backup: return KNOT_ENOTSUP when trying to restore from possible future backup format version

Returning KNOT_ENOTSUP makes more sense than returning KNOT_EMALF in such situations.

src/knot/zone/backup_dir.c

@@ -155,7 +155,9 @@ static int get_backup_format(zone_backup_ctx_t *ctx)
 	while (knot_getline(&line, &line_size, file) != -1) {
 		int value;
 		if (sscanf(line, LABEL_FILE_FORMAT, &value) != 0) {
-			if ((BACKUP_FORMAT_1 < value) && (value < BACKUP_FORMAT_TERM)) {
+			if (value >= BACKUP_FORMAT_TERM) {
+				ret = KNOT_ENOTSUP;
+			} else if (value > BACKUP_FORMAT_1) {
 				ctx->backup_format = value;
 				ret = KNOT_EOK;
 			}

tests-extra/tests/zone/backup_lock/data/backup7/knot_backup.label

+label: Knot DNS Backup
+backup_format: 1
+identity: tester.knot-dns.cz
+started_time: 2021-07-07 14:39:48 CEST
+finished_time: 2021-07-07 14:39:48 CEST
+knot_version: 3.1.dev.1625122029.e48145931
+parameters: +zonefile +nojournal +timers +kaspdb +catalog +backupdir backup2
+zone_count: 3

tests-extra/tests/zone/backup_lock/data/backup7/zonefiles/example1.zone

+;; Zone dump (Knot DNS 3.1.dev.1625122029.e48145931)
+example1.           	10	SOA	a.ns.example1. admin.example1. 1 10 10 120 10
+example1.           	10	NS	a.ns.example1.
+example1.           	10	NS	b.ns.example1.
+example1.           	10	NS	ns.out.
+deleg.example1.     	10	NS	a.ns.deleg.example1.
+deleg.example1.     	10	NS	ns.out.
+a.ns.deleg.example1.	10	A	10.0.1.1
+a.ns.deleg.example1.	10	AAAA	fd00::1:1
+a.mail.example1.    	10	A	10.0.1.1
+b.mail.example1.    	10	AAAA	fd00::1:1
+cname.mail.example1.	10	CNAME	a.mail.example1.
+mx.example1.        	10	MX	10 a.mail.example1.
+mx.example1.        	10	MX	20 b.mail.example1.
+mx.example1.        	10	MX	30 mail.out.
+mx-cname.example1.  	10	MX	10 cname.mail.example1.
+a.ns.example1.      	10	A	10.0.0.1
+a.ns.example1.      	10	AAAA	fd00::a1
+b.ns.example1.      	10	AAAA	fd00::b1
+b.ns.example1.      	10	AAAA	fd00::b2
+ptr.example1.       	10	PTR	target.example1.
+a.service.example1. 	10	TXT	"no address"
+b.service.example1. 	10	AAAA	fd00::2:1
+b.service.example1. 	10	AAAA	fd00::2:2
+b.service.example1. 	10	AAAA	fd00::2:3
+srv.example1.       	10	SRV	10 0 1000 a.service.example1.
+srv.example1.       	10	SRV	10 0 1000 b.service.example1.
+srv.example1.       	10	SRV	10 0 1000 service.out.
+target.example1.    	10	A	10.0.3.1
+target.example1.    	10	AAAA	fd00::3:1
+;; Written 29 records
+;; Time 2021-07-07 14:39:48 CEST

tests-extra/tests/zone/backup_lock/data/backup7/zonefiles/example2.zone

+;; Zone dump (Knot DNS 3.1.dev.1625122029.e48145931)
+example2.           	3600	SOA	dns1.example2. hostmaster.example2. 1 1 1 10 600
+example2.           	3600	NS	dns1.example2.
+dns1.example2.      	3600	A	192.0.2.1
+;; Written 3 records
+;; Time 2021-07-07 14:39:48 CEST

tests-extra/tests/zone/backup_lock/data/backup7/zonefiles/example3.zone

+;; Zone dump (Knot DNS 3.1.dev.1625122029.e48145931)
+example3.           	3600	SOA	dns1.example3. hostmaster.example3. 2010111213 10800 3600 1209600 7200
+example3.           	3600	NS	dns1.example3.
+example3.           	3600	NS	dns2.example3.
+added.example3.     	3600	A	1.2.3.4
+dns1.example3.      	3600	A	192.0.2.1
+dns1.example3.      	3600	AAAA	2001:db8::1
+dns2.example3.      	3600	A	192.0.2.2
+dns2.example3.      	3600	AAAA	2001:db8::2
+;; Written 8 records
+;; Time 2021-07-07 14:39:48 CEST

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

@@ -31,7 +31,7 @@ zones2 = t.zone("example1.", file_name="example1.file", storage=".")  \
          + t.zone("example2.", file_name="example2.file", storage=".") \
          + t.zone("example3.", file_name="example3.file", storage=".")
 t.link(zones2, master2)
-for i in range(2, 7):
+for i in range(2, 8):
     dir_from = os.path.join(t.data_dir, "backup%d" % i)
     dir_to = os.path.join(master2.dir, "backup%d" % i)
     shutil.copytree(dir_from, dir_to)
@@ -151,11 +151,18 @@ try:
 except:
     pass
 
-# Attempt to restore from unsupported backup format number, expected (malformed data).
+# Attempt to restore from unsupported backup format number, expected (operation not supported).
 try:
     master2.ctl("-f zone-restore +backupdir %s" % backup6_dir, wait=True)
     set_err("RESTORE FROM UNSUPPORTED BACKUP FORMAT VERSION ALLOWED")
 except:
     pass
 
+# Attempt to restore from non-existant backup format number, expected (malformed data).
+try:
+    master2.ctl("-f zone-restore +backupdir %s" % backup7_dir, wait=True)
+    set_err("RESTORE FROM NON-EXISTANT BACKUP FORMAT VERSION ALLOWED")
+except:
+    pass
+
 t.stop()