1 files changed, 28 insertions, 3 deletions
diff --git a/synapse/events/__init__.py b/synapse/events/__init__.py
index 12056d5be2..1edd19cc13 100644
--- a/synapse/events/__init__.py
+++ b/synapse/events/__init__.py
@@ -21,6 +21,7 @@ import six
 
 from unpaddedbase64 import encode_base64
 
+from synapse.api.errors import UnsupportedRoomVersionError
 from synapse.api.room_versions import KNOWN_ROOM_VERSIONS, EventFormatVersions
 from synapse.util.caches import intern_dict
 from synapse.util.frozenutils import freeze
@@ -335,13 +336,32 @@ class FrozenEventV2(EventBase):
         return self.__repr__()
 
     def __repr__(self):
-        return "<FrozenEventV2 event_id='%s', type='%s', state_key='%s'>" % (
+        return "<%s event_id='%s', type='%s', state_key='%s'>" % (
+            self.__class__.__name__,
             self.event_id,
             self.get("type", None),
             self.get("state_key", None),
         )
 
 
+class FrozenEventV3(FrozenEventV2):
+    """FrozenEventV3, which differs from FrozenEventV2 only in the event_id format"""
+    format_version = EventFormatVersions.V3  # All events of this type are V3
+
+    @property
+    def event_id(self):
+        # We have to import this here as otherwise we get an import loop which
+        # is hard to break.
+        from synapse.crypto.event_signing import compute_event_reference_hash
+
+        if self._event_id:
+            return self._event_id
+        self._event_id = "$" + encode_base64(
+            compute_event_reference_hash(self)[1], urlsafe=True
+        )
+        return self._event_id
+
+
 def room_version_to_event_format(room_version):
     """Converts a room version string to the event format
 
@@ -350,12 +370,15 @@ def room_version_to_event_format(room_version):
 
     Returns:
         int
+
+    Raises:
+        UnsupportedRoomVersionError if the room version is unknown
     """
     v = KNOWN_ROOM_VERSIONS.get(room_version)
 
     if not v:
-        # We should have already checked version, so this should not happen
-        raise RuntimeError("Unrecognized room version %s" % (room_version,))
+        # this can happen if support is withdrawn for a room version
+        raise UnsupportedRoomVersionError()
 
     return v.event_format
 
@@ -376,6 +399,8 @@ def event_type_from_format_version(format_version):
         return FrozenEvent
     elif format_version == EventFormatVersions.V2:
         return FrozenEventV2
+    elif format_version == EventFormatVersions.V3:
+        return FrozenEventV3
     else:
         raise Exception(
             "No event format %r" % (format_version,)