refine DHCP value acquisition

dhcpv4/client.go

@@ -26,19 +26,41 @@ type Client struct {
 	tIPLease   uint32
 	currentXID uint32
 	state      ClientState
-	offer      [4]byte
+	offer      addr4
-	svip       [4]byte // OptServerIdentification.
+	svip       addr4 // OptServerIdentification.
-	siip       [4]byte // SIAddr.
+	siip       addr4 // SIAddr.
-	reqIP      [4]byte
+	reqIP      addr4
-	router     [4]byte
+	router     addr4
-	subnet     [4]byte
+	subnet     addr4
-	broadcast  [4]byte
+	broadcast  addr4
-	gateway    [4]byte
+	gateway    addr4
 	clientMAC  [6]byte
 
 	auxbuf [64]byte
 }
 
+type addr4 struct {
+	addr  [4]byte
+	valid bool
+}
+
+func (a *addr4) unpack() ([4]byte, bool) {
+	return a.addr, a.valid
+}
+
+func (a *addr4) setmaybe(data []byte) {
+	if len(data) == 4 {
+		a.set4([4]byte(data[:]))
+	} else {
+		a.valid = false
+	}
+}
+
+func (a *addr4) set4(addr [4]byte) {
+	a.valid = true
+	a.addr = addr
+}
+
 type RequestConfig struct {
 	RequestedAddr      [4]byte
 	ClientHardwareAddr [6]byte
@@ -59,7 +81,7 @@ func (c *Client) BeginRequest(xid uint32, cfg RequestConfig) error {
 	c.state = StateInit
 	c.currentXID = xid
 	c.reqHostname = cfg.Hostname
-	c.reqIP = cfg.RequestedAddr
+	c.reqIP = addr4{addr: cfg.RequestedAddr, valid: true}
 	c.clientMAC = cfg.ClientHardwareAddr
 	return nil
 }
@@ -91,7 +113,7 @@ func (c *Client) setIP(b []byte, frameOffset int) {
 func (c *Client) Encapsulate(carrierFrame []byte, frameOffset int) (int, error) {
 	if c.isClosed() {
 		return 0, net.ErrClosed
-	} else if c.state == StateSelecting && c.offer == [4]byte{} {
+	} else if c.state == StateSelecting && !c.offer.valid {
 		return 0, nil // No offer received yet.
 	} else if c.state == StateBound {
 		return 0, nil // Done!
@@ -123,22 +145,22 @@ func (c *Client) Encapsulate(carrierFrame []byte, frameOffset int) (int, error)
 		}
 		n, _ = EncodeOption16(opts[numOpts:], OptMaximumMessageSize, uint16(maxlen))
 		numOpts += n
-		if c.reqIP != [4]byte{} {
+		if !c.reqIP.valid {
-			n, _ = EncodeOption(opts[numOpts:], OptRequestedIPaddress, c.reqIP[:]...)
+			n, _ = EncodeOption(opts[numOpts:], OptRequestedIPaddress, c.reqIP.addr[:]...)
 			numOpts += n
 		}
 		nextState = StateSelecting
 
 	case StateSelecting:
-		if c.offer == ([4]byte{}) {
+		if !c.offer.valid {
 			return 0, nil // Offer not yet received.
 		}
 		// Send out request, we know we've received an offer by now.
 		n, _ := EncodeOption(opts[numOpts:], OptMessageType, byte(MsgRequest))
 		numOpts += n
-		n, _ = EncodeOption(opts[numOpts:], OptRequestedIPaddress, c.offer[:]...)
+		n, _ = EncodeOption(opts[numOpts:], OptRequestedIPaddress, c.offer.addr[:]...)
 		numOpts += n
-		n, _ = EncodeOption(opts[numOpts:], OptServerIdentification, c.svip[:]...)
+		n, _ = EncodeOption(opts[numOpts:], OptServerIdentification, c.svip.addr[:]...)
 		numOpts += n
 		nextState = StateRequesting
 
@@ -193,11 +215,11 @@ func (c *Client) Demux(carrierData []byte, frameOffset int) error {
 
 	switch c.state {
 	case StateSelecting:
-		if msgType == MsgOffer && c.offer == [4]byte{} {
+		if msgType == MsgOffer && !c.offer.valid {
 			// Lock in on this offer.
-			c.gateway = *frm.GIAddr()
+			c.gateway.set4(*frm.GIAddr())
-			c.offer = *frm.YIAddr()
+			c.offer.set4(*frm.YIAddr())
-			c.siip = *frm.SIAddr()
+			c.siip.set4(*frm.SIAddr())
 		}
 
 	case StateRequesting:
@@ -237,13 +259,13 @@ func (c *Client) setOptions(frm Frame) error {
 		case OptRebindingTimeValue:
 			c.tRebind = maybeU32(data)
 		case OptServerIdentification:
-			c.svip = maybe4byte(data)
+			c.svip.setmaybe(data)
 		case OptRouter:
-			c.router = maybe4byte(data)
+			c.router.setmaybe(data)
 		case OptBroadcastAddress:
-			c.broadcast = maybe4byte(data)
+			c.broadcast.setmaybe(data)
 		case OptSubnetMask:
-			c.subnet = maybe4byte(data)
+			c.subnet.setmaybe(data)
 
 		case OptHostName:
 			if len(data) < maxHostSize {
@@ -271,7 +293,7 @@ func (c *Client) setHeader(frm Frame) {
 	frm.SetHardware(1, 6, 0)
 	frm.SetSecs(1)
 	if c.state.HasIP() {
-		*frm.CIAddr() = c.offer
+		*frm.CIAddr() = c.offer.addr
 	}
 	if c.state == StateInit {
 		siaddr := frm.SIAddr()[:]
@@ -279,13 +301,13 @@ func (c *Client) setHeader(frm Frame) {
 			siaddr[i] = 255
 		}
 	} else {
-		if c.siip == [4]byte{} {
+		if !c.siip.valid {
-			*frm.SIAddr() = c.svip
+			*frm.SIAddr() = c.svip.addr
 		} else {
-			*frm.SIAddr() = c.siip
+			*frm.SIAddr() = c.siip.addr
 		}
 	}
-	*frm.YIAddr() = c.offer
+	*frm.YIAddr() = c.offer.addr
 	copy(frm.CHAddrAs6()[:], c.clientMAC[:])
 	frm.SetMagicCookie(MagicCookie)
 }
@@ -302,11 +324,12 @@ func (c *Client) reset(xid uint32) {
 
 func (d *Client) State() ClientState { return d.state }
 
-func (d *Client) BroadcastAddr() [4]byte                         { return d.broadcast }
+func (d *Client) BroadcastAddr() ([4]byte, bool)                 { return d.broadcast.unpack() }
-func (d *Client) AssignedAddr() [4]byte                          { return d.offer }
+func (d *Client) AssignedAddr() ([4]byte, bool)                  { return d.offer.unpack() }
-func (d *Client) ServerAddr() [4]byte                            { return d.svip }
+func (d *Client) ServerAddr() ([4]byte, bool)                    { return d.svip.unpack() }
-func (d *Client) RouterAddr() [4]byte                            { return d.router }
+func (d *Client) RouterAddr() ([4]byte, bool)                    { return d.router.unpack() }
-func (d *Client) GatewayAddr() [4]byte                           { return d.gateway }
+func (d *Client) GatewayAddr() ([4]byte, bool)                   { return d.gateway.unpack() }
+func (d *Client) Subnet() ([4]byte, bool)                        { return d.subnet.unpack() }
 func (d *Client) RebindingSeconds() uint32                       { return d.tRebind }
 func (d *Client) RenewalSeconds() uint32                         { return d.tRenew }
 func (d *Client) IPLeaseSeconds() uint32                         { return d.tIPLease }
@@ -318,11 +341,12 @@ func (d *Client) DNSServerFirst() netip.Addr {
 	}
 	return d.dns[0]
 }
+
 func (d *Client) CIDRBits() uint8 {
-	if d.subnet == [4]byte{} {
+	if !d.subnet.valid {
 		return 0
 	}
-	v := binary.BigEndian.Uint32(d.subnet[:])
+	v := binary.BigEndian.Uint32(d.subnet.addr[:])
 	return 32 - uint8(bits.TrailingZeros32(v))
 }
 

examples/bridge/main.go

@@ -121,18 +121,29 @@ func run() (err error) {
 			dhcpIsDone := stack.dhcp.State() == dhcpv4.StateBound
 			if dhcpIsDone {
 				state = stateInitARP
-				err = stack.ip.SetAddr(netip.AddrFrom4(stack.dhcp.AssignedAddr()))
+				assigned4, ok := stack.dhcp.AssignedAddr()
+				if !ok {
+					return errors.New("DHCP client address not assigned")
+				}
+				err = stack.ip.SetAddr(netip.AddrFrom4(assigned4))
 				if err != nil {
 					return err
 				}
-				err = stack.StartResolveHardwareAddress6(netip.AddrFrom4(stack.dhcp.RouterAddr()))
+				routeraddr, ok := stack.dhcp.RouterAddr()
+				if !ok {
+					return errors.New("DHCP router address not assigned")
+				}
+				err = stack.StartResolveHardwareAddress6(netip.AddrFrom4(routeraddr))
 				if err != nil {
 					return err
 				}
 			}
 
 		case stateInitARP:
-			router := stack.dhcp.RouterAddr()
+			router, ok := stack.dhcp.RouterAddr()
+			if !ok {
+				return errors.New("DHCP router address not assigned")
+			}
 			hw, err := stack.ResultResolveHardwareAddress6(netip.AddrFrom4(router))
 			if err == nil {
 				stack.link.SetGateway6(hw)