[cdc_stream] Switch asset_stream_manager to use Lyra (#25)

Switch asset_stream_manager to use Lyra

Lyra has a nice simple interface, but a few quirks that we work
around, mainly in the BaseCommand class:
- It does not support return values from running a command.
- It does not support return values from a custom arg parser.
- Lyra interprets --bad_arg as positional argument.

Fixes #15

asset_stream_manager/start_service_command.h

@@ -0,0 +1,51 @@
+/*
+ * 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 ASSET_STREAM_MANAGER_START_SERVICE_COMMAND_H_
+#define ASSET_STREAM_MANAGER_START_SERVICE_COMMAND_H_
+
+#include "asset_stream_manager/asset_stream_config.h"
+#include "asset_stream_manager/base_command.h"
+
+namespace cdc_ft {
+
+// Handler for the start-service command. Starts the asset streaming service
+// and returns when the service is shut down.
+class StartServiceCommand : public BaseCommand {
+ public:
+  explicit StartServiceCommand(int* exit_code);
+  ~StartServiceCommand();
+
+  // BaseCommand:
+  void RegisterCommandLineFlags(lyra::command& cmd) override;
+  absl::Status Run() override;
+
+ private:
+  // Initializes LOG* logging.
+  // Depending on the flags, might log to console or to a file.
+  absl::Status InitLogging();
+
+  // Runs the asset streaming service.
+  absl::Status RunService();
+
+  AssetStreamConfig cfg_;
+  std::string config_file_;
+  std::string log_dir_;
+};
+
+}  // namespace cdc_ft
+
+#endif  // ASSET_STREAM_MANAGER_START_SERVICE_COMMAND_H_