Allow configuring default service configs in grpc_cli

test/cpp/util/grpc_cli.cc

@@ -51,6 +51,9 @@
        --decode=grpc.testing.SimpleResponse \
        src/proto/grpc/testing/messages.proto \
        < output.bin > output.txt
+   10. --default_service_config, optional default service config to use
+       on the channel. Note that this may be ignored if the name resolver
+       returns a service config.
 */
 
 #include <fstream>

test/cpp/util/grpc_tool.cc

@@ -57,6 +57,11 @@ DEFINE_string(proto_path, ".", "Path to look for the proto file.");
 DEFINE_string(protofiles, "", "Name of the proto file.");
 DEFINE_bool(binary_input, false, "Input in binary format");
 DEFINE_bool(binary_output, false, "Output in binary format");
+DEFINE_string(
+    default_service_config, "",
+    "Default service config to use on the channel, if non-empty. Note "
+    "that this will be ignored if the name resolver returns a service "
+    "config.");
 DEFINE_bool(json_input, false, "Input in json format");
 DEFINE_bool(json_output, false, "Output in json format");
 DEFINE_string(infile, "", "Input file (default is stdin)");
@@ -217,6 +222,10 @@ std::shared_ptr<grpc::Channel> CreateCliChannel(
   if (!cred.GetSslTargetNameOverride().empty()) {
     args.SetSslTargetNameOverride(cred.GetSslTargetNameOverride());
   }
+  if (!FLAGS_default_service_config.empty()) {
+    args.SetString(GRPC_ARG_SERVICE_CONFIG,
+                   FLAGS_default_service_config.c_str());
+  }
   return ::grpc::CreateCustomChannel(server_address, cred.GetCredentials(),
                                      args);
 }

test/cpp/util/grpc_tool_test.cc

@@ -118,6 +118,7 @@ DECLARE_bool(batch);
 DECLARE_string(metadata);
 DECLARE_string(protofiles);
 DECLARE_string(proto_path);
+DECLARE_string(default_service_config);
 
 namespace {
 
@@ -1192,6 +1193,28 @@ TEST_F(GrpcToolTest, ListCommand_OverrideSslHostName) {
   ShutdownServer();
 }
 
+TEST_F(GrpcToolTest, ConfiguringDefaultServiceConfig) {
+  // Test input "grpc_cli list localhost:<port>
+  // --default_service_config={\"loadBalancingConfig\":[{\"pick_first\":{}}]}"
+  std::stringstream output_stream;
+  const grpc::string server_address = SetUpServer();
+  const char* argv[] = {"grpc_cli", "ls", server_address.c_str()};
+  // Just check that the tool is still operational when --default_service_config
+  // is configured. This particular service config is in reality redundant with
+  // the channel's default configuration.
+  FLAGS_l = false;
+  FLAGS_default_service_config =
+      "{\"loadBalancingConfig\":[{\"pick_first\":{}}]}";
+  EXPECT_TRUE(0 == GrpcToolMainLib(ArraySize(argv), argv, TestCliCredentials(),
+                                   std::bind(PrintStream, &output_stream,
+                                             std::placeholders::_1)));
+  FLAGS_default_service_config = "";
+  EXPECT_TRUE(0 == strcmp(output_stream.str().c_str(),
+                          "grpc.testing.EchoTestService\n"
+                          "grpc.reflection.v1alpha.ServerReflection\n"));
+  ShutdownServer();
+}
+
 }  // namespace testing
 }  // namespace grpc