add demo ntp server

testing/ntp-example-server/ntpserver.go

@@ -0,0 +1,110 @@
+package main
+
+import (
+	"encoding/binary"
+	"fmt"
+	"net"
+	"os"
+	"os/signal"
+	"syscall"
+	"time"
+)
+
+const (
+	NTP_EPOCH_OFFSET = 2208988800 // Time offset between 1900 and 1970 (Unix Epoch)
+)
+
+type NTPPacket struct {
+	LiVnMode       byte
+	Stratum        byte
+	Poll           byte
+	Precision      byte
+	RootDelay      uint32
+	RootDispersion uint32
+	ReferenceID    uint32
+	RefTimestamp   uint64
+	OrigTimestamp  uint64
+	RxTimestamp    uint64
+	TxTimestamp    uint64
+}
+
+func corruptNTPPacket(packet *NTPPacket) {
+	packet.Stratum = 0 // Invalid stratum
+}
+
+func handleConnection(conn *net.UDPConn, fixedTime uint64, corrupt bool) {
+	buffer := make([]byte, 48)
+	for {
+		_, addr, err := conn.ReadFromUDP(buffer)
+		if err != nil {
+			fmt.Println("Error reading from UDP:", err)
+			continue
+		}
+
+		packet := &NTPPacket{
+			LiVnMode:  0x23,
+			Stratum:   1,
+			Precision: 0xFA,
+			RxTimestamp: fixedTime,
+			TxTimestamp: fixedTime,
+		}
+
+		if corrupt {
+			corruptNTPPacket(packet)
+		}
+
+		buffer[0] = packet.LiVnMode
+		buffer[1] = packet.Stratum
+		buffer[2] = packet.Poll
+		buffer[3] = packet.Precision
+		binary.BigEndian.PutUint32(buffer[32:], uint32(packet.RxTimestamp>>32)) // Seconds
+		binary.BigEndian.PutUint32(buffer[36:], uint32(packet.RxTimestamp))     // Fractional seconds
+		binary.BigEndian.PutUint32(buffer[40:], uint32(packet.TxTimestamp>>32)) // Seconds
+		binary.BigEndian.PutUint32(buffer[44:], uint32(packet.TxTimestamp))     // Fractional seconds
+
+		_, err = conn.WriteToUDP(buffer, addr)
+		if err != nil {
+			fmt.Println("Failed to send UDP:", err)
+		}
+	}
+}
+
+func main() {
+	port := ":123"
+	corrupt := false
+	args := os.Args[1:]
+	if len(args) > 0 && args[0] == "--corrupt" {
+		corrupt = true
+	}
+
+	addr, err := net.ResolveUDPAddr("udp", port)
+	if err != nil {
+		fmt.Println("Failed to resolve UDP address:", err)
+		return
+	}
+
+	conn, err := net.ListenUDP("udp", addr)
+	if err != nil {
+		fmt.Println("Failed to listen on UDP:", err)
+		return
+	}
+	defer conn.Close()
+
+	fmt.Println("NTP Server started on", port)
+
+	fixedDate := time.Date(2002, time.September, 11, 14, 14, 0, 0, time.UTC)
+	fixedUnix := fixedDate.Unix()
+	fixedNTP := (uint64(fixedUnix) + NTP_EPOCH_OFFSET) << 32 // Shift left to put into the upper 32 bits
+
+	c := make(chan os.Signal, 1)
+	signal.Notify(c, os.Interrupt, syscall.SIGTERM)
+	go func() {
+		<-c
+		fmt.Println("\nNTP Server shutting down")
+		conn.Close()
+		os.Exit(0)
+	}()
+
+	handleConnection(conn, fixedNTP, corrupt)
+}
+