Move methods involving event authentication to EventAuthHandler. (#10268)

Instead of mixing them with user authentication methods.

synapse/handlers/event_auth.py

@@ -11,8 +11,9 @@
 # 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 TYPE_CHECKING, Collection, Optional
+from typing import TYPE_CHECKING, Collection, List, Optional, Union
 
+from synapse import event_auth
 from synapse.api.constants import (
     EventTypes,
     JoinRules,
@@ -20,9 +21,11 @@ from synapse.api.constants import (
     RestrictedJoinRuleTypes,
 )
 from synapse.api.errors import AuthError
-from synapse.api.room_versions import RoomVersion
+from synapse.api.room_versions import KNOWN_ROOM_VERSIONS, RoomVersion
 from synapse.events import EventBase
+from synapse.events.builder import EventBuilder
 from synapse.types import StateMap
+from synapse.util.metrics import Measure
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
@@ -34,8 +37,63 @@ class EventAuthHandler:
     """
 
     def __init__(self, hs: "HomeServer"):
+        self._clock = hs.get_clock()
         self._store = hs.get_datastore()
 
+    async def check_from_context(
+        self, room_version: str, event, context, do_sig_check=True
+    ) -> None:
+        auth_event_ids = event.auth_event_ids()
+        auth_events_by_id = await self._store.get_events(auth_event_ids)
+        auth_events = {(e.type, e.state_key): e for e in auth_events_by_id.values()}
+
+        room_version_obj = KNOWN_ROOM_VERSIONS[room_version]
+        event_auth.check(
+            room_version_obj, event, auth_events=auth_events, do_sig_check=do_sig_check
+        )
+
+    def compute_auth_events(
+        self,
+        event: Union[EventBase, EventBuilder],
+        current_state_ids: StateMap[str],
+        for_verification: bool = False,
+    ) -> List[str]:
+        """Given an event and current state return the list of event IDs used
+        to auth an event.
+
+        If `for_verification` is False then only return auth events that
+        should be added to the event's `auth_events`.
+
+        Returns:
+            List of event IDs.
+        """
+
+        if event.type == EventTypes.Create:
+            return []
+
+        # Currently we ignore the `for_verification` flag even though there are
+        # some situations where we can drop particular auth events when adding
+        # to the event's `auth_events` (e.g. joins pointing to previous joins
+        # when room is publicly joinable). Dropping event IDs has the
+        # advantage that the auth chain for the room grows slower, but we use
+        # the auth chain in state resolution v2 to order events, which means
+        # care must be taken if dropping events to ensure that it doesn't
+        # introduce undesirable "state reset" behaviour.
+        #
+        # All of which sounds a bit tricky so we don't bother for now.
+
+        auth_ids = []
+        for etype, state_key in event_auth.auth_types_for_event(event):
+            auth_ev_id = current_state_ids.get((etype, state_key))
+            if auth_ev_id:
+                auth_ids.append(auth_ev_id)
+
+        return auth_ids
+
+    async def check_host_in_room(self, room_id: str, host: str) -> bool:
+        with Measure(self._clock, "check_host_in_room"):
+            return await self._store.is_host_joined(room_id, host)
+
     async def check_restricted_join_rules(
         self,
         state_ids: StateMap[str],