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/base/cdc_interface.h

@@ -0,0 +1,73 @@
+/*
+ * 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_BASE_CDC_INTERFACE_H_
+#define CDC_RSYNC_BASE_CDC_INTERFACE_H_
+
+#include <string>
+
+#include "absl/status/status.h"
+#include "common/threadpool.h"
+
+namespace cdc_ft {
+
+class MessagePump;
+
+class ReportCdcProgress {
+ public:
+  virtual ~ReportCdcProgress() = default;
+  virtual void ReportSyncProgress(size_t num_client_bytes_processed,
+                                  size_t num_server_bytes_processed) = 0;
+};
+
+// Creates signatures, diffs and patches files. Abstraction layer for fastcdc
+// chunking and blake3 hashing.
+class CdcInterface {
+ public:
+  explicit CdcInterface(MessagePump* message_pump);
+
+  // Creates the signature of the file at |filepath| and sends it to the socket.
+  // Typically called on the server.
+  absl::Status CreateAndSendSignature(const std::string& filepath);
+
+  // Receives the server-side signature of |file| from the socket, creates diff
+  // data using the signature and the file, and sends the diffs to the socket.
+  // Typically called on the client.
+  absl::Status ReceiveSignatureAndCreateAndSendDiff(
+      FILE* file, ReportCdcProgress* progress);
+
+  // Receives diffs from the socket and patches the file at |basis_filepath|.
+  // The patched data is written to |patched_file|, which must be open in "wb"
+  // mode. Sets |is_executable| to true if the patched file is an executable
+  // (based on magic headers).
+  // Typically called on the server.
+  absl::Status ReceiveDiffAndPatch(const std::string& basis_filepath,
+                                   FILE* patched_file, bool* is_executable);
+
+ private:
+  MessagePump* const message_pump_;
+
+  // Thread pool for computing chunk hashes.
+  std::unique_ptr<Threadpool> hash_pool_;
+
+  // List of unused hash computation tasks. Tasks are reused by the hash pool
+  // in order to prevent buffer reallocation.
+  std::vector<std::unique_ptr<Task>> free_tasks_;
+};
+
+}  // namespace cdc_ft
+
+#endif  // CDC_RSYNC_BASE_CDC_INTERFACE_H_