fix(zonefinder): handle underscores in dns records

Signed-off-by: Arthur Le Roux <[email protected]>

Author: arthlr

provider/zonefinder.go

@@ -29,12 +29,34 @@ func (z ZoneIDName) Add(zoneID, zoneName string) {
 	z[zoneID] = zoneName
 }
 
+// FindZone identifies the most suitable DNS zone for a given hostname.
+// It returns the zone ID and name that best match the hostname.
+//
+// The function processes the hostname by splitting it into labels and
+// converting each label to its Unicode form using IDNA (Internationalized
+// Domain Names for Applications) standards.
+//
+// Labels containing underscores ('_') are skipped during Unicode conversion.
+// This is because underscores are often used in special DNS records (e.g.,
+// SRV records as per RFC 2782, or TXT record for services) that are not
+// IDNA-aware and cannot represent non-ASCII labels. Skipping these labels
+// ensures compatibility with such use cases.
 func (z ZoneIDName) FindZone(hostname string) (suitableZoneID, suitableZoneName string) {
-	name, err := idna.Lookup.ToUnicode(hostname)
-	if err != nil {
-		log.Warnf("Failed to convert hostname '%s' to its Unicode form: %v", hostname, err)
-		name = hostname
+	var name string
+	domain_labels := strings.Split(hostname, ".")
+	for i, label := range domain_labels {
+		if strings.Contains(label, "_") {
+			continue
+		}
+		convertedLabel, err := idna.Lookup.ToUnicode(label)
+		if err != nil {
+			log.Warnf("Failed to convert label '%s' of hostname '%s' to its Unicode form: %v", label, hostname, err)
+			convertedLabel = label
+		}
+		domain_labels[i] = convertedLabel
 	}
+	name = strings.Join(domain_labels, ".")
+
 	for zoneID, zoneName := range z {
 		if name == zoneName || strings.HasSuffix(name, "."+zoneName) {
 			if suitableZoneName == "" || len(zoneName) > len(suitableZoneName) {

provider/zonefinder_test.go

@@ -30,11 +30,15 @@ func TestZoneIDName(t *testing.T) {
 	z.Add("123456", "qux.baz")
 	z.Add("654321", "foo.qux.baz")
 	z.Add("987654", "エイミー.みんな")
+	z.Add("123123", "_metadata.example.com")
+	z.Add("456456", "_metadata.エイミー.みんな")
 
 	assert.Equal(t, ZoneIDName{
 		"123456": "qux.baz",
 		"654321": "foo.qux.baz",
 		"987654": "エイミー.みんな",
+		"123123": "_metadata.example.com",
+		"456456": "_metadata.エイミー.みんな",
 	}, z)
 
 	// simple entry in a domain
@@ -73,6 +77,6 @@ func TestZoneIDName(t *testing.T) {
 	assert.Equal(t, "987654", zoneID)
 
 	b := testutils.LogsToBuffer(log.WarnLevel, t)
-	zoneID, zoneName = z.FindZone("???")
-	assert.Contains(t, b.String(), "level=warning msg=\"Failed to convert hostname '???' to its Unicode form: idna: disallowed rune U+003F\"")
+	_, _ = z.FindZone("???")
+	assert.Contains(t, b.String(), "level=warning msg=\"Failed to convert label '???' of hostname '???' to its Unicode form: idna: disallowed rune U+003F\"")
 }