def convert_errno(e):
        """
        Convert an errno value (as from an ``OSError`` or ``IOError``) into a
        standard SFTP result code.  This is a convenience function for trapping
        exceptions in server code and returning an appropriate result.

        :param int e: an errno code, as from ``OSError.errno``.
        :return: an `int` SFTP error code like ``SFTP_NO_SUCH_FILE``.
        """
        if e == errno.EACCES:
            # permission denied
            return SFTP_PERMISSION_DENIED
        elif (e == errno.ENOENT) or (e == errno.ENOTDIR):
            # no such file
            return SFTP_NO_SUCH_FILE
        else:
            return SFTP_FAILURE