Function readFileHandleWithUserBuffer

lib/internal/fs/promises.js:1164–1212

(filehandle, options, size)

}

async function readFileHandleWithUserBuffer(filehandle, options, size) {
  const signal = options?.signal;
  const encoding = options?.encoding;
  const buffer = getReadFileBuffer(options, size);
  const byteLengthName = getReadFileBufferByteLengthName(options);
  let totalRead = 0;

  while (totalRead < buffer.byteLength) {
    checkAborted(signal);

    const length = size === 0 ?
      buffer.byteLength - totalRead :
      MathMin(size - totalRead, kReadFileBufferLength);

    const bytesRead = (await PromisePrototypeThen(
      binding.read(filehandle.fd, buffer, totalRead, length, -1, kUsePromises),
      undefined,
      handleErrorFromBinding,
    )) ?? 0;

    totalRead += bytesRead;

    if (bytesRead === 0 || totalRead === size) {
      const result = buffer.subarray(0, totalRead);
      return encoding ? result.toString(encoding) : result;
    }
  }

  if (size === 0) {
    checkAborted(signal);

    const extraBuffer = Buffer.allocUnsafeSlow(1);
    const bytesRead = (await PromisePrototypeThen(
      binding.read(filehandle.fd, extraBuffer, 0, 1, -1, kUsePromises),
      undefined,
      handleErrorFromBinding,
    )) ?? 0;

    if (bytesRead !== 0) {
      throw new ERR_INVALID_ARG_VALUE(
        byteLengthName,
        buffer.byteLength,
        'is too small to contain the entire file',
      );
    }
  }

  return encoding ? buffer.toString(encoding) : buffer.subarray(0, totalRead);
}

async function readFileHandle(filehandle, options) {
  const signal = options?.signal;