caddytls: Refactor sni matcher (#6812)

modules/caddytls/matchers.go

@@ -56,7 +56,7 @@ func (MatchServerName) CaddyModule() caddy.ModuleInfo {
 
 // Match matches hello based on SNI.
 func (m MatchServerName) Match(hello *tls.ClientHelloInfo) bool {
-	repl := caddy.NewReplacer()
+	var repl *caddy.Replacer
 	// caddytls.TestServerNameMatcher calls this function without any context
 	if ctx := hello.Context(); ctx != nil {
 		// In some situations the existing context may have no replacer
@@ -65,6 +65,10 @@ func (m MatchServerName) Match(hello *tls.ClientHelloInfo) bool {
 		}
 	}
 
+	if repl == nil {
+		repl = caddy.NewReplacer()
+	}
+
 	for _, name := range m {
 		rs := repl.ReplaceAll(name, "")
 		if certmagic.MatchWildcard(hello.ServerName, rs) {