pkt: add knot_pkt_rr_offset() to get RR position in wire

src/libknot/packet/pkt.c

@@ -599,6 +599,16 @@ const knot_rrset_t *knot_pkt_rr(const knot_pktsection_t *section, uint16_t i)
 	return section->pkt->rr + section->pos + i;
 }
 
+_public_
+uint16_t knot_pkt_rr_offset(const knot_pktsection_t *section, uint16_t i)
+{
+	if (section == NULL || section->pkt == NULL) {
+		return -1;
+	}
+
+	return section->pkt->rr_info[section->pos + i].pos;
+}
+
 _public_
 int knot_pkt_parse(knot_pkt_t *pkt, unsigned flags)
 {

src/libknot/packet/pkt.h

@@ -245,6 +245,10 @@ const knot_pktsection_t *knot_pkt_section(const knot_pkt_t *pkt,
 
 /*! \brief Get RRSet from the packet section. */
 const knot_rrset_t *knot_pkt_rr(const knot_pktsection_t *section, uint16_t i);
+
+/*! \brief Get RRSet offset in the packet wire. */
+uint16_t knot_pkt_rr_offset(const knot_pktsection_t *section, uint16_t i);
+
 /*
  * Packet parsing API.
  */