convertWindowsErrorToString method Null safety

String convertWindowsErrorToString(
  1. int windowsError
)

Converts a Windows error into a friendly string.

Takes one numeric paramenter, which may be a general Windows error or an HRESULT, and converts it into a String representation using the Win32 FormatMessage() function. For example, E_INVALIDARG (0x80070057) converts to The parameter is incorrect.

Implementation

String convertWindowsErrorToString(int windowsError) {
  final buffer = calloc<Uint16>(256).cast<Utf16>();

  // If FormatMessage fails, it returns 0; otherwise it returns the number of
  // characters in the buffer.
  try {
    String errorMessage;
    final result = FormatMessage(
        FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
        nullptr,
        windowsError,
        0, // default language
        buffer,
        256,
        nullptr);

    if (result == 0) {
      // Failed to get error string
      errorMessage = '';
    } else {
      errorMessage = buffer.toDartString();
    }

    // Strip off CRLF in the returned error message, if it exists
    if (errorMessage.endsWith('\r\n')) {
      errorMessage = errorMessage.substring(0, errorMessage.length - 2);
    }

    return errorMessage;
  } finally {
    free(buffer);
  }
}