Move get_random_mac into neutron-lib

get_random_mac is used by networking-ovn, tap-as-a-service,
neutron-vpnaas, and vmware-nsx, so we should move it into the
neutron-lib repository.

Change-Id: I391300e6f1d04b2413084bccdbacb038071c4509

neutron_lib/tests/unit/utils/test_net.py

@@ -27,3 +27,22 @@ class TestGetHostname(base.BaseTestCase):
         self.assertEqual('fake-host-name',
                          net.get_hostname())
         mock_gethostname.assert_called_once_with()
+
+
+class TestGetRandomMac(base.BaseTestCase):
+
+    def _test_get_random_mac(self, base_mac, startswith_len):
+        random_mac = net.get_random_mac(base_mac.split(':'))
+        self.assertEqual(base_mac[:startswith_len],
+                         random_mac[:startswith_len])
+        self.assertEqual(len(base_mac), len(random_mac))
+        for i in random_mac.split(':'):
+            int(i, 16)
+
+    def test_get_random_mac_with_three_octets(self):
+        base_mac = 'fa:16:3e:00:00:00'
+        self._test_get_random_mac(base_mac, 9)
+
+    def test_get_random_mac_with_four_octets(self):
+        base_mac = 'fa:16:3e:fe:00:00'
+        self._test_get_random_mac(base_mac, 12)

neutron_lib/utils/net.py

@@ -11,6 +11,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import random
 import socket
 
 
@@ -20,3 +21,17 @@ def get_hostname():
     :returns: The hostname of the system.
     """
     return socket.gethostname()
+
+
+def get_random_mac(base_mac):
+    """Get a random MAC address string of the specified base format.
+
+    :param base_mac: The base MAC address format for the MAC address string.
+    :returns: The MAC address string.
+    """
+    mac = [int(base_mac[0], 16), int(base_mac[1], 16),
+           int(base_mac[2], 16), random.randint(0x00, 0xff),
+           random.randint(0x00, 0xff), random.randint(0x00, 0xff)]
+    if base_mac[3] != '00':
+        mac[3] = int(base_mac[3], 16)
+    return ':'.join(["%02x" % x for x in mac])

releasenotes/notes/move-get-random-mac-98f47d81cb34483d.yaml

@@ -0,0 +1,4 @@
+---
+features:
+  - The ``get_random_mac`` utility function from ``neutron.common.utils`` is
+    now in ``neutron_lib.utils.net`` with the same name, ``get_random_mac``.