   (err) => cb(err, 0, buf));
    },
    writev: (fd, buffers, pos, cb) => {
      PromisePrototypeThen(handle.writev(buffers, pos),
                           (r) => cb(null, r.bytesWritten, r.buffers),
                           (err) => cb(err, 0, buffers));
    }
  };
};

function close(stream, err, cb) {
  if (!stream.fd) {
    cb(err);
  } else {
    stream[kFs].close(stream.fd, (er) => {
      cb(er || err);
    });
    stream.fd = null;
  }
}

function importFd(stream, options) {
  if (typeof options.fd === 'number') {
    // When fd is a raw descriptor, we must keep our fingers crossed
    // that the descriptor won't get closed, or worse, replaced with
    // another one
    // https://github.com/nodejs/node/issues/35862
    stream[kFs] = options.fs || fs;
    return options.fd;
  } else if (typeof options.fd === 'object' &&
             options.fd instanceof FileHandle) {
    // When fd is a FileHandle we can listen for 'close' events
    if (options.fs) {
      // FileHandle is not supported with custom fs operations
      throw new ERR_METHOD_NOT_IMPLEMENTED('FileHandle with fs');
    }
    stream[kHandle] = options.fd;
    stream[kFs] = FileHandleOperations(stream[kHandle]);
    stream[kHandle][kRef]();
    options.fd.on('close', FunctionPrototypeBind(stream.close, stream));
    return options.fd.fd;
  }

  throw ERR_INVALID_ARG_TYPE('options.fd',
                             ['number', 'FileHandle'], options.fd);
}

function ReadStream(path, options) {
  if (!(this instanceof ReadStream))
    return new ReadStream(path, options);

  // A little bit bigger buffer and water marks by default
  options = copyObject(getOptions(options, {}));
  if (options.highWaterMark === undefined)
    options.highWaterMark = 64 * 1024;

  if (options.autoDestroy === undefined) {
    options.autoDestroy = false;
  }

  if (options.fd == null) {
    this.fd = null;
    this[kFs] = options.fs || fs;
    validateFunction(this[kFs].open, 'options.fs.open');

    // Path will be ignored when fd is specified, so it can be falsy
    this.path = toPathIfFileURL(path);
    this.flags = options.flags === undefined ? 'r' : options.flags;
    this.mode = options.mode === undefined ? 0o666 : options.mode;

    validatePath(this.path);
  } else {
    this.fd = getValidatedFd(importFd(this, options));
  }

  options.autoDestroy = options.autoClose === undefined ?
    true : options.autoClose;

  validateFunction(this[kFs].read, 'options.fs.read');

  if (options.autoDestroy) {
    validateFunction(this[kFs].close, 'options.fs.close');
  }

  this.start = options.start;
  this.end = options.end;
  this.pos = undefined;
  this.bytesRead = 0;
  this[kIsPerformingIO] = false;

  if (this.start !== undefined) {
    validateInteger(this.start, 'start', 0);

    this.pos = this.start;
  }


  if (this.end === undefined) {
    this.end = Infinity;
  } else if (this.end !== Infinity) {
    validateInteger(this.end, 'end', 0);

    if (this.start !== undefined && this.start > this.end) {
      throw new ERR_OUT_OF_RANGE(
        'start',
        `<= "end" (here: ${this.end})`,
        this.start
      );
    }
  }

  ReflectApply(Readable, this, [options]);
}
ObjectSetPrototypeOf(ReadStream.prototype, Readable.prototype);
ObjectSetPrototypeOf(ReadStream, Readable);

ObjectDefineProperty(ReadStream.prototype, 'autoClose', {
  get() {
    return this._readableState.autoDestroy;
  },
  set(val) {
    this._readableState.autoDestroy = val;
  }
});

const openReadFs = deprecate(function() {
  // Noop.
}, 'ReadStream.prototype.open() is deprecated', 'DEP0135');
ReadStream.prototype.open = openReadFs;

ReadStream.prototype._construct = _construct;

ReadStream.prototype._read = function(n) {
  n = this.pos !== undefined ?
    MathMin(this.end - this.pos + 1, n) :
    MathMin(this.end - this.bytesRead + 1, n);

  if (n <= 0) {
    this.push(null);
    return;
  }

  const buf = Buffer.allocUnsafeSlow(n);

  this[kIsPerformingIO] = true;
  this[kFs]
    .read(this.fd, buf, 0, n, this.pos, (er, bytesRead, buf) => {
      this[kIsPerformingIO] = false;

      // Tell ._destroy() that it's safe to close the fd now.
      if (this.destroyed) {
        this.emit(kIoDone, er);
        return;
      }

      if (er) {
        errorOrDestroy(this, er);
      } else if (bytesRead > 0) {
        if (this.pos !== undefined) {
          this.pos += bytesRead;
        }

        this.bytesRead += bytesRead;

        if (bytesRead !== buf.length) {
          // Slow path. Shrink to fit.
          // Copy instead of slice so that we don't retain
          // large backing buffer for small reads.
          const dst = Buffer.allocUnsafeSlow(bytesRead);
          buf.copy(dst, 0, 0, bytesRead);
          buf = dst;
        }

        this.push(buf);
      } else {
        this.push(null);
      }
    });
};

ReadStream.prototype._destroy = function(err, cb) {
  // Usually for async IO it is safe to close a file descriptor
  // even when there are pending operations. However, due to platform
  // differences file IO is implemented using synchronous operations
  // running in a thread pool. Therefore, file descriptors are not safe
  // to close while used in a pending read or write operation. Wait for
  // any pending IO (kIsPerformingIO) to complete (kIoDone).
  if (this[kIsPerformingIO]) {
    this.once(kIoDone, (er) => close(this, err || er, cb));
  } else {
    close(this, err, cb);
  }
};

ReadStream.prototype.close = function(cb) {
  if (typeof cb === 'function') finished(this, cb);
  this.destroy();
};

ObjectDefineProperty(ReadStream.prototype, 'pending', {
  get() { return this.fd === null; },
  configurable: true
});

function WriteStream(path, options) {
  if (!(this instanceof WriteStream))
    return new WriteStream(path, options);

  options = copyObject(getOptions(options, {}));

  // Only buffers are supported.
  options.decodeStrings = true;

  if (options.fd == null) {
    this.fd = null;
    this[kFs] = options.fs || fs;
    validateFunction(this[kFs].open, 'options.fs.open');

    // Path will be ignored when fd is specified, so it can be falsy
    this.path = toPathIfFileURL(path);
    this.flags = options.flags === undefined ? 'w' : options.flags;
    this.mode = options.mode === undefined ? 0o666 : options.mode;

    validatePath(this.path);
  } else {
    this.fd = getValidatedFd(importFd(this, options));
  }

  options.autoDestroy = options.autoClose === undefined ?
    true : options.autoClose;

  if (!this[kFs].write && !this[kFs].writev) {
    throw new ERR_INVALID_ARG_TYPE('options.fs.write', 'function',
                                   this[kFs].write);
  }

  if (this[kFs].write) {
    validateFunction(this[kFs].write, 'options.fs.write');
  }

  if (this[kFs].writev) {
    validateFunction(this[kFs].writev, 'options.fs.writev');
  }

  if (options.autoDestroy) {
    validateFunction(this[kFs].close, 'options.fs.close');
  }

  // It's enough to override either, in which case only one will be used.
  if (!this[kFs].write) {
    this._write = null;
  }
  if (!this[kFs].writev) {
    this._writev = null;
  }

  this.start = options.start;
  this.pos = undefined;
  this.bytesWritten = 0;
  this[kIsPerformingIO] = false;

  if (this.start !== undefined) {
    validateInteger(this.start, 'start', 0);

    this.pos = this.start;
  }

  ReflectApply(Writable, this, [options]);

  if (options.encoding)
    this.setDefaultEncoding(options.encoding);
}
ObjectSetPrototypeOf(WriteStream.prototype, Writable.prototype);
ObjectSetPrototypeOf(WriteStream, Writable);

ObjectDefineProperty(WriteStream.prototype, 'autoClose', {
  get() {
    return this._writableState.autoDestroy;
  },
  set(val) {
    this._writableState.autoDestroy = val;
  }
});

const openWriteFs = deprecate(function() {
  // Noop.
}, 'WriteStream.prototype.open() is deprecated', 'DEP0135');
WriteStream.prototype.open = openWriteFs;

WriteStream.prototype._construct = _construct;

WriteStream.prototype._write = function(data, encoding, cb) {
  this[kIsPerformingIO] = true;
  this[kFs].write(this.fd, data, 0, data.length, this.pos, (er, bytes) => {
    this[kIsPerformingIO] = false;
    if (this.destroyed) {
      // Tell ._destroy() that it's safe to close the fd now.
      cb(er);
      return this.emit(kIoDone, er);
    }

    if (er) {
      return cb(er);
    }

    this.bytesWritten += bytes;
    cb();
  });

  if (this.pos !== undefined)
    this.pos += data.length;
};

WriteStream.prototype._writev = function(data, cb) {
  const len = data.length;
  const chunks = new Array(len);
  let size = 0;

  for (let i = 0; i < len; i++) {
    const chunk = data[i].chunk;

    chunks[i] = chunk;
    size += chunk.length;
  }

  this[kIsPerformingIO] = true;
  this[kFs].writev(this.fd, chunks, this.pos, (er, bytes) => {
    this[kIsPerformingIO] = false;
    if (this.destroyed) {
      // Tell ._destroy() that it's safe to close the fd now.
      cb(er);
      return this.emit(kIoDone, er);
    }

    if (er) {
      return cb(er);
    }

    this.bytesWritten += bytes;
    cb();
  });

  if (this.pos !== undefined)
    this.pos += size;
};

WriteStream.prototype._destroy = function(err, cb) {
  // Usually for async IO it is safe to close a file descriptor
  // even when there are pending operations. However, due to platform
  // differences file IO is implemented using synchronous operations
  // running in a thread pool. Therefore, file descriptors are not safe
  // to close while used in a pending read or write operation. Wait for
  // any pending IO (kIsPerformingIO) to complete (kIoDone).
  if (this[kIsPerformingIO]) {
    this.once(kIoDone, (er) => close(this, err || er, cb));
  } else {
    close(this, err, cb);
  }
};

WriteStream.prototype.close = function(cb) {
  if (cb) {
    if (this.closed) {
      process.nextTick(cb);
      return;
    }
    this.on('close', cb);
  }

  // If we are not autoClosing, we should call
  // destroy on 'finish'.
  if (!this.autoClose) {
    this.on('finish', this.destroy);
  }

  // We use end() instead of destroy() because of
  // https://github.com/nodejs/node/issues/2006
  this.end();
};

// There is no shutdown() for files.
WriteStream.prototype.destroySoon = WriteStream.prototype.end;

ObjectDefineProperty(WriteStream.prototype, 'pending', {
  get() { return this.fd === null; },
  configurable: true
});

module.exports = {
  ReadStream,
  WriteStream
};
