add pcap printing to examples/xnet

internet/pcap/format.go

@@ -0,0 +1,142 @@
+package pcap
+
+import (
+	"encoding/hex"
+	"fmt"
+	"net/netip"
+	"slices"
+	"strconv"
+	"strings"
+
+	"github.com/soypat/lneto"
+	"github.com/soypat/lneto/tcp"
+)
+
+type Formatter struct {
+	FieldSep      string
+	FrameSep      string
+	FilterClasses []FieldClass
+	buf           []byte
+}
+
+// FormatFrames appends the formatted frame data to the destination buffer according the Formatter state.
+// Is equivalent to [Formatter.FormatFrame] called on each Frame with the FrameSep inserted between frames.
+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
+}
+
+// FormatFrame
+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 {
+			// TCP flags pretty print special case.
+			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:
+		// Binary data to be printed as hexadecimal.
+		dst = append(dst, "0x"...)
+		dst = hex.AppendEncode(dst, f.buf)
+	case FieldClassText:
+		dst = strconv.AppendQuote(dst, string(f.buf))
+	case FieldClassDst, FieldClassSrc, FieldClassSize, FieldClassAddress:
+		// 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
+}