firewall: rewrite ip allocation policy

fixes #88

circle/firewall/models.py

 # -*- coding: utf-8 -*-
 
-from itertools import islice, chain
+from itertools import islice, ifilter
 import logging
 from netaddr import IPSet, EUI
 
@@ -298,19 +298,12 @@ class Vlan(AclBase, models.Model):
     def prefix6(self):
         return self.network6.prefixlen
 
-    def get_next_address(self, used_v4):
-        try:
-            last_address = list(used_v4)[-1]
-        except IndexError:
-            return []
-        next_address = last_address + 1
-
-        if next_address in self.network4.iter_hosts():
-            logger.debug("Found unused IPv4 address %s after %s.",
-                         next_address, last_address)
-            return [next_address]
-        else:
-            return []
+    def get_random_addresses(self, used_v4, buffer_size=100, max_hosts=10000):
+        addresses = islice(self.network4.iter_hosts(), max_hosts)
+        unused_addresses = list(islice(
+            ifilter(lambda x: x not in used_v4, addresses), buffer_size))
+        random.shuffle(unused_addresses)
+        return unused_addresses
 
     def get_new_address(self):
         hosts = self.host_set
@@ -318,14 +311,11 @@ class Vlan(AclBase, models.Model):
         used_v6 = IPSet(hosts.exclude(ipv6__isnull=True)
                         .values_list('ipv6', flat=True))
 
-        for ipv4 in chain(self.get_next_address(used_v4),
-                          islice(self.network4.iter_hosts(), 10000)):
-            ipv4 = str(ipv4)
-            if ipv4 not in used_v4:
+        for ipv4 in self.get_random_addresses(used_v4):
             logger.debug("Found unused IPv4 address %s.", ipv4)
             ipv6 = None
             if self.network6 is not None:
-                    ipv6 = ipv4_2_ipv6(self.ipv6_template, ipv4)
+                ipv6 = convert_ipv4_to_ipv6(self.ipv6_template, ipv4)
                 if ipv6 in used_v6:
                     continue
                 else:

circle/firewall/tests/test_firewall.py

+from netaddr import IPSet
+
 from django.test import TestCase
 from django.contrib.auth.models import User
 from ..admin import HostAdmin
@@ -75,13 +77,9 @@ class GetNewAddressTestCase(TestCase):
              vlan=self.vlan, owner=self.u1).save()
         self.assertRaises(ValidationError, self.vlan.get_new_address)
 
-    def test_new_addr_last(self):
-        self.assertEqual(self.vlan.get_new_address()['ipv4'], '10.0.0.6')
-
-    def test_new_addr_w_overflow(self):
-        Host(hostname='h-6', mac='01:02:03:04:05:06',
-             ipv4='10.0.0.6', vlan=self.vlan, owner=self.u1).save()
-        self.assertEqual(self.vlan.get_new_address()['ipv4'], '10.0.0.2')
+    def test_new_addr(self):
+        used_v4 = IPSet(self.vlan.host_set.values_list('ipv4', flat=True))
+        assert self.vlan.get_new_address()['ipv4'] not in used_v4
 
 
 class HostGetHostnameTestCase(TestCase):