From 3cb05c5cdc9394e0a3791698796a4bb2b8fdf637 Mon Sep 17 00:00:00 2001
From: Kristoffer Dalby <kristoffer@tailscale.com>
Date: Fri, 12 Jul 2024 11:02:02 +0200
Subject: [PATCH] fix tests and alias

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>
---
 hscontrol/app.go          |  4 +++-
 hscontrol/types/config.go | 26 ++++++++++++++++++++++++--
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/hscontrol/app.go b/hscontrol/app.go
index a4995d09cf0..726b9d0bd2f 100644
--- a/hscontrol/app.go
+++ b/hscontrol/app.go
@@ -1021,8 +1021,10 @@ func (h *Headscale) loadACLPolicy() error {
 	switch h.cfg.Policy.Mode {
 	case types.PolicyModeFile:
 		path := h.cfg.Policy.Path
+
+		// It is fine to start headscale without a policy file.
 		if len(path) == 0 {
-			return fmt.Errorf("policy path is empty")
+			return nil
 		}
 
 		absPath := util.AbsolutePathFromConfigPath(path)
diff --git a/hscontrol/types/config.go b/hscontrol/types/config.go
index 46758d91a9c..6eae9a32f89 100644
--- a/hscontrol/types/config.go
+++ b/hscontrol/types/config.go
@@ -207,8 +207,6 @@ func LoadConfig(path string, isFile bool) error {
 	viper.AutomaticEnv()
 
 	viper.SetDefault("policy.mode", "file")
-	// This maintains backward-compatibility with the old config file.
-	viper.RegisterAlias("acl_policy_path", "policy.path")
 
 	viper.SetDefault("tls_letsencrypt_cache_dir", "/var/www/.cache")
 	viper.SetDefault("tls_letsencrypt_challenge_type", HTTP01ChallengeType)
@@ -267,6 +265,13 @@ func LoadConfig(path string, isFile bool) error {
 		return fmt.Errorf("fatal error reading config file: %w", err)
 	}
 
+	// Register aliases for backward compatibility
+	// Has to be called _after_ viper.ReadInConfig()
+	// https://github.com/spf13/viper/issues/560
+
+	// Alias the old ACL Policy path with the new configuration option.
+	registerAliasAndDeprecate("policy.path", "acl_policy_path")
+
 	// Collect any validation errors and return them all at once
 	var errorText string
 	if (viper.GetString("tls_letsencrypt_hostname") != "") &&
@@ -802,3 +807,20 @@ func GetHeadscaleConfig() (*Config, error) {
 func IsCLIConfigured() bool {
 	return viper.GetString("cli.address") != "" && viper.GetString("cli.api_key") != ""
 }
+
+// registerAliasAndDeprecate will register an alias between the newKey and the oldKey,
+// and log a deprecation warning if the oldKey is set.
+func registerAliasAndDeprecate(newKey, oldKey string) {
+	// NOTE: RegisterAlias is called with NEW KEY -> OLD KEY
+	viper.RegisterAlias(newKey, oldKey)
+	if viper.IsSet(oldKey) {
+		log.Warn().Msgf("The %q configuration key is deprecated. Please use %q instead. %q will be removed in the future.", oldKey, newKey, oldKey)
+	}
+}
+
+// deprecateAndFatal will log a fatal deprecation warning if the oldKey is set.
+func deprecateAndFatal(newKey, oldKey string) {
+	if viper.IsSet(oldKey) {
+		log.Fatal().Msgf("The %q configuration key is deprecated. Please use %q instead. %q has been removed.", oldKey, newKey, oldKey)
+	}
+}