Starting DHCP packets.

dhcp/BUILD.bazel

@@ -0,0 +1,15 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "dhcp",
+    srcs = [
+        "options.go",
+        "packet.go",
+    ],
+    importpath = "git.wntrmute.dev/kyle/kdhcp/dhcp",
+    visibility = ["//visibility:public"],
+    deps = [
+        "//log",
+        "@com_github_davecgh_go_spew//spew",
+    ],
+)

dhcp/options.go

@@ -0,0 +1,46 @@
+package dhcp
+
+import (
+	"errors"
+	"io"
+)
+
+type OptionTag uint8
+
+type Option func(req *BootRequest, r io.Reader) error
+
+const (
+	OptionTagPadding              OptionTag = 0
+	OptionTagHostName                       = 12
+	OptionTagMessageType                    = 53
+	OptionTagParameterRequestList           = 55
+	OptionTagEnd                            = 255
+)
+
+var optionRegistry = map[OptionTag]Option{
+	OptionTagPadding:              OptionTag,
+	OptionTagHostName:             OptionHostName,
+	OptionTagMessageType:          OptionMessageType,
+	OptionTagParameterRequestList: OptionParameterRequestList,
+	OptionTagEnd:                  OptionEnd,
+}
+
+func OptionPad(req *BootRequest, r io.Reader) error {
+	return nil
+}
+
+func OptionHostName(req *BootRequest, r io.Reader) error {
+	return errors.New("dhcp: option not implemented yet")
+}
+
+func OptionMessageType(req *BootRequest, r io.Reader) error {
+	return errors.New("dhcp: option not implemented yet")
+}
+
+func OptionParameterRequestList(req *BootRequest, r io.Reader) error {
+	return errors.New("dhcp: option not implemented yet")
+}
+
+func OptionEnd(req *BootRequest, r io.Reader) error {
+	return errors.New("dhcp: option not implemented yet")
+}

dhcp/packet.go

@@ -0,0 +1,143 @@
+package dhcp
+
+import (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+	"net"
+	"strings"
+
+	"git.wntrmute.dev/kyle/kdhcp/log"
+	"github.com/davecgh/go-spew/spew"
+)
+
+const (
+	maxHardwareAddrLen = 16
+	maxServerName      = 64
+	maxFileName        = 128
+)
+
+var anyAddr = net.IP([]byte{0, 0, 0, 0})
+
+func formatMAC(mac []byte) string {
+	s := []string{}
+	for i := 0; i < len(mac); i++ {
+		s = append(s, fmt.Sprintf("%0x", mac[i:i+1]))
+	}
+
+	return strings.Join(s, ":")
+}
+
+type BootRequest struct {
+	MessageType     uint8
+	HardwareType    uint8
+	HardwareAddress []byte
+	Hops            uint8
+	TransactionID   uint32
+	SecondsElapsed  uint16
+	Flags           uint16
+	ServerName      string
+	FileName        string
+
+	ClientIP net.IP
+	YourIP   net.IP
+	NextIP   net.IP
+	RelayIP  net.IP
+
+	DHCPType          uint8  // option 53
+	HostName          string // option 12
+	ParameterRequests []string
+}
+
+func (req *BootRequest) Read(packet []byte) error {
+	buf := bytes.NewBuffer(packet)
+	read := func(v any) error {
+		return binary.Read(buf, binary.BigEndian, v)
+	}
+
+	if err := read(&req.MessageType); err != nil {
+		return err
+	}
+
+	if err := read(&req.HardwareType); err != nil {
+		return err
+	}
+
+	var hwaLength uint8
+	if err := read(&hwaLength); err != nil {
+		return err
+	}
+
+	if err := read(&req.Hops); err != nil {
+		return err
+	}
+
+	if err := read(&req.TransactionID); err != nil {
+		return err
+	}
+
+	if err := read(&req.SecondsElapsed); err != nil {
+		return err
+	}
+
+	if err := read(&req.Flags); err != nil {
+		return err
+	}
+
+	req.ClientIP = anyAddr[:]
+	if _, err := buf.Read(req.ClientIP); err != nil {
+		return err
+	}
+
+	req.YourIP = anyAddr[:]
+	if _, err := buf.Read(req.YourIP); err != nil {
+		return err
+	}
+
+	req.NextIP = anyAddr[:]
+	if _, err := buf.Read(req.NextIP); err != nil {
+		return err
+	}
+
+	req.RelayIP = anyAddr[:]
+	if _, err := buf.Read(req.RelayIP); err != nil {
+		return err
+	}
+
+	req.HardwareAddress = make([]byte, int(hwaLength))
+	if _, err := buf.Read(req.HardwareAddress); err != nil {
+		return err
+	}
+
+	hwaPad := make([]byte, maxHardwareAddrLen-hwaLength)
+	if _, err := buf.Read(hwaPad); err != nil {
+		return err
+	}
+	log.Debugf("padding: %x", hwaPad)
+
+	tempBuf := make([]byte, maxServerName)
+	if _, err := buf.Read(tempBuf); err != nil {
+		return err
+	}
+	req.ServerName = string(bytes.Trim(tempBuf, "\x00"))
+
+	tempBuf = make([]byte, maxFileName)
+	if _, err := buf.Read(tempBuf); err != nil {
+		return err
+	}
+	req.FileName = string(bytes.Trim(tempBuf, "\x00"))
+
+	spew.Dump(*req)
+	return nil
+}
+
+func ReadRequest(pkt []byte) (*BootRequest, error) {
+	req := &BootRequest{}
+	err := req.Read(pkt)
+	if err != nil {
+		return nil, err
+	}
+
+	log.Debugf("dhcp: BOOTP request with txid %d for %s", req.TransactionID, formatMAC(req.HardwareAddress))
+	return req, nil
+}