AU: SplitWriter class for parsing our full update files.

src/platform/update_engine/file_writer.cc

 // 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.
 
 #include "update_engine/file_writer.h"
 #include <errno.h>
 
 namespace chromeos_update_engine {
 
 int DirectFileWriter::Open(const char* path, int flags, mode_t mode) {
   CHECK_EQ(fd_, -1);
   fd_ = open(path, flags, mode);
   if (fd_ < 0)
     return -errno;
   return 0;
 }
 
-int DirectFileWriter::Write(const void* bytes, size_t count) {
+ssize_t DirectFileWriter::Write(const void* bytes, size_t count) {
   CHECK_GE(fd_, 0);
   const char* char_bytes = reinterpret_cast<const char*>(bytes);
 
   size_t bytes_written = 0;
   while (bytes_written < count) {
     ssize_t rc = write(fd_, char_bytes + bytes_written,
                        count - bytes_written);
     if (rc < 0)
       return -errno;
     bytes_written += rc;
   }
   CHECK_EQ(bytes_written, count);
   return bytes_written;
 }
 
 int DirectFileWriter::Close() {
   CHECK_GE(fd_, 0);
   int rc = close(fd_);
 
   // This can be any negative number that's not -1. This way, this FileWriter
   // won't be used again for another file.
   fd_ = -2;
 
   if (rc < 0)
     return -errno;
   return rc;
 }
 
 }  // namespace chromeos_update_engine