Split `event_auth.check` into two parts (#10940)

Broadly, the existing `event_auth.check` function has two parts:
 * a validation section: checks that the event isn't too big, that it has the rught signatures, etc. 
   This bit is independent of the rest of the state in the room, and so need only be done once 
   for each event.
 * an auth section: ensures that the event is allowed, given the rest of the state in the room.
   This gets done multiple times, against various sets of room state, because it forms part of
   the state res algorithm.

Currently, this is implemented with `do_sig_check` and `do_size_check` parameters, but I think
that makes everything hard to follow. Instead, we split the function in two and call each part
separately where it is needed.

1 files changed, 18 insertions, 12 deletions

diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 3b0b895b07..0a10a5c28a 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -40,6 +40,10 @@ from synapse.api.errors import (
 )
 from synapse.api.room_versions import KNOWN_ROOM_VERSIONS, RoomVersion, RoomVersions
 from synapse.crypto.event_signing import compute_event_signature
+from synapse.event_auth import (
+    check_auth_rules_for_event,
+    validate_event_for_room_version,
+)
 from synapse.events import EventBase
 from synapse.events.snapshot import EventContext
 from synapse.events.validator import EventValidator
@@ -742,10 +746,9 @@ class FederationHandler(BaseHandler):
 
         # The remote hasn't signed it yet, obviously. We'll do the full checks
         # when we get the event back in `on_send_join_request`
-        await self._event_auth_handler.check_from_context(
-            room_version.identifier, event, context, do_sig_check=False
+        await self._event_auth_handler.check_auth_rules_from_context(
+            room_version, event, context
         )
-
         return event
 
     async def on_invite_request(
@@ -916,8 +919,8 @@ class FederationHandler(BaseHandler):
         try:
             # The remote hasn't signed it yet, obviously. We'll do the full checks
             # when we get the event back in `on_send_leave_request`
-            await self._event_auth_handler.check_from_context(
-                room_version_obj.identifier, event, context, do_sig_check=False
+            await self._event_auth_handler.check_auth_rules_from_context(
+                room_version_obj, event, context
             )
         except AuthError as e:
             logger.warning("Failed to create new leave %r because %s", event, e)
@@ -978,8 +981,8 @@ class FederationHandler(BaseHandler):
         try:
             # The remote hasn't signed it yet, obviously. We'll do the full checks
             # when we get the event back in `on_send_knock_request`
-            await self._event_auth_handler.check_from_context(
-                room_version_obj.identifier, event, context, do_sig_check=False
+            await self._event_auth_handler.check_auth_rules_from_context(
+                room_version_obj, event, context
             )
         except AuthError as e:
             logger.warning("Failed to create new knock %r because %s", event, e)
@@ -1168,7 +1171,8 @@ class FederationHandler(BaseHandler):
                 auth_for_e[(EventTypes.Create, "")] = create_event
 
             try:
-                event_auth.check(room_version, e, auth_events=auth_for_e)
+                validate_event_for_room_version(room_version, e)
+                check_auth_rules_for_event(room_version, e, auth_for_e)
             except SynapseError as err:
                 # we may get SynapseErrors here as well as AuthErrors. For
                 # instance, there are a couple of (ancient) events in some
@@ -1266,8 +1270,9 @@ class FederationHandler(BaseHandler):
             event.internal_metadata.send_on_behalf_of = self.hs.hostname
 
             try:
-                await self._event_auth_handler.check_from_context(
-                    room_version_obj.identifier, event, context
+                validate_event_for_room_version(room_version_obj, event)
+                await self._event_auth_handler.check_auth_rules_from_context(
+                    room_version_obj, event, context
                 )
             except AuthError as e:
                 logger.warning("Denying new third party invite %r because %s", event, e)
@@ -1317,8 +1322,9 @@ class FederationHandler(BaseHandler):
         )
 
         try:
-            await self._event_auth_handler.check_from_context(
-                room_version_obj.identifier, event, context
+            validate_event_for_room_version(room_version_obj, event)
+            await self._event_auth_handler.check_auth_rules_from_context(
+                room_version_obj, event, context
             )
         except AuthError as e:
             logger.warning("Denying third party invite %r because %s", event, e)