[subnet_division] Fixed overlapping subnets with different sizes #864

Refactored the allocation logic to use netaddr.IPSet for mathematical
gap-filling. Added a guard for /32 rules on /32 master subnets and
restored the exhaustion logger expected by legacy tests.

Fixes #864

Author: Piyushkhobragade

openwisp_controller/subnet_division/rule_types/base.py

@@ -20,6 +20,7 @@
 SubnetDivisionIndex = load_model("subnet_division", "SubnetDivisionIndex")
 VpnClient = load_model("config", "VpnClient")
 
+
 class BaseSubnetDivisionRuleType(object):
     provision_signal = None
     provision_sender = None
@@ -142,7 +143,7 @@ def get_config(cls, instance):
     @staticmethod
     def get_max_subnet(master_subnet, division_rule):
         master_network = IPNetwork(str(master_subnet.subnet))
-        
+
         if not Subnet.objects.filter(master_subnet_id=master_subnet.id).exists():
             first_candidate = next(master_network.subnet(prefixlen=division_rule.size))
             if division_rule.size > master_network.prefixlen: