NetworkMonitor/main.go

package main

import (
	"bytes"
	_ "embed"
	"fmt"
	"log"
	"net"
	"net/http"
	"os"
	"os/signal"
	"strings"
	"syscall"
	"text/template"
	"time"
)

//go:embed index.html
var tmpl string

var report = template.Must(template.New("").Parse(tmpl))
var write_report chan bool
var interval = time.Second * 2

type Network struct {
	Name   string
	IP     string
	OnFail string
}

var Networks = []*Network{
	{
		Name:   "DSL",
		IP:     "220.135.85.67",
		OnFail: "nmcli connection up DSL",
	},
	{
		Name: "Asus",
		IP:   "192.168.50.48",
	},
}

func main() {
	write_report = make(chan bool, 1)

	file, err := os.OpenFile("network.log", os.O_WRONLY|os.O_APPEND|os.O_CREATE, os.ModePerm)
	if err != nil {
		log.Panicln(err)
	}
	defer file.Close()

	log.Println("starting network monitor")

	go func() {

		perr := false
		derr := false

		for reducer := 0; ; reducer++ {
			now := time.Now().Format("2006-01-02 15:04:05")

			// Public
			go func(print bool) {
				_, err = net.LookupIP("google.com")
				if err != nil {
					if !perr {
						perr = true
						log.Println(err)
					}
					fmt.Fprintf(file, `{"x": "%s", "y": "%s", "name": "%s"},`, now, "failed", "Public")
					fmt.Fprintf(file, "\n")
				} else {
					perr = false
					if print {
						fmt.Fprintf(file, `{"x": "%s", "y": "%s", "name": "%s"},`, now, "ok", "Public")
						fmt.Fprintf(file, "\n")
					}
				}
			}(reducer == 0)

			// devices
			go func(print bool) {
				for i := range Networks {
					_, err = GetOutboundIP(Networks[i].IP + ":0")
					if err != nil {
						if !derr {
							derr = true
							log.Println(err)
						}
						fmt.Fprintf(file, `{"x": "%s", "y": "%s", "name": "%s"},`, now, "failed", Networks[i].Name)
						fmt.Fprintf(file, "\n")
						// fmt.Fprintf(file, "%s\t%s\t%s\n", now, Networks[i].Name, "failed")
					} else {
						derr = false
						if print {
							fmt.Fprintf(file, `{"x": "%s", "y": "%s", "name": "%s"},`, now, "ok", Networks[i].Name)
							fmt.Fprintf(file, "\n")
						}
					}
				}
			}(reducer == 0)

			<-time.After(interval)
			if reducer >= 9 {
				reducer = -1
			}
		}
	}()

	go func() {
		for {
			<-time.After(time.Minute * 10)
			WriteReport()
		}
	}()

	go func() {
		http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
			http.ServeFile(w, r, strings.TrimPrefix(r.URL.Path, "/"))
		})
		if err := http.ListenAndServe("0.0.0.0:1080", nil); err != nil {
			log.Fatalln(err)
		}
	}()

	wait := make(chan os.Signal, 1)
	signal.Notify(wait, syscall.SIGINT, syscall.SIGTERM)

	<-wait
	WriteReport()
}

func WriteReport() {

	select {
	case write_report <- true:

	default:
		return
	}
	defer func() { <-write_report }()

	f, err := os.OpenFile("report.html", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, os.ModePerm)
	if err != nil {
		log.Println(err)
		return
	}
	defer f.Close()

	data, err := os.ReadFile("network.log")
	if err != nil {
		log.Println(err)
		return
	}

	content := &bytes.Buffer{}
	if err = report.Execute(content, map[string]string{"Data": string(data)}); err != nil {
		log.Println(err)
		return
	}
	content.WriteTo(f)

}

// Get preferred outbound ip of this machine
func GetOutboundIP(addr string) (net.IP, error) {

	iface, err := net.ResolveUDPAddr("udp", addr)
	if err != nil {
		return nil, err
	}

	dialer := &net.Dialer{LocalAddr: iface}

	conn, err := dialer.Dial("udp", "8.8.8.8:80")
	if err != nil {
		return nil, err
	}
	defer conn.Close()

	localAddr := conn.LocalAddr().(*net.UDPAddr)

	return localAddr.IP, nil
}