Always close _all_ `ijson` coroutines, even if doing so raises Exceptions (#14065)

2 files changed, 38 insertions, 5 deletions

diff --git a/synapse/federation/transport/client.py b/synapse/federation/transport/client.py
index 32074b8ca6..cd39d4d111 100644
--- a/synapse/federation/transport/client.py
+++ b/synapse/federation/transport/client.py
@@ -45,6 +45,7 @@ from synapse.federation.units import Transaction
 from synapse.http.matrixfederationclient import ByteParser
 from synapse.http.types import QueryParams
 from synapse.types import JsonDict
+from synapse.util import ExceptionBundle
 
 logger = logging.getLogger(__name__)
 
@@ -926,8 +927,7 @@ class SendJoinParser(ByteParser[SendJoinResponse]):
         return len(data)
 
     def finish(self) -> SendJoinResponse:
-        for c in self._coros:
-            c.close()
+        _close_coros(self._coros)
 
         if self._response.event_dict:
             self._response.event = make_event_from_dict(
@@ -970,6 +970,27 @@ class _StateParser(ByteParser[StateRequestResponse]):
         return len(data)
 
     def finish(self) -> StateRequestResponse:
-        for c in self._coros:
-            c.close()
+        _close_coros(self._coros)
         return self._response
+
+
+def _close_coros(coros: Iterable[Generator[None, bytes, None]]) -> None:
+    """Close each of the given coroutines.
+
+    Always calls .close() on each coroutine, even if doing so raises an exception.
+    Any exceptions raised are aggregated into an ExceptionBundle.
+
+    :raises ExceptionBundle: if at least one coroutine fails to close.
+    """
+    exceptions = []
+    for c in coros:
+        try:
+            c.close()
+        except Exception as e:
+            exceptions.append(e)
+
+    if exceptions:
+        # raise from the first exception so that the traceback has slightly more context
+        raise ExceptionBundle(
+            f"There were {len(exceptions)} errors closing coroutines", exceptions
+        ) from exceptions[0]
diff --git a/synapse/util/__init__.py b/synapse/util/__init__.py
index a90f08dd4c..7be9d5f113 100644
--- a/synapse/util/__init__.py
+++ b/synapse/util/__init__.py
@@ -15,7 +15,7 @@
 import json
 import logging
 import typing
-from typing import Any, Callable, Dict, Generator, Optional
+from typing import Any, Callable, Dict, Generator, Optional, Sequence
 
 import attr
 from frozendict import frozendict
@@ -193,3 +193,15 @@ def log_failure(
 # Version string with git info. Computed here once so that we don't invoke git multiple
 # times.
 SYNAPSE_VERSION = get_distribution_version_string("matrix-synapse", __file__)
+
+
+class ExceptionBundle(Exception):
+    # A poor stand-in for something like Python 3.11's ExceptionGroup.
+    # (A backport called `exceptiongroup` exists but seems overkill: we just want a
+    # container type here.)
+    def __init__(self, message: str, exceptions: Sequence[Exception]):
+        parts = [message]
+        for e in exceptions:
+            parts.append(str(e))
+        super().__init__("\n  - ".join(parts))
+        self.exceptions = exceptions