From 3e58ce72b42f2ae473c1e76a967548cd6fa7e2e6 Mon Sep 17 00:00:00 2001
From: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>
Date: Tue, 6 Oct 2020 10:03:39 +0100
Subject: [PATCH] Don't bother responding to client requests that have already
 disconnected (#8465)

This PR ports the quick fix from https://github.com/matrix-org/synapse/pull/2796 to further methods which handle media, URL preview and `/key/v2/server` requests. This prevents a harmless `ERROR` that comes up in the logs when we were unable to respond to a client request when the client had already disconnected. In this case we simply bail out if the client has already done so.

This is the 'simple fix' as suggested by https://github.com/matrix-org/synapse/issues/5304#issuecomment-574740003.

Fixes https://github.com/matrix-org/synapse/issues/6700
Fixes https://github.com/matrix-org/synapse/issues/5304
---
 changelog.d/8465.bugfix        | 1 +
 synapse/http/server.py         | 5 +++++
 synapse/rest/media/v1/_base.py | 6 ++++++
 3 files changed, 12 insertions(+)
 create mode 100644 changelog.d/8465.bugfix

diff --git a/changelog.d/8465.bugfix b/changelog.d/8465.bugfix
new file mode 100644
index 0000000000..73f895b268
--- /dev/null
+++ b/changelog.d/8465.bugfix
@@ -0,0 +1 @@
+Don't attempt to respond to some requests if the client has already disconnected.
\ No newline at end of file
diff --git a/synapse/http/server.py b/synapse/http/server.py
index 09ed74f6ce..00b98af3d4 100644
--- a/synapse/http/server.py
+++ b/synapse/http/server.py
@@ -651,6 +651,11 @@ def respond_with_json_bytes(
     Returns:
         twisted.web.server.NOT_DONE_YET if the request is still active.
     """
+    if request._disconnected:
+        logger.warning(
+            "Not sending response to request %s, already disconnected.", request
+        )
+        return
 
     request.setResponseCode(code)
     request.setHeader(b"Content-Type", b"application/json")
diff --git a/synapse/rest/media/v1/_base.py b/synapse/rest/media/v1/_base.py
index 6568e61829..67aa993f19 100644
--- a/synapse/rest/media/v1/_base.py
+++ b/synapse/rest/media/v1/_base.py
@@ -213,6 +213,12 @@ async def respond_with_responder(
         file_size (int|None): Size in bytes of the media. If not known it should be None
         upload_name (str|None): The name of the requested file, if any.
     """
+    if request._disconnected:
+        logger.warning(
+            "Not sending response to request %s, already disconnected.", request
+        )
+        return
+
     if not responder:
         respond_404(request)
         return