* or 1 if *len and *data have correct values. Note that these values are
* destroyed with the pdu.
*/
-int coap_get_data(coap_pdu_t *pdu, size_t *len, unsigned char **data);
+int coap_get_data(const coap_pdu_t *pdu, size_t *len, unsigned char **data);
#endif /* _PDU_H_ */