Tcp rst handling (#40)

* claude suggests a way forward

* add timing to capture printer

* add pcap.Flags

* fix ICMP CRC calculation and add test

* bugfix: still send data on half-close state(close-wait)

* fix pcap test

x/xnet/pcap-printer.go

@@ -3,12 +3,19 @@ package xnet
 import (
 	"io"
 	"strconv"
+	"time"
 
 	"github.com/soypat/lneto/internet/pcap"
 )
 
 type CapturePrinterConfig struct {
 	NamespaceWidth int
+	// TimePrecision if non-zero is used to print timestamp
+	// at which the packet was received. By default the amount of
+	// seconds since configuration is printed.
+	TimePrecision int
+	// Now returns the current time.
+	Now func() time.Time
 }
 
 // CapturePrinter prints internet packets using the [pcap.PacketBreakdown] and [pcap.Formatter] types.
@@ -20,9 +27,18 @@ type CapturePrinter struct {
 	fmtPcapBuf []byte
 	// minimum length of namespace on print.
 	namespaceminwidth int
+
+	timeprec int
+	origin   time.Time
+	now      func() time.Time
 }
 
 func (stack *CapturePrinter) Configure(writer io.Writer, cfg CapturePrinterConfig) error {
+	stack.timeprec = cfg.TimePrecision
+	stack.now = cfg.Now
+	if stack.printTimestamps() {
+		stack.origin = cfg.Now()
+	}
 	stack.namespaceminwidth = cfg.NamespaceWidth
 	stack.write = writer.Write
 	return nil
@@ -36,9 +52,19 @@ func (stack *CapturePrinter) Formatter() *pcap.Formatter {
 
 func (stack *CapturePrinter) PrintPacket(prefix string, pkt []byte) {
 	fmtbuf := stack.fmtPcapBuf[:0]
+	useTimestamps := stack.printTimestamps()
+	var captime time.Time
+	if useTimestamps {
+		captime = stack.now()
+	}
 	var err error
 	stack.frms, err = stack.cap.CaptureEthernet(stack.frms[:0], pkt, 0)
 	if err == nil {
+		if useTimestamps {
+			diff := captime.Sub(stack.origin)
+			fmtbuf = strconv.AppendFloat(fmtbuf, diff.Seconds(), 'f', stack.timeprec, 32)
+			fmtbuf = append(fmtbuf, ' ')
+		}
 		fmtbuf = append(fmtbuf, prefix...)
 		// Ensure minimum width of packet length display for less jitter in log viewline.
 		prevlen := len(prefix)
@@ -60,3 +86,7 @@ func (stack *CapturePrinter) PrintPacket(prefix string, pkt []byte) {
 	stack.write(fmtbuf)
 	stack.fmtPcapBuf = fmtbuf[:0] // Reuse buffer if allocated at larger size.
 }
+
+func (stack *CapturePrinter) printTimestamps() bool {
+	return stack.timeprec > 0 && stack.now != nil
+}