--- /dev/null
+//
+// Copyright 2019 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+// This is similar to the sockaddr resolver, except that it supports a
+// bunch of query args that are useful for dependency injection in tests.
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/ext/filters/client_channel/resolver/dns/dns_resolver_selection.h"
+
+GPR_GLOBAL_CONFIG_DEFINE_STRING(
+ grpc_dns_resolver, "",
+ "Declares which DNS resolver to use. The default is ares if gRPC is built "
+ "with c-ares support. Otherwise, the value of this environment variable is "
+ "ignored.")