Reduce the amount of incredibly spammy stack traces. Expected errors (e.g....

Reduce the amount of incredibly spammy stack traces. Expected errors (e.g. SynapseErrors) shouldn't have their full trace logged every time. Don't send responses to disconnected requests.

synapse/http/server.py

@@ -132,7 +132,11 @@ class JsonResource(HttpServer, resource.Resource):
                 {"error": "Unrecognized request"}
             )
         except CodeMessageException as e:
-            logger.exception(e)
+            if isinstance(e, SynapseError):
+                logger.error("%s SynapseError: %s - %s", request, e.code,
+                             e.msg)
+            else:
+                logger.exception(e)
             self._send_response(
                 request,
                 e.code,
@@ -147,6 +151,14 @@ class JsonResource(HttpServer, resource.Resource):
             )
 
     def _send_response(self, request, code, response_json_object):
+        # could alternatively use request.notifyFinish() and flip a flag when
+        # the Deferred fires, but since the flag is RIGHT THERE it seems like
+        # a waste.
+        if request._disconnected:
+            logger.warn(
+                "Not sending response to request %s, already disconnected.",
+                request)
+            return
 
         if not self._request_user_agent_is_curl(request):
             json_bytes = encode_canonical_json(response_json_object)