public static extern UInt64 zip_source_seek_compute_offset(UInt64 offset, UInt64 length, IntPtr data, UInt64 data_length, out zip_error_t error);
public static extern IntPtr zip_open_from_source(IntPtr source, OpenFlags flags, out zip_error_t errorp);
public static extern IntPtr zip_source_function_create(
[MarshalAs(UnmanagedType.FunctionPtr)] zip_source_callback callback, IntPtr user_data, out zip_error_t errorp);