cull fmt package use and prevent aggressive DCE in MWE example with TinyGo

arp/frame.go

@@ -2,9 +2,6 @@ package arp
 
 import (
 	"encoding/binary"
-	"fmt"
-	"net"
-	"net/netip"
 
 	"github.com/soypat/lneto"
 	"github.com/soypat/lneto/ethernet"
@@ -147,21 +144,8 @@ func (afrm Frame) ValidateSize(v *lneto.Validator) {
 
 func (afrm Frame) String() string {
 	opstr := afrm.Operation().String()
-	hwt, _ := afrm.Hardware()
+	var rawbuf [11]byte
-	ptt, _ := afrm.Protocol()
+	b := append(rawbuf[:0], "ARP "...)
-	sndhw, sndpt := afrm.Sender()
+	b = append(b, opstr...)
-	tgthw, tgtpt := afrm.Target()
+	return string(rawbuf[:len(b)])
-	var sndstr, tgtstr string
-	if ptt == ethernet.TypeIPv4 || ptt == ethernet.TypeIPv6 {
-		sender, _ := netip.AddrFromSlice(sndpt)
-		target, _ := netip.AddrFromSlice(tgtpt)
-		sndstr = sender.String()
-		tgtstr = target.String()
-	} else {
-		sndstr = net.HardwareAddr(sndpt).String()
-		tgtstr = net.HardwareAddr(tgtpt).String()
-	}
-	return fmt.Sprintf("ARP %s HW=(%d,SENDER=%s,TARGET=%s) PROTO=(%s,SENDER=%s,TARGET=%s)",
-		opstr, hwt, net.HardwareAddr(sndhw).String(), net.HardwareAddr(tgthw).String(),
-		ptt.String(), sndstr, tgtstr)
 }

dhcp/dhcpv4/server.go

@@ -3,7 +3,6 @@ package dhcpv4
 import (
 	"encoding/binary"
 	"errors"
-	"fmt"
 
 	"github.com/soypat/lneto"
 	"github.com/soypat/lneto/internal"
@@ -220,10 +219,10 @@ func (sv *Server) Demux(carrierData []byte, frameOffset int) error {
 		}
 
 	default:
-		err = fmt.Errorf("unhandled message type %s", msgType.String())
+		err = errors.New("unhandled message type: " + msgType.String())
 	}
 	if err != nil {
-		return fmt.Errorf("msgtype=%s client=%+v: %w", msgType.String(), client, err)
+		return errors.New("dhcpv4 server demux fail on " + msgType.String())
 	}
 	sv.hosts[clientIDRaw] = client
 	return nil

dns/dns.go

@@ -3,6 +3,7 @@ package dns
 import (
 	"bytes"
 	"encoding/binary"
+	"encoding/hex"
 	"math"
 	"net/netip"
 	"slices"
@@ -426,10 +427,64 @@ func (m *Message) Reset() {
 	m.Additionals = m.Additionals[:0]
 }
 
+// AppendText appends a human readable representation of the Message's resources
+// to b and returns the resulting slice. It implements [encoding.TextAppender].
+func (m *Message) AppendText(b []byte) (_ []byte, err error) {
+	if len(m.Questions) > 0 {
+		b = append(b, "-- Questions\n"...)
+		for i := range m.Questions {
+			b, err = m.Questions[i].AppendText(b)
+			if err != nil {
+				return b, err
+			}
+			b = append(b, '\n')
+		}
+	}
+	b, err = appendResourcesText(b, "-- Answers\n", m.Answers)
+	if err != nil {
+		return b, err
+	}
+	b, err = appendResourcesText(b, "-- Authorities\n", m.Authorities)
+	if err != nil {
+		return b, err
+	}
+	return appendResourcesText(b, "-- Additionals\n", m.Additionals)
+}
+
+func appendResourcesText(b []byte, title string, resources []Resource) (_ []byte, err error) {
+	if len(resources) == 0 {
+		return b, nil
+	}
+	b = append(b, title...)
+	for i := range resources {
+		b, err = resources[i].AppendText(b)
+		if err != nil {
+			return b, err
+		}
+		b = append(b, '\n')
+	}
+	return b, nil
+}
+
 // String returns a string representation of the header.
 func (h *ResourceHeader) String() string {
-	return h.Name.String() + " " + h.Type.String() + " " + h.Class.String() +
+	b, _ := h.AppendText(make([]byte, 0, 64))
-		" ttl=" + strconv.FormatUint(uint64(h.TTL), 10) + " len=" + strconv.FormatUint(uint64(h.Length), 10)
+	return string(b)
+}
+
+// AppendText appends a human readable representation of the header to b and
+// returns the resulting slice. It implements [encoding.TextAppender].
+func (h *ResourceHeader) AppendText(b []byte) ([]byte, error) {
+	b = h.Name.AppendDottedTo(b)
+	b = append(b, ' ')
+	b = append(b, h.Type.String()...)
+	b = append(b, ' ')
+	b = append(b, h.Class.String()...)
+	b = append(b, " ttl="...)
+	b = strconv.AppendUint(b, uint64(h.TTL), 10)
+	b = append(b, " len="...)
+	b = strconv.AppendUint(b, uint64(h.Length), 10)
+	return b, nil
 }
 
 func (r *Resource) Reset() {
@@ -456,6 +511,29 @@ func (r *Resource) CNAMEView() Name {
 	return Name{data: r.RawData()}
 }
 
+// String returns a string representation of the Resource: its header followed by
+// the record's data.
+func (r *Resource) String() string {
+	b, _ := r.AppendText(make([]byte, 0, 96))
+	return string(b)
+}
+
+// AppendText appends a human readable representation of the Resource to b: the
+// header followed by the record's data, in dotted format for CNAME records and
+// hexadecimal otherwise. It implements [encoding.TextAppender].
+func (r *Resource) AppendText(b []byte) (_ []byte, err error) {
+	b, err = r.header.AppendText(b)
+	if err != nil {
+		return b, err
+	}
+	b = append(b, " data="...)
+	if r.header.Type == TypeCNAME {
+		cname := r.CNAMEView()
+		return cname.AppendDottedTo(b), nil
+	}
+	return hex.AppendEncode(b, r.RawData()), nil
+}
+
 func (q *Question) Reset() {
 	q.Name.Reset()
 	*q = Question{Name: q.Name} // Reuse Name's buffer.
@@ -494,7 +572,19 @@ func (q *Question) appendTo(buf []byte) (_ []byte, err error) {
 
 // String returns a string representation of the Question with the Name in dotted format.
 func (q *Question) String() string {
-	return q.Name.String() + " " + q.Type.String() + " " + q.Class.String()
+	b, _ := q.AppendText(make([]byte, 0, 32))
+	return string(b)
+}
+
+// AppendText appends a human readable representation of the Question to b with
+// the Name in dotted format. It implements [encoding.TextAppender].
+func (q *Question) AppendText(b []byte) ([]byte, error) {
+	b = q.Name.AppendDottedTo(b)
+	b = append(b, ' ')
+	b = append(b, q.Type.String()...)
+	b = append(b, ' ')
+	b = append(b, q.Class.String()...)
+	return b, nil
 }
 
 func (r *Resource) Decode(b []byte, off uint16) (uint16, error) {

dns/dns_test.go

@@ -1,7 +1,6 @@
 package dns
 
 import (
-	"fmt"
 	"net/netip"
 	"strings"
 	"testing"
@@ -195,33 +194,8 @@ func TestMessageAppendEncodeIncompleteOK(t *testing.T) {
 }
 
 func (m *Message) String() string {
-	// s := fmt.Sprintf("Message: %#v\n", &m.Header)
+	b, _ := m.AppendText(nil)
-	var s strings.Builder
+	return string(b)
-	if len(m.Questions) > 0 {
-		s.WriteString("-- Questions\n")
-		for _, q := range m.Questions {
-			s.WriteString(fmt.Sprintf("%#v\n", q))
-		}
-	}
-	if len(m.Answers) > 0 {
-		s.WriteString("-- Answers\n")
-		for _, a := range m.Answers {
-			s.WriteString(fmt.Sprintf("%#v\n", a))
-		}
-	}
-	if len(m.Authorities) > 0 {
-		s.WriteString("-- Authorities\n")
-		for _, ns := range m.Authorities {
-			s.WriteString(fmt.Sprintf("%#v\n", ns))
-		}
-	}
-	if len(m.Additionals) > 0 {
-		s.WriteString("-- Additionals\n")
-		for _, e := range m.Additionals {
-			s.WriteString(fmt.Sprintf("%#v\n", e))
-		}
-	}
-	return s.String()
 }
 
 func TestDecodeMessage(t *testing.T) {

examples/min-working-example/main-mwe.go

@@ -2,7 +2,7 @@ package main
 
 import (
 	"context"
-	"fmt"
+	"errors"
 	"net"
 	"net/netip"
 	"os"
@@ -46,7 +46,7 @@ func main() {
 	var stack xnet.StackAsync
 	ctx := context.Background()
 	if err := run(ctx, &stack); err != nil {
-		fmt.Println(err)
+		os.Stdout.WriteString(err.Error())
 		os.Exit(1)
 	}
 }
@@ -71,7 +71,7 @@ func run(ctx context.Context, stack *xnet.StackAsync) error {
 		HardwareAddress: hwaddr,
 	})
 	if err != nil {
-		return fmt.Errorf("configuring stack: %w", err)
+		return makeMsgErr("configuring stack", err)
 	}
 	ctx, cancel := context.WithCancel(ctx)
 	defer cancel()
@@ -82,15 +82,15 @@ func run(ctx context.Context, stack *xnet.StackAsync) error {
 	rstack := stack.StackRetrying(stackBackoff)
 	results, err := rstack.DoDHCPv4([4]byte{}, protoTimeout, protoRetries)
 	if err != nil {
-		return fmt.Errorf("doing DHCP: %w", err)
+		return makeMsgErr("doing DHCP", err)
 	}
 	err = stack.AssimilateDHCPResults(results)
 	if err != nil {
-		return fmt.Errorf("assimilating DHCP: %w", err)
+		return makeMsgErr("assimilating DHCP", err)
 	}
 	gateway, err := rstack.DoResolveHardwareAddress6(results.Router, protoTimeout, protoRetries)
 	if err != nil {
-		return fmt.Errorf("resolving router MAC: %w", err)
+		return makeMsgErr("resolving Router MAC", err)
 	}
 	stack.SetGatewayHardwareAddr(gateway)
 	berkstack := stack.StackBlocking(stackBackoff).StackGo(xnet.StackGoConfig{
@@ -111,14 +111,14 @@ func run(ctx context.Context, stack *xnet.StackAsync) error {
 	const sockstream = 0x1
 	c, err := berkstack.Socket(ctx, "tcp", syscall.AF_INET, sockstream, laddr, nil)
 	if err != nil {
-		return fmt.Errorf("creating AF_INET stream socket: %w", err)
+		return makeMsgErr("creating AF_INET stream socket", err)
 	}
 	listener := c.(net.Listener)
 	for ctx.Err() == nil {
 		time.Sleep(pollTime)
 		conn, err := listener.Accept()
 		if err != nil {
-			fmt.Println("conn failed:", err)
+			return makeMsgErr("listener.Accept failed", err)
 		}
 		go handleConn(conn)
 	}
@@ -145,18 +145,18 @@ func stackLoop(ctx context.Context, stack *xnet.StackAsync) {
 	for ctx.Err() == nil {
 		nwrite, err := stack.EgressEthernet(buf[:])
 		if err != nil {
-			fmt.Println("encaps err:", err)
+			os.Stderr.WriteString(err.Error())
 		} else if nwrite > 0 {
 			network.SendEth(buf[:nwrite])
 			cap.PrintEthernet("OUT", buf[:nwrite])
 		}
 		nread, err := network.RecvEth(buf[:])
 		if err != nil {
-			fmt.Println("network read err:", err)
+			os.Stderr.WriteString(err.Error())
 		} else if nread > 0 {
 			err = stack.IngressEthernet(buf[:nread])
 			if err != nil && err != lneto.ErrPacketDrop {
-				fmt.Println("demux err:", err)
+				os.Stderr.WriteString(err.Error())
 			} else {
 				cap.PrintEthernet("IN ", buf[:nread])
 			}
@@ -191,3 +191,7 @@ func tcpBackoff(consecutiveBackoffs uint) time.Duration {
 	wait := min(shifted, maxWait)
 	return time.Duration(wait)
 }
+
+func makeMsgErr(msg string, err error) error {
+	return errors.New(msg + ": " + err.Error())
+}

examples/min-working-example/nic.go

@@ -0,0 +1,37 @@
+package main
+
+import (
+	"math/rand"
+	"time"
+
+	"github.com/soypat/lneto/ethernet"
+)
+
+func init() {
+	mn := &mockNetwork{
+		rng: rand.New(rand.NewSource(time.Now().UnixNano())),
+	}
+	network = mn
+}
+
+type mockNetwork struct {
+	rng *rand.Rand
+}
+
+func (m *mockNetwork) SendEth(frame []byte) error {
+	return nil
+}
+func (m *mockNetwork) RecvEth(dst []byte) (int, error) {
+	n := m.rng.Int() % ethernet.MaxFrameLength
+	if n < ethernet.MinimumFrameLength {
+		return 0, nil
+	}
+	n, _ = m.rng.Read(dst[:min(len(dst), n)])
+	return n, nil
+}
+func (m *mockNetwork) HardwareAddress6() ([6]byte, error) {
+	return [6]byte{0xde, 0xad, 0xbe, 0xef, 0x00, 0x00}, nil
+}
+func (m *mockNetwork) MaxFrameLength() (int, error) {
+	return ethernet.MaxFrameLength, nil
+}

internal/strconv.go

@@ -1,5 +1,15 @@
 package internal
 
+import "strconv"
+
+// AppendStrDecimal appends pfx followed by value in base 10 to dst and returns
+// the resulting slice. It condenses the prefixed-number pattern common to
+// AppendString/AppendText methods, i.e. `internal.AppendStrDecimal(b, " len=", 4)`.
+func AppendStrDecimal(dst []byte, pfx string, value int64) []byte {
+	dst = append(dst, pfx...)
+	return strconv.AppendInt(dst, value, 10)
+}
+
 // IntLen returns the number of bytes [strconv.AppendInt] emits for value in the
 // given base, including a leading minus sign for negatives. Lets callers size a
 // buffer, or test whether a value fits an existing slot, before writing a byte.

internet/pcap/capture.go

@@ -987,16 +987,13 @@ func (frm Frame) AppendString(b []byte) []byte {
 	bitlen := frm.LenBits()
 	b = append(b, frm.Protocol...)
 	if bitlen%8 == 0 {
-		b = append(b, " len="...)
+		b = internal.AppendStrDecimal(b, " len=", int64(bitlen/8))
-		b = strconv.AppendInt(b, int64(bitlen/8), 10)
 	} else {
-		b = append(b, " bits="...)
+		b = internal.AppendStrDecimal(b, " bits=", int64(bitlen))
-		b = strconv.AppendInt(b, int64(bitlen), 10)
 	}
 	iopt, err := frm.FieldByClass(FieldClassOptions)
 	if err == nil {
-		b = append(b, " optlen="...)
+		b = internal.AppendStrDecimal(b, " optlen=", int64((frm.Fields[iopt].BitLength+7)/8))
-		b = strconv.AppendInt(b, int64((frm.Fields[iopt].BitLength+7)/8), 10)
 	}
 	for _, err := range frm.Errors {
 		b = append(b, ' ')

ipv4/frame.go

@@ -2,8 +2,6 @@ package ipv4
 
 import (
 	"encoding/binary"
-	"fmt"
-	"net/netip"
 
 	"github.com/soypat/lneto"
 )
@@ -238,14 +236,10 @@ func (ifrm Frame) ValidateExceptCRC(v *lneto.Validator) {
 }
 
 func (ifrm Frame) String() string {
-	dst := netip.AddrFrom4(*ifrm.DestinationAddr())
+	proto := ifrm.Protocol().String()
-	src := netip.AddrFrom4(*ifrm.SourceAddr())
+	b := make([]byte, 0, 5+len(proto))
-
+	b = append(b, "IP ("...)
-	hl := ifrm.HeaderLength()
+	b = append(b, proto...)
-	tl := int(ifrm.TotalLength())
+	b = append(b, ')')
-	ttl := ifrm.TTL()
+	return string(b)
-	id := ifrm.ID()
-	proto := ifrm.Protocol()
-	tos := ifrm.ToS()
-	return fmt.Sprintf("IP %s SRC=%s DST=%s LEN=%d OPT=%d TTL=%d ID=%d ToS=0x%x", proto.String(), src.String(), dst.String(), tl, tl-hl, ttl, id, tos)
 }

tcp/definitions.go

@@ -2,12 +2,12 @@ package tcp
 
 import (
 	"errors"
-	"fmt"
 	"math/bits"
 	"strconv"
 	"unsafe"
 
 	"github.com/soypat/lneto"
+	"github.com/soypat/lneto/internal"
 )
 
 //go:generate stringer -type=State,OptionKind -linecomment -output stringers.go .
@@ -73,10 +73,19 @@ func (seg Segment) isFirstSYN() bool {
 }
 
 func (seg Segment) String() string {
-	if seg.DATALEN == 0 {
+	return string(seg.AppendString(nil))
-		return fmt.Sprintf("SEG %s ACK=%d SEQ=%d WND=%d", seg.Flags, seg.ACK, seg.SEQ, seg.WND)
+}
+
+func (seg Segment) AppendString(b []byte) []byte {
+	b = append(b, "SEG "...)
+	b = append(b, seg.Flags.String()...)
+	b = internal.AppendStrDecimal(b, " ACK=", int64(seg.ACK))
+	b = internal.AppendStrDecimal(b, " SEQ=", int64(seg.SEQ))
+	b = internal.AppendStrDecimal(b, " WND=", int64(seg.WND))
+	if seg.DATALEN > 0 {
+		b = internal.AppendStrDecimal(b, " DATALEN=", int64(seg.DATALEN))
 	}
-	return fmt.Sprintf("SEG %s ACK=%d SEQ=%d WND=%d DATALEN=%d", seg.Flags, seg.ACK, seg.SEQ, seg.WND, seg.DATALEN)
+	return b
 }
 
 // ClientSynSegment is a the first packet sent over a TCP connection to a server. Typically the client

tcp/frame.go

@@ -2,10 +2,10 @@ package tcp
 
 import (
 	"encoding/binary"
-	"fmt"
 	"math"
 
 	"github.com/soypat/lneto"
+	"github.com/soypat/lneto/internal"
 )
 
 const (
@@ -170,7 +170,12 @@ func (tfrm Frame) String() string {
 	src := tfrm.SourcePort()
 	dst := tfrm.DestinationPort()
 	seg := tfrm.Segment(len(tfrm.Payload()))
-	return fmt.Sprintf("TCP :%d -> :%d %s", src, dst, seg.String())
+	b := make([]byte, 0, 64)
+	b = append(b, "TCP "...)
+	b = internal.AppendStrDecimal(b, " src=", int64(src))
+	b = internal.AppendStrDecimal(b, " dst=", int64(dst))
+	b = append(b, ' ')
+	return string(seg.AppendString(b))
 }
 
 //

udp/handler.go

@@ -1,7 +1,6 @@
 package udp
 
 import (
-	"fmt"
 	"net"
 
 	"github.com/soypat/lneto"
@@ -117,7 +116,7 @@ func (h *Handler) Send(buf []byte) (int, error) {
 	dgram := internal.SliceDequeueFront(&h.txDgrams)
 	n, err := h.txRing.Read(buf[8 : 8+dgram.length])
 	if err != nil || n != int(dgram.length) {
-		panic(fmt.Sprintf("udp send handler failure %d %s", n, err))
+		panic("udp send handler failure")
 	}
 	ufrm.SetSourcePort(h.lport)
 	ufrm.SetDestinationPort(h.rport)
@@ -152,13 +151,13 @@ func (h *Handler) ReadNext(b []byte) (int, error) {
 	dgram := internal.SliceDequeueFront(&h.rxDgrams)
 	n, err := h.rxRing.Read(b[:min(len(b), int(dgram.length))])
 	if err != nil {
-		panic(fmt.Sprintf("udp read handler failure %d %s", n, err))
+		panic("udp readnext rx ring failure")
 	}
 	discard := int(dgram.length) - len(b)
 	if discard > 0 {
 		err = h.rxRing.ReadDiscard(discard)
 		if err != nil {
-			panic(fmt.Sprintf("udp readdiscard handler failure %d %s", n, err))
+			panic("udp readnext discard failure")
 		}
 	}
 	return n, nil

udp/mux.go

@@ -1,7 +1,6 @@
 package udp
 
 import (
-	"fmt"
 	"math"
 	"net"
 	"net/netip"
@@ -226,7 +225,7 @@ func (mh *muxHandler) Encapsulate(carrierData []byte, ipOffset, frameOffset int)
 
 	n, err := mh.txRing.Read(buf[8 : 8+dgram.length])
 	if err != nil || n != int(dgram.length) {
-		panic(fmt.Sprintf("udp send handler failure %d %s", n, err))
+		panic("udp muxh encaps fail txring read")
 	}
 	ufrm.SetSourcePort(dgram.lport)
 	ufrm.SetDestinationPort(dgram.rport)

validation.go

@@ -2,7 +2,6 @@ package lneto
 
 import (
 	"errors"
-	"fmt"
 	"strconv"
 )
 
@@ -82,7 +81,7 @@ type BitPosErr struct {
 }
 
 func (bpe *BitPosErr) Error() string {
-	return fmt.Sprintf("%s at bits %d..%d", bpe.Err.Error(), bpe.BitStart, bpe.BitStart+bpe.BitLen)
+	return bpe.Err.Error()
 }
 
 func (bpe *BitPosErr) AppendError(dst []byte) []byte {