vppn/node/main.go

package node

import (
	"encoding/json"
	"flag"
	"fmt"
	"io"
	"log"
	"net"
	"net/http"
	"net/netip"
	"os"
	"runtime/debug"
	"vppn/m"
)

func panicHandler() {
	if r := recover(); r != nil {
		log.Fatalf("\n %v\n\nstacktrace from panic: %s\n", r, string(debug.Stack()))
	}
}

func Main() {
	defer panicHandler()

	var (
		netName  string
		initURL  string
		listenIP string
		port     int
	)

	flag.StringVar(&netName, "name", "", "[REQUIRED] The network name.")
	flag.StringVar(&initURL, "init-url", "", "Initializes peer from the hub URL.")
	flag.StringVar(&listenIP, "listen-ip", "", "IP address to listen on.")
	flag.IntVar(&port, "port", 0, "Port to listen on.")
	flag.Parse()

	if netName == "" {
		flag.Usage()
		os.Exit(1)
	}

	if initURL != "" {
		mainInit(netName, initURL)
		return
	}

	main(netName, listenIP, uint16(port))
}

func mainInit(netName, initURL string) {
	if _, err := loadPeerConfig(netName); err == nil {
		log.Fatalf("Network is already initialized.")
	}

	resp, err := http.Get(initURL)
	if err != nil {
		log.Fatalf("Failed to fetch data from hub: %v", err)
	}
	defer resp.Body.Close()

	data, err := io.ReadAll(resp.Body)
	if err != nil {
		log.Fatalf("Failed to read response body: %v", err)
	}

	peerConfig := m.PeerConfig{}
	if err := json.Unmarshal(data, &peerConfig); err != nil {
		log.Fatalf("Failed to parse configuration: %v", err)
	}

	if err := storePeerConfig(netName, peerConfig); err != nil {
		log.Fatalf("Failed to store configuration: %v", err)
	}

	log.Print("Initialization successful.")
}

// ----------------------------------------------------------------------------

func main(netName, listenIP string, port uint16) {
	conf, err := loadPeerConfig(netName)
	if err != nil {
		log.Fatalf("Failed to load configuration: %v", err)
	}

	port = determinePort(conf.Port, port)

	iface, err := openInterface(conf.Network, conf.PeerIP, netName)
	if err != nil {
		log.Fatalf("Failed to open interface: %v", err)
	}

	myAddr, err := net.ResolveUDPAddr("udp", fmt.Sprintf("%s:%d", listenIP, port))
	if err != nil {
		log.Fatalf("Failed to resolve UDP address: %v", err)
	}

	conn, err := net.ListenUDP("udp", myAddr)
	if err != nil {
		log.Fatalf("Failed to open UDP port: %v", err)
	}

	connWriter := newConnWriter(conn)
	ifWriter := newIFWriter(iface)

	peers := remotePeers{}

	for i := range peers {
		peers[i] = newRemotePeer(conf, byte(i), ifWriter, connWriter)
	}

	go newHubPoller(netName, conf, peers).Run()
	go readFromConn(conn, peers)
	readFromIFace(iface, peers)

}

// ----------------------------------------------------------------------------

func determinePort(confPort, portFromCommandLine uint16) uint16 {
	if portFromCommandLine != 0 {
		return portFromCommandLine
	}
	if confPort != 0 {
		return confPort
	}
	return 456
}

// ----------------------------------------------------------------------------

func readFromConn(conn *net.UDPConn, peers remotePeers) {

	defer panicHandler()

	var (
		remoteAddr netip.AddrPort
		n          int
		err        error
		buf        = make([]byte, bufferSize)
		data       []byte
		h          header
	)

	for {
		n, remoteAddr, err = conn.ReadFromUDPAddrPort(buf[:bufferSize])
		if err != nil {
			log.Fatalf("Failed to read from UDP port: %v", err)
		}

		data = buf[:n]

		if n < headerSize {
			continue // Packet it soo short.
		}

		h.Parse(data)
		peers[h.SourceIP].HandlePacket(remoteAddr, h, data)
	}
}

// ----------------------------------------------------------------------------

func readFromIFace(iface io.ReadWriteCloser, peers remotePeers) {

	var (
		buf      = make([]byte, bufferSize)
		packet   []byte
		remoteIP byte
		err      error
	)

	for {
		packet, remoteIP, err = readNextPacket(iface, buf)
		if err != nil {
			log.Fatalf("Failed to read from interface: %v", err)
		}

		peers[remoteIP].SendData(packet)
	}
}