[client] Renew the Android TUN only when the routes it carries change (#7396)

client/internal/routemanager/notifier/notifier_android.go

@@ -4,8 +4,6 @@ package notifier
 
 import (
 	"net/netip"
-	"slices"
-	"sort"
 	"sync"
 
 	"github.com/netbirdio/netbird/client/internal/listener"
@@ -75,19 +73,3 @@ func (n *Notifier) notifyLocked() {
 func (n *Notifier) Close() {
 	// unused
 }
-
-func routesToStrings(routes []*route.Route) []string {
-	nets := make([]string, 0, len(routes))
-	for _, r := range routes {
-		nets = append(nets, r.NetString())
-	}
-	return nets
-}
-
-func hasRouteDiff(a []*route.Route, b []*route.Route) bool {
-	as := routesToStrings(a)
-	bs := routesToStrings(b)
-	sort.Strings(as)
-	sort.Strings(bs)
-	return !slices.Equal(as, bs)
-}

client/internal/routemanager/notifier/route_diff.go

@@ -0,0 +1,27 @@
+package notifier
+
+import (
+	"slices"
+	"sort"
+
+	"github.com/netbirdio/netbird/route"
+)
+
+// routePrefixes returns the distinct prefixes a route set covers, sorted.
+// Duplicates are dropped deliberately: an HA group hands us one route per
+// peer serving the same prefix, and the platform is given the prefix, not the
+// candidates. Counting them would report a change every time a peer joins or
+// leaves a group, and on Android each report renews the TUN.
+func routePrefixes(routes []*route.Route) []string {
+	nets := make([]string, 0, len(routes))
+	for _, r := range routes {
+		nets = append(nets, r.NetString())
+	}
+	sort.Strings(nets)
+	return slices.Compact(nets)
+}
+
+// hasRouteDiff reports whether the prefixes the two route sets cover differ.
+func hasRouteDiff(a []*route.Route, b []*route.Route) bool {
+	return !slices.Equal(routePrefixes(a), routePrefixes(b))
+}

client/internal/routemanager/notifier/route_diff_test.go

@@ -0,0 +1,88 @@
+package notifier
+
+import (
+	"net/netip"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"github.com/netbirdio/netbird/route"
+)
+
+func routeFor(id route.ID, prefix string) *route.Route {
+	return &route.Route{
+		ID:      id,
+		NetID:   "net",
+		Network: netip.MustParsePrefix(prefix),
+	}
+}
+
+// TestHasRouteDiff_IgnoresHACandidateCount is the reason the comparison
+// deduplicates. Every notification renews the TUN, and a renewed TUN
+// invalidates the sockets the embedded servers are listening on, so a peer
+// joining or leaving an HA group must not count as a route change when the
+// prefixes the TUN carries are identical.
+func TestHasRouteDiff_IgnoresHACandidateCount(t *testing.T) {
+	onePeer := []*route.Route{routeFor("a", "10.0.0.0/24")}
+	twoPeers := []*route.Route{
+		routeFor("a", "10.0.0.0/24"),
+		routeFor("b", "10.0.0.0/24"),
+	}
+
+	assert.False(t, hasRouteDiff(onePeer, twoPeers),
+		"a second peer serving the same prefix is not a route change")
+	assert.False(t, hasRouteDiff(twoPeers, onePeer),
+		"losing one of two peers serving the same prefix is not a route change")
+}
+
+func TestHasRouteDiff_ReportsRealChanges(t *testing.T) {
+	tests := []struct {
+		name string
+		a    []*route.Route
+		b    []*route.Route
+		want bool
+	}{
+		{
+			name: "added prefix",
+			a:    []*route.Route{routeFor("a", "10.0.0.0/24")},
+			b:    []*route.Route{routeFor("a", "10.0.0.0/24"), routeFor("b", "10.0.1.0/24")},
+			want: true,
+		},
+		{
+			name: "removed prefix",
+			a:    []*route.Route{routeFor("a", "10.0.0.0/24"), routeFor("b", "10.0.1.0/24")},
+			b:    []*route.Route{routeFor("a", "10.0.0.0/24")},
+			want: true,
+		},
+		{
+			name: "replaced prefix",
+			a:    []*route.Route{routeFor("a", "10.0.0.0/24")},
+			b:    []*route.Route{routeFor("a", "10.0.1.0/24")},
+			want: true,
+		},
+		{
+			name: "same prefix, different order",
+			a:    []*route.Route{routeFor("a", "10.0.1.0/24"), routeFor("b", "10.0.0.0/24")},
+			b:    []*route.Route{routeFor("b", "10.0.0.0/24"), routeFor("a", "10.0.1.0/24")},
+			want: false,
+		},
+		{
+			name: "all routes gone",
+			a:    []*route.Route{routeFor("a", "10.0.0.0/24")},
+			b:    nil,
+			want: true,
+		},
+		{
+			name: "both empty",
+			a:    nil,
+			b:    nil,
+			want: false,
+		},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			assert.Equal(t, tc.want, hasRouteDiff(tc.a, tc.b),
+				"route diff for %s", tc.name)
+		})
+	}
+}