code: func (fixedHeader FixedHeader) ptype() (byte, error) {
  	// Check the length of the fixed header.
  	if len(fixedHeader) < 1 {
  		return 0x00, ErrInvalidFixedHeaderLen
  	}
  
  	// Extract the MQTT Control Packet type from
  	// the fixed header and return it.
  	return fixedHeader[0] >> 4, nil
  }
docs: // ptype extracts the MQTT Control Packet type from
  // the fixed header and returns it.