Update serial number correctly

lib.py

@@ -82,6 +82,17 @@ def get_serial(dns_zone):
 
     return serial
 
+def update_serial(serial, serial_bits=32):
+    """Update serial number
+
+    According to RFC 1982 and Knot implementation.
+    SERIAL_BITS = 32 by default.
+    """
+
+    serial = serial + 1 % 2**32
+
+    return serial
+
 def soa_handler(re2o_zone, dns_zone):
     """Handler for SOA record"""
 
@@ -93,6 +104,7 @@ def soa_handler(re2o_zone, dns_zone):
     
     origin = dns_zone.origin
     serial = get_serial(origin)
+    serial = update_serial(serial)
     logging.debug(f"[SOA] zone_origin={origin} serial={serial}")
 
     soa_obj = SOA.SOA(