kr_zonecut_move(): new function

It's more efficient for some our use cases,
and hopefully also more idiomatic.

lib/resolve.c

@@ -246,13 +246,13 @@ static int ns_fetch_cut(struct kr_query *qry, const knot_dname_t *requested_name
 	if (ret == kr_error(ENOENT)) {
 		/* No cached cut found, start from SBELT
 		 * and issue priming query. */
+		kr_zonecut_deinit(&cut_found);
 		ret = kr_zonecut_set_sbelt(req->ctx, &qry->zone_cut);
 		if (ret != 0) {
 			return KR_STATE_FAIL;
 		}
 		VERBOSE_MSG(qry, "=> using root hints\n");
 		qry->flags.AWAIT_CUT = false;
-		kr_zonecut_deinit(&cut_found);
 		return KR_STATE_DONE;
 	} else if (ret != kr_ok()) {
 		kr_zonecut_deinit(&cut_found);
@@ -295,12 +295,8 @@ static int ns_fetch_cut(struct kr_query *qry, const knot_dname_t *requested_name
 		qry->flags.AWAIT_CUT = false;
 		return KR_STATE_DONE;
 	}
-	/* Copy fetched name */
-	qry->zone_cut.name = knot_dname_copy(cut_found.name, qry->zone_cut.pool);
-	/* Copy fetched address set */
-	kr_zonecut_copy(&qry->zone_cut, &cut_found);
-	/* Copy fetched ta & keys */
-	kr_zonecut_copy_trust(&qry->zone_cut, &cut_found);
+	/* Use the found zone cut. */
+	kr_zonecut_move(&qry->zone_cut, &cut_found);
 	/* Check if there's a non-terminal between target and current cut. */
 	struct kr_cache *cache = &req->ctx->cache;
 	check_empty_nonterms(qry, pkt, cache, qry->timestamp.tv_sec);

lib/zonecut.c

@@ -98,6 +98,13 @@ void kr_zonecut_deinit(struct kr_zonecut *cut)
 	knot_rrset_free(cut->trust_anchor, cut->pool);
 }
 
+void kr_zonecut_move(struct kr_zonecut *to, const struct kr_zonecut *from)
+{
+	if (!to || !from) abort();
+	kr_zonecut_deinit(to);
+	memcpy(to, from, sizeof(*to));
+}
+
 void kr_zonecut_set(struct kr_zonecut *cut, const knot_dname_t *name)
 {
 	if (!cut || !name) {

lib/zonecut.h

@@ -53,6 +53,14 @@ int kr_zonecut_init(struct kr_zonecut *cut, const knot_dname_t *name, knot_mm_t
 KR_EXPORT
 void kr_zonecut_deinit(struct kr_zonecut *cut);
 
+/**
+ * Move a zonecut, transferring ownership of any pointed-to memory.
+ * @param to the target - it gets deinit-ed
+ * @param from the source - not modified, but shouldn't be used afterward
+ */
+KR_EXPORT
+void kr_zonecut_move(struct kr_zonecut *to, const struct kr_zonecut *from);
+
 /**
  * Reset zone cut to given name and clear address list.
  * @note This clears the address list even if the name doesn't change. TA and DNSKEY don't change.