restructure package, rename module/repo

2026-09-10 16:49:37 +00:00 · 2025-01-07 11:34:35 -03:00
parent 73f0b547b3
commit 9abf0c11b9
30 changed files with 20 additions and 18 deletions
@@ -0,0 +1,260 @@
+package dhcpv4
+
+import (
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"io"
+	"math"
+	"math/bits"
+)
+
+type Client struct {
+	reqHostname string
+	hostname    []byte
+	dns         [][4]byte
+
+	tRenew     uint32
+	tRebind    uint32
+	tIPLease   uint32
+	currentXID uint32
+	state      ClientState
+	offer      [4]byte
+	svip       [4]byte
+	reqIP      [4]byte
+	router     [4]byte
+	subnet     [4]byte
+	broadcast  [4]byte
+	gateway    [4]byte
+	clientMAC  [6]byte
+
+	auxbuf [64]byte
+}
+
+type RequestConfig struct {
+	RequestedAddr      [4]byte
+	ClientHardwareAddr [6]byte
+	// Optional hostname to request.
+	Hostname string
+}
+
+func (c *Client) BeginRequest(xid uint32, cfg RequestConfig) error {
+	if len(cfg.Hostname) > 36 {
+		return errors.New("requested hostname too long")
+	}
+	c.reset(xid)
+	c.currentXID = xid
+	c.reqHostname = cfg.Hostname
+	c.reqIP = cfg.RequestedAddr
+	c.clientMAC = cfg.ClientHardwareAddr
+	return nil
+}
+
+func (c *Client) Send(dst []byte) (int, error) {
+	if c.isClosed() {
+		return 0, io.EOF
+	} else if c.state == StateSelecting && c.offer == [4]byte{} {
+		return 0, nil // No offer received yet.
+	} else if c.state == StateBound {
+		return 0, nil // Done!
+	}
+	frm, err := NewFrame(dst)
+	if err != nil {
+		return 0, err
+	}
+
+	// var options []Option
+	// var nextState ClientState
+	optBuf := c.auxbuf[:0]
+	var nextState ClientState
+	switch c.state {
+	case StateInit:
+		// Send out discover.
+		optBuf = AppendOption(optBuf, OptMessageType, byte(MsgDiscover))
+		optBuf = AppendOption(optBuf, OptParameterRequestList, defaultParamReqList...)
+		optBuf = AppendOption(optBuf, OptClientIdentifier, c.clientMAC[:]...)
+		maxlen := len(dst)
+		if maxlen > math.MaxUint16 {
+			maxlen = math.MaxUint16
+		}
+		optBuf = AppendOption(optBuf, OptMaximumMessageSize, byte(maxlen>>8), byte(maxlen))
+		if c.reqIP != [4]byte{} {
+			optBuf = AppendOption(optBuf, OptRequestedIPaddress, c.reqIP[:]...)
+		}
+		nextState = StateSelecting
+
+	case StateSelecting:
+		// Send out request, we know we've received an offer by now.
+		optBuf = AppendOption(optBuf, OptMessageType, byte(MsgRequest))
+		optBuf = AppendOption(optBuf, OptRequestedIPaddress, c.offer[:]...)
+		optBuf = AppendOption(optBuf, OptServerIdentification, c.svip[:]...)
+		nextState = StateRequesting
+
+	default:
+		return 0, errors.New("unhandled state")
+	}
+	if len(c.reqHostname) > 0 {
+		optBuf = append(optBuf, byte(OptHostName), byte(len(c.hostname)))
+		optBuf = append(optBuf, c.hostname...)
+	}
+	optBuf = append(optBuf, 0xff) // End mark.
+	options := frm.OptionsPayload()
+	if len(optBuf) > len(options) {
+		return 0, errors.New("DHCPv4 short buffer for options")
+	}
+	c.setHeader(frm)
+	n := copy(options, optBuf)
+	c.state = nextState
+	return optionsOffset + n, nil
+}
+
+func (c *Client) Recv(pkt []byte) error {
+	if c.isClosed() {
+		return io.EOF
+	}
+	frm, err := NewFrame(pkt)
+	if err != nil {
+		return err
+	} else if frm.XID() != c.currentXID {
+		return errors.New("dhcpv4 unexpected transaction ID")
+	} else if frm.MagicCookie() != MagicCookie {
+		return errors.New("dhcpv4 bad magic cookie")
+	}
+	msgType := c.getMessageType(frm)
+	if msgType == MsgNack {
+		return errors.New("dhcp nack received")
+	}
+
+	msgOK := msgType == MsgOffer || msgType == MsgAck
+	if !msgOK {
+		return fmt.Errorf("invalid DHCP message received or none got=%d", msgType)
+	}
+	err = c.setOptions(frm)
+	if err != nil {
+		return err
+	}
+
+	switch c.state {
+	case StateSelecting:
+		if msgType == MsgOffer && c.offer == [4]byte{} {
+			// Lock in on this offer.
+			c.gateway = *frm.GIAddr()
+			c.offer = *frm.YIAddr()
+		}
+
+	case StateRequesting:
+		if msgType == MsgAck {
+			c.state = StateBound
+		}
+	default:
+		return fmt.Errorf("dcpv4 unexpected state in recv %s", c.state.String())
+	}
+	return nil
+}
+
+func (c *Client) getMessageType(frm Frame) MessageType {
+	c.auxbuf[0] = 255
+	ptrMsgType := &c.auxbuf[0]
+	frm.ForEachOption(func(opt OptNum, data []byte) error {
+		if len(data) == 1 {
+			*ptrMsgType = data[0]
+			return io.EOF
+		}
+		return nil
+	})
+	return MessageType(*ptrMsgType)
+}
+
+func (c *Client) setOptions(frm Frame) error {
+	return frm.ForEachOption(func(opt OptNum, data []byte) error {
+		switch opt {
+		case OptRenewTimeValue:
+			c.tRenew = maybeU32(data)
+		case OptIPAddressLeaseTime:
+			c.tIPLease = maybeU32(data)
+		case OptRebindingTimeValue:
+			c.tRebind = maybeU32(data)
+
+		case OptServerIdentification:
+			c.svip = maybe4byte(data)
+		case OptRouter:
+			c.router = maybe4byte(data)
+		case OptBroadcastAddress:
+			c.broadcast = maybe4byte(data)
+		case OptSubnetMask:
+			c.subnet = maybe4byte(data)
+
+		case OptHostName:
+			if len(data) < maxHostSize {
+				c.hostname = append(c.hostname[:0], data...)
+			}
+		case OptDNSServers:
+			if len(c.dns) > 0 || len(data)%4 != 0 {
+				return nil // No DNS parsing if already got in previous exchange.
+			}
+			for i := 0; i < len(data); i += 4 {
+				c.dns = append(c.dns, [4]byte(data[i:i+4]))
+			}
+		}
+		return nil
+	})
+}
+
+func (c *Client) isClosed() bool { return c.state == 0 || c.currentXID == 0 }
+
+func (c *Client) setHeader(frm Frame) {
+	frm.ClearHeader()
+	frm.SetOp(OpRequest)
+	frm.SetXID(c.currentXID)
+	frm.SetHardware(1, 6, 0)
+	frm.SetSecs(1)
+	// copy(frm.CIAddr()[:], c.offer[:])
+	copy(frm.SIAddr()[:], c.svip[:])
+	copy(frm.YIAddr()[:], c.offer[:])
+	copy(frm.CHAddrAs6()[:], c.clientMAC[:])
+	frm.SetMagicCookie(MagicCookie)
+}
+
+func (c *Client) reset(xid uint32) {
+	*c = Client{
+		reqHostname: c.reqHostname,
+		currentXID:  xid,
+		reqIP:       c.reqIP,
+		clientMAC:   c.clientMAC,
+	}
+}
+
+func (d *Client) State() ClientState { return d.state }
+
+func (d *Client) CIDRBits() uint8 {
+	if d.subnet == [4]byte{} {
+		return 0
+	}
+	v := binary.BigEndian.Uint32(d.subnet[:])
+	return 32 - uint8(bits.TrailingZeros32(v))
+}
+
+var defaultParamReqList = []byte{
+	byte(OptSubnetMask),
+	byte(OptTimeOffset),
+	byte(OptRouter),
+	byte(OptInterfaceMTUSize),
+	byte(OptBroadcastAddress),
+	byte(OptDNSServers),
+	byte(OptDomainName),
+	byte(OptNTPServersAddresses),
+}
+
+func maybeU32(b []byte) uint32 {
+	if len(b) < 4 {
+		return 0
+	}
+	return binary.BigEndian.Uint32(b)
+}
+
+func maybe4byte(b []byte) [4]byte {
+	if len(b) != 4 {
+		return [4]byte{}
+	}
+	return [4]byte(b)
+}