adriano/go-dhcp
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feat: Working impl with offer / ack

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This commit is contained in:
Adrian Rumpold
2022-02-06 12:14:50 +01:00
parent ed6198f71a
commit 9f83d6f3f5
7 changed files with 1307 additions and 53 deletions
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213
main.go
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@@ -4,35 +4,13 @@ import (
"bytes"
"encoding/binary"
"net"
"time"
"unsafe"
"go.uber.org/zap"
)
type DhcpOp uint8
const (
BOOTREQUEST DhcpOp = iota + 1
BOOTREPLY
)
type DhcpMessage struct {
Op DhcpOp
Htype uint8
Hlen uint8
Hops uint8
Xid uint32
Secs uint16
Flags uint16
Ciaddr uint32
Yiaddr uint32
Siaddr uint32
Giaddr uint32
Chaddr [16]byte
Sname [64]byte
File [128]byte
Magic [4]byte
}
var leases []Lease = make([]Lease, 0)
func (dhcp DhcpMessage) Debug(s *zap.SugaredLogger) {
s.Debugf("op=%x, htype=%x, hlen=%x, hops=%x", dhcp.Op, dhcp.Htype, dhcp.Hlen, dhcp.Hops)
@@ -49,17 +27,21 @@ func (dhcp DhcpMessage) Debug(s *zap.SugaredLogger) {
s.Debugf("magic=%x", dhcp.Magic)
}
func parseOptions(data []byte) {
func parseOptions(data []byte) Options {
s := zap.S()
i := 0
for i < len(data) {
code := data[i]
if code == 255 {
s.Debug("Found END option at offset ", i)
break
}
if code == 0 {
options := make(Options)
out:
for i < len(data) {
code := OptionCode(data[i])
switch code {
case OptionEnd:
s.Debug("Found END option at offset ", i)
break out
case OptionPad:
s.Debug("Found padding option at offset ", i)
i += 1
continue
@@ -69,8 +51,12 @@ func parseOptions(data []byte) {
payload := data[i+2 : i+2+size]
s.Debugf("code=%d, size=%d, payload=%x", code, size, payload)
options[code] = Option{Code: code, Data: data[i+1 : i+2+size]}
i += size + 2
}
s.Debugf("Parsed options: ", options)
return options
}
func prepareOffer(request DhcpMessage) DhcpMessage {
@@ -98,6 +84,133 @@ func prepareOffer(request DhcpMessage) DhcpMessage {
return dhcp
}
func prepareAck(request DhcpMessage) DhcpMessage {
var sname [64]byte
var file [128]byte
copy(sname[:], "go-dhcp-server")
dhcp := DhcpMessage{
Op: BOOTREPLY,
Htype: 1, // Ethernet
Hlen: 6, // Ethernet address length
Hops: 0,
Secs: 0,
Flags: 0,
Xid: request.Xid,
Siaddr: binary.BigEndian.Uint32(net.IPv4(10, 0, 0, 1).To4()),
Ciaddr: request.Ciaddr,
Yiaddr: binary.BigEndian.Uint32(net.IPv4(10, 0, 0, 2).To4()),
Giaddr: request.Giaddr,
Chaddr: request.Chaddr,
Magic: [4]byte{0x63, 0x82, 0x53, 0x63},
Sname: sname,
File: file,
}
return dhcp
}
// sendMessage transmits a DHCP message with options via a UDP connection
// The end option (code 255) is automatically appended and does not need to
// be passed explicitly.
func sendMessage(conn *net.UDPConn, message DhcpMessage, options []Option) error {
buf := make([]byte, 0)
w := bytes.NewBuffer(buf)
err := binary.Write(w, binary.BigEndian, message)
if err != nil {
return err
}
for _, v := range options {
err = w.WriteByte(byte(v.Code))
if err != nil {
return err
}
_, err = w.Write(v.Data)
if err != nil {
return err
}
}
// Automatically add END option, so the caller doesn't
// need to specificy it for every invocation.
err = w.WriteByte(byte(OptionEnd))
if err != nil {
return err
}
msg := w.Bytes()
zap.S().Debug("Msg", msg)
_, err = conn.Write(msg)
if err != nil {
return err
}
return nil
}
func handleOffer(dhcp DhcpMessage, remote *net.UDPAddr) error {
s := zap.S()
offer := prepareOffer(dhcp)
localAddr, _ := net.ResolveUDPAddr("udp", "172.17.0.1:68")
clientAddr, _ := net.ResolveUDPAddr("udp", "255.255.255.255:68")
conn, err := net.DialUDP("udp", localAddr, clientAddr)
if err != nil {
panic(err)
}
defer conn.Close()
s.Info("Sending DHCPOFFER...")
options := []Option{
{
Code: OptionDHCPMessageType,
Data: []byte{1, byte(MessageTypeOffer)},
},
}
sendMessage(conn, offer, options)
return nil
}
func handleAck(dhcp DhcpMessage, remote *net.UDPAddr) error {
s := zap.S()
ack := prepareAck(dhcp)
options := []Option{
{
Code: OptionDHCPMessageType,
Data: []byte{1, byte(MessageTypeAck)},
},
{
Code: OptionIPAddressLeaseTime,
Data: append([]byte{4}, u32tob(3600)...),
},
}
s.Debug("Options: ", options)
localAddr, _ := net.ResolveUDPAddr("udp", "172.17.0.1:68")
clientAddr, _ := net.ResolveUDPAddr("udp", "255.255.255.255:68")
conn, err := net.DialUDP("udp", localAddr, clientAddr)
if err != nil {
panic(err)
}
defer conn.Close()
s.Info("Sending DHCPACK")
sendMessage(conn, ack, options)
lease := Lease{
TransactionId: ack.Xid,
TTL: time.Now().Add(1 * time.Hour),
State: Requested,
ClientAddr: ack.Chaddr,
Address: int2ip(ack.Yiaddr),
}
leases = append(leases, lease)
return nil
}
func handleMsg(data []byte, remote *net.UDPAddr) {
s := zap.S()
@@ -116,26 +229,17 @@ func handleMsg(data []byte, remote *net.UDPAddr) {
optData := data[optDataOffset:]
s.Debug("Raw options data:", optData)
parseOptions(optData)
options := parseOptions(optData)
dhcpMsgType := options[OptionDHCPMessageType]
s.Info("DHCP message type ", dhcpMsgType)
offer := prepareOffer(dhcp)
localAddr, _ := net.ResolveUDPAddr("udp", "172.17.0.1:68")
clientAddr, _ := net.ResolveUDPAddr("udp", "255.255.255.255:68")
conn, err := net.DialUDP("udp", localAddr, clientAddr)
if err != nil {
panic(err)
switch MessageType(dhcpMsgType.Data[1]) {
case MessageTypeDiscover:
go handleOffer(dhcp, remote)
case MessageTypeRequest:
go handleAck(dhcp, remote)
}
defer conn.Close()
s.Info("Sending DHCPOFFER...")
buf := make([]byte, 0)
w := bytes.NewBuffer(buf)
binary.Write(w, binary.BigEndian, offer)
w.Write([]byte{53, 1, 2})
w.WriteByte(255)
msg := w.Bytes()
s.Debug("Msg", msg)
conn.Write(msg)
}
func main() {
@@ -155,12 +259,17 @@ func main() {
for {
buf := make([]byte, 1024)
rlen, remote, err := conn.ReadFromUDP(buf[:])
rlen, remote, err := conn.ReadFrom(buf[:])
if err != nil {
panic(err)
}
// Do stuff with the read bytes
handleMsg(buf[0:rlen], remote)
remoteAddr, ok := remote.(*net.UDPAddr)
if !ok {
zap.S().Warn("Not a valid remote IP address: ", remote)
continue
}
go handleMsg(buf[0:rlen], remoteAddr)
}
}