switch to encoding DHCP options instead of appending

dhcpv4/dhcp_test.go

@@ -78,3 +78,65 @@ func TestClientServer(t *testing.T) {
 	}
 	assertClState(StateBound)
 }
+
+func TestExample(t *testing.T) {
+	const (
+		xid        = 1
+		offerLease = 9001
+	)
+	var cl Client
+	clientHwaddr := [6]byte{0, 0, 0, 0, 0, 1}
+	clientReqAddr := [4]byte{192, 168, 1, 2}
+	clientHostname := "client"
+	serverIP := [4]byte{192, 168, 1, 1}
+	subnetMask := [4]byte{255, 255, 255, 0}
+	routerAddr := [4]byte{192, 168, 1, 0}
+	dnsAddr := [4]byte{192, 168, 1, 255}
+	cl.BeginRequest(xid, RequestConfig{
+		RequestedAddr:      clientReqAddr,
+		ClientHardwareAddr: clientHwaddr,
+		Hostname:           clientHostname,
+	})
+	buf := make([]byte, 2048)
+	n, err := cl.Encapsulate(buf, 0)
+	if err != nil {
+		t.Fatal(err)
+	} else if n <= 0 {
+		t.Fatal("no data sent out by client after starting request")
+	}
+
+	dfrm, _ := NewFrame(buf)
+	dfrm.ClearHeader()
+	dfrm.SetOp(OpReply)
+	dfrm.SetHardware(1, 6, 0)
+	dfrm.SetFlags(0)
+	dfrm.SetXID(xid)
+	dfrm.SetSecs(1)
+	*dfrm.YIAddr() = clientReqAddr
+	copy(dfrm.CHAddr()[:], clientHwaddr[:])
+	dfrm.SetMagicCookie(MagicCookie)
+	ntot := 0
+	nopt, _ := EncodeOption(buf[optionsOffset+ntot:], OptMessageType, byte(MsgOffer))
+	ntot += nopt
+	nopt, _ = EncodeOption(buf[optionsOffset+ntot:], OptServerIdentification, serverIP[:]...)
+	ntot += nopt
+	nopt, _ = EncodeOption32(buf[optionsOffset+ntot:], OptServerIdentification, offerLease)
+	ntot += nopt
+	nopt, _ = EncodeOption(buf[optionsOffset+ntot:], OptSubnetMask, subnetMask[:]...)
+	ntot += nopt
+	nopt, _ = EncodeOption(buf[optionsOffset+ntot:], OptRouter, routerAddr[:]...)
+	ntot += nopt
+	nopt, _ = EncodeOption(buf[optionsOffset+ntot:], OptDNSServers, dnsAddr[:]...)
+	ntot += nopt
+	nopt, _ = EncodeOption(buf[optionsOffset+ntot:], OptEnd, dnsAddr[:]...)
+	ntot += nopt
+
+	err = cl.Demux(buf[:optionsOffset+ntot], 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	// frame := buf[:optionsOffset]
+	// frame = AppendOption(frame, OptMessageType, byte(MsgOffer))
+	// frame = AppendOption(frame, OptServerIdentification, serverIP[:]...)
+	// frame = AppendOption(frame, OptIPAddressLeaseTime, serverIP[:]...)
+}