fix httptap incorrectly capturing GRO frames

ethernet/frame.go

@@ -44,7 +44,7 @@ func (efrm Frame) Payload() []byte {
 	hl := efrm.HeaderLength()
 	et := efrm.EtherTypeOrSize()
 	if et.IsSize() {
-		return efrm.buf[hl:et]
+		return efrm.buf[hl : hl+int(et)]
 	}
 	return efrm.buf[hl:]
 }

examples/tap/main.go

@@ -5,17 +5,16 @@ import (
 	"flag"
 	"fmt"
 	"log"
+	"math"
 	"net"
 	"net/http"
 	"net/netip"
 	"strings"
 	"time"
 
-	"github.com/soypat/lneto"
 	"github.com/soypat/lneto/internal"
 	"github.com/soypat/lneto/internal/ltesto"
 	"github.com/soypat/lneto/internet/pcap"
-	"github.com/soypat/lneto/tcp"
 )
 
 func main() {
@@ -30,9 +29,14 @@ func main() {
 func run() error {
 	var (
 		flagInterface = "tap0"
+		flagMinMTU    = math.MaxUint16
 	)
 	flag.StringVar(&flagInterface, "i", flagInterface, "Interface to select. tap* creates a tap interface. Any other name will create a bridge to the name of the interface i.e: 'enp7s0', 'wlp8s0', 'lo'")
+	flag.IntVar(&flagMinMTU, "mtu", flagMinMTU, "Set the interface minimum MTU to use for buffer.")
 	flag.Parse()
+	if flagMinMTU < 1500 {
+		return errors.New("minimum MTU too small")
+	}
 	var (
 		flagNet             = "192.168.10.1/24"
 		flagiface           = "tap0"
@@ -57,7 +61,7 @@ func run() error {
 		iface = br
 	}
 
-	sv, err := ltesto.NewHTTPTapServer(iface, flagPacketQueueSize, flagPacketQueueSize)
+	sv, err := ltesto.NewHTTPTapServer(iface, flagMinMTU, flagPacketQueueSize, flagPacketQueueSize)
 	if err != nil {
 		return err
 	}
@@ -91,31 +95,3 @@ func run() error {
 	http.ListenAndServe(":7070", sv)
 	return errors.New("finished")
 }
-
-func getTCPData(frames []pcap.Frame, pkt []byte) (flags tcp.Flags, src, dst uint16) {
-	for i := range frames {
-		proto := frames[i].Protocol
-		if proto == lneto.IPProtoTCP {
-			return tcp.Flags(getFrameClassUint(frames[i], pkt, pcap.FieldClassFlags)),
-				uint16(getFrameClassUint(frames[i], pkt, pcap.FieldClassSrc)),
-				uint16(getFrameClassUint(frames[i], pkt, pcap.FieldClassDst))
-		} else if proto == lneto.IPProtoUDP {
-			return 0,
-				uint16(getFrameClassUint(frames[i], pkt, pcap.FieldClassSrc)),
-				uint16(getFrameClassUint(frames[i], pkt, pcap.FieldClassDst))
-		}
-	}
-	return 0, 0, 0
-}
-
-func getFrameClassUint(frame pcap.Frame, pkt []byte, class pcap.FieldClass) uint64 {
-	iflags, err := frame.FieldByClass(class)
-	if err != nil {
-		return 0
-	}
-	v, err := frame.FieldAsUint(iflags, pkt)
-	if err != nil {
-		return 0
-	}
-	return v
-}

examples/xnet/main.go

@@ -1,11 +1,13 @@
 package main
 
 import (
+	"encoding/hex"
 	"errors"
 	"flag"
 	"fmt"
 	"log"
 	"log/slog"
+	"math"
 	"net"
 	"net/netip"
 	"os"
@@ -107,7 +109,7 @@ func run() (err error) {
 	// Loop goroutine.
 	go func() {
 		lastAction := time.Now()
-		buf := make([]byte, mtu)
+		buf := make([]byte, math.MaxUint16) // Generic-receive Offload (GRO) can aggregate packets.
 		var cap pcap.PacketBreakdown
 		var frames []pcap.Frame
 		pf := pcap.Formatter{
@@ -120,9 +122,11 @@ func run() (err error) {
 			}
 			frames, err = cap.CaptureEthernet(frames[:0], pkt, 0)
 			if err != nil {
+				pkt := hex.EncodeToString(pkt)
+				slog.Error(err.Error(), slog.Any("pkt", pkt))
 				return err
 			}
-			pfbuf = append(pfbuf[:0], context...)
+			pfbuf = fmt.Appendf(pfbuf[:0], "%-3s %3d", context, len(pkt))
 			pfbuf = append(pfbuf, ' ', '[')
 			pfbuf, err = pf.FormatFrames(pfbuf, frames, pkt)
 			pfbuf = append(pfbuf, ']', '\n')
@@ -133,7 +137,6 @@ func run() (err error) {
 			return err
 		}
 		for {
-			clear(buf)
 			nwrite, err := stack.Encapsulate(buf[:], -1, 0)
 			if err != nil {
 				log.Println("ERR:ENCAPSULATE", err)
@@ -150,7 +153,7 @@ func run() (err error) {
 				}
 			}
 
-			clear(buf)
+			clear(buf[:nwrite])
 			nread, err := iface.Read(buf)
 			if err != nil {
 				log.Fatal("groutine read:", err)
@@ -165,7 +168,7 @@ func run() (err error) {
 					}
 				}
 			}
-
+			clear(buf[:nread])
 			if nread == 0 && nwrite == 0 && time.Since(lastAction) > 4*time.Second {
 				time.Sleep(5 * time.Millisecond)
 			} else {

internal/ltesto/httptap.go

@@ -183,16 +183,15 @@ func (sv *HTTPTapServer) OnTransfer(cb func(channel int, pkt []byte)) {
 	sv.onTx = cb
 }
 
-func NewHTTPTapServer(iface Interface, queueOut, queueIn int) (*HTTPTapServer, error) {
+func NewHTTPTapServer(iface Interface, minMTU, queueOut, queueIn int) (*HTTPTapServer, error) {
 	if iface == nil {
 		return nil, errors.New("nil interface argument to HTTP interface server")
 	}
 	mtu, err := iface.MTU()
 	if err != nil {
 		return nil, err
-	} else if mtu < minMTU {
-		return nil, errors.New("too small MTU")
 	}
+	bufferSize := max(mtu, minMTU)
 	netmask, err := iface.IPMask()
 	if err != nil {
 		return nil, err
@@ -202,7 +201,7 @@ func NewHTTPTapServer(iface Interface, queueOut, queueIn int) (*HTTPTapServer, e
 	taps := &HTTPTapServer{
 		router: sv,
 		tap:    iface,
-		buf:    make([]byte, mtu),
+		buf:    make([]byte, bufferSize),
 	}
 	sv.HandleFunc("/send", func(w http.ResponseWriter, r *http.Request) {
 		retries := 10