1 files changed, 120 insertions, 0 deletions
diff --git a/ipn/ipnlocal/diskcache_test.go b/ipn/ipnlocal/diskcache_test.go
new file mode 100644
index 000000000..0b064b8ab
--- /dev/null
+++ b/ipn/ipnlocal/diskcache_test.go
@@ -0,0 +1,120 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+package ipnlocal
+
+import (
+	"net/netip"
+	"testing"
+
+	"tailscale.com/tailcfg"
+	"tailscale.com/tstest"
+	"tailscale.com/types/netmap"
+	"tailscale.com/util/eventbus"
+	"tailscale.com/wgengine/magicsock"
+)
+
+// newCacheTestNetmap returns a minimal valid netmap suitable for testing disk
+// cache operations.
+func newCacheTestNetmap() *netmap.NetworkMap {
+	return &netmap.NetworkMap{
+		SelfNode: (&tailcfg.Node{
+			Name: "test-node.ts.net",
+			User: tailcfg.UserID(1),
+			Addresses: []netip.Prefix{
+				netip.MustParsePrefix("100.64.0.1/32"),
+			},
+		}).View(),
+		UserProfiles: map[tailcfg.UserID]tailcfg.UserProfileView{
+			tailcfg.UserID(1): (&tailcfg.UserProfile{
+				LoginName:   "user@example.com",
+				DisplayName: "Test User",
+			}).View(),
+		},
+	}
+}
+
+func TestWriteAndLoadHomeDERP(t *testing.T) {
+	b := newTestBackend(t)
+
+	nm := newCacheTestNetmap()
+	b.currentNode().SetNetMap(nm)
+
+	const wantDERP = 7
+	b.currentNode().homeDERP.Store(wantDERP)
+
+	b.mu.Lock()
+	defer b.mu.Unlock()
+
+	if err := b.writeNetmapToDiskLocked(nm); err != nil {
+		t.Fatalf("writeNetmapToDiskLocked: %v", err)
+	}
+
+	loaded, ok := b.loadDiskCacheLocked()
+	if !ok {
+		t.Fatal("loadDiskCacheLocked returned ok=false")
+	}
+	if !loaded.SelfNode.Valid() {
+		t.Fatal("loaded netmap SelfNode is invalid")
+	}
+	if got := loaded.SelfNode.HomeDERP(); got != wantDERP {
+		t.Errorf("loaded SelfNode.HomeDERP() = %d, want %d", got, wantDERP)
+	}
+}
+
+func TestOnHomeDERPUpdate(t *testing.T) {
+	b := newTestBackend(t)
+	done := make(chan struct{})
+	tstest.Replace(t, &testOnlyHomeDERPUpdate, func() { close(done) })
+
+	nm := newCacheTestNetmap()
+	b.currentNode().SetNetMap(nm)
+
+	// Publish a NewHomeDERP event via the backend's event bus.
+	bus := b.Sys().Bus.Get()
+	ec := bus.Client("test.TestOnHomeDERPUpdate")
+	pub := eventbus.Publish[magicsock.NewHomeDERP](ec)
+
+	const wantDERP = 11
+	pub.Publish(magicsock.NewHomeDERP{Old: 0, New: wantDERP})
+	<-done
+
+	if got := b.currentNode().homeDERP.Load(); got != wantDERP {
+		t.Errorf("b.homeDERP = %d, want %d", got, wantDERP)
+	}
+
+	// Verify the value was persisted to the disk cache.
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	loaded, ok := b.loadDiskCacheLocked()
+	if !ok {
+		t.Fatal("loadDiskCacheLocked returned ok=false after homeDERP update")
+	}
+	if got := loaded.SelfNode.HomeDERP(); got != wantDERP {
+		t.Errorf("cached SelfNode.HomeDERP() = %d, want %d", got, wantDERP)
+	}
+}
+
+func TestWriteNetmapDoesNotMutateOriginal(t *testing.T) {
+	b := newTestBackend(t)
+
+	nm := newCacheTestNetmap()
+	b.currentNode().SetNetMap(nm)
+
+	originalDERP := nm.SelfNode.HomeDERP() // expected to be 0 initially
+
+	const storeDERP = 5
+	b.currentNode().homeDERP.Store(storeDERP)
+
+	b.mu.Lock()
+	defer b.mu.Unlock()
+
+	if err := b.writeNetmapToDiskLocked(nm); err != nil {
+		t.Fatalf("writeNetmapToDiskLocked: %v", err)
+	}
+
+	// The original netmap must not have been mutated.
+	if got := nm.SelfNode.HomeDERP(); got != originalDERP {
+		t.Errorf("original nm.SelfNode.HomeDERP() = %d after write, want %d (original was mutated)", got, originalDERP)
+	}
+}