util/syspolicy: finish plumbing policyclient, add feature/syspolicy, move global impl

This is step 4 of making syspolicy a build-time feature.

This adds a policyclient.Get() accessor to return the correct
implementation to use: either the real one, or the no-op one. (A third
type, a static one for testing, also exists, so in general a
policyclient.Client should be plumbed around and not always fetched
via policyclient.Get whenever possible, especially if tests need to use
alternate syspolicy)

Updates #16998
Updates #12614

Change-Id: Iaf19670744a596d5918acfa744f5db4564272978
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

tsd/syspolicy_off.go

@@ -1,12 +0,0 @@
-// Copyright (c) Tailscale Inc & AUTHORS
-// SPDX-License-Identifier: BSD-3-Clause
-
-//go:build ts_omit_syspolicy
-
-package tsd
-
-import (
-	"tailscale.com/util/syspolicy/policyclient"
-)
-
-func getPolicyClient() policyclient.Client { return policyclient.NoPolicyClient{} }

tsd/syspolicy_on.go

@@ -1,64 +0,0 @@
-// Copyright (c) Tailscale Inc & AUTHORS
-// SPDX-License-Identifier: BSD-3-Clause
-
-//go:build !ts_omit_syspolicy
-
-package tsd
-
-import (
-	"time"
-
-	"tailscale.com/util/syspolicy"
-	"tailscale.com/util/syspolicy/pkey"
-	"tailscale.com/util/syspolicy/policyclient"
-	"tailscale.com/util/syspolicy/ptype"
-)
-
-func getPolicyClient() policyclient.Client { return globalSyspolicy{} }
-
-// globalSyspolicy implements [policyclient.Client] using the syspolicy global
-// functions and global registrations.
-//
-// TODO: de-global-ify. This implementation using the old global functions
-// is an intermediate stage while changing policyclient to be modular.
-type globalSyspolicy struct{}
-
-func (globalSyspolicy) GetBoolean(key pkey.Key, defaultValue bool) (bool, error) {
-	return syspolicy.GetBoolean(key, defaultValue)
-}
-
-func (globalSyspolicy) GetString(key pkey.Key, defaultValue string) (string, error) {
-	return syspolicy.GetString(key, defaultValue)
-}
-
-func (globalSyspolicy) GetStringArray(key pkey.Key, defaultValue []string) ([]string, error) {
-	return syspolicy.GetStringArray(key, defaultValue)
-}
-
-func (globalSyspolicy) SetDebugLoggingEnabled(enabled bool) {
-	syspolicy.SetDebugLoggingEnabled(enabled)
-}
-
-func (globalSyspolicy) GetUint64(key pkey.Key, defaultValue uint64) (uint64, error) {
-	return syspolicy.GetUint64(key, defaultValue)
-}
-
-func (globalSyspolicy) GetDuration(name pkey.Key, defaultValue time.Duration) (time.Duration, error) {
-	return syspolicy.GetDuration(name, defaultValue)
-}
-
-func (globalSyspolicy) GetPreferenceOption(name pkey.Key) (ptype.PreferenceOption, error) {
-	return syspolicy.GetPreferenceOption(name)
-}
-
-func (globalSyspolicy) GetVisibility(name pkey.Key) (ptype.Visibility, error) {
-	return syspolicy.GetVisibility(name)
-}
-
-func (globalSyspolicy) HasAnyOf(keys ...pkey.Key) (bool, error) {
-	return syspolicy.HasAnyOf(keys...)
-}
-
-func (globalSyspolicy) RegisterChangeCallback(cb func(policyclient.PolicyChange)) (unregister func(), err error) {
-	return syspolicy.RegisterChangeCallback(cb)
-}

tsd/tsd.go

@@ -175,7 +175,7 @@ func (s *System) PolicyClientOrDefault() policyclient.Client {
 	if client, ok := s.PolicyClient.GetOK(); ok {
 		return client
 	}
-	return getPolicyClient()
+	return policyclient.Get()
 }
 
 // SubSystem represents some subsystem of the Tailscale node daemon.