Custom validators for IP range/IP address overlaps

As suggested in issue netbox-community#113, provide custom validators that check for
overlaps between IP ranges and IP addresses:
- CheckAddressNotInRange, which validates that an IP address is not in any
  existing IP range,
- CheckRangeDoesNotIncludeAddress, which validates than an IP Range
  does not include any existing IP address.

custom_validators/iprange.py

@@ -0,0 +1,94 @@
+#
+# This file includes two custom validators that check for overlaps
+# between IP ranges and IP addresses:
+# - CheckAddressNotInRange, which validates that an IP address is not in any
+#   existing IP range,
+# - CheckRangeDoesNotIncludeAddress, which validates than an IP Range
+#   does not include any existing IP address.
+#
+# Usage:
+#
+# Create a "validators" directory in netbox and copy this file into it:
+#
+#    mkdir -p /opt/netbox/netbox/validators
+#    cp iprange.py /opt/netbox/netbox/validators
+#
+# Activate the validators by adding the following lines to
+# /opt/netbox/netbox/netbox/configuration.py:
+#
+#        from validators.iprange import CheckAddressNotInRange, CheckRangeDoesNotIncludeAddress
+#        CUSTOM_VALIDATORS = {
+#            "ipam.ipaddress": ( CheckAddressNotInRange(), ),
+#            "ipam.iprange": ( CheckRangeDoesNotIncludeAddress(), ),
+#        }
+#
+from extras.validators import CustomValidator
+from django.db.models import Q
+import netaddr
+
+
+#
+# Check if an IP address is included in an existing IP range
+#
+def address_in_range(ip):
+    from ipam.models.ip import IPRange
+
+    try:
+        including_ranges = IPRange.objects.filter(vrf=ip.vrf).filter(
+            Q(start_address__lte=ip.address) & Q(end_address__gte=ip.address)
+        )
+        if including_ranges.exists():
+            return including_ranges.first()
+    except:
+        pass
+
+    return None
+
+
+#
+# Check if a range includes an existing IP address
+#
+def range_includes_address(rg):
+    from ipam.models.ip import IPAddress
+
+    try:
+        start = rg.start_address
+        end = rg.end_address
+        included_addresses = IPAddress.objects.filter(vrf=rg.vrf).filter(
+            Q(address__gte=start) & Q(address__lte=end)
+        )
+        if included_addresses.exists():
+            return list([str(ip) for ip in included_addresses])
+    except:
+        pass
+
+    return None
+
+
+class CheckAddressNotInRange(CustomValidator):
+    """Make sure an IP address is not in any existing IP range. Usage:
+
+    from validators.iprange import CheckAddressNotInRange
+    CUSTOM_VALIDATORS = {
+            "ipam.ipaddress": ( CheckAddressNotInRange(), ),
+    }
+    """
+
+    def validate(self, ip, instance):
+        if (rg := address_in_range(ip)) is not None:
+            self.fail(f"IP address '{ip}' used in range '{rg}'", field="address")
+
+
+class CheckRangeDoesNotIncludeAddress(CustomValidator):
+    """Make sure an IP Range does not include any existing IP address. Usage:
+
+    from validators.iprange import CheckRangeDoesNotIncludeAddress
+    CUSTOM_VALIDATORS = {
+        "ipam.iprange": ( CheckRangeDoesNotIncludeAddress(), ),
+    }
+    """
+
+    def validate(self, iprange, instance):
+        if (addresses := range_includes_address(iprange)) is not None:
+            msg = f"Range '{iprange}' includes existing addresses: {addresses}"
+            self.fail(msg, field="start_address")