Add DNS query function

src/ddns_service/dns.py

@@ -10,6 +10,7 @@ import dns.name
 import dns.query
 import dns.rcode
 import dns.rdatatype
+import dns.resolver
 import dns.tsigkeyring
 import dns.update
 
@@ -353,6 +354,38 @@ class DNSService:
             return hostname[:-len(zone_suffix)]
         return hostname
 
+    def query_record(self, hostname, zone, record_type):
+        """
+        Check if DNS record exists.
+
+        Args:
+            hostname: Hostname (without zone suffix).
+            zone: DNS zone name.
+            record_type: Record type string (A or AAAA).
+
+        Returns:
+            IP address string if record exists, None otherwise.
+        """
+        fqdn = f"{self._get_relative_name(hostname, zone)}.{zone}"
+        if not fqdn.endswith("."):
+            fqdn += "."
+        try:
+            resolver = dns.resolver.Resolver()
+            resolver.nameservers = [self.server]
+            resolver.port = self.port
+            resolver.lifetime = self.timeout
+            answers = resolver.resolve(fqdn, record_type)
+            return str(answers[0]) if answers else None
+        except (dns.resolver.NXDOMAIN, dns.resolver.NoAnswer,
+                dns.resolver.NoNameservers):
+            return None
+        except Exception as e:
+            logging.warning(
+                f"DNS query failed: hostname={hostname} zone={zone} "
+                f"type={record_type}: {e}"
+            )
+            return None
+
     def update_record(self, hostname, zone, ip, ttl):
         """
         Update a DNS record for the given hostname.