dhcp4d: implement permanent leases (no expiration)

cmd/dhcp4d/dhcp4d.go

@@ -27,7 +27,7 @@ func loadLeases(h *dhcp4d.Handler, fn string) error {
 		return err
 	}
 	var leases []*dhcp4d.Lease
-	if err := json.Unmarshal(b, leases); err != nil {
+	if err := json.Unmarshal(b, &leases); err != nil {
 		return err
 	}
 	h.SetLeases(leases)

internal/dhcp4d/dhcp4d.go

@@ -21,6 +21,10 @@ type Lease struct {
 	Expiry       time.Time `json:"expiry"`
 }
 
+func (l *Lease) Expired(at time.Time) bool {
+	return !l.Expiry.IsZero() && at.After(l.Expiry)
+}
+
 type Handler struct {
 	serverIP    net.IP
 	start       net.IP // first IP address to hand out
@@ -80,11 +84,11 @@ func (h *Handler) findLease() int {
 	if len(h.leasesIP) < h.leaseRange {
 		// TODO: hash the hwaddr like dnsmasq
 		i := rand.Intn(h.leaseRange)
-		if l, ok := h.leasesIP[i]; !ok || now.After(l.Expiry) {
+		if l, ok := h.leasesIP[i]; !ok || l.Expired(now) {
 			return i
 		}
 		for i := 0; i < h.leaseRange; i++ {
-			if l, ok := h.leasesIP[i]; !ok || now.After(l.Expiry) {
+			if l, ok := h.leasesIP[i]; !ok || l.Expired(now) {
 				return i
 			}
 		}
@@ -111,7 +115,7 @@ func (h *Handler) canLease(reqIP net.IP, hwaddr string) int {
 		return leaseNum // lease already owned by requestor
 	}
 
-	if h.timeNow().After(l.Expiry) {
+	if l.Expired(h.timeNow()) {
 		return leaseNum // lease expired
 	}
 
@@ -174,8 +178,14 @@ func (h *Handler) ServeDHCP(p dhcp4.Packet, msgType dhcp4.MessageType, options d
 			Hostname:     string(options[dhcp4.OptionHostName]),
 		}
 
-		// Release any old leases for this client
 		if l, ok := h.leasesHW[lease.HardwareAddr]; ok {
+			if l.Expiry.IsZero() {
+				// Retain permanent lease properties
+				lease.Expiry = time.Time{}
+				lease.Hostname = l.Hostname
+			}
+
+			// Release any old leases for this client
 			delete(h.leasesIP, l.Num)
 		}
 

internal/dhcp4d/dhcp4d_test.go

@@ -224,6 +224,43 @@ func TestPreviousLease(t *testing.T) {
 	}
 }
 
+func TestPermanentLease(t *testing.T) {
+	handler, cleanup := testHandler(t)
+	defer cleanup()
+	now := time.Now()
+	handler.timeNow = func() time.Time { return now }
+
+	var (
+		addr         = net.IP{192, 168, 42, 23}
+		hardwareAddr = net.HardwareAddr{0x11, 0x22, 0x33, 0x44, 0x55, 0x66}
+	)
+
+	handler.SetLeases([]*Lease{
+		{
+			Num:          2,
+			Addr:         addr,
+			HardwareAddr: hardwareAddr.String(),
+		},
+	})
+
+	p := request(addr, hardwareAddr)
+	resp := handler.ServeDHCP(p, dhcp4.Request, p.ParseOptions())
+	if got, want := resp.YIAddr().To4(), addr.To4(); !bytes.Equal(got, want) {
+		t.Errorf("DHCPREQUEST resulted in wrong IP: got %v, want %v", got, want)
+	}
+
+	now = now.Add(3 * time.Hour)
+
+	hardwareAddr[len(hardwareAddr)-1] = 0x77
+
+	p = request(addr, hardwareAddr)
+	resp = handler.ServeDHCP(p, dhcp4.Request, p.ParseOptions())
+	opts := resp.ParseOptions()
+	if got, want := dhcp4.MessageType(opts[dhcp4.OptionDHCPMessageType][0]), dhcp4.NAK; got != want {
+		t.Errorf("DHCPREQUEST resulted in unexpected message type: got %v, want %v", got, want)
+	}
+}
+
 func TestExpiration(t *testing.T) {
 	handler, cleanup := testHandler(t)
 	defer cleanup()