fix: never lower a serial or cap it at 99

mdb/forms.py

@@ -10,8 +10,8 @@ class SerialNumberInput(NumberInput):
     """Number input for DNS SOA serials (YYYYMMDDXX).
 
     Renders wide enough to show the full 10-digit serial and adds a button
-    that prefills the field with today's date plus the next available XX
-    counter (incrementing if the field already holds today's serial).
+    that prefills the field with the next serial: today's first, or one more than
+    the current serial when that is higher.
     """
 
     def __init__(self, attrs=None):
@@ -35,12 +35,14 @@ if (typeof window.mdbBumpSerial === 'undefined') {
         var today = '' + now.getFullYear()
             + String(now.getMonth() + 1).padStart(2, '0')
             + String(now.getDate()).padStart(2, '0');
-        var current = (input.value || '').trim();
-        var xx = 1;
-        if (current.length === 10 && current.slice(0, 8) === today) {
-            xx = Math.min(parseInt(current.slice(8), 10) + 1, 99);
+        // As mdb.utils.format_domain_serial_and_add_one: never lower than the current
+        // serial, so past XX = 99 it carries into the date.
+        var current = parseInt((input.value || '').trim(), 10);
+        var next = parseInt(today + '01', 10);
+        if (!isNaN(current) && current + 1 > next) {
+            next = current + 1;
         }
-        input.value = today + String(xx).padStart(2, '0');
+        input.value = String(next);
     };
 }
 </script>

mdb/signals.py

@@ -136,12 +136,12 @@ def create_pxe_key_and_write_pxe_files_when_host_changes(
 def update_domain_serial_when_interface_deleted(sender, instance, **kwargs):
     if instance.domain is not None:
         domain = instance.domain
-        domain.domain_serial += 1
+        domain.domain_serial = format_domain_serial_and_add_one(domain.domain_serial)
         domain.save()
 
     if instance.ip4address is not None:
         subnet = instance.ip4address.subnet
-        subnet.domain_serial += 1
+        subnet.domain_serial = format_domain_serial_and_add_one(subnet.domain_serial)
         subnet.save()
 
 

mdb/utils.py

@@ -1,34 +1,16 @@
 import datetime
-import re
 
 
 def format_domain_serial_and_add_one(serial):
-    today = datetime.datetime.now()
-    res = re.findall(
-        rf"^{today.year:4d}{today.month:02d}{today.day:02d}(\d\d)$",
-        str(serial),
-        re.DOTALL,
-    )
+    """Return the serial after `serial`, in the YYYYMMDDnn form where it can be.
 
-    if len(res) == 0:
-        """ This probably means that the serial is malformed
-        or the date is wrong. We assume that if the date is wrong,
-        it is in the past. Just create a new serial starting from 1."""
-        return f"{today.year:4d}{today.month:02d}{today.day:02d}01"
-    elif len(res) == 1:
-        """ The serial contains todays date, just update it. """
+    The serial must always increase, or named and dhcpd ignore the change. Today's first
+    serial is used while it is higher. Otherwise the serial goes up by one: past nn = 99
+    it carries into the date (2026110299 -> 2026110300), and a serial already ahead of
+    today, from that carry or a dynamic update, keeps counting from where it is.
+    """
+    today_first = int(datetime.date.today().strftime("%Y%m%d")) * 100 + 1
     try:
-            number = int(res[0])
-        except ValueError:
-            number = 1
-        if number >= 99:
-            """ This is bad... Just keep the number on 99.
-            We also send a mail to sysadmins telling them that
-            something is wrong..."""
-
-        else:
-            number += 1
-        return f"{today.year:4d}{today.month:02d}{today.day:02d}{number:02d}"
-    else:
-        """ Just return the first serial for today. """
-        return f"{today.year:4d}{today.month:02d}{today.day:02d}01"
+        return max(int(serial) + 1, today_first)
+    except TypeError, ValueError:
+        return today_first

tests/test_signals.py

@@ -1,6 +1,7 @@
 import pytest
+from freezegun import freeze_time
 
-from mdb.models import DhcpConfig, Ip4Subnet, Ip6Subnet
+from mdb.models import DhcpConfig, Domain, Interface, Ip4Subnet, Ip6Subnet
 
 # ---------------------------------------------------------------------------
 # pre_save signals: populate domain_name once, then leave it frozen
@@ -65,3 +66,21 @@ def test_ip6_signal_sets_domain_name():
         domain_filename="db.reverse-v6",
     )
     assert subnet.domain_name == "0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa"
+
+
+# ---------------------------------------------------------------------------
+# pre_delete Interface: the zones it was in get a new serial
+# ---------------------------------------------------------------------------
+
+
+@freeze_time("2026-11-02")
+def test_deleting_interface_raises_zone_serials(domain):
+    subnet = Interface.objects.get(pk=1).ip4address.subnet
+    Domain.objects.filter(pk=domain.pk).update(domain_serial=2026110299)
+    Ip4Subnet.objects.filter(pk=subnet.pk).update(domain_serial=2015010101)
+
+    Interface.objects.get(pk=1).delete()
+
+    # Past 99 the serial carries into the date instead of going back.
+    assert Domain.objects.get(pk=domain.pk).domain_serial == 2026110300
+    assert Ip4Subnet.objects.get(pk=subnet.pk).domain_serial == 2026110201

tests/test_utils.py

@@ -0,0 +1,32 @@
+import pytest
+from freezegun import freeze_time
+
+from mdb.utils import format_domain_serial_and_add_one
+
+
+@freeze_time("2026-11-02")
+@pytest.mark.parametrize(
+    ("serial", "expected"),
+    [
+        (2026110205, 2026110206),  # today: next number
+        (2025010107, 2026110201),  # an earlier day: today's first
+        (1, 2026110201),  # not a date at all
+        (2026110298, 2026110299),
+        (2026110299, 2026110300),  # used to stay at 99, so the change never synced
+        (2026110300, 2026110301),  # ahead of today: never goes back
+        (2026110505, 2026110506),
+        (None, 2026110201),
+        ("garbage", 2026110201),
+    ],
+)
+def test_next_serial(serial, expected):
+    assert format_domain_serial_and_add_one(serial) == expected
+
+
+@freeze_time("2026-11-02")
+def test_serial_always_increases():
+    serial = 2026110290
+    for _ in range(30):
+        new = format_domain_serial_and_add_one(serial)
+        assert new > serial
+        serial = new