output skb like tcpdump

main.go

@@ -3,7 +3,6 @@ package main
 import (
 	"context"
 	"encoding/json"
-	"fmt"
 	"log"
 	"os"
 	"os/signal"
@@ -107,13 +106,13 @@ func main() {
 			err = errors.WithStack(err)
 			return
 		}
+		skbPrint(skb, linktype)
 		captureInfo := gopacket.CaptureInfo{
 			Timestamp:      bootTime.Add(time.Duration(skb.Meta.TimeNs)),
 			CaptureLength:  len(skb.Data),
 			Length:         len(skb.Data),
 			InterfaceIndex: int(skb.Meta.Ifindex),
 		}
-		fmt.Printf("%+v\n", captureInfo)
 		if _, err = skbw.Write(append(jb, '\n')); err != nil {
 			err = errors.WithStack(err)
 			return

skbprint.go

@@ -0,0 +1,146 @@
+package main
+
+import (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+	"net"
+	"strings"
+
+	"github.com/google/gopacket"
+	"github.com/google/gopacket/layers"
+	"github.com/jschwinger233/skbdump/internal/bpf"
+)
+
+var strfuncs map[string]func([]byte) string
+
+func init() {
+	strfuncs = map[string]func([]byte) string{
+		"Ethernet": stringifyEthernet,
+		"ARP":      stringifyARP,
+		"IPv4":     stringifyIPv4,
+		"IPv6":     stringifyIPv6,
+		"TCP":      stringifyTCP,
+		"Payload":  stringifyPayload,
+	}
+}
+
+func skbPrint(skb bpf.Skb, linktype layers.LinkType) {
+	direction := " egress"
+	if skb.Meta.IsIngress {
+		direction = "ingress"
+	}
+	firstLayer := layers.LayerTypeEthernet
+	if linktype == layers.LinkTypeRaw {
+		switch skb.Meta.Protocol {
+		case 0x0800:
+			firstLayer = layers.LayerTypeIPv4
+		case 0x86DD:
+			firstLayer = layers.LayerTypeIPv6
+		case 0x0806:
+			firstLayer = layers.LayerTypeARP
+		}
+	}
+	fmt.Printf("%s@%d ", direction, skb.Meta.Ifindex)
+	packet := gopacket.NewPacket(skb.Data, firstLayer, gopacket.NoCopy)
+
+	layerNum := len(packet.Layers())
+	for idx, layer := range packet.Layers() {
+
+		layerType := layer.LayerType().String()
+		strfunc, ok := strfuncs[layerType]
+		if ok {
+			fmt.Printf("%s: %s", layerType, strfunc(layer.LayerContents()))
+		} else {
+			fmt.Printf("%s", layerType)
+		}
+
+		if idx+1 < layerNum {
+			fmt.Printf(" | ")
+		} else {
+			fmt.Printf("\n")
+		}
+	}
+}
+
+func stringifyEthernet(data []byte) string {
+	return fmt.Sprintf("%x:%x:%x:%x:%x:%x > %x:%x:%x:%x:%x:%x",
+		data[6], data[7], data[8], data[9], data[10], data[11],
+		data[0], data[1], data[2], data[3], data[4], data[5],
+	)
+}
+
+func stringifyIPv4(data []byte) string {
+	src := net.IPv4(data[12], data[13], data[14], data[15])
+	dest := net.IPv4(data[16], data[17], data[18], data[19])
+	return fmt.Sprintf("%s > %s", src.String(), dest.String())
+}
+
+func stringifyARP(data []byte) string {
+	if !bytes.Equal(data[:2], []byte{0x0, 0x1}) {
+		// hardware type != ethernet
+		return ""
+	}
+	if !bytes.Equal(data[2:4], []byte{0x8, 0x0}) {
+		// proto type != ipv4
+		return ""
+	}
+	var senderMac, targetMac [6]byte
+	copy(senderMac[:], data[8:14])
+	senderIP := net.IPv4(data[14], data[15], data[16], data[17]).String()
+	copy(targetMac[:], data[18:24])
+	targetIP := net.IPv4(data[24], data[25], data[26], data[27]).String()
+
+	switch data[7] {
+	case 1:
+		return fmt.Sprintf("who-has %s tell %s", targetIP, senderIP)
+	case 2:
+		return fmt.Sprintf("%s is-at %x:%x:%x:%x:%x:%x", senderIP, senderMac[0], senderMac[1], senderMac[2], senderMac[3], senderMac[4], senderMac[5])
+	default:
+		return ""
+	}
+	return ""
+}
+
+func stringifyIPv6(data []byte) string {
+	src := net.IP{data[8], data[9], data[10], data[11], data[12], data[13], data[14], data[15], data[16], data[17], data[18], data[19], data[20], data[21], data[22], data[23]}
+	dest := net.IP{data[24], data[25], data[26], data[27], data[28], data[29], data[30], data[31], data[32], data[33], data[34], data[35], data[36], data[37], data[38], data[39]}
+	return fmt.Sprintf("%s > %s", src.To16().String(), dest.To16().String())
+}
+
+func stringifyUDP(data []byte) string {
+	sport := binary.BigEndian.Uint16(data[:2])
+	dport := binary.BigEndian.Uint16(data[2:4])
+	return fmt.Sprintf("%d > %d", sport, dport)
+}
+
+func stringifyTCP(data []byte) string {
+	sport := binary.BigEndian.Uint16(data[:2])
+	dport := binary.BigEndian.Uint16(data[2:4])
+	flags := []string{}
+	if data[13]&0b00100000 != 0 {
+		flags = append(flags, "U")
+	}
+	if data[13]&0b00010000 != 0 {
+		flags = append(flags, ".")
+	}
+	if data[13]&0b00001000 != 0 {
+		flags = append(flags, "P")
+	}
+	if data[13]&0b00000100 != 0 {
+		flags = append(flags, "R")
+	}
+	if data[13]&0b00000010 != 0 {
+		flags = append(flags, "S")
+	}
+	if data[13]&0b00000001 != 0 {
+		flags = append(flags, "F")
+	}
+	seq := binary.BigEndian.Uint32(data[4:8])
+	ack := binary.BigEndian.Uint32(data[8:12])
+	return fmt.Sprintf("%d > %d [%s] S %d . %d", sport, dport, strings.Join(flags, ""), seq%10000, ack%10000)
+}
+
+func stringifyPayload(data []byte) string {
+	return fmt.Sprintf("%d bytes", len(data))
+}