add reverse dns lookup code

nsupdate/main/_tests/test_dnstools.py

@@ -8,7 +8,7 @@ pytestmark = pytest.mark.django_db
 
 from dns.resolver import NXDOMAIN, NoAnswer
 
-from ..dnstools import add, delete, update, query_ns, parse_name, update_ns, SameIpError, DnsUpdateError
+from ..dnstools import add, delete, update, query_ns, rev_lookup, parse_name, update_ns, SameIpError, DnsUpdateError
 
 # see also conftest.py
 BASEDOMAIN = 'nsupdate.info'
@@ -107,6 +107,16 @@ class TestQuery(object):
         assert query_ns(TEST_HOST, 'AAAA') == ipv6
 
 
+class TestReverseLookup(object):
+    def test_rev_lookup_v4(self):
+        name, ip = 'google-public-dns-a.google.com', '8.8.8.8'
+        assert rev_lookup(ip) == name
+
+    def test_rev_lookup_v6(self):
+        name, ip = 'google-public-dns-a.google.com', '2001:4860:4860::8888'
+        assert rev_lookup(ip) == name
+
+
 class TestUpdate(object):
     def test_parse1(self):
         host, domain = 'test', BASEDOMAIN

nsupdate/main/dnstools.py

@@ -20,6 +20,8 @@ from datetime import timedelta
 import logging
 logger = logging.getLogger(__name__)
 
+import socket
+
 import dns.inet
 import dns.name
 import dns.resolver
@@ -181,6 +183,16 @@ def query_ns(qname, rdtype, origin=None):
         raise
 
 
+def rev_lookup(ipaddr):
+    """
+    do a normal reverse DNS lookup, IP to name
+
+    :param ipaddr: ip address (str)
+    :return: hostname
+    """
+    return socket.gethostbyaddr(ipaddr)[0]
+
+
 def parse_name(fqdn, origin=None):
     """
     Parse a fully qualified domain name into a relative name