Issue #20480: Add ipaddress.reverse_pointer. Patch by Leon Weber.

2 files changed, 37 insertions, 0 deletions

diff --git a/Lib/ipaddress.py b/Lib/ipaddress.py
index 54df39a..1e451f8 100644
--- a/Lib/ipaddress.py
+++ b/Lib/ipaddress.py
@@ -436,6 +436,17 @@ class _IPAddressBase(_TotalOrderingMixin):
         return str(self)
 
     @property
+    def reverse_pointer(self):
+        """The name of the reverse DNS pointer for the IP address, e.g.:
+            >>> ipaddress.ip_address("127.0.0.1").reverse_pointer
+            '1.0.0.127.in-addr.arpa'
+            >>> ipaddress.ip_address("2001:db8::1").reverse_pointer
+            '1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa'
+
+        """
+        return self._reverse_pointer()
+
+    @property
     def version(self):
         msg = '%200s has no version specified' % (type(self),)
         raise NotImplementedError(msg)
@@ -1221,6 +1232,15 @@ class _BaseV4:
             return True
         return False
 
+    def _reverse_pointer(self):
+        """Return the reverse DNS pointer name for the IPv4 address.
+
+        This implements the method described in RFC1035 3.5.
+
+        """
+        reverse_octets = str(self).split('.')[::-1]
+        return '.'.join(reverse_octets) + '.in-addr.arpa'
+
     @property
     def max_prefixlen(self):
         return self._max_prefixlen
@@ -1784,6 +1804,15 @@ class _BaseV6:
             return '%s/%d' % (':'.join(parts), self._prefixlen)
         return ':'.join(parts)
 
+    def _reverse_pointer(self):
+        """Return the reverse DNS pointer name for the IPv6 address.
+
+        This implements the method described in RFC3596 2.5.
+
+        """
+        reverse_chars = self.exploded[::-1].replace(':', '')
+        return '.'.join(reverse_chars) + '.ip6.arpa'
+
     @property
     def max_prefixlen(self):
         return self._max_prefixlen
diff --git a/Lib/test/test_ipaddress.py b/Lib/test/test_ipaddress.py
index f2947b9..33adb3b 100644
--- a/Lib/test/test_ipaddress.py
+++ b/Lib/test/test_ipaddress.py
@@ -1593,6 +1593,14 @@ class IpaddrUnitTest(unittest.TestCase):
                          addr3.exploded)
         self.assertEqual('192.168.178.1', addr4.exploded)
 
+    def testReversePointer(self):
+        addr1 = ipaddress.IPv4Address('127.0.0.1')
+        addr2 = ipaddress.IPv6Address('2001:db8::1')
+        self.assertEqual('1.0.0.127.in-addr.arpa', addr1.reverse_pointer)
+        self.assertEqual('1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.' +
+                         'b.d.0.1.0.0.2.ip6.arpa',
+                         addr2.reverse_pointer)
+
     def testIntRepresentation(self):
         self.assertEqual(16909060, int(self.ipv4_address))
         self.assertEqual(42540616829182469433547762482097946625,