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.

data_store/mem_data_store.h

@@ -0,0 +1,82 @@
+/*
+ * 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 DATA_STORE_MEM_DATA_STORE_H_
+#define DATA_STORE_MEM_DATA_STORE_H_
+
+#include <string>
+#include <vector>
+
+#include "data_store/data_store_writer.h"
+#include "manifest/content_id.h"
+
+namespace cdc_ft {
+
+// In-memory implementation of a DataStoreWriter. Data needs to be pre-
+// populated manually using AddData() and AddProto(). Useful for testing.
+class MemDataStore : public DataStoreWriter {
+ public:
+  using ChunkMap = std::unordered_map<ContentIdProto, std::vector<char>>;
+
+  MemDataStore();
+  MemDataStore(const MemDataStore&) = delete;
+  MemDataStore& operator=(const MemDataStore&) = delete;
+
+  virtual ~MemDataStore();
+
+  // TODO: Extract AddData in a helper function.
+  // Adds |data| to the memory-backed storage and returns the id to it.
+  ContentIdProto AddData(std::vector<char> data);
+
+  // TODO: Extract AddProto in a helper function.
+  // Serializes |message|, adds it to the memory-backed storage, and returns the
+  // id to it.
+  ContentIdProto AddProto(const google::protobuf::MessageLite& message);
+
+  // Note: DO NOT MIX Add* get Get* methods in a multi-threaded environment!
+  // Get* methods are thread-safe as they are read-only, but Add* methods write
+  // to the data. They are not thread-safe.
+
+  // DataStoreReader:
+  absl::StatusOr<size_t> Get(const ContentIdProto& id, void* data,
+                             size_t offset, size_t size) override;
+  absl::Status Get(const ContentIdProto& content_id, Buffer* data) override;
+  absl::Status Get(ChunkTransferList* chunks) override;
+
+  // DataStoreWriter:
+  bool Contains(const ContentIdProto& content_id) override;
+
+  absl::Status Put(const ContentIdProto& content_id, const void* data,
+                   size_t size) override;
+
+  absl::Status Remove(const ContentIdProto& content_id) override;
+
+  absl::Status Wipe() override;
+
+  absl::Status Prune(std::unordered_set<ContentIdProto> ids_to_keep) override;
+
+  // Direct access to the chunks for testing.
+  const ChunkMap& Chunks() const { return data_lookup_; }
+  ChunkMap& Chunks() { return data_lookup_; }
+
+ private:
+  // Maps content IDs to chunks.
+  ChunkMap data_lookup_;
+};
+
+}  // namespace cdc_ft
+
+#endif  // DATA_STORE_MEM_DATA_STORE_H_