Releasing the former Stadia file transfer tools

The tools allow efficient and fast synchronization of large directory
trees from a Windows workstation to a Linux target machine.

cdc_rsync* support efficient copy of files by using content-defined
chunking (CDC) to identify chunks within files that can be reused.

asset_stream_manager + cdc_fuse_fs support efficient streaming of a
local directory to a remote virtual file system based on FUSE. It also
employs CDC to identify and reuse unchanged data chunks.

asset_stream_manager/session.h

@@ -0,0 +1,90 @@
+/*
+ * 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_SESSION_H_
+#define ASSET_STREAM_MANAGER_SESSION_H_
+
+#include <memory>
+#include <string>
+#include <unordered_map>
+
+#include "absl/status/status.h"
+#include "asset_stream_manager/metrics_recorder.h"
+#include "asset_stream_manager/session_config.h"
+#include "common/remote_util.h"
+
+namespace cdc_ft {
+
+class CdcFuseManager;
+class ProcessFactory;
+class Process;
+
+// Manages the connection of a workstation to a single gamelet.
+class Session {
+ public:
+  // |instance_id| is a unique id for the remote instance.
+  // |instance_ip| is the IP address of the remote instance.
+  // |instance_port| is the SSH tunnel port for connecting to the instance.
+  // |cfg| contains generic configuration parameters for the session.
+  // |process_factory| abstracts process creation.
+  Session(std::string instance_id, std::string instance_ip,
+          uint16_t instance_port, SessionConfig cfg,
+          ProcessFactory* process_factory,
+          std::unique_ptr<SessionMetricsRecorder> metrics_recorder);
+  ~Session();
+
+  // Starts the CDC FUSE on the instance with established port forwarding.
+  // |local_port| is the local reverse forwarding port to use.
+  // [|first_remote_port|, |last_remote_port|] are the allowed remote ports.
+  absl::Status Start(int local_port, int first_remote_port,
+                     int last_remote_port);
+
+  // Shuts down the connection to the instance.
+  absl::Status Stop() ABSL_LOCKS_EXCLUDED(transferred_data_mu_);
+
+  // Returns true if the FUSE process is running.
+  bool IsHealthy();
+
+  // Record an event for the session.
+  void RecordEvent(metrics::DeveloperLogEvent event,
+                   metrics::EventType code) const;
+
+  // Is called when content was sent during the session.
+  void OnContentSent(size_t bytes, size_t chunks)
+      ABSL_LOCKS_EXCLUDED(transferred_data_mu_);
+
+  // Records heart beat data if it has changed since last record.
+  void RecordHeartBeatIfChanged() ABSL_LOCKS_EXCLUDED(transferred_data_mu_);
+
+ private:
+  const std::string instance_id_;
+  const SessionConfig cfg_;
+  ProcessFactory* const process_factory_;
+
+  RemoteUtil remote_util_;
+  std::unique_ptr<CdcFuseManager> fuse_;
+  std::unique_ptr<SessionMetricsRecorder> metrics_recorder_;
+
+  absl::Mutex transferred_data_mu_;
+  uint64_t transferred_bytes_ ABSL_GUARDED_BY(transferred_data_mu_) = 0;
+  uint64_t transferred_chunks_ ABSL_GUARDED_BY(transferred_data_mu_) = 0;
+  uint64_t last_read_bytes_ = 0;
+  uint64_t last_read_chunks_ = 0;
+};
+
+}  // namespace cdc_ft
+
+#endif  // ASSET_STREAM_MANAGER_SESSION_H_