diff --git a/file_writer.h b/file_writer.h
new file mode 100644
index 0000000..223cd6e
--- /dev/null
+++ b/file_writer.h
@@ -0,0 +1,79 @@
+// 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 UPDATE_ENGINE_FILE_WRITER_H__
+#define UPDATE_ENGINE_FILE_WRITER_H__
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include "glog/logging.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:
+  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;
+};
+
+// 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) {
+    CHECK_EQ(-1, fd_);
+    fd_ = open(path, flags, mode);
+    if (fd_ < 0)
+      return -errno;
+    return 0;
+  }
+
+  virtual int Write(const void* bytes, size_t count) {
+    CHECK_GE(fd_, 0);
+    ssize_t rc = write(fd_, bytes, count);
+    if (rc < 0)
+      return -errno;
+    return rc;
+  }
+
+  virtual int 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;
+  }
+
+ private:
+  int fd_;
+};
+
+}  // namespace chromeos_update_engine
+
+#endif  // UPDATE_ENGINE_FILE_WRITER_H__
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