Remove frozendict_json_encoder and support frozendicts everywhere

Not being able to serialise `frozendicts` is fragile, and it's annoying to have
to think about which serialiser you want. There's no real downside to
supporting frozendicts, so let's just have one json encoder.

7 files changed, 32 insertions, 38 deletions

diff --git a/changelog.d/8678.bugfix b/changelog.d/8678.bugfix
new file mode 100644
index 0000000000..0508d8f109
--- /dev/null
+++ b/changelog.d/8678.bugfix
@@ -0,0 +1 @@
+Fix `Object of type frozendict is not JSON serializable` exceptions when using third-party event rules.
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index d6855c60ea..fb0a04e9a7 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -50,9 +50,8 @@ from synapse.replication.http.send_event import ReplicationSendEventRestServlet
 from synapse.storage.databases.main.events_worker import EventRedactBehaviour
 from synapse.storage.state import StateFilter
 from synapse.types import Requester, RoomAlias, StreamToken, UserID, create_requester
-from synapse.util import json_decoder
+from synapse.util import json_decoder, json_encoder
 from synapse.util.async_helpers import Linearizer
-from synapse.util.frozenutils import frozendict_json_encoder
 from synapse.util.metrics import measure_func
 from synapse.visibility import filter_events_for_client
 
@@ -928,7 +927,7 @@ class EventCreationHandler:
 
         # Ensure that we can round trip before trying to persist in db
         try:
-            dump = frozendict_json_encoder.encode(event.content)
+            dump = json_encoder.encode(event.content)
             json_decoder.decode(dump)
         except Exception:
             logger.exception("Failed to encode content: %r", event.content)
diff --git a/synapse/http/server.py b/synapse/http/server.py
index 00b98af3d4..29dd604f85 100644
--- a/synapse/http/server.py
+++ b/synapse/http/server.py
@@ -620,7 +620,7 @@ def respond_with_json(
     if pretty_print:
         encoder = iterencode_pretty_printed_json
     else:
-        if canonical_json or synapse.events.USE_FROZEN_DICTS:
+        if canonical_json:
             encoder = iterencode_canonical_json
         else:
             encoder = _encode_json_bytes
diff --git a/synapse/storage/databases/main/censor_events.py b/synapse/storage/databases/main/censor_events.py
index 849bd5ba7a..3e26d5ba87 100644
--- a/synapse/storage/databases/main/censor_events.py
+++ b/synapse/storage/databases/main/censor_events.py
@@ -22,7 +22,7 @@ from synapse.storage._base import SQLBaseStore
 from synapse.storage.database import DatabasePool
 from synapse.storage.databases.main.cache import CacheInvalidationWorkerStore
 from synapse.storage.databases.main.events_worker import EventsWorkerStore
-from synapse.util.frozenutils import frozendict_json_encoder
+from synapse.util import json_encoder
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
@@ -104,7 +104,7 @@ class CensorEventsStore(EventsWorkerStore, CacheInvalidationWorkerStore, SQLBase
                 and original_event.internal_metadata.is_redacted()
             ):
                 # Redaction was allowed
-                pruned_json = frozendict_json_encoder.encode(
+                pruned_json = json_encoder.encode(
                     prune_event_dict(
                         original_event.room_version, original_event.get_dict()
                     )
@@ -170,7 +170,7 @@ class CensorEventsStore(EventsWorkerStore, CacheInvalidationWorkerStore, SQLBase
                 return
 
             # Prune the event's dict then convert it to JSON.
-            pruned_json = frozendict_json_encoder.encode(
+            pruned_json = json_encoder.encode(
                 prune_event_dict(event.room_version, event.get_dict())
             )
 
diff --git a/synapse/storage/databases/main/events.py b/synapse/storage/databases/main/events.py
index 87808c1483..90fb1a1f00 100644
--- a/synapse/storage/databases/main/events.py
+++ b/synapse/storage/databases/main/events.py
@@ -34,7 +34,7 @@ from synapse.storage.database import DatabasePool, LoggingTransaction
 from synapse.storage.databases.main.search import SearchEntry
 from synapse.storage.util.id_generators import MultiWriterIdGenerator
 from synapse.types import StateMap, get_domain_from_id
-from synapse.util.frozenutils import frozendict_json_encoder
+from synapse.util import json_encoder
 from synapse.util.iterutils import batch_iter
 
 if TYPE_CHECKING:
@@ -769,9 +769,7 @@ class PersistEventsStore:
                     logger.exception("")
                     raise
 
-                metadata_json = frozendict_json_encoder.encode(
-                    event.internal_metadata.get_dict()
-                )
+                metadata_json = json_encoder.encode(event.internal_metadata.get_dict())
 
                 sql = "UPDATE event_json SET internal_metadata = ? WHERE event_id = ?"
                 txn.execute(sql, (metadata_json, event.event_id))
@@ -826,10 +824,10 @@ class PersistEventsStore:
                 {
                     "event_id": event.event_id,
                     "room_id": event.room_id,
-                    "internal_metadata": frozendict_json_encoder.encode(
+                    "internal_metadata": json_encoder.encode(
                         event.internal_metadata.get_dict()
                     ),
-                    "json": frozendict_json_encoder.encode(event_dict(event)),
+                    "json": json_encoder.encode(event_dict(event)),
                     "format_version": event.format_version,
                 }
                 for event, _ in events_and_contexts
diff --git a/synapse/util/__init__.py b/synapse/util/__init__.py
index d55b93d763..517686f0a6 100644
--- a/synapse/util/__init__.py
+++ b/synapse/util/__init__.py
@@ -18,6 +18,7 @@ import logging
 import re
 
 import attr
+from frozendict import frozendict
 
 from twisted.internet import defer, task
 
@@ -31,9 +32,26 @@ def _reject_invalid_json(val):
     raise ValueError("Invalid JSON value: '%s'" % val)
 
 
-# Create a custom encoder to reduce the whitespace produced by JSON encoding and
-# ensure that valid JSON is produced.
-json_encoder = json.JSONEncoder(allow_nan=False, separators=(",", ":"))
+def _handle_frozendict(obj):
+    """Helper for json_encoder. Makes frozendicts serializable by returning
+    the underlying dict
+    """
+    if type(obj) is frozendict:
+        # fishing the protected dict out of the object is a bit nasty,
+        # but we don't really want the overhead of copying the dict.
+        return obj._dict
+    raise TypeError(
+        "Object of type %s is not JSON serializable" % obj.__class__.__name__
+    )
+
+
+# A custom JSON encoder which:
+#   * handles frozendicts
+#   * produces valid JSON (no NaNs etc)
+#   * reduces redundant whitespace
+json_encoder = json.JSONEncoder(
+    allow_nan=False, separators=(",", ":"), default=_handle_frozendict
+)
 
 # Create a custom decoder to reject Python extensions to JSON.
 json_decoder = json.JSONDecoder(parse_constant=_reject_invalid_json)
diff --git a/synapse/util/frozenutils.py b/synapse/util/frozenutils.py
index bf094c9386..5f7a6dd1d3 100644
--- a/synapse/util/frozenutils.py
+++ b/synapse/util/frozenutils.py
@@ -13,8 +13,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import json
-
 from frozendict import frozendict
 
 
@@ -49,23 +47,3 @@ def unfreeze(o):
         pass
 
     return o
-
-
-def _handle_frozendict(obj):
-    """Helper for EventEncoder. Makes frozendicts serializable by returning
-    the underlying dict
-    """
-    if type(obj) is frozendict:
-        # fishing the protected dict out of the object is a bit nasty,
-        # but we don't really want the overhead of copying the dict.
-        return obj._dict
-    raise TypeError(
-        "Object of type %s is not JSON serializable" % obj.__class__.__name__
-    )
-
-
-# A JSONEncoder which is capable of encoding frozendicts without barfing.
-# Additionally reduce the whitespace produced by JSON encoding.
-frozendict_json_encoder = json.JSONEncoder(
-    allow_nan=False, separators=(",", ":"), default=_handle_frozendict,
-)