fixed dns-sd instance name escaping

discovery.go

@@ -15,11 +15,18 @@ import (
 	"github.com/linksmart/thing-directory/catalog"
 )
 
+// escape special characters as recommended by https://tools.ietf.org/html/rfc6763#section-4.3
+func escapeDNSSDServiceInstance(instance string) (escaped string) {
+	// replace \ by \\
+	escaped = strings.ReplaceAll(instance, "\\", "\\\\")
+	// replace . by \.
+	escaped = strings.ReplaceAll(escaped, ".", "\\.")
+	return escaped
+}
+
 // register as a DNS-SD Service
 func registerDNSSDService(conf *Config) (func(), error) {
-	// escape special characters (https://tools.ietf.org/html/rfc6763#section-4.3)
-	instance := strings.ReplaceAll(conf.DNSSD.Publish.Instance, ".", "\\.")
-	instance = strings.ReplaceAll(conf.DNSSD.Publish.Instance, "\\", "\\\\")
+	instance := escapeDNSSDServiceInstance(conf.DNSSD.Publish.Instance)
 
 	log.Printf("DNS-SD: registering as \"%s.%s.%s\", subtype: %s",
 		instance, catalog.DNSSDServiceType, conf.DNSSD.Publish.Domain, catalog.DNSSDServiceSubtype)

discovery_test.go

@@ -0,0 +1,31 @@
+package main
+
+import "testing"
+
+func TestEscapeDNSSDServiceInstance(t *testing.T) {
+	t.Run("no escaping", func(t *testing.T) {
+		instance := "thing-directory"
+		escaped := escapeDNSSDServiceInstance(instance)
+		if escaped != instance {
+			t.Fatalf("Unexpected escaping of %s to %s", instance, escaped)
+		}
+	})
+
+	t.Run("escape dot", func(t *testing.T) {
+		instance := "thing.directory"   // from thing.directory
+		expected := "thing\\.directory" // to   thing\.directory
+		escaped := escapeDNSSDServiceInstance(instance)
+		if escaped != expected {
+			t.Fatalf("Escaped value for %s is %s. Expected %s", instance, escaped, expected)
+		}
+	})
+
+	t.Run("escape backslash", func(t *testing.T) {
+		instance := "thing\\directory"   // from thing\directory
+		expected := "thing\\\\directory" // to   thing\\directory
+		escaped := escapeDNSSDServiceInstance(instance)
+		if escaped != expected {
+			t.Fatalf("Escaped value for %s is %s. Expected %s", instance, escaped, expected)
+		}
+	})
+}