Introduce unique_fd

/*

 * Copyright (C) 2015 The Android Open Source Project

 *

 * 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 ANDROID_BASE_UNIQUE_FD_H

#define ANDROID_BASE_UNIQUE_FD_H

#include <unistd.h>

#include <base/macros.h>

/* Container for a file descriptor that automatically closes the descriptor as

 * it goes out of scope.

 *

 *      unique_fd ufd(open("/some/path", "r"));

 *

 *      if (ufd.get() < 0) // invalid descriptor

 *          return error;

 *

 *      // Do something useful

 *

 *      return 0; // descriptor is closed here

 */

namespace android {

namespace base {

class unique_fd final {

 public:

  unique_fd() : value_(-1) {}

  explicit unique_fd(int value) : value_(value) {}

  ~unique_fd() { clear(); }

  unique_fd(unique_fd&& other) : value_(other.release()) {}

  unique_fd& operator = (unique_fd&& s) {

    reset(s.release());

    return *this;

  }

  void reset(int new_value) {

    if (value_ >= 0)

      close(value_);

    value_ = new_value;

  }

  void clear() {

    reset(-1);

  }

  int get() const { return value_; }

  int release() {

    int ret = value_;

    value_ = -1;

    return ret;

  }

 private:

  int value_;

  DISALLOW_COPY_AND_ASSIGN(unique_fd);

};

}  // namespace base

}  // namespace android

#endif // ANDROID_BASE_UNIQUE_FD_H