add some more form to DoDHCP

cmd/cyrw/main.go

@@ -5,6 +5,7 @@ import (
 	"encoding/hex"
 	"errors"
 	"time"
+	"unsafe"
 
 	"github.com/soypat/cyw43439/cyrw"
 	"github.com/soypat/cyw43439/internal/slog"
@@ -94,6 +95,7 @@ func DoDHCP(s *tcpctl.Stack, dev *cyrw.Device) error {
 	var ehdr eth.EthernetHeader
 	var ihdr eth.IPv4Header
 	var uhdr eth.UDPHeader
+	var dhdr DHCPHeader
 
 	copy(ehdr.Destination[:], eth.BroadcastHW())
 	copy(ehdr.Source[:], dev.MAC())
@@ -112,9 +114,18 @@ func DoDHCP(s *tcpctl.Stack, dev *cyrw.Device) error {
 	ehdr.Put(txbuf[:])
 	ihdr.Put(txbuf[eth.SizeEthernetHeader:])
 	uhdr.Put(txbuf[eth.SizeEthernetHeader+4*ihdr.IHL():])
-	dhcppayload := txbuf[eth.SizeEthernetHeader+4*ihdr.IHL()+eth.SizeUDPHeader:]
 
-	dev.SendEth(txbuf[:])
+	dhcppayload := txbuf[eth.SizeEthernetHeader+4*ihdr.IHL()+eth.SizeUDPHeader:]
+	dhdr.OP = 1
+	dhdr.HType = 1
+	dhdr.HLen = 6
+	dhdr.Xid = 0x12345678
+	// What do with addrs?
+
+	// Send DHCP Discover.
+	dhdr.Put(dhcppayload[:])
+	totalSize := eth.SizeEthernetHeader + 4*ihdr.IHL() + eth.SizeUDPHeader + 44
+	dev.SendEth(txbuf[:totalSize])
 	for retry := 0; retry < 20 && state == none; retry++ {
 		time.Sleep(50 * time.Millisecond)
 		// We should see received packets received on callback passed into OpenUDP.
@@ -125,26 +136,28 @@ func DoDHCP(s *tcpctl.Stack, dev *cyrw.Device) error {
 	return nil
 }
 
-// DHCPHeader specifies the first 44 bytes of a DHCP packet payload
-// not including BOOTP, magic cookie and options.
+// DHCPHeader specifies the first 34 bytes of a DHCP packet payload. It does
+// not include BOOTP, magic cookie and options.
 type DHCPHeader struct {
-	OP     byte        // 0:1
-	HType  byte        // 1:2
-	HLen   byte        // 2:3
-	HOps   byte        // 3:4
-	Xid    uint32      // 4:8
-	Secs   uint16      // 8:10
-	Flags  uint16      // 10:12
-	CIAddr [4]byte     // 12:16
-	YIAddr [4]byte     // 16:20
-	SIAddr [4]byte     // 20:24
-	GIAddr [4]byte     // 24:28
-	CHAddr [4 * 4]byte // 28:44
+	OP     byte    // 0:1
+	HType  byte    // 1:2
+	HLen   byte    // 2:3
+	HOps   byte    // 3:4
+	Xid    uint32  // 4:8
+	Secs   uint16  // 8:10
+	Flags  uint16  // 10:12
+	CIAddr [4]byte // 12:16
+	YIAddr [4]byte // 16:20
+	SIAddr [4]byte // 20:24
+	GIAddr [4]byte // 24:28
+	CHAddr [6]byte // 28:34
 	// BOOTP, Magic Cookie, and DHCP Options not included.
 }
 
+const a = unsafe.Sizeof(DHCPHeader{})
+
 func (d *DHCPHeader) Put(dst []byte) {
-	_ = dst[43]
+	_ = dst[33]
 	dst[0] = d.OP
 	dst[1] = d.HType
 	dst[2] = d.HLen
@@ -156,11 +169,11 @@ func (d *DHCPHeader) Put(dst []byte) {
 	copy(dst[16:20], d.YIAddr[:])
 	copy(dst[20:24], d.SIAddr[:])
 	copy(dst[24:28], d.GIAddr[:])
-	copy(dst[28:44], d.CHAddr[:])
+	copy(dst[28:34], d.CHAddr[:])
 }
 
 func DecodeDHCPHeader(src []byte) (d DHCPHeader) {
-	_ = src[43]
+	_ = src[33]
 	d.OP = src[0]
 	d.HType = src[1]
 	d.HLen = src[2]
@@ -172,6 +185,6 @@ func DecodeDHCPHeader(src []byte) (d DHCPHeader) {
 	copy(d.YIAddr[:], src[16:20])
 	copy(d.SIAddr[:], src[20:24])
 	copy(d.GIAddr[:], src[24:28])
-	copy(d.CHAddr[:], src[28:44])
+	copy(d.CHAddr[:], src[28:34])
 	return d
 }