def _read_from_seg(self, n):
    """Read from current seg.

    Args:
      n: max number of bytes to read.

    Returns:
      valid bytes from the current seg. "" if no more is left.
    """
    result = self._seg.read(size=n)
    if result == "":
      return result
    offset = self._seg.tell()
    if offset > self._seg_valid_length:
      extra = offset - self._seg_valid_length
      result = result[:-1*extra]
    self._offset += len(result)
    return result
Read from current seg.

    Args:
      n: max number of bytes to read.

    Returns:
      valid bytes from the current seg. "" if no more is left.