thrift: keep downstream connection on routing error (#20756)

By default the router closes downstream connection if the current request is not routable or the upstream connection is broken. This causes oneway (or async) requests pending on wire or in kernel buffers will be also dropped even if they are routable and their target cluster is perfectly healthy.

Risk Level: low
Testing: unit test
Docs Changes: Comment added to the new API field.
Fixes #12836
Signed-off-by: Tamas Kovacs <tamas.2.kovacs@nokia-sbell.com>

Mirrored from https://github.com/envoyproxy/envoy @ 65a4fc4977c4e50e722461a1d68278d404610342

envoy/extensions/filters/network/thrift_proxy/router/v3/router.proto

@@ -2,6 +2,8 @@ syntax = "proto3";
 
 package envoy.extensions.filters.network.thrift_proxy.router.v3;
 
+import "google/protobuf/wrappers.proto";
+
 import "udpa/annotations/status.proto";
 import "udpa/annotations/versioning.proto";
 
@@ -18,4 +20,7 @@ option (udpa.annotations.file_status).package_version_status = ACTIVE;
 message Router {
   option (udpa.annotations.versioning).previous_message_type =
       "envoy.config.filter.thrift.router.v2alpha1.Router";
+
+  // Close downstream connection in case of routing or upstream connection problem. Default: true
+  google.protobuf.BoolValue close_downstream_on_upstream_error = 1;
 }