Merge pull request #13 from soypat/pcap-formatter

add pcap formatting

examples/tap/main.go

@@ -63,22 +63,24 @@ func run() error {
 	}
 	defer sv.Close()
 	var cap pcap.PacketBreakdown
+	pf := pcap.Formatter{
+		FilterClasses: []pcap.FieldClass{pcap.FieldClassDst, pcap.FieldClassSrc, pcap.FieldClassSize, pcap.FieldClassFlags},
+	}
+	var pfbuf []byte
 	sv.OnTransfer(func(channel int, pkt []byte) {
 		captime := time.Now()
 		frames, err := cap.CaptureEthernet(nil, pkt, 0)
 		if err == nil {
-			flags, src, dst := getTCPData(frames, pkt)
+			pfbuf = append(pfbuf[:0], '[')
-			if src != 0 {
+			pfbuf, err = pf.FormatFrames(pfbuf, frames, pkt)
-				if flags != 0 {
+			pfbuf = append(pfbuf, ']')
-					fmt.Println(channel, captime.Format("15:04:05.000"), frames, flags.String(), src, "->", dst)
+			if err != nil {
-				} else {
+				fmt.Printf("%d %s !err:%s\n", channel, captime.Format("15:04:05.000"), err)
-					fmt.Println(channel, captime.Format("15:04:05.000"), frames, src, "->", dst)
-				}
 			} else {
-				fmt.Println(channel, captime.Format("15:04:05.000"), frames)
+				fmt.Printf("%d %s %s\n", channel, captime.Format("15:04:05.000"), pfbuf)
 			}
 		} else {
-			fmt.Println(channel, captime.Format("15:04:05.000"), "ERR", frames, err.Error())
+			fmt.Println(channel, captime.Format("15:04:05.000"), "cap ERR", frames, err.Error())
 		}
 	})
 	hwaddr, err := sv.HardwareAddress6()

internet/pcap/capture.go

@@ -3,9 +3,14 @@ package pcap
 //go:generate stringer -type=FieldClass -linecomment -output stringers.go .
 import (
 	"encoding/binary"
+	"encoding/hex"
 	"errors"
 	"fmt"
 	"math"
+	"net/netip"
+	"slices"
+	"strconv"
+	"strings"
 
 	"github.com/soypat/lneto"
 	"github.com/soypat/lneto/arp"
@@ -530,17 +535,7 @@ func (frm Frame) FieldAsUint(fieldIdx int, pkt []byte) (uint64, error) {
 		return badUint64, errors.New("invalid field index")
 	}
 	field := frm.Fields[fieldIdx]
-	octets := (field.BitLength + 7) / 8
+	return fieldAsUint(pkt, frm.PacketBitOffset+field.FrameBitOffset, field.BitLength, field.RightAligned)
-	if octets > 8 {
-		return badUint64, errors.New("field too long to be represented by uint64")
-	}
-	var buf [8]byte
-	_, err := frm.AppendField(buf[8-octets:8-octets], fieldIdx, pkt)
-	if err != nil {
-		return badUint64, err
-	}
-	v := binary.BigEndian.Uint64(buf[:])
-	return v, nil
 }
 
 func (frm Frame) AppendField(dst []byte, fieldIdx int, pkt []byte) ([]byte, error) {
@@ -548,9 +543,27 @@ func (frm Frame) AppendField(dst []byte, fieldIdx int, pkt []byte) ([]byte, erro
 		return dst, errors.New("invalid field index")
 	}
 	field := frm.Fields[fieldIdx]
-	fieldBitStart := frm.PacketBitOffset + field.FrameBitOffset
+	return appendField(dst, pkt, frm.PacketBitOffset+field.FrameBitOffset, field.BitLength, field.RightAligned)
-	fieldBitEnd := fieldBitStart + field.BitLength
+}
-	octets := (field.BitLength + 7) / 8 // total octets needed to represent field.
+
+func fieldAsUint(pkt []byte, fieldBitStart, bitlen int, rightAligned bool) (uint64, error) {
+	const badUint64 = math.MaxUint64
+	octets := (bitlen + 7) / 8
+	if octets > 8 {
+		return badUint64, errors.New("field too long to be represented by uint64")
+	}
+	var buf [8]byte
+	_, err := appendField(buf[8-octets:8-octets], pkt, fieldBitStart, bitlen, rightAligned)
+	if err != nil {
+		return badUint64, err
+	}
+	v := binary.BigEndian.Uint64(buf[:])
+	return v, nil
+}
+
+func appendField(dst, pkt []byte, fieldBitStart, bitlen int, rightAligned bool) ([]byte, error) {
+	fieldBitEnd := fieldBitStart + bitlen
+	octets := (bitlen + 7) / 8 // total octets needed to represent field.
 	octetsStart := fieldBitStart / 8
 	if octets+octetsStart > len(pkt) {
 		return dst, errors.New("buffer overflow")
@@ -558,7 +571,7 @@ func (frm Frame) AppendField(dst []byte, fieldIdx int, pkt []byte) ([]byte, erro
 	firstBitOffset := fieldBitStart % 8
 	lastOctetExcessBits := fieldBitEnd % 8
 	if firstBitOffset == 0 {
-		if field.RightAligned {
+		if rightAligned {
 			return dst, errors.New("invalid right aligned set for fully aligned field")
 		}
 		// Optimized path: field starts at byte boundary.
@@ -570,17 +583,21 @@ func (frm Frame) AppendField(dst []byte, fieldIdx int, pkt []byte) ([]byte, erro
 	}
 
 	mask := byte(1<<firstBitOffset) - 1
-	if field.RightAligned {
+	if rightAligned {
 		if lastOctetExcessBits == 0 {
 			// Right aligned with no loose trailing bits. i.e: TCP flags.
 			dst = append(dst, pkt[octetsStart]&mask)
 			dst = append(dst, pkt[octetsStart+1:octetsStart+octets]...)
 			return dst, nil
 		}
-		// Right aligned with trailing bits. i.e: ???
+		// Right aligned with trailing bits. i.e: IPv6 Traffic Class.
-		for i := 1; i < octets; i++ {
+		// Field spans an extra byte, so need octets+1 bytes from packet.
-			b := pkt[octetsStart+i] >> (8 - lastOctetExcessBits)
+		if octets+octetsStart+1 > len(pkt) {
-			b |= pkt[octetsStart+i-1] & mask
+			return dst, errors.New("buffer overflow")
+		}
+		for i := 0; i < octets; i++ {
+			b := (pkt[octetsStart+i] & mask) << (8 - firstBitOffset)
+			b |= pkt[octetsStart+i+1] >> firstBitOffset
 			dst = append(dst, b)
 		}
 		return dst, nil
@@ -599,6 +616,129 @@ func (frm Frame) AppendField(dst []byte, fieldIdx int, pkt []byte) ([]byte, erro
 	return dst, nil
 }
 
+type Formatter struct {
+	FieldSep      string
+	FrameSep      string
+	FilterClasses []FieldClass
+	buf           []byte
+}
+
+func (f *Formatter) FormatFrames(dst []byte, frms []Frame, pkt []byte) (_ []byte, err error) {
+	sep := f.FrameSep
+	if sep == "" {
+		sep = " | "
+	}
+	for ifrm := range frms {
+		if ifrm != 0 {
+			dst = append(dst, sep...)
+		}
+		dst, err = f.FormatFrame(dst, frms[ifrm], pkt)
+		if err != nil {
+			return dst, err
+		}
+	}
+	return dst, nil
+}
+
+func (f *Formatter) FormatFrame(dst []byte, frm Frame, pkt []byte) (_ []byte, err error) {
+	sep := f.FieldSep
+	if sep == "" {
+		sep = "; " // default field separator
+	}
+	bitlen := frm.LenBits()
+	if bitlen%8 == 0 {
+		dst = fmt.Appendf(dst, "%s len=%d", frm.Protocol, bitlen/8)
+	} else {
+		dst = fmt.Appendf(dst, "%s bitlen=%d", frm.Protocol, bitlen)
+	}
+
+	for ifield := range frm.Fields {
+		field := frm.Fields[ifield]
+		if f.filterField(field) {
+			continue
+		}
+		dst = append(dst, sep...)
+		if field.Class == FieldClassFlags && frm.Protocol == lneto.IPProtoTCP {
+			dst = append(dst, "flags="...)
+			v, err := fieldAsUint(pkt, frm.PacketBitOffset+field.FrameBitOffset, field.BitLength, field.RightAligned)
+			if err != nil {
+				return dst, err
+			}
+			dst = tcp.Flags(v).AppendFormat(dst)
+			continue
+		}
+		dst, err = f.formatField(dst, frm.PacketBitOffset, field, pkt)
+		if err != nil {
+			return dst, err
+		}
+	}
+	return dst, nil
+}
+
+func (f *Formatter) filterField(field FrameField) bool {
+	return f.FilterClasses != nil && !slices.Contains(f.FilterClasses, field.Class)
+}
+
+func (f *Formatter) FormatField(dst []byte, pktStartOff int, field FrameField, pkt []byte) (_ []byte, err error) {
+	return f.formatField(dst, pktStartOff, field, pkt)
+}
+
+func (f *Formatter) formatField(dst []byte, pktStartOff int, field FrameField, pkt []byte) (_ []byte, err error) {
+	name := field.Name
+	if name == "" {
+		name = field.Class.String()
+	}
+	hasSpaces := strings.IndexByte(name, ' ') >= 0
+	if hasSpaces {
+		dst = append(dst, '(')
+	}
+	dst = append(dst, name...)
+	if hasSpaces {
+		dst = append(dst, ')')
+	}
+	dst = append(dst, '=')
+	f.buf, err = appendField(f.buf[:0], pkt, field.FrameBitOffset+pktStartOff, field.BitLength, field.RightAligned)
+	if err != nil {
+		return dst, err
+	}
+	fieldBitStart := pktStartOff + field.FrameBitOffset
+	switch field.Class {
+	default:
+		fallthrough
+	case FieldClassChecksum, FieldClassID, FieldClassFlags, FieldClassOptions, FieldClassAddress:
+		// Binary data to be printed as hexadecimal.
+		dst = append(dst, "0x"...)
+		dst = hex.AppendEncode(dst, f.buf)
+	case FieldClassDst, FieldClassSrc, FieldClassSize:
+		// IP, MAC addresses and ports.
+		if field.BitLength <= 16 {
+			v, err := fieldAsUint(pkt, fieldBitStart, field.BitLength, field.RightAligned)
+			if err != nil {
+				return dst, err
+			}
+			dst = strconv.AppendUint(dst, v, 10)
+		} 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)
+			}
+		} else if field.BitLength == 16*8 {
+			dst = netip.AddrFrom16([16]byte(f.buf)).AppendTo(dst)
+		} else {
+			dst = append(dst, "0x"...)
+			dst = hex.AppendEncode(dst, f.buf)
+		}
+	}
+	return dst, err
+}
+
 func (frm Frame) String() string {
 	return string(frm.AppendString(nil))
 }

internet/pcap/capture_test.go

@@ -1,6 +1,7 @@
 package pcap
 
 import (
+	"encoding/binary"
 	"math"
 	"math/rand"
 	"testing"
@@ -10,6 +11,7 @@ import (
 	"github.com/soypat/lneto/http/httpraw"
 	"github.com/soypat/lneto/internal/ltesto"
 	"github.com/soypat/lneto/ipv4"
+	"github.com/soypat/lneto/ipv6"
 	"github.com/soypat/lneto/tcp"
 )
 
@@ -121,3 +123,244 @@ func TestCap(t *testing.T) {
 		t.Errorf("want %q HTTP body, got %q", httpBody, gotBody)
 	}
 }
+
+// TestRightAlignedFields tests extraction of fields that span byte boundaries
+// with right-aligned output, such as IPv6 Traffic Class and Flow Label.
+func TestRightAlignedFields(t *testing.T) {
+	// Build a minimal IPv6 packet with known Traffic Class and Flow Label values.
+	// IPv6 header: 40 bytes minimum.
+	// Byte 0-3: Version (4 bits) + Traffic Class (8 bits) + Flow Label (20 bits)
+	const (
+		wantVersion      = 6
+		wantTrafficClass = 0xAB        // 8 bits at bit offset 4
+		wantFlowLabel    = 0x000C_DEF0 // 20 bits at bit offset 12 (we'll use 0xCDEF0 masked to 20 bits = 0xDEF0)
+	)
+	// Actually flow label is 20 bits, so max is 0xFFFFF. Use 0xDEF01 masked.
+	const wantFlow20 = 0xDEF01 & 0xFFFFF // 0xDEF01
+
+	var pkt [14 + 40 + 20]byte // Ethernet + IPv6 header + TCP header
+	// Set up Ethernet frame.
+	efrm, _ := ethernet.NewFrame(pkt[:])
+	efrm.SetEtherType(ethernet.TypeIPv6)
+
+	// Set up IPv6 header manually.
+	i6frm, _ := ipv6.NewFrame(efrm.Payload())
+	i6frm.SetVersionTrafficAndFlow(wantVersion, ipv6.ToS(wantTrafficClass), wantFlow20)
+	i6frm.SetPayloadLength(20) // TCP header size
+	i6frm.SetNextHeader(lneto.IPProtoTCP)
+	i6frm.SetHopLimit(64)
+
+	// Set up minimal TCP header.
+	tfrm, _ := tcp.NewFrame(i6frm.Payload())
+	tfrm.SetOffsetAndFlags(5, 0) // 5 words = 20 bytes, no flags
+
+	// Verify our setup is correct.
+	gotVer, gotToS, gotFlow := i6frm.VersionTrafficAndFlow()
+	if gotVer != wantVersion {
+		t.Fatalf("setup: version mismatch: got %d, want %d", gotVer, wantVersion)
+	}
+	if uint8(gotToS) != wantTrafficClass {
+		t.Fatalf("setup: traffic class mismatch: got 0x%02x, want 0x%02x", gotToS, wantTrafficClass)
+	}
+	if gotFlow != wantFlow20 {
+		t.Fatalf("setup: flow label mismatch: got 0x%05x, want 0x%05x", gotFlow, wantFlow20)
+	}
+
+	// Capture the packet.
+	var pbreak PacketBreakdown
+	frames, err := pbreak.CaptureEthernet(nil, pkt[:], 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(frames) < 2 {
+		t.Fatalf("expected at least 2 frames (Ethernet + IPv6), got %d", len(frames))
+	}
+
+	// Find IPv6 frame.
+	var ipv6Frame *Frame
+	for i := range frames {
+		if frames[i].Protocol == ethernet.TypeIPv6 {
+			ipv6Frame = &frames[i]
+			break
+		}
+	}
+	if ipv6Frame == nil {
+		t.Fatal("IPv6 frame not found")
+	}
+
+	// Helper to get field by name.
+	getByName := func(name string) (uint64, error) {
+		for i, f := range ipv6Frame.Fields {
+			if f.Name == name {
+				return ipv6Frame.FieldAsUint(i, pkt[:])
+			}
+		}
+		return 0, nil
+	}
+
+	// Test Traffic Class (Type of Service) - 8 bits at bit offset 4, right-aligned.
+	gotTrafficClass, err := getByName("Type of Service")
+	if err != nil {
+		t.Fatalf("failed to get Traffic Class: %v", err)
+	}
+	if uint8(gotTrafficClass) != wantTrafficClass {
+		t.Errorf("Traffic Class: got 0x%02x, want 0x%02x", gotTrafficClass, wantTrafficClass)
+	}
+
+	// Test Flow Label - 20 bits at bit offset 12, right-aligned.
+	gotFlowLabel, err := getByName("Flow Label")
+	if err != nil {
+		t.Fatalf("failed to get Flow Label: %v", err)
+	}
+	if uint32(gotFlowLabel) != wantFlow20 {
+		t.Errorf("Flow Label: got 0x%05x, want 0x%05x", gotFlowLabel, wantFlow20)
+	}
+
+	// Test Version - 4 bits at bit offset 0, not right-aligned.
+	gotVersion, err := getByName("")
+	if err != nil {
+		t.Fatalf("failed to get Version: %v", err)
+	}
+	if len(ipv6Frame.Fields) > 0 && ipv6Frame.Fields[0].Class == FieldClassVersion {
+		gotVersion, _ = ipv6Frame.FieldAsUint(0, pkt[:])
+	}
+	if uint8(gotVersion) != wantVersion {
+		t.Errorf("Version: got %d, want %d", gotVersion, wantVersion)
+	}
+}
+
+// TestAppendFieldRightAligned directly tests the appendField function
+// with right-aligned fields that have trailing bits.
+func TestAppendFieldRightAligned(t *testing.T) {
+	testCases := []struct {
+		name           string
+		pkt            []byte
+		fieldBitStart  int
+		bitlen         int
+		rightAligned   bool
+		wantData       []byte
+	}{
+		{
+			// IPv6 Traffic Class: bits 4-11 (8 bits spanning bytes 0-1)
+			name:          "IPv6 Traffic Class 0xAB",
+			pkt:           []byte{0x6A, 0xB0, 0x00, 0x00}, // Version=6, TC=0xAB, Flow=0
+			fieldBitStart: 4,
+			bitlen:        8,
+			rightAligned:  true,
+			wantData:      []byte{0xAB},
+		},
+		{
+			// IPv6 Traffic Class with different value
+			name:          "IPv6 Traffic Class 0xFF",
+			pkt:           []byte{0x6F, 0xF0, 0x00, 0x00}, // Version=6, TC=0xFF, Flow=0
+			fieldBitStart: 4,
+			bitlen:        8,
+			rightAligned:  true,
+			wantData:      []byte{0xFF},
+		},
+		{
+			// IPv6 Traffic Class at minimum
+			name:          "IPv6 Traffic Class 0x00",
+			pkt:           []byte{0x60, 0x00, 0x00, 0x00}, // Version=6, TC=0x00, Flow=0
+			fieldBitStart: 4,
+			bitlen:        8,
+			rightAligned:  true,
+			wantData:      []byte{0x00},
+		},
+		{
+			// IPv6 Flow Label: bits 12-31 (20 bits spanning bytes 1-3)
+			name:          "IPv6 Flow Label 0xDEF01",
+			pkt:           []byte{0x60, 0x0D, 0xEF, 0x01}, // Version=6, TC=0, Flow=0xDEF01
+			fieldBitStart: 12,
+			bitlen:        20,
+			rightAligned:  true,
+			wantData:      []byte{0x0D, 0xEF, 0x01}, // 20 bits right-aligned in 3 bytes
+		},
+		{
+			// Flow Label max value
+			name:          "IPv6 Flow Label 0xFFFFF",
+			pkt:           []byte{0x60, 0xFF, 0xFF, 0xFF}, // Version=6, TC=0, Flow=0xFFFFF
+			fieldBitStart: 12,
+			bitlen:        20,
+			rightAligned:  true,
+			wantData:      []byte{0x0F, 0xFF, 0xFF}, // 20 bits right-aligned in 3 bytes
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			got, err := appendField(nil, tc.pkt, tc.fieldBitStart, tc.bitlen, tc.rightAligned)
+			if err != nil {
+				t.Fatalf("appendField error: %v", err)
+			}
+			if len(got) != len(tc.wantData) {
+				t.Fatalf("length mismatch: got %d bytes, want %d bytes", len(got), len(tc.wantData))
+			}
+			for i := range got {
+				if got[i] != tc.wantData[i] {
+					t.Errorf("byte %d: got 0x%02x, want 0x%02x", i, got[i], tc.wantData[i])
+				}
+			}
+			// Also verify as uint64 for single/double byte cases.
+			if len(tc.wantData) <= 8 {
+				gotVal, err := fieldAsUint(tc.pkt, tc.fieldBitStart, tc.bitlen, tc.rightAligned)
+				if err != nil {
+					t.Fatalf("fieldAsUint error: %v", err)
+				}
+				var wantVal uint64
+				for _, b := range tc.wantData {
+					wantVal = wantVal<<8 | uint64(b)
+				}
+				if gotVal != wantVal {
+					t.Errorf("as uint: got 0x%x, want 0x%x", gotVal, wantVal)
+				}
+			}
+		})
+	}
+}
+
+// TestFieldAsUintRightAligned tests fieldAsUint with the same buffer
+// used in the appendField fix, ensuring consistency.
+func TestFieldAsUintRightAligned(t *testing.T) {
+	// Build IPv6 first 4 bytes with known values.
+	// Format: VVVV TTTT TTTT FFFF FFFF FFFF FFFF FFFF
+	// V=version (4 bits), T=traffic class (8 bits), F=flow label (20 bits)
+	var buf [4]byte
+	const version = 6
+	const trafficClass = 0xAB
+	const flowLabel = 0xCDEF0
+
+	// Encode: version in bits 0-3, traffic class in bits 4-11, flow label in bits 12-31
+	val := uint32(version)<<28 | uint32(trafficClass)<<20 | flowLabel
+	binary.BigEndian.PutUint32(buf[:], val)
+
+	// Verify encoding.
+	t.Logf("Encoded bytes: %02x %02x %02x %02x", buf[0], buf[1], buf[2], buf[3])
+
+	// Test version extraction (bits 0-3, 4 bits, left-aligned)
+	gotVersion, err := fieldAsUint(buf[:], 0, 4, false)
+	if err != nil {
+		t.Fatalf("version extraction failed: %v", err)
+	}
+	if gotVersion != version {
+		t.Errorf("version: got %d, want %d", gotVersion, version)
+	}
+
+	// Test traffic class extraction (bits 4-11, 8 bits, right-aligned)
+	gotTC, err := fieldAsUint(buf[:], 4, 8, true)
+	if err != nil {
+		t.Fatalf("traffic class extraction failed: %v", err)
+	}
+	if gotTC != trafficClass {
+		t.Errorf("traffic class: got 0x%02x, want 0x%02x", gotTC, trafficClass)
+	}
+
+	// Test flow label extraction (bits 12-31, 20 bits, right-aligned)
+	gotFlow, err := fieldAsUint(buf[:], 12, 20, true)
+	if err != nil {
+		t.Fatalf("flow label extraction failed: %v", err)
+	}
+	if gotFlow != flowLabel {
+		t.Errorf("flow label: got 0x%05x, want 0x%05x", gotFlow, flowLabel)
+	}
+}