zone: flush zone after retransfer even if serial not changed

src/knot/events/handlers/refresh.c

@@ -1180,6 +1180,7 @@ int event_refresh(conf_t *conf, zone_t *zone)
 	if (zone->flags & ZONE_FORCE_AXFR) {
 		zone->flags &= ~ZONE_FORCE_AXFR;
 		trctx.force_axfr = true;
+		zone->zonefile.retransfer = true;
 	}
 
 	int ret = zone_master_try(conf, zone, try_refresh, &trctx, "refresh");

src/knot/zone/zone.c

@@ -91,7 +91,7 @@ static int flush_journal(conf_t *conf, zone_t *zone, bool allow_empty_zone)
 	zone_contents_t *contents = zone->contents;
 	uint32_t serial_to = zone_contents_serial(contents);
 	if (!force && zone->zonefile.exists && zone->zonefile.serial == serial_to &&
-	    !zone->zonefile.resigned) {
+	    !zone->zonefile.retransfer && !zone->zonefile.resigned) {
 		ret = KNOT_EOK; /* No differences. */
 		goto flush_journal_replan;
 	}
@@ -132,6 +132,7 @@ static int flush_journal(conf_t *conf, zone_t *zone, bool allow_empty_zone)
 	zone->zonefile.mtime = st.st_mtim;
 	zone->zonefile.serial = serial_to;
 	zone->zonefile.resigned = false;
+	zone->zonefile.retransfer = false;
 
 	/* Flush journal. */
 	if (journal_is_existing(j)) {

src/knot/zone/zone.h

@@ -58,6 +58,7 @@ typedef struct zone
 		uint32_t serial;
 		bool exists;
 		bool resigned;
+		bool retransfer;
 	} zonefile;
 
 	/*! \brief Zone events. */

tests-extra/tests/zone/retransfer/data/example.com.zone.master

+$ORIGIN example.com.
+$TTL 3600
+
+@	SOA	dns1 hostmaster 2010111201 10800 3600 1209600 7200
+	NS	dns1
+	NS	dns2
+	MX	10 mail
+
+dns1	A	192.0.2.1
+	AAAA	2001:DB8::1
+
+dns2	A	192.0.2.2
+	AAAA	2001:DB8::2
+
+mail	A	192.0.2.3
+	AAAA	2001:DB8::3
+
+diff    A       1.2.3.4

tests-extra/tests/zone/retransfer/test.py

@@ -13,8 +13,13 @@ slave = t.server("knot")
 zone = t.zone("example.com.", storage=".")
 t.link(zone, master, slave)
 
+slave.zonefile_sync = 0
+
 # Load newer zone to the slave
-slave.update_zonefile(zone, version=1)
+slave.update_zonefile(zone, version="slave")
+
+zfpath = slave.zones[zone[0].name].zfile.path
+mtime0 = os.stat(zfpath).st_mtime
 
 t.start()
 
@@ -24,11 +29,29 @@ serial_slave = slave.zone_wait(zone)
 # Check that the slave's serial is larger than master's
 assert serial_master <= serial_slave
 
-# Force refresh
+# Retransfer zone with lower serial
 slave.ctl("zone-retransfer example.com.")
 t.sleep(2)
 
 serial_slave = slave.zone_wait(zone)
 compare(serial_slave, serial_master, "Serial after retransfer")
 
+mtime1 = os.stat(zfpath).st_mtime
+if mtime1 == mtime0:
+    set_err("Not flushed after retransfer")
+
+# Retransfer zone with the same serial
+master.update_zonefile(zone, version="master")
+master.reload()
+
+slave.ctl("zone-retransfer example.com.")
+t.sleep(2)
+
+resp = slave.dig("diff.example.com", "A")
+resp.check(rcode="NOERROR")
+
+mtime2 = os.stat(zfpath).st_mtime
+if mtime2 == mtime1:
+    set_err("Not flushed after retransfer")
+
 t.end()