Add method is_valid_cidr to netutils

This method exists in Nova[1], Magnum[2] and neutron_client[3],
and can be leveraged by other projects as well.

[1]https://github.com/openstack/nova/blob/13.0.0.0b2/nova/utils.py#L657
[2]https://github.com/openstack/magnum/blob/1.1.0/magnum/common/utils.py#L256
[3]https://github.com/openstack/python-neutronclient/blob/4.0.0/neutronclient/common/utils.py#L187

Change-Id: Ia9c8c0123e6d1e9f8bd2b662871b4d01f14bd06d

oslo_utils/netutils.py

@@ -111,6 +111,32 @@ def is_valid_ipv6(address):
         return False
 
 
+def is_valid_cidr(address):
+    """Verify that address represents a valid CIDR address.
+
+    :param address: Value to verify
+    :type address: string
+    :returns: bool
+
+    .. versionadded:: 3.8
+    """
+    try:
+        # Validate the correct CIDR Address
+        netaddr.IPNetwork(address)
+    except netaddr.AddrFormatError:
+        return False
+
+    # Prior validation partially verify /xx part
+    # Verify it here
+    ip_segment = address.split('/')
+
+    if (len(ip_segment) <= 1 or
+            ip_segment[1] == ''):
+        return False
+
+    return True
+
+
 def get_ipv6_addr_by_EUI64(prefix, mac):
     """Calculate IPv6 address using EUI-64 specification.
 

oslo_utils/tests/test_netutils.py

@@ -180,6 +180,17 @@ class NetworkUtilsTest(test_base.BaseTestCase):
 
         self.assertFalse(netutils.is_valid_ip(''))
 
+    def test_is_valid_cidr(self):
+        self.assertTrue(netutils.is_valid_cidr('10.0.0.0/24'))
+        self.assertTrue(netutils.is_valid_cidr('10.0.0.1/32'))
+        self.assertTrue(netutils.is_valid_cidr('0.0.0.0/0'))
+        self.assertTrue(netutils.is_valid_cidr('2600::/64'))
+        self.assertTrue(netutils.is_valid_cidr(
+                        '0000:0000:0000:0000:0000:0000:0000:0001/32'))
+
+        self.assertFalse(netutils.is_valid_cidr('10.0.0.1'))
+        self.assertFalse(netutils.is_valid_cidr('10.0.0.1/33'))
+
     def test_valid_port(self):
         valid_inputs = [1, '1', 2, '3', '5', 8, 13, 21,
                         '80', '3246', '65535']