Quotas: carry what was used when a rule counts differently

model.QuotaCarry says what becomes of a quota's use when its rule
changes how it counts; the firewall's apply follows it, comparing with
the rules in force: per address to a total starts at the addresses' sum,
wider groups add up their addresses, and what can't be carried (a total
to per address, per source to per destination, finer groups) starts
again, with the engine warning quota_restarts on that change. Before,
per source to per destination kept the sources' use as destinations',
and regrouping left old entries behind.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/nft/nft_test.go

@@ -197,6 +197,21 @@ func TestQuotasInContainer(t *testing.T) {
 	if t2, d2 := used(); t2 > total-1000 || t2 < total-2000 || d2 != 0 {
 		t.Errorf("after giving back: total %d (was %d, gave 1000), per destination %d (was %d, reset)", t2, total, d2, dev)
 	}
+	// Counted in total now: what the addresses used carries over.
+	ping("127.0.0.3")
+	_, dev = used()
+	st.Rules[1].Quota.PerDestination = false
+	if err := fw.Apply(ctx, st); err != nil {
+		t.Fatal(err)
+	}
+	tb, _ := fw.Table(ctx)
+	if tb.Quotas["quota_r2"] < dev || dev == 0 {
+		t.Errorf("per destination to a total: %d, was %d", tb.Quotas["quota_r2"], dev)
+	}
+	st.Rules[1].Quota.PerDestination = true
+	if err := fw.Apply(ctx, st); err != nil {
+		t.Fatal(err)
+	}
 	// Reset by hand.
 	if err := fw.ResetQuota(ctx, 1, false); err != nil {
 		t.Fatal(err)
@@ -211,7 +226,7 @@ func TestQuotasInContainer(t *testing.T) {
 	// saved usage comes back.
 	ping("127.0.0.2")
 	ping("127.0.0.3")
-	tb, _ := fw.Table(ctx)
+	tb, _ = fw.Table(ctx)
 	saved := tb.QuotaUsage
 	exec.Command("docker", "exec", name, "nft", "delete", "table", "inet", "housecarl").Run()
 	fw.RestoreQuotas(&saved)
@@ -240,6 +255,45 @@ func TestQuotaAdjust(t *testing.T) {
 	}
 }
 
+// TestQuotaCarry: usage follows a rule counting its quota differently.
+func TestQuotaCarry(t *testing.T) {
+	perSource := &model.Rule{ID: 2, Quota: &model.Quota{Bytes: 1 << 30, PerSource: true}}
+	usage := func() QuotaUsage {
+		return QuotaUsage{Quotas: map[string]int64{}, QuotaSets: map[string][]render.Element{
+			"quota_r2_v4": {{Addr: "10.0.0.1", Used: 100}, {Addr: "10.0.0.2", Used: 50}},
+			"quota_r2_v6": {{Addr: "2001:db8:0:1::", Used: 7}, {Addr: "2001:db8:0:2::", Used: 3}}}}
+	}
+	was := map[int64]*model.Rule{2: perSource}
+	with := func(f func(r *model.Rule)) *model.State {
+		r := *perSource
+		q := *perSource.Quota
+		r.Quota = &q
+		f(&r)
+		return &model.State{Rules: []*model.Rule{&r}}
+	}
+	u := usage()
+	u.carry(was, with(func(r *model.Rule) { r.Quota.PerSource = false }))
+	if u.Quotas["quota_r2"] != 160 || len(u.QuotaSets["quota_r2_v4"]) != 0 {
+		t.Errorf("to a total: %+v", u)
+	}
+	u = usage()
+	u.carry(was, with(func(r *model.Rule) { r.GroupV4, r.GroupV6 = 24, 48 }))
+	want := map[string][]render.Element{"quota_r2_v4": {{Addr: "10.0.0.0", Used: 150}}, "quota_r2_v6": {{Addr: "2001:db8::", Used: 10}}}
+	if !reflect.DeepEqual(u.QuotaSets, want) {
+		t.Errorf("wider groups: %+v", u.QuotaSets)
+	}
+	u = usage()
+	u.carry(was, with(func(r *model.Rule) { r.Quota.PerSource, r.Quota.PerDestination = false, true }))
+	if len(u.QuotaSets) != 0 {
+		t.Errorf("per destination now: %+v", u.QuotaSets)
+	}
+	u = usage()
+	u.carry(nil, with(func(r *model.Rule) { r.Quota.PerSource = false }))
+	if len(u.QuotaSets["quota_r2_v4"]) != 2 || u.Quotas["quota_r2"] != 0 {
+		t.Errorf("nothing to compare with (the first apply): %+v", u)
+	}
+}
+
 // TestDeviceCountsInContainer: the per-device counters are read back and
 // survive a reload.
 func TestDeviceCountsInContainer(t *testing.T) {