Merge pull request #2711 from matrix-org/rav/fix_dns_errhandler

Fix error handling on dns lookup

synapse/http/endpoint.py

@@ -362,8 +362,10 @@ def _get_hosts_for_srv_record(dns_client, host):
         return res
 
     # no logcontexts here, so we can safely fire these off and gatherResults
-    d1 = dns_client.lookupAddress(host).addCallbacks(cb, eb)
-    d2 = dns_client.lookupIPV6Address(host).addCallbacks(cb, eb)
+    d1 = dns_client.lookupAddress(host).addCallbacks(
+        cb, eb, errbackArgs=("A", ))
+    d2 = dns_client.lookupIPV6Address(host).addCallbacks(
+        cb, eb, errbackArgs=("AAAA", ))
     results = yield defer.DeferredList(
         [d1, d2], consumeErrors=True)