resolved: rr - introduce dns_resource_key_new_cname()

Creates a new CNAME RR key with the same class and name as an existing key.

src/resolve/resolved-dns-rr.c

@@ -48,6 +48,12 @@ DnsResourceKey* dns_resource_key_new(uint16_t class, uint16_t type, const char *
         return k;
 }
 
+DnsResourceKey* dns_resource_key_new_cname(const DnsResourceKey *key) {
+        assert(key);
+
+        return dns_resource_key_new(key->class, DNS_TYPE_CNAME, DNS_RESOURCE_KEY_NAME(key));
+}
+
 DnsResourceKey* dns_resource_key_new_consume(uint16_t class, uint16_t type, char *name) {
         DnsResourceKey *k;
 

src/resolve/resolved-dns-rr.h

@@ -177,6 +177,7 @@ static inline const char* DNS_RESOURCE_KEY_NAME(const DnsResourceKey *key) {
 }
 
 DnsResourceKey* dns_resource_key_new(uint16_t class, uint16_t type, const char *name);
+DnsResourceKey* dns_resource_key_new_cname(const DnsResourceKey *key);
 DnsResourceKey* dns_resource_key_new_consume(uint16_t class, uint16_t type, char *name);
 DnsResourceKey* dns_resource_key_ref(DnsResourceKey *key);
 DnsResourceKey* dns_resource_key_unref(DnsResourceKey *key);