[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.h

@@ -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.
+ */
+
+#ifndef CDC_STREAM_BACKGROUND_SERVICE_CLIENT_H_
+#define CDC_STREAM_BACKGROUND_SERVICE_CLIENT_H_
+
+#include <memory>
+
+#include "absl/status/status.h"
+#include "absl/status/statusor.h"
+#include "proto/background_service.grpc.pb.h"
+
+namespace grpc_impl {
+class Channel;
+}
+
+namespace cdc_ft {
+
+// gRpc client for managing the asset streaming service.
+class BackgroundServiceClient {
+ public:
+  // |channel| is a grpc channel to use.
+  explicit BackgroundServiceClient(std::shared_ptr<grpc::Channel> channel);
+
+  ~BackgroundServiceClient();
+
+  // Initialize service shutdown.
+  absl::Status Exit();
+
+  // Returns the PID of the service process.
+  absl::StatusOr<int> GetPid();
+
+  // Verifies that the service is running and able to take requests.
+  absl::Status IsHealthy();
+
+ private:
+  using BackgroundService = backgroundservice::BackgroundService;
+  std::unique_ptr<BackgroundService::Stub> stub_;
+};
+
+}  // namespace cdc_ft
+
+#endif  // CDC_STREAM_BACKGROUND_SERVICE_CLIENT_H_