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.

cdc_rsync/zstd_stream.h

@@ -0,0 +1,65 @@
+/*
+ * 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_RSYNC_ZSTD_STREAM_H_
+#define CDC_RSYNC_ZSTD_STREAM_H_
+
+#include <thread>
+
+#include "absl/status/status.h"
+#include "absl/synchronization/mutex.h"
+#include "cdc_rsync/base/socket.h"
+#include "common/buffer.h"
+#include "lib/zstd.h"
+
+namespace cdc_ft {
+
+// Streaming compression using zstd.
+class ZstdStream {
+ public:
+  ZstdStream(Socket* socket, int level, uint32_t num_threads);
+  ~ZstdStream();
+
+  // Sends the given |data| to the compressor.
+  absl::Status Write(const void* data, size_t size) ABSL_LOCKS_EXCLUDED(mutex_);
+
+  // Flushes all remaining data and sends the compressed data to the socket.
+  absl::Status Flush() ABSL_LOCKS_EXCLUDED(mutex_);
+
+ private:
+  // Initializes the compressor and related data.
+  absl::Status Initialize(int level, uint32_t num_threads)
+      ABSL_LOCKS_EXCLUDED(mutex_);
+
+  // Compressor thread, pushes |in_buffer_| to the zstd compressor and sends
+  // compressed data to the socket.
+  void ThreadCompressorMain() ABSL_LOCKS_EXCLUDED(mutex_);
+
+  Socket* const socket_;
+  ZSTD_CCtx* cctx_;
+
+  absl::Mutex mutex_;
+  Buffer in_buffer_ ABSL_GUARDED_BY(mutex_);
+  bool shutdown_ ABSL_GUARDED_BY(mutex_) = false;
+  bool last_chunk_ ABSL_GUARDED_BY(mutex_) = false;
+  bool last_chunk_sent_ ABSL_GUARDED_BY(mutex_) = false;
+  absl::Status status_ ABSL_GUARDED_BY(mutex_);
+  std::thread compressor_thread_;
+};
+
+}  // namespace cdc_ft
+
+#endif  // CDC_RSYNC_ZSTD_STREAM_H_