Update

vendor/tailscale.com/util/def/def.go

@@ -0,0 +1,45 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Package def parses strings and environment variables with fallback default values.
+package def
+
+import (
+	"os"
+	"strconv"
+	"time"
+)
+
+// Bool parses s as a bool, returning def when s is empty or invalid.
+func Bool(s string, def bool) bool {
+	if s == "" {
+		return def
+	}
+	v, err := strconv.ParseBool(s)
+	if err != nil {
+		return def
+	}
+	return v
+}
+
+// Duration parses s as a time.Duration, returning def when s is empty or invalid.
+func Duration(s string, def time.Duration) time.Duration {
+	if s == "" {
+		return def
+	}
+	v, err := time.ParseDuration(s)
+	if err != nil {
+		return def
+	}
+	return v
+}
+
+// LookupEnv retrieves the value of the environment variable named by the key.
+// If the variable is present in the environment the value (which may be
+// empty) is returned. Otherwise, it returns def.
+func LookupEnv(key, def string) string {
+	if v, ok := os.LookupEnv(key); ok {
+		return v
+	}
+	return def
+}