From c132c8e505acd567dac9ae23019b4dc1c763e41c Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Wed, 10 Apr 2019 10:39:54 +0100
Subject: [PATCH 1/3] Handle the case of `get_missing_events` failing

Currently if a call to `/get_missing_events` fails we log an exception
and stop processing the top level event we received over federation.
Instead let's try and handle it sensibly given it is a somewhat expected
failure mode.
---
 synapse/handlers/federation.py | 29 ++++++++++++++++++++---------
 1 file changed, 20 insertions(+), 9 deletions(-)

diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 0684778882..07a5dc182d 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -35,6 +35,7 @@ from synapse.api.errors import (
     CodeMessageException,
     FederationDeniedError,
     FederationError,
+    RequestSendFailed,
     StoreError,
     SynapseError,
 )
@@ -493,15 +494,25 @@ class FederationHandler(BaseHandler):
         #
         # All that said: Let's try increasing the timout to 60s and see what happens.
 
-        missing_events = yield self.federation_client.get_missing_events(
-            origin,
-            room_id,
-            earliest_events_ids=list(latest),
-            latest_events=[pdu],
-            limit=10,
-            min_depth=min_depth,
-            timeout=60000,
-        )
+        try:
+            missing_events = yield self.federation_client.get_missing_events(
+                origin,
+                room_id,
+                earliest_events_ids=list(latest),
+                latest_events=[pdu],
+                limit=10,
+                min_depth=min_depth,
+                timeout=60000,
+            )
+        except RequestSendFailed as e:
+            # We failed to get the missing events, but since we need to handle
+            # the case of `get_missing_events` not returning the necessary
+            # events anyway, it is safe to simply log the error and continue.
+            logger.warn(
+                "[%s %s]: Failed to get prev_events for %s: %s",
+                room_id, event_id, e,
+            )
+            return
 
         logger.info(
             "[%s %s]: Got %d prev_events: %s",

From 42e1aa5b2cf34a4c788d23d3376c5f58990a63c9 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Wed, 10 Apr 2019 10:43:47 +0100
Subject: [PATCH 2/3] Newsfile

---
 changelog.d/5042.bugfix | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 changelog.d/5042.bugfix

diff --git a/changelog.d/5042.bugfix b/changelog.d/5042.bugfix
new file mode 100644
index 0000000000..736b07c790
--- /dev/null
+++ b/changelog.d/5042.bugfix
@@ -0,0 +1 @@
+Fix bug processing incoming events over federation if call to `/get_missing_events` fails.

From 2b20d0fb59f78c29e55901754aca2944cbb947b9 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Tue, 18 Jun 2019 16:12:53 +0100
Subject: [PATCH 3/3] Fix logline

---
 synapse/handlers/federation.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index cc08e3e027..09af6a41a0 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -513,7 +513,7 @@ class FederationHandler(BaseHandler):
             # the case of `get_missing_events` not returning the necessary
             # events anyway, it is safe to simply log the error and continue.
             logger.warn(
-                "[%s %s]: Failed to get prev_events for %s: %s",
+                "[%s %s]: Failed to get prev_events: %s",
                 room_id, event_id, e,
             )
             return