go-emlid/cmd/proxy/main.go

package main

import (
	"context"
	"flag"
	"fmt"
	"log/slog"
	"net"
	"net/http"
	"net/http/httputil"
	"net/url"
	"os"
	"os/signal"
	"strconv"

	"forge.cadoles.com/cadoles/go-emlid/reach/discovery"
	"github.com/grandcat/zeroconf"
	"github.com/pkg/errors"
	sloghttp "github.com/samber/slog-http"
	"github.com/wlynxg/anet"
)

var (
	address = ":8080"
	host    = "192.168.42.1"
	name    = ""
)

func init() {
	flag.StringVar(&address, "address", address, "proxy listening address")
	flag.StringVar(&host, "host", host, "reachview host adress")
	flag.StringVar(&name, "name", name, "reachview service name, default machine hostname")
}

func main() {
	flag.Parse()

	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()

	server, err := startProxy(ctx, address, host)
	if err != nil {
		slog.Error("could not start proxy", slog.Any("error", errors.WithStack(err)))
		os.Exit(1)
	}

	defer server.Close()

	service, err := startMDNSService(ctx, address, name)
	if err != nil {
		slog.Error("could not start mdns service", slog.Any("error", errors.WithStack(err)))
		os.Exit(1)
	}

	defer service.Shutdown()

	interrupt := make(chan os.Signal, 1)
	signal.Notify(interrupt, os.Interrupt)

	slog.Info("Ctrl+C to interrupt")

	<-interrupt
}

func startProxy(ctx context.Context, address string, host string) (*http.Server, error) {
	backendURL, err := url.Parse(fmt.Sprintf("http://%s", host))
	if err != nil {
		return nil, errors.WithStack(err)
	}

	proxy := httputil.NewSingleHostReverseProxy(backendURL)

	handler := sloghttp.Recovery(proxy)
	handler = sloghttp.New(slog.Default())(handler)

	server := &http.Server{
		Addr:    address,
		Handler: handler,
	}

	go func() {
		slog.Info("starting proxy server", slog.Any("address", server.Addr))

		if err := server.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
			slog.Error("could not listen and proxy http requests", slog.Any("error", errors.WithStack(err)))
		}
	}()

	go func() {
		<-ctx.Done()
		if err := server.Close(); err != nil {
			slog.Error("could not close proxy server", slog.Any("error", errors.WithStack(err)))
		}
	}()

	return server, nil
}

func startMDNSService(ctx context.Context, address string, name string) (*zeroconf.Server, error) {
	if name == "" {
		hostname, err := os.Hostname()
		if err != nil {
			return nil, errors.WithStack(err)
		}

		name = hostname
	}

	ifaces, err := anet.Interfaces()
	if err != nil {
		return nil, errors.WithStack(err)
	}

	ips, err := GetLANIPv4Addrs()
	if err != nil {
		return nil, errors.WithStack(err)
	}

	info := []string{
		fmt.Sprintf("local_name=%s", name),
		"device=ReachProxy",
		"manufacturer_data=egoHIABggkMnZWSuoy0KAgAA",
	}

	host, rawPort, err := net.SplitHostPort(address)
	if err != nil {
		return nil, errors.WithStack(err)
	}

	var port int64
	if rawPort != "" {
		port, err = strconv.ParseInt(rawPort, 10, 32)
		if err != nil {
			return nil, errors.WithStack(err)
		}
	}

	if host != "" {
		ips = []string{host}
	}

	slog.Info("announcing mdns service", slog.Any("ips", ips), slog.Any("info", info))

	server, err := zeroconf.RegisterProxy("Reach", discovery.ReachService, "local.", int(port), name, ips, info, ifaces)
	if err != nil {
		return nil, errors.WithStack(err)
	}

	go func() {
		<-ctx.Done()
		server.Shutdown()
	}()

	return server, nil
}

var (
	_, lanA, _ = net.ParseCIDR("10.0.0.0/8")
	_, lanB, _ = net.ParseCIDR("172.16.0.0/12")
	_, lanC, _ = net.ParseCIDR("192.168.0.0/16")
)

func GetLANIPv4Addrs() ([]string, error) {
	ips := make([]string, 0)

	addrs, err := anet.InterfaceAddrs()
	if err != nil {
		return nil, errors.WithStack(err)
	}

	for _, address := range addrs {
		if ipnet, ok := address.(*net.IPNet); ok && !ipnet.IP.IsLoopback() {
			ipv4 := ipnet.IP.To4()
			if ipv4 == nil {
				continue
			}

			isLAN := lanA.Contains(ipv4) || lanB.Contains(ipv4) || lanC.Contains(ipv4)
			if !isLAN {
				continue
			}

			ips = append(ips, ipv4.String())
		}
	}

	return ips, nil
}