From 326c993612df33f8ae796d652157bf49281a1596 Mon Sep 17 00:00:00 2001
From: Jonni Liljamo <jonni@liljamo.com>
Date: Thu, 24 Oct 2024 12:11:39 +0300
Subject: [PATCH] feat: zoneOf function

---
 internal/dns/misc.go      | 26 ++++++++++++++++++++++++++
 internal/dns/misc_test.go | 10 ++++++++++
 2 files changed, 36 insertions(+)
 create mode 100644 internal/dns/misc.go
 create mode 100644 internal/dns/misc_test.go

diff --git a/internal/dns/misc.go b/internal/dns/misc.go
new file mode 100644
index 0000000..85a5cca
--- /dev/null
+++ b/internal/dns/misc.go
@@ -0,0 +1,26 @@
+/*
+ * Copyright (C) 2024 Jonni Liljamo <jonni@liljamo.com>
+ *
+ * This file is licensed under AGPL-3.0-or-later, see NOTICE and LICENSE for
+ * more information.
+ */
+
+package dns
+
+import (
+	"log/slog"
+	"strings"
+)
+
+func zoneOf(fqdn string, zone string) bool {
+	// Get the index of the first '.', and compare everything after that to zone.
+	if index := strings.IndexByte(fqdn, '.'); index >= 0 {
+		index++
+		return fqdn[index:] == zone
+	}
+
+	// Probably both fqdn and zone were just '.'. Crossing my fingers and hoping
+	// this can't be reached in correct configuration.
+	slog.Error("Invalid use of zone_of", slog.String("fqdn", fqdn), slog.String("zone", zone))
+	return false
+}
diff --git a/internal/dns/misc_test.go b/internal/dns/misc_test.go
new file mode 100644
index 0000000..0d01113
--- /dev/null
+++ b/internal/dns/misc_test.go
@@ -0,0 +1,10 @@
+package dns
+
+import "testing"
+
+func TestZoneOf(t *testing.T) {
+	want := "test.ddns.felu.arpa."
+	if !zoneOf("_acme-challenge.test.ddns.felu.arpa.", want) {
+		t.Error("zoneOf")
+	}
+}
-- 
2.44.1