add stringer methods

README.md

@@ -27,4 +27,11 @@ go mod download github.com/soypat/lneto@latest
 ```
 
 
+## Developing (linux)
 
+- [`tap`](./examples/tap) (linux only, root privilidges required) Program opens a TAP interface and assigns an IP address to it and exposes the interface via a HTTP interface. This program is run with root privilidges to facilitate debugging of lneto since no root privilidges are required to interact with the HTTP interface exposed.
+    - `POST http://127.0.0.1:7070/send`: Receives a POST with request body containing JSON string of data to send over TAP interface. Response contains only status code.
+    - `GET http://127.0.0.1:7070/recv`: Receives a GET request. Response contains a JSON string of oldest unread TAP interface packet. If string is empty then there is no more data to read.
+
+- [`stack`](./examples/stack) Contains stack implementation which can interact with `tap` program. No root privilidges required.
+    - Can expose a HTTP server.

examples/stack/main.go

@@ -394,6 +394,7 @@ func (ts *TCPStack) Recv(ipFrame []byte, tcpOff int) error {
 	case 4:
 		ifrm, _ := ipv4.NewFrame(ipFrame)
 		ifrm.CRCWriteTCPPseudo(&ts.crc)
+		ts.log.Info("tcpStack:recv", slog.String("ipfrm", ifrm.String()), slog.String("frame", tfrm.String()))
 	case 6:
 		i6frm, _ := ipv6.NewFrame(ipFrame)
 		i6frm.CRCWritePseudo(&ts.crc)
@@ -435,6 +436,7 @@ func (ts *TCPStack) Handle(ipFrame []byte, tcpOff int) (n int, err error) {
 	}
 	// TCP packet written.
 	tfrm, _ := tcp.NewFrame(ipFrame[tcpOff : tcpOff+n])
+
 	ts.validator.ResetErr()
 	tfrm.ValidateSize(&ts.validator) // Perform basic validation.
 	if err = ts.validator.Err(); err != nil {
@@ -445,6 +447,7 @@ func (ts *TCPStack) Handle(ipFrame []byte, tcpOff int) (n int, err error) {
 	case 4:
 		ifrm, _ := ipv4.NewFrame(ipFrame)
 		ifrm.CRCWriteTCPPseudo(&ts.crc)
+		ts.log.Info("tcpStack:send", slog.String("ipfrm", ifrm.String()), slog.String("frame", tfrm.String()))
 	case 6:
 		i6frm, _ := ipv6.NewFrame(ipFrame)
 		i6frm.CRCWritePseudo(&ts.crc)

ipv4/frame.go

@@ -3,6 +3,8 @@ package ipv4
 import (
 	"encoding/binary"
 	"errors"
+	"fmt"
+	"net/netip"
 
 	"github.com/soypat/lneto/lneto2"
 )
@@ -218,3 +220,16 @@ func (ifrm Frame) ValidateExceptCRC(v *lneto2.Validator) {
 		v.AddError(errEvil)
 	}
 }
+
+func (ifrm Frame) String() string {
+	dst := netip.AddrFrom4(*ifrm.DestinationAddr())
+	src := netip.AddrFrom4(*ifrm.SourceAddr())
+
+	hl := ifrm.HeaderLength()
+	tl := int(ifrm.TotalLength())
+	ttl := ifrm.TTL()
+	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

@@ -73,6 +73,13 @@ func (seg Segment) isFirstSYN() bool {
 	return seg.Flags == FlagSYN && seg.ACK == 0 && seg.DATALEN == 0 && seg.WND > 0
 }
 
+func (seg Segment) String() string {
+	if seg.DATALEN == 0 {
+		return fmt.Sprintf("SEG %s ACK=%d SEQ=%d WND=%d", seg.Flags, seg.ACK, seg.SEQ, seg.WND)
+	}
+	return fmt.Sprintf("SEG %s ACK=%d SEQ=%d WND=%d DATALEN=%d", seg.Flags, seg.ACK, seg.SEQ, seg.WND, seg.DATALEN)
+}
+
 // ClientSynSegment is a the first packet sent over a TCP connection to a server. Typically the client
 // will call ClientSynSegment to generate a new SYN packet to send over to the server to initiate communications:
 //

tcp/frame.go

@@ -174,8 +174,10 @@ func (frm Frame) ClearHeader() {
 }
 
 func (tfrm Frame) String() string {
+	src := tfrm.SourcePort()
+	dst := tfrm.DestinationPort()
 	seg := tfrm.Segment(len(tfrm.Payload()))
-	return fmt.Sprintf("%+v", seg)
+	return fmt.Sprintf("TCP :%d -> :%d %s", src, dst, seg.String())
 }
 
 //

tcp/handler.go

@@ -11,7 +11,8 @@ import (
 )
 
 var (
-	errMismatchedPort = errors.New("mismatched port")
+	errMismatchedSrcPort = errors.New("source port mismatch")
+	errMismatchedDstPort = errors.New("destination port mismatch")
 )
 
 // Handler is a low level TCP handling data structure. It implements logic
@@ -120,13 +121,14 @@ func (h *Handler) Recv(b []byte) error {
 	if err != nil {
 		return err
 	}
+
 	remotePort := tfrm.SourcePort()
 	if h.remotePort != 0 && remotePort != h.remotePort {
-		return errMismatchedPort
+		return errMismatchedSrcPort
 	}
 	dstPort := tfrm.DestinationPort()
 	if h.localPort != dstPort {
-		return errMismatchedPort
+		return errMismatchedDstPort
 	}
 	payload := tfrm.Payload()
 	if len(payload) > h.bufRx.Free() {
@@ -160,6 +162,9 @@ func (h *Handler) Recv(b []byte) error {
 		h.debug("tcp.Handler:rx-remoteport-set", slog.Uint64("port", uint64(h.localPort)), slog.Uint64("remoteport", uint64(remotePort)))
 		h.remotePort = remotePort
 	}
+	if h.logenabled(internal.LevelTrace) {
+		h.trace("tcp.Handler:rx-done", slog.Uint64("port", uint64(h.localPort)), slog.Uint64("remoteport", uint64(remotePort)), slog.String("seg", segIncoming.String()))
+	}
 	return nil
 }