AU: Class to perform delta updates.

src/platform/update_engine/file_writer.h

 // Copyright (c) 2009 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_FILE_WRITER_H__
 #define CHROMEOS_PLATFORM_UPDATE_ENGINE_FILE_WRITER_H__
 
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
 #include <unistd.h>
 #include "chromeos/obsolete_logging.h"
 #include "update_engine/utils.h"
 
 // FileWriter is a class that is used to (synchronously, for now) write to
 // a file. This file is a thin wrapper around open/write/close system calls,
 // but provides and interface that can be customized by subclasses that wish
 // to filter the data.
 
 namespace chromeos_update_engine {
 
 class FileWriter {
  public:
+  FileWriter() {}
   virtual ~FileWriter() {}
 
   // Wrapper around open. Returns 0 on success or -errno on error.
   virtual int Open(const char* path, int flags, mode_t mode) = 0;
 
   // Wrapper around write. Returns bytes written on success or
   // -errno on error.
   virtual int Write(const void* bytes, size_t count) = 0;
 
   // Wrapper around close. Returns 0 on success or -errno on error.
   virtual int Close() = 0;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(FileWriter);
 };
 
 // Direct file writer is probably the simplest FileWriter implementation.
 // It calls the system calls directly.
 
 class DirectFileWriter : public FileWriter {
  public:
   DirectFileWriter() : fd_(-1) {}
   virtual ~DirectFileWriter() {}
 
   virtual int Open(const char* path, int flags, mode_t mode);
   virtual int Write(const void* bytes, size_t count);
   virtual int Close();
 
   int fd() const { return fd_; }
 
  private:
   int fd_;
+  
+  DISALLOW_COPY_AND_ASSIGN(DirectFileWriter);
 };
 
 class ScopedFileWriterCloser {
  public:
   explicit ScopedFileWriterCloser(FileWriter* writer) : writer_(writer) {}
   ~ScopedFileWriterCloser() {
     int err = writer_->Close();
     if (err)
       LOG(ERROR) << "FileWriter::Close failed: "
                  << utils::ErrnoNumberAsString(-err);
   }
  private:
   FileWriter* writer_;
+  
+  DISALLOW_COPY_AND_ASSIGN(ScopedFileWriterCloser);
 };
 
 }  // namespace chromeos_update_engine
 
 #endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_FILE_WRITER_H__