AU: Speed up updates by using buffered writes.

buffered_file_writer.h

Index: buffered_file_writer.h
diff --git a/buffered_file_writer.h b/buffered_file_writer.h
new file mode 100644
index 0000000000000000000000000000000000000000..0457285c4584dc4da1ceaf46219bdc711e5a9d5c
--- /dev/null
+++ b/buffered_file_writer.h
@@ -0,0 +1,53 @@
+// Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROMEOS_PLATFORM_UPDATE_ENGINE_BUFFERED_FILE_WRITER_H__
+#define CHROMEOS_PLATFORM_UPDATE_ENGINE_BUFFERED_FILE_WRITER_H__
+
+#include <base/scoped_ptr.h>
+#include <gtest/gtest_prod.h>  // for FRIEND_TEST
+
+#include "update_engine/file_writer.h"
+
+// BufferedFileWriter is an implementation of FileWriter that buffers all data
+// before passing it onto another FileWriter.
+
+namespace chromeos_update_engine {
+
+class BufferedFileWriter : public FileWriter {
+ public:
+  BufferedFileWriter(FileWriter* next, size_t buffer_size);
+  virtual ~BufferedFileWriter();
+
+  virtual int Open(const char* path, int flags, mode_t mode);
+  virtual ssize_t Write(const void* bytes, size_t count);
+  virtual int Close();
+
+ private:
+  FRIEND_TEST(BufferedFileWriterTest, CloseErrorTest);
+  FRIEND_TEST(BufferedFileWriterTest, CloseNoDataTest);
+  FRIEND_TEST(BufferedFileWriterTest, CloseWriteErrorTest);
+  FRIEND_TEST(BufferedFileWriterTest, ConstructorTest);
+  FRIEND_TEST(BufferedFileWriterTest, WriteBufferNoDataTest);
+  FRIEND_TEST(BufferedFileWriterTest, WriteBufferTest);
+  FRIEND_TEST(BufferedFileWriterTest, WriteErrorTest);
+  FRIEND_TEST(BufferedFileWriterTest, WriteTest);
+  FRIEND_TEST(BufferedFileWriterTest, WriteWrapBufferTest);
+
+  // If non-empty, sends the buffer to the next FileWriter.
+  ssize_t WriteBuffer();
+
+  // The FileWriter that we write all buffered data to.
+  FileWriter* const next_;
+
+  scoped_array<char> buffer_;
+  size_t buffer_size_;
+  size_t buffered_bytes_;
+
+  DISALLOW_COPY_AND_ASSIGN(BufferedFileWriter);
+};
+
+}  // namespace chromeos_update_engine
+
+#endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_BUFFERED_FILE_WRITER_H__