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.

common/buffer.h

@@ -0,0 +1,87 @@
+/*
+ * 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 COMMON_BUFFER_H_
+#define COMMON_BUFFER_H_
+
+#include <cstdlib>
+#include <initializer_list>
+
+namespace cdc_ft {
+
+// Buffer for generic data blobs. It is a managed and dynamically sized memory
+// buffer with an interface similar to that of std::vector. It can be used as an
+// in-place replacement in some use cases like reading files.
+// The class solves a performance problem on Linux where resize() can be
+// relatively expensive since a vector default-constructs elements. This can
+// be a big performance bottleneck in some cases.
+class Buffer {
+ public:
+  Buffer();
+  explicit Buffer(size_t size);
+  Buffer(std::initializer_list<char> list);
+
+  ~Buffer();
+
+  // Non-copyable, non-assignable for safety.
+  Buffer(const Buffer& other) = delete;
+  Buffer& operator=(const Buffer& other) = delete;
+
+  Buffer(Buffer&& other) noexcept;
+  Buffer& operator=(Buffer&& other) noexcept;
+
+  bool operator==(const Buffer& other) const;
+  bool operator!=(const Buffer& other) const;
+
+  // Resizes the buffer. Only reallocates if the size increases. In that case,
+  // allocates 1.5x more than required. If size shrinks, keeps the buffer.
+  // Does not initialize the buffer.
+  void resize(size_t new_size);
+
+  // Makes sure the buffer capacity is at least the given number of bytes.
+  void reserve(size_t capacity);
+
+  // Returns the current size of the buffer.
+  size_t size() const { return size_; }
+
+  // Returns true if the size is zero.
+  bool empty() const { return size_ == 0; }
+
+  // Returns the currently allocated buffer size.
+  size_t capacity() const { return capacity_; }
+
+  // Resizes the buffer to 0.
+  void clear() { size_ = 0; }
+
+  // Returns the data pointer.
+  char* data() { return data_; }
+
+  // Returns the data pointer.
+  const char* data() const { return data_; }
+
+  // Appends |data| of size |data_size| to the end of the buffer. The behavior
+  // is undefined if the provided memory range overlaps with the buffer's data.
+  void append(const void* data, size_t data_size);
+
+ private:
+  char* data_ = nullptr;
+  size_t size_ = 0;
+  size_t capacity_ = 0;
+};
+
+}  // namespace cdc_ft
+
+#endif  // COMMON_BUFFER_H_