util/syspolicy, ipn/ipnlocal: update syspolicy package to utilize syspolicy/rsop

In this PR, we update the syspolicy package to utilize syspolicy/rsop under the hood,
and remove syspolicy.CachingHandler, syspolicy.windowsHandler and related code
which is no longer used.

We mark the syspolicy.Handler interface and RegisterHandler/SetHandlerForTest functions
as deprecated, but keep them temporarily until they are no longer used in other repos.

We also update the package to register setting definitions for all existing policy settings
and to register the Registry-based, Windows-specific policy stores when running on Windows.

Finally, we update existing internal and external tests to use the new API and add a few more
tests and benchmarks.

Updates #12687

Signed-off-by: Nick Khyl <nickk@tailscale.com>

ipn/ipnlocal/local_test.go

@@ -54,6 +54,8 @@ import (
 	"tailscale.com/util/must"
 	"tailscale.com/util/set"
 	"tailscale.com/util/syspolicy"
+	"tailscale.com/util/syspolicy/setting"
+	"tailscale.com/util/syspolicy/source"
 	"tailscale.com/wgengine"
 	"tailscale.com/wgengine/filter"
 	"tailscale.com/wgengine/wgcfg"
@@ -1559,94 +1561,6 @@ func dnsResponse(domain, address string) []byte {
 	return must.Get(b.Finish())
 }
 
-type errorSyspolicyHandler struct {
-	t         *testing.T
-	err       error
-	key       syspolicy.Key
-	allowKeys map[syspolicy.Key]*string
-}
-
-func (h *errorSyspolicyHandler) ReadString(key string) (string, error) {
-	sk := syspolicy.Key(key)
-	if _, ok := h.allowKeys[sk]; !ok {
-		h.t.Errorf("ReadString: %q is not in list of permitted keys", h.key)
-	}
-	if sk == h.key {
-		return "", h.err
-	}
-	return "", syspolicy.ErrNoSuchKey
-}
-
-func (h *errorSyspolicyHandler) ReadUInt64(key string) (uint64, error) {
-	h.t.Errorf("ReadUInt64(%q) unexpectedly called", key)
-	return 0, syspolicy.ErrNoSuchKey
-}
-
-func (h *errorSyspolicyHandler) ReadBoolean(key string) (bool, error) {
-	h.t.Errorf("ReadBoolean(%q) unexpectedly called", key)
-	return false, syspolicy.ErrNoSuchKey
-}
-
-func (h *errorSyspolicyHandler) ReadStringArray(key string) ([]string, error) {
-	h.t.Errorf("ReadStringArray(%q) unexpectedly called", key)
-	return nil, syspolicy.ErrNoSuchKey
-}
-
-type mockSyspolicyHandler struct {
-	t *testing.T
-	// stringPolicies is the collection of policies that we expect to see
-	// queried by the current test. If the policy is expected but unset, then
-	// use nil, otherwise use a string equal to the policy's desired value.
-	stringPolicies map[syspolicy.Key]*string
-	// stringArrayPolicies is the collection of policies that we expected to see
-	// queries by the current test, that return policy string arrays.
-	stringArrayPolicies map[syspolicy.Key][]string
-	// failUnknownPolicies is set if policies other than those in stringPolicies
-	// (uint64 or bool policies are not supported by mockSyspolicyHandler yet)
-	// should be considered a test failure if they are queried.
-	failUnknownPolicies bool
-}
-
-func (h *mockSyspolicyHandler) ReadString(key string) (string, error) {
-	if s, ok := h.stringPolicies[syspolicy.Key(key)]; ok {
-		if s == nil {
-			return "", syspolicy.ErrNoSuchKey
-		}
-		return *s, nil
-	}
-	if h.failUnknownPolicies {
-		h.t.Errorf("ReadString(%q) unexpectedly called", key)
-	}
-	return "", syspolicy.ErrNoSuchKey
-}
-
-func (h *mockSyspolicyHandler) ReadUInt64(key string) (uint64, error) {
-	if h.failUnknownPolicies {
-		h.t.Errorf("ReadUInt64(%q) unexpectedly called", key)
-	}
-	return 0, syspolicy.ErrNoSuchKey
-}
-
-func (h *mockSyspolicyHandler) ReadBoolean(key string) (bool, error) {
-	if h.failUnknownPolicies {
-		h.t.Errorf("ReadBoolean(%q) unexpectedly called", key)
-	}
-	return false, syspolicy.ErrNoSuchKey
-}
-
-func (h *mockSyspolicyHandler) ReadStringArray(key string) ([]string, error) {
-	if h.failUnknownPolicies {
-		h.t.Errorf("ReadStringArray(%q) unexpectedly called", key)
-	}
-	if s, ok := h.stringArrayPolicies[syspolicy.Key(key)]; ok {
-		if s == nil {
-			return []string{}, syspolicy.ErrNoSuchKey
-		}
-		return s, nil
-	}
-	return nil, syspolicy.ErrNoSuchKey
-}
-
 func TestSetExitNodeIDPolicy(t *testing.T) {
 	pfx := netip.MustParsePrefix
 	tests := []struct {
@@ -1856,23 +1770,18 @@ func TestSetExitNodeIDPolicy(t *testing.T) {
 		},
 	}
 
+	syspolicy.RegisterWellKnownSettingsForTest(t)
+
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
 			b := newTestBackend(t)
-			msh := &mockSyspolicyHandler{
-				t: t,
-				stringPolicies: map[syspolicy.Key]*string{
-					syspolicy.ExitNodeID: nil,
-					syspolicy.ExitNodeIP: nil,
-				},
-			}
-			if test.exitNodeIDKey {
-				msh.stringPolicies[syspolicy.ExitNodeID] = &test.exitNodeID
-			}
-			if test.exitNodeIPKey {
-				msh.stringPolicies[syspolicy.ExitNodeIP] = &test.exitNodeIP
-			}
-			syspolicy.SetHandlerForTest(t, msh)
+
+			policyStore := source.NewTestStoreOf(t,
+				source.TestSettingOf(syspolicy.ExitNodeID, test.exitNodeID),
+				source.TestSettingOf(syspolicy.ExitNodeIP, test.exitNodeIP),
+			)
+			syspolicy.MustRegisterStoreForTest(t, "TestStore", setting.DeviceScope, policyStore)
+
 			if test.nm == nil {
 				test.nm = new(netmap.NetworkMap)
 			}
@@ -1994,13 +1903,13 @@ func TestUpdateNetmapDeltaAutoExitNode(t *testing.T) {
 			report:                    report,
 		},
 	}
-	msh := &mockSyspolicyHandler{
-		t: t,
-		stringPolicies: map[syspolicy.Key]*string{
-			syspolicy.ExitNodeID: ptr.To("auto:any"),
-		},
-	}
-	syspolicy.SetHandlerForTest(t, msh)
+
+	syspolicy.RegisterWellKnownSettingsForTest(t)
+	policyStore := source.NewTestStoreOf(t, source.TestSettingOf(
+		syspolicy.ExitNodeID, "auto:any",
+	))
+	syspolicy.MustRegisterStoreForTest(t, "TestStore", setting.DeviceScope, policyStore)
+
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			b := newTestLocalBackend(t)
@@ -2049,13 +1958,11 @@ func TestAutoExitNodeSetNetInfoCallback(t *testing.T) {
 	}
 	cc = newClient(t, opts)
 	b.cc = cc
-	msh := &mockSyspolicyHandler{
-		t: t,
-		stringPolicies: map[syspolicy.Key]*string{
-			syspolicy.ExitNodeID: ptr.To("auto:any"),
-		},
-	}
-	syspolicy.SetHandlerForTest(t, msh)
+	syspolicy.RegisterWellKnownSettingsForTest(t)
+	policyStore := source.NewTestStoreOf(t, source.TestSettingOf(
+		syspolicy.ExitNodeID, "auto:any",
+	))
+	syspolicy.MustRegisterStoreForTest(t, "TestStore", setting.DeviceScope, policyStore)
 	peer1 := makePeer(1, withCap(26), withDERP(3), withSuggest(), withExitRoutes())
 	peer2 := makePeer(2, withCap(26), withDERP(2), withSuggest(), withExitRoutes())
 	selfNode := tailcfg.Node{
@@ -2160,13 +2067,11 @@ func TestSetControlClientStatusAutoExitNode(t *testing.T) {
 		DERPMap: derpMap,
 	}
 	b := newTestLocalBackend(t)
-	msh := &mockSyspolicyHandler{
-		t: t,
-		stringPolicies: map[syspolicy.Key]*string{
-			syspolicy.ExitNodeID: ptr.To("auto:any"),
-		},
-	}
-	syspolicy.SetHandlerForTest(t, msh)
+	syspolicy.RegisterWellKnownSettingsForTest(t)
+	policyStore := source.NewTestStoreOf(t, source.TestSettingOf(
+		syspolicy.ExitNodeID, "auto:any",
+	))
+	syspolicy.MustRegisterStoreForTest(t, "TestStore", setting.DeviceScope, policyStore)
 	b.netMap = nm
 	b.lastSuggestedExitNode = peer1.StableID()
 	b.sys.MagicSock.Get().SetLastNetcheckReportForTest(b.ctx, report)
@@ -2400,17 +2305,16 @@ func TestApplySysPolicy(t *testing.T) {
 		},
 	}
 
+	syspolicy.RegisterWellKnownSettingsForTest(t)
+
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			msh := &mockSyspolicyHandler{
-				t:              t,
-				stringPolicies: make(map[syspolicy.Key]*string, len(tt.stringPolicies)),
-			}
+			settings := make([]source.TestSetting[string], 0, len(tt.stringPolicies))
 			for p, v := range tt.stringPolicies {
-				v := v // construct a unique pointer for each policy value
-				msh.stringPolicies[p] = &v
+				settings = append(settings, source.TestSettingOf(p, v))
 			}
-			syspolicy.SetHandlerForTest(t, msh)
+			policyStore := source.NewTestStoreOf(t, settings...)
+			syspolicy.MustRegisterStoreForTest(t, "TestStore", setting.DeviceScope, policyStore)
 
 			t.Run("unit", func(t *testing.T) {
 				prefs := tt.prefs.Clone()
@@ -2546,35 +2450,19 @@ func TestPreferencePolicyInfo(t *testing.T) {
 		},
 	}
 
+	syspolicy.RegisterWellKnownSettingsForTest(t)
+
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			for _, pp := range preferencePolicies {
 				t.Run(string(pp.key), func(t *testing.T) {
-					var h syspolicy.Handler
-
-					allPolicies := make(map[syspolicy.Key]*string, len(preferencePolicies)+1)
-					allPolicies[syspolicy.ControlURL] = nil
-					for _, pp := range preferencePolicies {
-						allPolicies[pp.key] = nil
+					s := source.TestSetting[string]{
+						Key:   pp.key,
+						Error: tt.policyError,
+						Value: tt.policyValue,
 					}
-
-					if tt.policyError != nil {
-						h = &errorSyspolicyHandler{
-							t:         t,
-							err:       tt.policyError,
-							key:       pp.key,
-							allowKeys: allPolicies,
-						}
-					} else {
-						msh := &mockSyspolicyHandler{
-							t:                   t,
-							stringPolicies:      allPolicies,
-							failUnknownPolicies: true,
-						}
-						msh.stringPolicies[pp.key] = &tt.policyValue
-						h = msh
-					}
-					syspolicy.SetHandlerForTest(t, h)
+					policyStore := source.NewTestStoreOf(t, s)
+					syspolicy.MustRegisterStoreForTest(t, "TestStore", setting.DeviceScope, policyStore)
 
 					prefs := defaultPrefs.AsStruct()
 					pp.set(prefs, tt.initialValue)
@@ -3825,15 +3713,16 @@ func TestShouldAutoExitNode(t *testing.T) {
 			expectedBool:          false,
 		},
 	}
+
+	syspolicy.RegisterWellKnownSettingsForTest(t)
+
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			msh := &mockSyspolicyHandler{
-				t: t,
-				stringPolicies: map[syspolicy.Key]*string{
-					syspolicy.ExitNodeID: ptr.To(tt.exitNodeIDPolicyValue),
-				},
-			}
-			syspolicy.SetHandlerForTest(t, msh)
+			policyStore := source.NewTestStoreOf(t, source.TestSettingOf(
+				syspolicy.ExitNodeID, tt.exitNodeIDPolicyValue,
+			))
+			syspolicy.MustRegisterStoreForTest(t, "TestStore", setting.DeviceScope, policyStore)
+
 			got := shouldAutoExitNode()
 			if got != tt.expectedBool {
 				t.Fatalf("expected %v got %v for %v policy value", tt.expectedBool, got, tt.exitNodeIDPolicyValue)
@@ -3971,17 +3860,13 @@ func TestFillAllowedSuggestions(t *testing.T) {
 			want:        []tailcfg.StableNodeID{"ABC", "def", "gHiJ"},
 		},
 	}
+	syspolicy.RegisterWellKnownSettingsForTest(t)
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			mh := mockSyspolicyHandler{
-				t: t,
-			}
-			if tt.allowPolicy != nil {
-				mh.stringArrayPolicies = map[syspolicy.Key][]string{
-					syspolicy.AllowedSuggestedExitNodes: tt.allowPolicy,
-				}
-			}
-			syspolicy.SetHandlerForTest(t, &mh)
+			policyStore := source.NewTestStoreOf(t, source.TestSettingOf(
+				syspolicy.AllowedSuggestedExitNodes, tt.allowPolicy,
+			))
+			syspolicy.MustRegisterStoreForTest(t, "TestStore", setting.DeviceScope, policyStore)
 
 			got := fillAllowedSuggestions()
 			if got == nil {