use lneto.ErrDropPacket where appropiate; clean up examples/xnet output

internet/definitions.go

@@ -6,6 +6,8 @@ import (
 	"math"
 	"net"
 	"slices"
+
+	"github.com/soypat/lneto"
 )
 
 // StackNode is an abstraction of a packet exchanging protocol controller. This is the building block for all protocols,
@@ -148,19 +150,20 @@ func (h *handlers) nodeByPortProto(port uint16, protocol uint16) *node {
 func (h *handlers) demuxByProto(buf []byte, offset int, proto uint16) (*node, error) {
 	node := h.nodeByProto(proto)
 	if node == nil {
-		return nil, nil
+		return nil, lneto.ErrPacketDrop
 	}
 	err := node.demux(buf, offset)
 	if h.tryHandleError(node, err) {
 		err = nil
 	}
+
 	return node, err
 }
 
 func (h *handlers) demuxByPort(buf []byte, offset int, port uint16) (*node, error) {
 	node := h.nodeByPort(port)
 	if node == nil {
-		return nil, nil
+		return nil, lneto.ErrPacketDrop
 	}
 	err := node.demux(buf, offset)
 	if h.tryHandleError(node, err) {

internet/pcap/format.go

@@ -9,6 +9,7 @@ import (
 	"strings"
 
 	"github.com/soypat/lneto"
+	"github.com/soypat/lneto/ethernet"
 	"github.com/soypat/lneto/tcp"
 )
 
@@ -122,15 +123,7 @@ func (f *Formatter) formatField(dst []byte, pktStartOff int, field FrameField, p
 		} else if field.BitLength == 4*8 {
 			dst = netip.AddrFrom4([4]byte(f.buf)).AppendTo(dst)
 		} else if field.BitLength == 6*8 {
-			for i := range f.buf {
-				if i != 0 {
-					dst = append(dst, ':')
-				}
-				if f.buf[i] < 16 {
-					dst = append(dst, '0')
-				}
-				dst = strconv.AppendUint(dst, uint64(f.buf[i]), 16)
-			}
+			dst = ethernet.AppendAddr(dst, [6]byte(f.buf))
 		} else if field.BitLength == 16*8 {
 			dst = netip.AddrFrom16([16]byte(f.buf)).AppendTo(dst)
 		} else {

internet/stack-ip.go

@@ -80,19 +80,21 @@ func (sb *StackIP) Demux(carrierData []byte, offset int) error {
 	}
 	dst := ifrm.DestinationAddr()
 	if sb.ip != ([4]byte{}) && *dst != sb.ip {
-		return errors.New("not meant for us") // Not meant for us.
+		sb.handlers.debug("ip:not-for-us")
+		return lneto.ErrPacketDrop // Not meant for us.
 	}
 
 	sb.validator.ResetErr()
 	ifrm.ValidateExceptCRC(&sb.validator)
 	if err = sb.validator.ErrPop(); err != nil {
+		sb.handlers.error("ip:Demux.validate")
 		return err
 	}
 	gotCRC := ifrm.CRC()
 	wantCRC := ifrm.CalculateHeaderCRC()
 	if gotCRC != wantCRC {
 		sb.handlers.error("StackIP:Demux:crc-mismatch", slog.Uint64("want", uint64(wantCRC)), slog.Uint64("got", uint64(gotCRC)))
-		return errors.New("IPv4 CRC mismatch")
+		return lneto.ErrBadCRC
 	}
 	off := ifrm.HeaderLength()
 	totalLen := ifrm.TotalLength()
@@ -104,8 +106,8 @@ func (sb *StackIP) Demux(carrierData []byte, offset int) error {
 	// nodeIdx := getNodeByProto(sb.handlers, uint16(proto))
 	if node == nil {
 		// Drop packet.
-		sb.handlers.info("iprecv:drop", slog.String("dstaddr", netip.AddrFrom4(*ifrm.DestinationAddr()).String()), slog.String("proto", ifrm.Protocol().String()))
-		return nil
+		sb.handlers.info("ip:demux.drop", slog.String("dstaddr", netip.AddrFrom4(*ifrm.DestinationAddr()).String()), slog.String("proto", ifrm.Protocol().String()))
+		return lneto.ErrPacketDrop
 	}
 	// Incoming CRC Validation of common IP Protocols.
 	var crc lneto.CRC791
@@ -118,7 +120,8 @@ func (sb *StackIP) Demux(carrierData []byte, offset int) error {
 		}
 		tfrm.CRCWrite(&crc)
 		if crc.Sum16() != tfrm.CRC() {
-			return errors.New("TCP CRC mismatch")
+			sb.handlers.error("ip:demux.tcpcrc")
+			return lneto.ErrBadCRC
 		}
 	case lneto.IPProtoUDP:
 		ifrm.CRCWriteUDPPseudo(&crc)
@@ -128,7 +131,8 @@ func (sb *StackIP) Demux(carrierData []byte, offset int) error {
 		}
 		ufrm.CRCWriteIPv4(&crc)
 		if crc.Sum16() != ufrm.CRC() {
-			return errors.New("UDP CRC mismatch")
+			sb.handlers.error("ip:demux.udpcrc")
+			return lneto.ErrBadCRC
 		}
 	}
 	sb.handlers.info("ipDemux", slog.String("ipproto", proto.String()), slog.Int("plen", int(totalLen)))

internet/stack-udpport.go

@@ -43,13 +43,13 @@ func (sudp *StackUDPPort) Demux(carrierData []byte, frameOffset int) error {
 	}
 	dst := ufrm.DestinationPort()
 	if dst != sudp.h.port {
-		return nil // Not meant for us.
+		return lneto.ErrPacketDrop // Not meant for us.
 	}
 	// TODO remote ip address handling.
 
 	src := ufrm.SourcePort()
 	if sudp.rmport != 0 && src != sudp.rmport {
-		return nil // Not from our target remote port.
+		return lneto.ErrPacketDrop // Not from our target remote port.
 	}
 	err = sudp.h.demux(carrierData, frameOffset+8)
 	if err != nil {