Reduce heap allocations (#42)

* pcap: reuse Frame memory

* slog: reduce heap allocations of addresses; also prevent heap alloc of dhcp options in pcap

* dns: heapless improvement; add StackAsync buffer for more heapless operation; start thinking of errors

* reuse function for reclaiming frames among all protocols for lower memory usage

* remove extraneous code

dhcpv4/client.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"log/slog"
 	"math"
 	"math/bits"
 	"net"
@@ -220,7 +221,8 @@ func (c *Client) Demux(carrierData []byte, frameOffset int) error {
 
 	msgOK := msgType == MsgOffer || msgType == MsgAck
 	if !msgOK {
-		return fmt.Errorf("invalid DHCP message received or none got=%d", msgType)
+		internal.LogAttrs(nil, slog.LevelError, "invalid DHCP message", slog.Uint64("type", uint64(msgType)))
+		return lneto.ErrBug
 	}
 	err = c.setOptions(frm)
 	if err != nil {

dns/dns.go

@@ -209,8 +209,9 @@ func (m *Message) AppendTo(buf []byte, txid uint16, flags HeaderFlags) (_ []byte
 	nans := uint16(len(m.Answers))
 	nauth := uint16(len(m.Authorities))
 	nadd := uint16(len(m.Additionals))
-	var hdr [SizeHeader]byte
+	buf = slices.Grow(buf, int(m.Len()))
-	f, err := NewFrame(hdr[:])
+	// Set the buffer directly with header fields.
+	f, err := NewFrame(buf[len(buf) : len(buf)+SizeHeader])
 	if err != nil {
 		return buf, err
 	}
@@ -220,9 +221,7 @@ func (m *Message) AppendTo(buf []byte, txid uint16, flags HeaderFlags) (_ []byte
 	f.SetANCount(nans)
 	f.SetNSCount(nauth)
 	f.SetARCount(nadd)
-
+	buf = buf[:len(buf)+SizeHeader]
-	buf = slices.Grow(buf, int(m.Len()))
-	buf = append(buf, hdr[:]...)
 	for _, q := range m.Questions {
 		buf, err = q.appendTo(buf)
 		if err != nil {

errors.go

@@ -20,6 +20,7 @@ type errGeneric uint8
 // Generic errors common to internet functioning.
 const (
 	_                  errGeneric = iota // non-initialized err
+	ErrBug                               // lneto-bug(use build tag "debugheaplog")
 	ErrPacketDrop                        // packet dropped
 	ErrBadCRC                            // incorrect checksum
 	ErrZeroSource                        // zero source(port/addr)

internal/slices.go

@@ -46,3 +46,22 @@ func SliceReuse[T any](buf *[]T, n int) {
 		*buf = (*buf)[:0]
 	}
 }
+
+// SliceReclaim extends the slice length by one and returns a pointer to
+// the new last element. The returned element is not zeroed, so callers
+// can reuse any existing allocations it may hold from prior use.
+//
+// Beware: as the name implies SliceReclaim reuses previously held memory
+// so it is up to caller to ensure the reclaimed data is coherent by zeroing out
+// the needed fields and reusing the previously held slices or pointers responsibly.
+func SliceReclaim[T any](ptr *[]T) *T {
+	b := *ptr
+	n := len(b)
+	if n == cap(b) {
+		var z T
+		*ptr = append(b, z)
+	} else {
+		*ptr = b[:n+1]
+	}
+	return &(*ptr)[n]
+}

internal/slogattr.go

@@ -0,0 +1,22 @@
+package internal
+
+import (
+	"encoding/binary"
+	"log/slog"
+)
+
+// SlogAddr4 returns a slog.Attr for a 4-byte IPv4 address
+// packed into a uint64 without allocating a string.
+func SlogAddr4(key string, addr *[4]byte) slog.Attr {
+	u64Addr := uint64(binary.BigEndian.Uint32(addr[:]))
+	return slog.Uint64(key, u64Addr)
+}
+
+// SlogAddr6 returns a slog.Attr for a 6-byte hardware (MAC) address
+// packed into a uint64 without allocating a string.
+func SlogAddr6(key string, addr *[6]byte) slog.Attr {
+	var buf [8]byte
+	copy(buf[2:], addr[:])
+	u64Addr := binary.BigEndian.Uint64(buf[:])
+	return slog.Uint64(key, u64Addr)
+}

internet/pcap/capture.go

@@ -14,6 +14,7 @@ import (
 	"github.com/soypat/lneto/dns"
 	"github.com/soypat/lneto/ethernet"
 	"github.com/soypat/lneto/http/httpraw"
+	"github.com/soypat/lneto/internal"
 	"github.com/soypat/lneto/ipv4"
 	"github.com/soypat/lneto/ipv4/icmpv4"
 	"github.com/soypat/lneto/ipv6"
@@ -43,7 +44,31 @@ type PacketBreakdown struct {
 	SubfieldLimit int
 }
 
+// initFrames pre-allocates a []Frame with per-position Fields capacity
+// sized for the protocol layers at each position. This avoids heap
+// allocations on the first packet when using SliceReclaim on subsequent calls.
+//
+// Pre-allocated capacities per position:
+//
+//	0: Ethernet (3 base + VLAN tag = 4)
+//	1: L3 max(IPv4=12, ARP=9, IPv6=8) = 12
+//	2: L4 max(TCP=10, ICMP=8, UDP=4) = 10
+//	3: App max(DHCP=15, NTP=13, HTTP=2, DNS=1) = 16
+//	4-5: overflow/remaining = 2
+func (pc *PacketBreakdown) initFrames() []Frame {
+	const nframes = 6
+	var fieldCaps = [nframes]int{4, 12, 10, 16, 2, 2}
+	frames := make([]Frame, nframes)
+	for i := range frames {
+		frames[i].Fields = make([]FrameField, 0, fieldCaps[i])
+	}
+	return frames[:0]
+}
+
 func (pc *PacketBreakdown) CaptureEthernet(dst []Frame, pkt []byte, bitOffset int) ([]Frame, error) {
+	if dst == nil {
+		dst = pc.initFrames()
+	}
 	if bitOffset%8 != 0 {
 		return dst, errors.New("ethernet must be parsed at byte boundary")
 	}
@@ -56,23 +81,17 @@ func (pc *PacketBreakdown) CaptureEthernet(dst []Frame, pkt []byte, bitOffset in
 		return dst, pc.validator().ErrPop()
 	}
 
-	finfo := Frame{
+	finfo := reclaimFrame(&dst, ProtoEthernet, bitOffset, baseEthernetFields[:])
-		Protocol:        ProtoEthernet,
-		PacketBitOffset: bitOffset,
-	}
-	finfo.Fields = append(finfo.Fields, baseEthernetFields[:]...)
 	etype := efrm.EtherTypeOrSize()
 	end := 14*octet + bitOffset
 	if etype.IsSize() {
 		finfo.Fields[len(finfo.Fields)-1].Class = FieldClassSize
-		dst = append(dst, finfo)
+		reclaimRemainingFrame(&dst, "Ethernet payload", FieldClassPayload, end, octet*len(pkt))
-		dst = append(dst, remainingFrameInfo("Ethernet payload", FieldClassPayload, end, octet*len(pkt)))
 		return dst, nil
 	}
-	dst = append(dst, finfo)
 	if efrm.IsVLAN() {
 		finfo.Fields = append(finfo.Fields, FrameField{Name: "VLAN Tag", Class: FieldClassType, FrameBitOffset: end, BitLength: 2 * octet})
-		dst = append(dst, remainingFrameInfo("Ethernet VLAN", FieldClassPayload, end+2*octet, octet*len(pkt)))
+		reclaimRemainingFrame(&dst, "Ethernet VLAN", FieldClassPayload, end+2*octet, octet*len(pkt))
 		return dst, nil
 	}
 	switch etype {
@@ -83,7 +102,7 @@ func (pc *PacketBreakdown) CaptureEthernet(dst []Frame, pkt []byte, bitOffset in
 	case ethernet.TypeIPv6:
 		dst, err = pc.CaptureIPv6(dst, pkt, end)
 	default:
-		dst = append(dst, remainingFrameInfo(etype, FieldClassPayload, end, octet*len(pkt)))
+		reclaimRemainingFrame(&dst, etype, FieldClassPayload, end, octet*len(pkt))
 	}
 	return dst, err
 }
@@ -101,13 +120,8 @@ func (pc *PacketBreakdown) CaptureARP(dst []Frame, pkt []byte, bitOffset int) ([
 		return dst, pc.validator().ErrPop()
 	}
 
-	finfo := Frame{
+	finfo := reclaimFrame(&dst, ethernet.TypeARP, bitOffset, baseARPFields[:])
-		Protocol:        ethernet.TypeARP,
-		PacketBitOffset: bitOffset,
-	}
-
 	const varstart = 8 * octet
-	finfo.Fields = append(finfo.Fields, baseARPFields[:]...)
 	_, hlen := afrm.Hardware()
 	_, plen := afrm.Protocol()
 	finfo.Fields = append(finfo.Fields,
@@ -136,7 +150,6 @@ func (pc *PacketBreakdown) CaptureARP(dst []Frame, pkt []byte, bitOffset int) ([
 			BitLength:      int(plen) * octet,
 		},
 	)
-	dst = append(dst, finfo)
 	return dst, nil
 }
 
@@ -152,12 +165,7 @@ func (pc *PacketBreakdown) CaptureIPv6(dst []Frame, pkt []byte, bitOffset int) (
 	if pc.validator().HasError() {
 		return dst, pc.validator().ErrPop()
 	}
-	finfo := Frame{
+	reclaimFrame(&dst, ethernet.TypeIPv6, bitOffset, baseIPv6Fields[:])
-		Protocol:        ethernet.TypeIPv6,
-		PacketBitOffset: bitOffset,
-	}
-	finfo.Fields = append(finfo.Fields, baseIPv6Fields[:]...)
-	dst = append(dst, finfo)
 	proto := ifrm6.NextHeader()
 	end := bitOffset + 40*octet
 	var protoErrs []error
@@ -201,11 +209,7 @@ func (pc *PacketBreakdown) CaptureIPv4(dst []Frame, pkt []byte, bitOffset int) (
 	}
 	// limit packet to the actual IPv4 frame size
 	pkt = pkt[:bitOffset/8+int(ifrm4.TotalLength())]
-	finfo := Frame{
+	finfo := reclaimFrame(&dst, ethernet.TypeIPv4, bitOffset, baseIPv4Fields[:])
-		Protocol:        ethernet.TypeIPv4,
-		PacketBitOffset: bitOffset,
-	}
-	finfo.Fields = append(finfo.Fields, baseIPv4Fields[:]...)
 	options := ifrm4.Options()
 	if len(options) > 0 {
 		finfo.Fields = append(finfo.Fields, FrameField{
@@ -217,7 +221,6 @@ func (pc *PacketBreakdown) CaptureIPv4(dst []Frame, pkt []byte, bitOffset int) (
 	if ifrm4.CalculateHeaderCRC() != 0 {
 		finfo.Errors = append(finfo.Errors, lneto.ErrBadCRC)
 	}
-	dst = append(dst, finfo)
 	proto := ifrm4.Protocol()
 	end := bitOffset + octet*ifrm4.HeaderLength()
 	var protoErrs []error
@@ -277,7 +280,7 @@ func (pc *PacketBreakdown) captureIPProto(proto lneto.IPProto, dst []Frame, pkt
 	case lneto.IPProtoICMP:
 		dst, err = pc.CaptureICMPv4(dst, pkt, bitOffset)
 	default:
-		dst = append(dst, remainingFrameInfo(proto, 0, bitOffset, octet*len(pkt)))
+		reclaimRemainingFrame(&dst, proto, 0, bitOffset, octet*len(pkt))
 	}
 	if len(ipProtoErrs) > 0 && len(dst) > nextFrame {
 		dst[nextFrame].Errors = append(dst[nextFrame].Errors, ipProtoErrs...)
@@ -298,11 +301,7 @@ func (pc *PacketBreakdown) CaptureTCP(dst []Frame, pkt []byte, bitOffset int) ([
 		return dst, pc.validator().ErrPop()
 	}
 	end := bitOffset + octet*tfrm.HeaderLength()
-	finfo := Frame{
+	finfo := reclaimFrame(&dst, lneto.IPProtoTCP, bitOffset, baseTCPFields[:])
-		Protocol:        lneto.IPProtoTCP,
-		PacketBitOffset: bitOffset,
-	}
-	finfo.Fields = append(finfo.Fields, baseTCPFields[:]...)
 	options := tfrm.Options()
 	if len(options) > 0 {
 		finfo.Fields = append(finfo.Fields, FrameField{
@@ -311,20 +310,16 @@ func (pc *PacketBreakdown) CaptureTCP(dst []Frame, pkt []byte, bitOffset int) ([
 			BitLength:      octet * len(options),
 		})
 	}
-	dst = append(dst, finfo)
 	payload := tfrm.Payload()
 	if len(payload) > 0 {
 		dst, err = pc.CaptureHTTP(dst, pkt, end)
 		if err != nil {
-			dst = append(dst, remainingFrameInfo(unknownPayloadProto, FieldClassPayload, end, octet*len(pkt)))
+			reclaimRemainingFrame(&dst, unknownPayloadProto, FieldClassPayload, end, octet*len(pkt))
 		}
 	}
 	return dst, nil
 }
 
-// func (pc *PacketBreakdown) CaptureDHCPv4(dst []Frame, pkt []byte, bitOffset int) ([]Frame, error) {
-// }
-
 func (pc *PacketBreakdown) CaptureUDP(dst []Frame, pkt []byte, bitOffset int) ([]Frame, error) {
 	if bitOffset%8 != 0 {
 		return dst, errors.New("UDP must be parsed at byte boundary")
@@ -337,12 +332,7 @@ func (pc *PacketBreakdown) CaptureUDP(dst []Frame, pkt []byte, bitOffset int) ([
 	if pc.validator().HasError() {
 		return dst, pc.validator().ErrPop()
 	}
-	finfo := Frame{
+	reclaimFrame(&dst, lneto.IPProtoUDP, bitOffset, baseUDPFields[:])
-		Protocol:        lneto.IPProtoUDP,
-		PacketBitOffset: bitOffset,
-	}
-	finfo.Fields = append(finfo.Fields, baseUDPFields[:]...)
-	dst = append(dst, finfo)
 	end := bitOffset + 8*octet
 	payload := ufrm.Payload()
 	dstport := ufrm.DestinationPort()
@@ -355,7 +345,7 @@ func (pc *PacketBreakdown) CaptureUDP(dst []Frame, pkt []byte, bitOffset int) ([
 		dst, err = pc.CaptureNTP(dst, pkt, end)
 	}
 	if err != nil {
-		dst = append(dst, remainingFrameInfo(unknownPayloadProto, FieldClassPayload, end, octet*len(pkt)))
+		reclaimRemainingFrame(&dst, unknownPayloadProto, FieldClassPayload, end, octet*len(pkt))
 	}
 	return dst, nil
 }
@@ -370,11 +360,7 @@ func (pc *PacketBreakdown) CaptureICMPv4(dst []Frame, pkt []byte, bitOffset int)
 		return dst, err
 	}
 
-	finfo := Frame{
+	finfo := reclaimFrame(&dst, lneto.IPProtoICMP, bitOffset, baseICMPv4Fields[:])
-		Protocol:        lneto.IPProtoICMP,
-		PacketBitOffset: bitOffset,
-	}
-	finfo.Fields = append(finfo.Fields, baseICMPv4Fields[:]...)
 
 	// Add type-specific fields.
 	switch ifrm.Type() {
@@ -421,13 +407,12 @@ func (pc *PacketBreakdown) CaptureICMPv4(dst []Frame, pkt []byte, bitOffset int)
 			})
 		}
 	}
-	dst = append(dst, finfo)
 	return dst, nil
 }
 
 func (pc *PacketBreakdown) CaptureDNS(dst []Frame, pkt []byte, bitOffset int) ([]Frame, error) {
 	if bitOffset%8 != 0 {
-		return nil, errors.New("DNS must be parsed at byte boundary")
+		return dst, errors.New("DNS must be parsed at byte boundary")
 	}
 	dnsData := pkt[bitOffset/8:]
 	pc.dmsg.LimitResourceDecoding(20, 20, 20, 20)
@@ -435,10 +420,7 @@ func (pc *PacketBreakdown) CaptureDNS(dst []Frame, pkt []byte, bitOffset int) ([
 	if err != nil && !incomplete {
 		return dst, err
 	}
-	finfo := Frame{
+	finfo := reclaimFrame(&dst, "DNS", bitOffset, nil)
-		Protocol:        "DNS",
-		PacketBitOffset: bitOffset,
-	}
 	if incomplete {
 		finfo.Errors = append(finfo.Errors, errors.New("pcap: could not parse all DNS resources; add higher limit"))
 	}
@@ -447,52 +429,46 @@ func (pc *PacketBreakdown) CaptureDNS(dst []Frame, pkt []byte, bitOffset int) ([
 		FrameBitOffset: 0,
 		BitLength:      int(off) * octet,
 	})
-	dst = append(dst, finfo)
 	return dst, nil
 }
 
 func (pc *PacketBreakdown) CaptureNTP(dst []Frame, pkt []byte, bitOffset int) ([]Frame, error) {
 	if bitOffset%8 != 0 {
-		return nil, errors.New("NTP must be parsed at byte boundary")
+		return dst, errors.New("NTP must be parsed at byte boundary")
 	}
 	ntpData := pkt[bitOffset/8:]
 	_, err := ntp.NewFrame(ntpData)
 	if err != nil {
 		return dst, err
 	}
-	finfo := Frame{
+	reclaimFrame(&dst, "NTP", bitOffset, baseNTPFields[:])
-		Protocol:        "NTP",
-		PacketBitOffset: bitOffset,
-	}
-	finfo.Fields = append(finfo.Fields, baseNTPFields[:]...)
-	dst = append(dst, finfo)
 	return dst, nil
 }
 
 func (pc *PacketBreakdown) CaptureDHCPv4(dst []Frame, pkt []byte, bitOffset int) ([]Frame, error) {
 	if bitOffset%8 != 0 {
-		return nil, errors.New("DHCP must be parsed at byte boundary")
+		return dst, errors.New("DHCP must be parsed at byte boundary")
 	}
 	dhcpData := pkt[bitOffset/8:]
 	dfrm, err := dhcpv4.NewFrame(dhcpData)
 	if err != nil {
-		return nil, err
+		return dst, err
-	}
-	finfo := Frame{
-		Protocol:        "DHCPv4",
-		PacketBitOffset: bitOffset,
 	}
+	finfo := reclaimFrame(&dst, "DHCPv4", bitOffset, baseDHCPv4Fields[:])
 	magic := dfrm.MagicCookie()
 	if magic != dhcpv4.MagicCookie {
 		finfo.Errors = append(finfo.Errors, errors.New("incorrect DHCPv4 magic cookie"))
 	}
-	finfo.Fields = append(finfo.Fields, baseDHCPv4Fields[:]...)
 	options := dfrm.OptionsPayload()
 
 	if len(options) > 0 && pc.SubfieldLimit > 0 {
-		var optfield FrameField
+		// Reclaim FrameField from Fields backing array to reuse its SubFields backing array.
-		optfield.Class = FieldClassOptions
+		optfield := internal.SliceReclaim(&finfo.Fields)
-		optfield.Name = "options"
+		*optfield = FrameField{ // Ensure consistent zeroing of memory, but keep slice reference for reuse.
+			Class:     FieldClassOptions,
+			SubFields: optfield.SubFields[:0],
+			Name:      "options",
+		}
 		err = dfrm.ForEachOption(func(optoff int, opt dhcpv4.OptNum, data []byte) error {
 			if len(optfield.SubFields) >= pc.SubfieldLimit {
 				return errors.New("option cap limit surpassed for DHCP")
@@ -544,12 +520,11 @@ func (pc *PacketBreakdown) CaptureDHCPv4(dst []Frame, pkt []byte, bitOffset int)
 			optfield.SubFields = append(optfield.SubFields, field)
 			return nil
 		})
-		finfo.Fields = append(finfo.Fields, optfield)
+		// optfield already in finfo.Fields via SliceReclaim, no append needed.
 		if err != nil {
 			finfo.Errors = append(finfo.Errors, err)
 		}
 	}
-	dst = append(dst, finfo)
 	return dst, nil
 }
 
@@ -589,7 +564,7 @@ func httpBodyClass(contentType, body []byte) FieldClass {
 func (pc *PacketBreakdown) CaptureHTTP(dst []Frame, pkt []byte, bitOffset int) ([]Frame, error) {
 	const httpProtocol = "HTTP"
 	if bitOffset%8 != 0 {
-		return nil, errors.New("HTTP must be parsed at byte boundary")
+		return dst, errors.New("HTTP must be parsed at byte boundary")
 	}
 	const asResponse = true
 	const asRequest = false
@@ -606,25 +581,22 @@ func (pc *PacketBreakdown) CaptureHTTP(dst []Frame, pkt []byte, bitOffset int) (
 	hdrLen := pc.hdr.BufferParsed()
 	body, _ := pc.hdr.Body()
 	bodyClass := httpBodyClass(pc.hdr.Get("Content-Type"), body)
-	dst = append(dst, Frame{
+	finfo := reclaimFrame(&dst, httpProtocol, bitOffset, nil)
-		Protocol:        httpProtocol,
+	finfo.Fields = append(finfo.Fields,
-		PacketBitOffset: bitOffset,
+		FrameField{
-		Fields: []FrameField{
+			Name:           "HTTP Header",
-			{
+			Class:          FieldClassText,
-				Name:           "HTTP Header",
+			FrameBitOffset: 0,
-				Class:          FieldClassText,
+			BitLength:      hdrLen * octet,
-				FrameBitOffset: 0,
-				BitLength:      hdrLen * octet,
-			},
-			{
-				Name:           "HTTP Body",
-				Class:          bodyClass,
-				FrameBitOffset: hdrLen * octet,
-				BitLength:      len(body) * octet,
-			},
 		},
-	})
+		FrameField{
-	return dst, err
+			Name:           "HTTP Body",
+			Class:          bodyClass,
+			FrameBitOffset: hdrLen * octet,
+			BitLength:      len(body) * octet,
+		},
+	)
+	return dst, nil
 }
 
 func (pc *PacketBreakdown) validator() *lneto.Validator {
@@ -653,9 +625,9 @@ func (ff Flags) IsLegacy() bool       { return ff&FlagLegacy != 0 }
 func (ff Flags) IsRightAligned() bool { return ff&FlagRightAligned != 0 }
 
 type Frame struct {
+	PacketBitOffset int
 	Protocol        any
 	Fields          []FrameField
-	PacketBitOffset int
 	Errors          []error
 }
 
@@ -1331,14 +1303,26 @@ var baseNTPFields = [...]FrameField{
 	},
 }
 
-func remainingFrameInfo(proto any, class FieldClass, pktBitOffset, pktBitLen int) Frame {
+// reclaimFrame extends dst via [internal.SliceReclaim], resets the reclaimed Frame
-	return Frame{
+// with the given protocol and bit offset while preserving Fields and Errors
+// backing arrays, and appends baseFields. Returns the Frame for further modification.
+func reclaimFrame(dst *[]Frame, proto any, bitOffset int, baseFields []FrameField) *Frame {
+	finfo := internal.SliceReclaim(dst)
+	*finfo = Frame{
+		PacketBitOffset: bitOffset,
 		Protocol:        proto,
-		PacketBitOffset: pktBitOffset,
+		Fields:          append(finfo.Fields[:0], baseFields...),
-		Fields: []FrameField{
+		Errors:          finfo.Errors[:0],
-			{
-				Class:     class,
-				BitLength: pktBitLen - pktBitOffset,
-			}},
 	}
+	return finfo
+}
+
+// reclaimRemainingFrame extends dst via SliceReclaim and populates the reclaimed
+// Frame as a single-field "remaining payload" frame, reusing the old Fields backing array.
+func reclaimRemainingFrame(dst *[]Frame, proto any, class FieldClass, pktBitOffset, pktBitLen int) {
+	finfo := reclaimFrame(dst, proto, pktBitOffset, nil)
+	finfo.Fields = append(finfo.Fields, FrameField{
+		Class:     class,
+		BitLength: pktBitLen - pktBitOffset,
+	})
 }

internet/pcap/format.go

@@ -5,6 +5,7 @@ import (
 	"encoding/hex"
 	"errors"
 	"fmt"
+	"math"
 	"net/netip"
 	"slices"
 	"strconv"
@@ -31,6 +32,7 @@ type Formatter struct {
 	DisableLegacyFilter bool
 	mubuf               sync.Mutex
 	buf                 []byte
+	uintBuf             [8]byte // scratch buffer for fieldAsUint to avoid TinyGo heap escape.
 }
 
 // FormatFrames appends the formatted frame data to the destination buffer according the Formatter state.
@@ -49,14 +51,17 @@ func (f *Formatter) FormatFrames(dst []byte, frms []Frame, pkt []byte) (_ []byte
 	return dst, nil
 }
 
-// FormatFrame
+// FormatFrame formats a single frame's protocol, fields, and errors into dst.
 func (f *Formatter) FormatFrame(dst []byte, frm Frame, pkt []byte) (_ []byte, err error) {
 	sep := f.fieldSep()
 	bitlen := frm.LenBits()
+	dst = appendProtocol(dst, frm.Protocol)
 	if bitlen%8 == 0 {
-		dst = fmt.Appendf(dst, "%s len=%d", frm.Protocol, bitlen/8)
+		dst = append(dst, " len="...)
+		dst = strconv.AppendInt(dst, int64(bitlen/8), 10)
 	} else {
-		dst = fmt.Appendf(dst, "%s bitlen=%d", frm.Protocol, bitlen)
+		dst = append(dst, " bitlen="...)
+		dst = strconv.AppendInt(dst, int64(bitlen), 10)
 	}
 
 	for ifield := range frm.Fields {
@@ -68,7 +73,7 @@ func (f *Formatter) FormatFrame(dst []byte, frm Frame, pkt []byte) (_ []byte, er
 		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.Flags.IsRightAligned())
+			v, err := f.fieldAsUint(pkt, frm.PacketBitOffset+field.FrameBitOffset, field.BitLength, field.Flags.IsRightAligned())
 			if err != nil {
 				return dst, err
 			}
@@ -158,7 +163,7 @@ func (f *Formatter) formatField(dst []byte, pktStartOff int, field FrameField, p
 	case FieldClassDst, FieldClassSrc, FieldClassSize, FieldClassAddress, FieldClassOperation:
 		// IP, MAC addresses and ports.
 		if field.BitLength <= 16 {
-			v, err := fieldAsUint(pkt, fieldBitStart, field.BitLength, field.Flags.IsRightAligned())
+			v, err := f.fieldAsUint(pkt, fieldBitStart, field.BitLength, field.Flags.IsRightAligned())
 			if err != nil {
 				return dst, err
 			}
@@ -198,3 +203,36 @@ func (f *Formatter) subfieldSep() string {
 	}
 	return sep
 }
+
+// fieldAsUint evaluates a packet field as a uint64 using the Formatter's
+// scratch buffer to avoid a TinyGo heap escape from a local [8]byte.
+func (f *Formatter) 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")
+	}
+	f.uintBuf = [8]byte{}
+	_, err := appendField(f.uintBuf[8-octets:8-octets], pkt, fieldBitStart, bitlen, rightAligned)
+	if err != nil {
+		return badUint64, err
+	}
+	return binary.BigEndian.Uint64(f.uintBuf[:]), nil
+}
+
+// appendProtocol appends the string representation of a Frame.Protocol value
+// to dst without going through fmt.Appendf reflect machinery.
+func appendProtocol(dst []byte, p any) []byte {
+	switch p := p.(type) {
+	case proto:
+		return append(dst, string(p)...)
+	case string:
+		return append(dst, p...)
+	case ethernet.Type:
+		return append(dst, p.String()...)
+	case lneto.IPProto:
+		return append(dst, p.String()...)
+	default:
+		return fmt.Appendf(dst, "%v", p)
+	}
+}

internet/stack-ethernet.go

@@ -6,10 +6,10 @@ import (
 	"io"
 	"log/slog"
 	"math"
-	"net"
 
 	"github.com/soypat/lneto"
 	"github.com/soypat/lneto/ethernet"
+	"github.com/soypat/lneto/internal"
 )
 
 // StackEthernetConfig contains configuration parameters for [StackEthernet].
@@ -132,7 +132,7 @@ func (ls *StackEthernet) Demux(carrierData []byte, frameOffset int) (err error)
 		return err
 	}
 DROP:
-	ls.handlers.info("LinkStack:drop-packet", slog.String("dsthw", net.HardwareAddr(dstaddr[:]).String()), slog.String("ethertype", efrm.EtherTypeOrSize().String()))
+	ls.handlers.info("LinkStack:drop-packet", internal.SlogAddr6("dsthw", dstaddr), slog.String("ethertype", efrm.EtherTypeOrSize().String()))
 	return lneto.ErrPacketDrop
 }
 

internet/stack-ip.go

@@ -104,7 +104,7 @@ func (sb *StackIP) Demux(carrierData []byte, offset int) error {
 	// nodeIdx := getNodeByProto(sb.handlers, uint16(proto))
 	if node == nil {
 		// Drop packet.
-		sb.handlers.info("ip:demux.drop", slog.String("dstaddr", netip.AddrFrom4(*ifrm.DestinationAddr()).String()), slog.String("proto", ifrm.Protocol().String()))
+		sb.handlers.info("ip:demux.drop", internal.SlogAddr4("dstaddr", ifrm.DestinationAddr()), slog.String("proto", ifrm.Protocol().String()))
 		return lneto.ErrPacketDrop
 	}
 	// Incoming CRC Validation of common IP Protocols.

stringers.go

@@ -194,15 +194,16 @@ func _() {
 	// An "invalid array index" compiler error signifies that the constant values have changed.
 	// Re-run the stringer command to generate them again.
 	var x [1]struct{}
-	_ = x[ErrPacketDrop-1]
+	_ = x[ErrBug-1]
-	_ = x[ErrBadCRC-2]
+	_ = x[ErrPacketDrop-2]
-	_ = x[ErrZeroSource-3]
+	_ = x[ErrBadCRC-3]
-	_ = x[ErrZeroDestination-4]
+	_ = x[ErrZeroSource-4]
+	_ = x[ErrZeroDestination-5]
 }
 
-const _errGeneric_name = "packet droppedincorrect checksumzero source(port/addr)zero destination(port/addr)"
+const _errGeneric_name = "lneto-bug(use build tag \"debugheaplog\")packet droppedincorrect checksumzero source(port/addr)zero destination(port/addr)"
 
-var _errGeneric_index = [...]uint8{0, 14, 32, 54, 81}
+var _errGeneric_index = [...]uint8{0, 39, 53, 71, 93, 120}
 
 func (i errGeneric) String() string {
 	i -= 1

x/xnet/stack-async.go

@@ -48,6 +48,8 @@ type StackAsync struct {
 
 	prng uint32
 
+	addrBuf [6]byte // Temporary buffer for As4()/HardwareAddr6() results to avoid heap escapes.
+
 	totalsent uint64
 	totalrecv uint64
 }
@@ -353,8 +355,8 @@ func (s *StackAsync) StartLookupIP(host string) error {
 	if err != nil {
 		return err
 	}
-	dns4 := s.dnssv.As4()
+	*(*[4]byte)(s.addrBuf[:4]) = s.dnssv.As4()
-	s.dnsUDP.SetStackNode(&s.dns, dns4[:], dns.ServerPort)
+	s.dnsUDP.SetStackNode(&s.dns, s.addrBuf[:4], dns.ServerPort)
 	err = s.udps.Register(&s.dnsUDP)
 	return err
 }
@@ -417,8 +419,8 @@ func (s *StackAsync) StartNTP(addr netip.Addr) error {
 	defer s.mu.Unlock()
 	s.ntp.Reset(s.sysprec, time.Now)
 
-	addr4 := addr.As4()
+	*(*[4]byte)(s.addrBuf[:4]) = addr.As4()
-	s.ntpUDP.SetStackNode(&s.ntp, addr4[:], ntp.ServerPort)
+	s.ntpUDP.SetStackNode(&s.ntp, s.addrBuf[:4], ntp.ServerPort)
 	err := s.udps.Register(&s.ntpUDP)
 	return err
 }