From 04d53794d6848cca2567d67f494ba8405d0bf1cf Mon Sep 17 00:00:00 2001
From: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
Date: Tue, 21 May 2019 13:47:25 +0100
Subject: [PATCH] Fix error handling for rooms whose versions are unknown.
 (#5219)

If we remove support for a particular room version, we should behave more
gracefully. This should make client requests fail with a 400 rather than a 500,
and will ignore individiual PDUs in a federation transaction, rather than the
whole transaction.
---
 changelog.d/5219.bugfix                 |  1 +
 synapse/api/errors.py                   | 18 ++++++++++++++++--
 synapse/events/__init__.py              |  8 ++++++--
 synapse/events/builder.py               |  6 +++---
 synapse/federation/federation_server.py | 14 +++++++++++++-
 5 files changed, 39 insertions(+), 8 deletions(-)
 create mode 100644 changelog.d/5219.bugfix

diff --git a/changelog.d/5219.bugfix b/changelog.d/5219.bugfix
new file mode 100644
index 000000000..c1e17adc5
--- /dev/null
+++ b/changelog.d/5219.bugfix
@@ -0,0 +1 @@
+Fix error handling for rooms whose versions are unknown.
diff --git a/synapse/api/errors.py b/synapse/api/errors.py
index ff89259de..e91697049 100644
--- a/synapse/api/errors.py
+++ b/synapse/api/errors.py
@@ -328,9 +328,23 @@ class RoomKeysVersionError(SynapseError):
         self.current_version = current_version
 
 
-class IncompatibleRoomVersionError(SynapseError):
-    """A server is trying to join a room whose version it does not support."""
+class UnsupportedRoomVersionError(SynapseError):
+    """The client's request to create a room used a room version that the server does
+    not support."""
+    def __init__(self):
+        super(UnsupportedRoomVersionError, self).__init__(
+            code=400,
+            msg="Homeserver does not support this room version",
+            errcode=Codes.UNSUPPORTED_ROOM_VERSION,
+        )
 
+
+class IncompatibleRoomVersionError(SynapseError):
+    """A server is trying to join a room whose version it does not support.
+
+    Unlike UnsupportedRoomVersionError, it is specific to the case of the make_join
+    failing.
+    """
     def __init__(self, room_version):
         super(IncompatibleRoomVersionError, self).__init__(
             code=400,
diff --git a/synapse/events/__init__.py b/synapse/events/__init__.py
index badeb903f..1edd19cc1 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
@@ -369,12 +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
 
diff --git a/synapse/events/builder.py b/synapse/events/builder.py
index fba27177c..1fe995f21 100644
--- a/synapse/events/builder.py
+++ b/synapse/events/builder.py
@@ -18,6 +18,7 @@ import attr
 from twisted.internet import defer
 
 from synapse.api.constants import MAX_DEPTH
+from synapse.api.errors import UnsupportedRoomVersionError
 from synapse.api.room_versions import (
     KNOWN_EVENT_FORMAT_VERSIONS,
     KNOWN_ROOM_VERSIONS,
@@ -178,9 +179,8 @@ class EventBuilderFactory(object):
         """
         v = KNOWN_ROOM_VERSIONS.get(room_version)
         if not v:
-            raise Exception(
-                "No event format defined for version %r" % (room_version,)
-            )
+            # this can happen if support is withdrawn for a room version
+            raise UnsupportedRoomVersionError()
         return self.for_room_version(v, key_values)
 
     def for_room_version(self, room_version, key_values):
diff --git a/synapse/federation/federation_server.py b/synapse/federation/federation_server.py
index df60828db..4c28c1dc3 100644
--- a/synapse/federation/federation_server.py
+++ b/synapse/federation/federation_server.py
@@ -33,6 +33,7 @@ from synapse.api.errors import (
     IncompatibleRoomVersionError,
     NotFoundError,
     SynapseError,
+    UnsupportedRoomVersionError,
 )
 from synapse.api.room_versions import KNOWN_ROOM_VERSIONS
 from synapse.crypto.event_signing import compute_event_signature
@@ -198,11 +199,22 @@ class FederationServer(FederationBase):
 
             try:
                 room_version = yield self.store.get_room_version(room_id)
-                format_ver = room_version_to_event_format(room_version)
             except NotFoundError:
                 logger.info("Ignoring PDU for unknown room_id: %s", room_id)
                 continue
 
+            try:
+                format_ver = room_version_to_event_format(room_version)
+            except UnsupportedRoomVersionError:
+                # this can happen if support for a given room version is withdrawn,
+                # so that we still get events for said room.
+                logger.info(
+                    "Ignoring PDU for room %s with unknown version %s",
+                    room_id,
+                    room_version,
+                )
+                continue
+
             event = event_from_pdu_json(p, format_ver)
             pdus_by_room.setdefault(room_id, []).append(event)