add FieldClassOperation to pcap and associated formatting changes

examples/xnet/main.go

@@ -115,7 +115,7 @@ func run() (err error) {
 		var cap pcap.PacketBreakdown
 		var frames []pcap.Frame
 		pf := pcap.Formatter{
-			FilterClasses: []pcap.FieldClass{pcap.FieldClassFlags, pcap.FieldClassDst, pcap.FieldClassSrc, pcap.FieldClassAddress},
+			FilterClasses: []pcap.FieldClass{pcap.FieldClassFlags, pcap.FieldClassOperation, pcap.FieldClassDst, pcap.FieldClassSrc, pcap.FieldClassAddress},
 		}
 		var pfbuf []byte
 		logFrames := func(context string, pkt []byte) error {
@@ -163,12 +163,11 @@ func run() (err error) {
 				log.Fatal("groutine read:", err)
 			} else if nread > 0 {
 				err = stack.Demux(buf[:nread], 0)
-				if err != nil {
-					if !errors.Is(err, lneto.ErrPacketDrop) {
-						err = logFrames("IN", buf[:nread])
-						if err != nil {
-							log.Println("ERR:INLOG", err)
-						}
+				if !errors.Is(err, lneto.ErrPacketDrop) {
+					// Only skip logging packet in case of dropped packet.
+					err = logFrames("IN", buf[:nread])
+					if err != nil {
+						log.Println("ERR:INLOG", err)
 					}
 				}
 			}

internet/pcap/capture.go

@@ -670,6 +670,7 @@ const (
 	FieldClassAddress                     // address
 	// FieldClassBinaryText represents long stretches of binary data such as BOOTP DHCPv4 field.
 	FieldClassBinaryText // binary-text
+	FieldClassOperation  // op
 )
 
 const octet = 8
@@ -718,8 +719,7 @@ var baseARPFields = [...]FrameField{
 		BitLength:      1 * octet,
 	},
 	{
-		Name:           "Opcode",
-		Class:          FieldClassType,
+		Class:          FieldClassOperation,
 		FrameBitOffset: 6 * octet,
 		BitLength:      2 * octet,
 	},
@@ -924,8 +924,7 @@ var baseUDPFields = [...]FrameField{
 
 var baseDHCPv4Fields = [...]FrameField{
 	{
-		Name:           "Opcode",
-		Class:          FieldClassType,
+		Class:          FieldClassOperation,
 		FrameBitOffset: 0,
 		BitLength:      1 * octet,
 	},

internet/pcap/format.go

@@ -112,7 +112,7 @@ func (f *Formatter) formatField(dst []byte, pktStartOff int, field FrameField, p
 		dst = hex.AppendEncode(dst, f.buf)
 	case FieldClassText:
 		dst = strconv.AppendQuote(dst, string(f.buf))
-	case FieldClassDst, FieldClassSrc, FieldClassSize, FieldClassAddress:
+	case FieldClassDst, FieldClassSrc, FieldClassSize, FieldClassAddress, FieldClassOperation:
 		// IP, MAC addresses and ports.
 		if field.BitLength <= 16 {
 			v, err := fieldAsUint(pkt, fieldBitStart, field.BitLength, field.RightAligned)

internet/pcap/stringers.go

@@ -23,11 +23,12 @@ func _() {
 	_ = x[FieldClassText-12]
 	_ = x[FieldClassAddress-13]
 	_ = x[FieldClassBinaryText-14]
+	_ = x[FieldClassOperation-15]
 }
 
-const _FieldClass_name = "undefinedsourcedestinationprotocolversiontypesizeflagsidentificationchecksumoptionspayloadtextaddressbinary-text"
+const _FieldClass_name = "undefinedsourcedestinationprotocolversiontypesizeflagsidentificationchecksumoptionspayloadtextaddressbinary-textop"
 
-var _FieldClass_index = [...]uint8{0, 9, 15, 26, 34, 41, 45, 49, 54, 68, 76, 83, 90, 94, 101, 112}
+var _FieldClass_index = [...]uint8{0, 9, 15, 26, 34, 41, 45, 49, 54, 68, 76, 83, 90, 94, 101, 112, 114}
 
 func (i FieldClass) String() string {
 	if i >= FieldClass(len(_FieldClass_index)-1) {

stringers.go

@@ -195,11 +195,12 @@ func _() {
 	// Re-run the stringer command to generate them again.
 	var x [1]struct{}
 	_ = x[ErrPacketDrop-1]
+	_ = x[ErrBadCRC-2]
 }
 
-const _errGeneric_name = "packet dropped"
+const _errGeneric_name = "packet droppedincorrect checksum"
 
-var _errGeneric_index = [...]uint8{0, 14}
+var _errGeneric_index = [...]uint8{0, 14, 32}
 
 func (i errGeneric) String() string {
 	i -= 1

x/xnet/xnet_test.go

@@ -2,7 +2,6 @@ package xnet
 
 import (
 	"bytes"
-	"encoding/binary"
 	"errors"
 	"math/rand"
 	"net/netip"
@@ -602,8 +601,5 @@ func (tst *tester) getFieldByClassLen(proto any, class pcap.FieldClass, octetLen
 
 func (tst *tester) getARPOperation() arp.Operation {
 	tst.t.Helper()
-	// ARP has 3 FieldClassType fields: Hardware type (0), Protocol type (1), Opcode (2)
-	// All are 2 bytes, so we need occurrence=2 to get Opcode.
-	data := tst.getFieldByClassLen(ethernet.TypeARP, pcap.FieldClassType, 2, 2)
-	return arp.Operation(binary.BigEndian.Uint16(data))
+	return arp.Operation(tst.getInt(ethernet.TypeARP, pcap.FieldClassOperation))
 }