[cdc_stream] Automatically start service (#28)

Starts the streaming service if it's not up and running. This required
adding the ability to run a detached process. By default, all child
processes are killed when the parent process exits. Since detached
child processes don't run with a console, they need to create sub-
processes with CREATE_NO_WINDOW since otherwise a new console pops up,
e.g. for every ssh command.

Polls for 20 seconds while the service starts up. For this purpose,
a BackgroundServiceClient is added. This will be reused in a future CL
by a new stop-service command to exit the service.

Also adds --service-port as additional argument to start-service.

cdc_stream/background_service_client.cc

@@ -0,0 +1,56 @@
+// Copyright 2022 Google LLC
+//
+// 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.
+
+#include "cdc_stream/background_service_client.h"
+
+#include "absl/status/status.h"
+#include "common/grpc_status.h"
+#include "common/status_macros.h"
+#include "grpcpp/channel.h"
+
+namespace cdc_ft {
+
+using GetPidResponse = backgroundservice::GetPidResponse;
+using EmptyProto = google::protobuf::Empty;
+
+BackgroundServiceClient::BackgroundServiceClient(
+    std::shared_ptr<grpc::Channel> channel) {
+  stub_ = BackgroundService::NewStub(std::move(channel));
+}
+
+BackgroundServiceClient::~BackgroundServiceClient() = default;
+
+absl::Status BackgroundServiceClient::Exit() {
+  EmptyProto request;
+  EmptyProto response;
+  grpc::ClientContext context;
+  return ToAbslStatus(stub_->Exit(&context, request, &response));
+}
+
+absl::StatusOr<int> BackgroundServiceClient::GetPid() {
+  EmptyProto request;
+  GetPidResponse response;
+  grpc::ClientContext context;
+  RETURN_IF_ERROR(ToAbslStatus(stub_->GetPid(&context, request, &response)));
+  return response.pid();
+}
+
+absl::Status BackgroundServiceClient::IsHealthy() {
+  EmptyProto request;
+  EmptyProto response;
+  grpc::ClientContext context;
+  return ToAbslStatus(stub_->HealthCheck(&context, request, &response));
+}
+
+}  // namespace cdc_ft