pub fn io_error_kind(&self) -> Option<std::io::ErrorKind> {
        if let ErrorCode::Io(io_error) = &self.err.code {
            Some(io_error.kind())
        } else {
            None
        }
    }
The kind reported by the underlying standard library I/O error, if this
error was caused by a failure to read or write bytes on an I/O stream.
src/error.rs