEventRules
     from synapse.server import HomeServer
 
 logger = logging.getLogger(__name__)
@@ -393,7 +394,9 @@ class EventCreationHandler:
         self.action_generator = hs.get_action_generator()
 
         self.spam_checker = hs.get_spam_checker()
-        self.third_party_event_rules = hs.get_third_party_event_rules()
+        self.third_party_event_rules = (
+            self.hs.get_third_party_event_rules()
+        )  # type: ThirdPartyEventRules
 
         self._block_events_without_consent_error = (
             self.config.block_events_without_consent_error
@@ -1229,11 +1232,7 @@ class EventCreationHandler:
                 # Since this is a dummy-event it is OK if it is sent by a
                 # shadow-banned user.
                 await self.handle_new_client_event(
-                    requester=requester,
-                    event=event,
-                    context=context,
-                    ratelimit=False,
-                    ignore_shadow_ban=True,
+                    requester, event, context, ratelimit=False, ignore_shadow_ban=True,
                 )
                 return True
             except ConsentNotGivenError:
diff --git a/synapse/module_api/__init__.py b/synapse/module_api/__init__.py
index b410e3ad9c..0142542852 100644
--- a/synapse/module_api/__init__.py
+++ b/synapse/module_api/__init__.py
@@ -18,11 +18,12 @@ from typing import TYPE_CHECKING, Iterable, Optional, Tuple
 
 from twisted.internet import defer
 
+from synapse.events import EventBase
 from synapse.http.client import SimpleHttpClient
 from synapse.http.site import SynapseRequest
 from synapse.logging.context import make_deferred_yieldable, run_in_background
 from synapse.storage.state import StateFilter
-from synapse.types import UserID
+from synapse.types import JsonDict, UserID, create_requester
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
@@ -320,6 +321,33 @@ class ModuleApi:
         state = yield defer.ensureDeferred(self._store.get_events(state_ids.values()))
         return state.values()
 
+    async def create_and_send_event_into_room(self, event_dict: JsonDict) -> EventBase:
+        """Create and send an event into a room. Membership events are currently not supported.
+
+        Args:
+            event_dict: A dictionary representing the event to send.
+                Required keys are `type`, `room_id`, `sender` and `content`.
+
+        Returns:
+            The event that was sent. If state event deduplication happened, then
+                the previous, duplicate event instead.
+
+        Raises:
+            SynapseError if the event was not allowed.
+        """
+        # Create a requester object
+        requester = create_requester(event_dict["sender"])
+
+        # Create and send the event
+        (
+            event,
+            _,
+        ) = await self._hs.get_event_creation_handler().create_and_send_nonmember_event(
+            requester, event_dict, ratelimit=False, ignore_shadow_ban=True,
+        )
+
+        return event
+
 
 class PublicRoomListManager:
     """Contains methods for adding to, removing from and querying whether a room
diff --git a/tests/module_api/test_api.py b/tests/module_api/test_api.py
index 7c790bee7d..9b573ac24d 100644
--- a/tests/module_api/test_api.py
+++ b/tests/module_api/test_api.py
@@ -12,9 +12,12 @@
 # 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 mock import Mock
 
+from synapse.events import EventBase
 from synapse.rest import admin
 from synapse.rest.client.v1 import login, room
+from synapse.types import create_requester
 
 from tests.unittest import HomeserverTestCase
 
@@ -29,6 +32,7 @@ class ModuleApiTestCase(HomeserverTestCase):
     def prepare(self, reactor, clock, homeserver):
         self.store = homeserver.get_datastore()
         self.module_api = homeserver.get_module_api()
+        self.event_creation_handler = homeserver.get_event_creation_handler()
 
     def test_can_register_user(self):
         """Tests that an external module can register a user"""
@@ -60,6 +64,97 @@ class ModuleApiTestCase(HomeserverTestCase):
         displayname = self.get_success(self.store.get_profile_displayname("bob"))
         self.assertEqual(displayname, "Bobberino")
 
+    def test_sending_events_into_room(self):
+        """Tests that a module can send events into a room"""
+        # Mock out create_and_send_nonmember_event to check whether events are being sent
+        self.event_creation_handler.create_and_send_nonmember_event = Mock(
+            spec=[],
+            side_effect=self.event_creation_handler.create_and_send_nonmember_event,
+        )
+
+        # Create a user and room to play with
+        user_id = self.register_user("summer", "monkey")
+        tok = self.login("summer", "monkey")
+        room_id = self.helper.create_room_as(user_id, tok=tok)
+
+        # Create and send a non-state event
+        content = {"body": "I am a puppet", "msgtype": "m.text"}
+        event_dict = {
+            "room_id": room_id,
+            "type": "m.room.message",
+            "content": content,
+            "sender": user_id,
+        }
+        event = self.get_success(
+            self.module_api.create_and_send_event_into_room(event_dict)
+        )  # type: EventBase
+        self.assertEqual(event.sender, user_id)
+        self.assertEqual(event.type, "m.room.message")
+        self.assertEqual(event.room_id, room_id)
+        self.assertFalse(hasattr(event, "state_key"))
+        self.assertDictEqual(event.content, content)
+
+        # Check that the event was sent
+        self.event_creation_handler.create_and_send_nonmember_event.assert_called_with(
+            create_requester(user_id),
+            event_dict,
+            ratelimit=False,
+            ignore_shadow_ban=True,
+        )
+
+        # Create and send a state event
+        content = {
+            "events_default": 0,
+            "users": {user_id: 100},
+            "state_default": 50,
+            "users_default": 0,
+            "events": {"test.event.type": 25},
+        }
+        event_dict = {
+            "room_id": room_id,
+            "type": "m.room.power_levels",
+            "content": content,
+            "sender": user_id,
+            "state_key": "",
+        }
+        event = self.get_success(
+            self.module_api.create_and_send_event_into_room(event_dict)
+        )  # type: EventBase
+        self.assertEqual(event.sender, user_id)
+        self.assertEqual(event.type, "m.room.power_levels")
+        self.assertEqual(event.room_id, room_id)
+        self.assertEqual(event.state_key, "")
+        self.assertDictEqual(event.content, content)
+
+        # Check that the event was sent
+        self.event_creation_handler.create_and_send_nonmember_event.assert_called_with(
+            create_requester(user_id),
+            {
+                "type": "m.room.power_levels",
+                "content": content,
+                "room_id": room_id,
+                "sender": user_id,
+                "state_key": "",
+            },
+            ratelimit=False,
+            ignore_shadow_ban=True,
+        )
+
+        # Check that we can't send membership events
+        content = {
+            "membership": "leave",
+        }
+        event_dict = {
+            "room_id": room_id,
+            "type": "m.room.member",
+            "content": content,
+            "sender": user_id,
+            "state_key": user_id,
+        }
+        self.get_failure(
+            self.module_api.create_and_send_event_into_room(event_dict), Exception
+        )
+
     def test_public_rooms(self):
         """Tests that a room can be added and removed from the public rooms list,
         as well as have its public rooms directory state queried.
diff --git a/tests/rest/client/test_third_party_rules.py b/tests/rest/client/test_third_party_rules.py
index c12518c931..d03e121664 100644
--- a/tests/rest/client/test_third_party_rules.py
+++ b/tests/rest/client/test_third_party_rules.py
@@ -13,10 +13,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import threading
+from typing import Dict
 
 from mock import Mock
 
 from synapse.events import EventBase
+from synapse.module_api import ModuleApi
 from synapse.rest import admin
 from synapse.rest.client.v1 import login, room
 from synapse.types import Requester, StateMap
@@ -27,10 +29,11 @@ thread_local = threading.local()
 
 
 class ThirdPartyRulesTestModule:
-    def __init__(self, config, module_api):
+    def __init__(self, config: Dict, module_api: ModuleApi):
         # keep a record of the "current" rules module, so that the test can patch
         # it if desired.
         thread_local.rules_module = self
+        self.module_api = module_api
 
     async def on_create_room(
         self, requester: Requester, config: dict, is_requester_admin: bool
@@ -142,3 +145,26 @@ class ThirdPartyRulesTestCase(unittest.HomeserverTestCase):
         self.assertEqual(channel.result["code"], b"200", channel.result)
         ev = channel.json_body
         self.assertEqual(ev["content"]["x"], "y")
+
+    def test_send_event(self):
+        """Tests that the module can send an event into a room via the module api"""
+        content = {
+            "msgtype": "m.text",
+            "body": "Hello!",
+        }
+        event_dict = {
+            "room_id": self.room_id,
+            "type": "m.room.message",
+            "content": content,
+            "sender": self.user_id,
+        }
+        event = self.get_success(
+            current_rules_module().module_api.create_and_send_event_into_room(
+                event_dict
+            )
+        )  # type: EventBase
+
+        self.assertEquals(event.sender, self.user_id)
+        self.assertEquals(event.room_id, self.room_id)
+        self.assertEquals(event.type, "m.room.message")
+        self.assertEquals(event.content, content)