Update dependencies

vendor/tailscale.com/util/syspolicy/handler.go

@@ -0,0 +1,83 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package syspolicy
+
+import (
+	"errors"
+	"sync/atomic"
+)
+
+var (
+	handlerUsed atomic.Bool
+	handler     Handler = defaultHandler{}
+)
+
+// Handler reads system policies from OS-specific storage.
+type Handler interface {
+	// ReadString reads the policy setting's string value for the given key.
+	// It should return ErrNoSuchKey if the key does not have a value set.
+	ReadString(key string) (string, error)
+	// ReadUInt64 reads the policy setting's uint64 value for the given key.
+	// It should return ErrNoSuchKey if the key does not have a value set.
+	ReadUInt64(key string) (uint64, error)
+	// ReadBool reads the policy setting's boolean value for the given key.
+	// It should return ErrNoSuchKey if the key does not have a value set.
+	ReadBoolean(key string) (bool, error)
+	// ReadStringArray reads the policy setting's string array value for the given key.
+	// It should return ErrNoSuchKey if the key does not have a value set.
+	ReadStringArray(key string) ([]string, error)
+}
+
+// ErrNoSuchKey is returned by a Handler when the specified key does not have a
+// value set.
+var ErrNoSuchKey = errors.New("no such key")
+
+// defaultHandler is the catch all syspolicy type for anything that isn't windows or apple.
+type defaultHandler struct{}
+
+func (defaultHandler) ReadString(_ string) (string, error) {
+	return "", ErrNoSuchKey
+}
+
+func (defaultHandler) ReadUInt64(_ string) (uint64, error) {
+	return 0, ErrNoSuchKey
+}
+
+func (defaultHandler) ReadBoolean(_ string) (bool, error) {
+	return false, ErrNoSuchKey
+}
+
+func (defaultHandler) ReadStringArray(_ string) ([]string, error) {
+	return nil, ErrNoSuchKey
+}
+
+// markHandlerInUse is called before handler methods are called.
+func markHandlerInUse() {
+	handlerUsed.Store(true)
+}
+
+// RegisterHandler initializes the policy handler and ensures registration will happen once.
+func RegisterHandler(h Handler) {
+	// Technically this assignment is not concurrency safe, but in the
+	// event that there was any risk of a data race, we will panic due to
+	// the CompareAndSwap failing.
+	handler = h
+	if !handlerUsed.CompareAndSwap(false, true) {
+		panic("handler was already used before registration")
+	}
+}
+
+// TB is a subset of testing.TB that we use to set up test helpers.
+// It's defined here to avoid pulling in the testing package.
+type TB interface {
+	Helper()
+	Cleanup(func())
+}
+
+func SetHandlerForTest(tb TB, h Handler) {
+	tb.Helper()
+	oldHandler := handler
+	handler = h
+	tb.Cleanup(func() { handler = oldHandler })
+}