internal/dhcp4d: handle DHCPDECLINE and fix bug regarding MacBook declining leases (#48)

Fixes #40

Signed-off-by: Matt Layher <mdlayher@gmail.com>

internal/dhcp4d/dhcp4d.go

@@ -353,6 +353,35 @@ func (h *Handler) serveDHCP(p dhcp4.Packet, msgType dhcp4.MessageType, options d
 			reqIP,
 			h.leasePeriodForDevice(hwAddr),
 			h.options.SelectOrderOrAll(options[dhcp4.OptionParameterRequestList]))
+	case dhcp4.Decline:
+		if h.expireLease(hwAddr) {
+			log.Printf("Expired leases for %v upon DHCPDECLINE", hwAddr)
+		}
+		// Decline does not expect an ACK response.
+		return nil
 	}
 	return nil
 }
+
+// expireLease expires the lease for hwAddr and reports whether or not the
+// lease was actually expired by this call.
+func (h *Handler) expireLease(hwAddr string) bool {
+	h.leasesMu.Lock()
+	defer h.leasesMu.Unlock()
+
+	// TODO: deduplicate with h.leaseHW which also acquires h.leasesMu.
+
+	num, ok := h.leasesHW[hwAddr]
+	if !ok {
+		return false
+	}
+	l, ok := h.leasesIP[num]
+	if !ok {
+		return false
+	}
+	if l.HardwareAddr != hwAddr {
+		return false
+	}
+	l.Expiry = time.Now()
+	return true
+}

internal/dhcp4d/dhcp4d_test.go

@@ -50,6 +50,10 @@ func discover(addr net.IP, hwaddr net.HardwareAddr, opts ...dhcp4.Option) dhcp4.
 	return packet(dhcp4.Discover, addr, hwaddr, opts)
 }
 
+func decline(addr net.IP, hwaddr net.HardwareAddr, opts ...dhcp4.Option) dhcp4.Packet {
+	return packet(dhcp4.Decline, addr, hwaddr, opts)
+}
+
 const goldenInterfaces = `
 {
   "interfaces":[
@@ -500,3 +504,56 @@ func TestMinimumLeaseTime(t *testing.T) {
 		}
 	}
 }
+
+func TestClientDecline(t *testing.T) {
+	handler, cleanup := testHandler(t)
+	defer cleanup()
+
+	now := time.Now()
+	handler.timeNow = func() time.Time { return now }
+
+	addr := net.IP{192, 168, 42, 23}
+
+	hardwareAddr := net.HardwareAddr{0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff}
+
+	// macbook requests a new lease
+	t.Run("mbp grabs an address", func(t *testing.T) {
+		p := request(addr, hardwareAddr)
+		resp := handler.serveDHCP(p, dhcp4.Request, p.ParseOptions())
+		if got, want := messageType(resp), dhcp4.ACK; got != want {
+			t.Errorf("DHCPREQUEST resulted in unexpected message type: got %v, want %v", got, want)
+		}
+	})
+
+	// macbook lease expires
+	now = now.Add(3 * time.Hour)
+
+	t.Run("mbp requests previous address", func(t *testing.T) {
+		p := request(addr, hardwareAddr)
+		resp := handler.serveDHCP(p, dhcp4.Discover, p.ParseOptions())
+		if got, want := resp.YIAddr().To4(), addr.To4(); !got.Equal(want) {
+			t.Errorf("DHCPOFFER for wrong IP: got %v, want %v", got, want)
+		}
+		p = request(addr, hardwareAddr)
+		resp = handler.serveDHCP(p, dhcp4.Request, p.ParseOptions())
+		if got, want := messageType(resp), dhcp4.ACK; got != want {
+			t.Errorf("DHCPREQUEST resulted in unexpected message type: got %v, want %v", got, want)
+		}
+	})
+
+	t.Run("mbp declines address", func(t *testing.T) {
+		p := decline(addr, hardwareAddr)
+		resp := handler.serveDHCP(p, dhcp4.Decline, p.ParseOptions())
+		if resp != nil {
+			t.Fatalf("DHCPDECLINE was unexpectedly answered: %v", messageType(resp))
+		}
+	})
+
+	t.Run("mbp requests any address", func(t *testing.T) {
+		p := request(net.IPv4zero, hardwareAddr)
+		resp := handler.serveDHCP(p, dhcp4.Discover, p.ParseOptions())
+		if got, want := resp.YIAddr().To4(), addr.To4(); got.Equal(want) {
+			t.Errorf("DHCPOFFER returned unexpected address: %v", got)
+		}
+	})
+}