From e58731bd34eebe03be8a625864e00819097c1d7d Mon Sep 17 00:00:00 2001
From: Toni <antpiasecki@gmail.com>
Date: Wed, 22 Jul 2026 10:37:46 +0200
Subject: [PATCH] move to ipv6

---
 client/main.go |  2 +-
 server/main.go | 48 +++++++++++++++++++++++++++++-------------------
 2 files changed, 30 insertions(+), 20 deletions(-)

diff --git a/client/main.go b/client/main.go
index 58b92ed..e34d271 100644
--- a/client/main.go
+++ b/client/main.go
@@ -118,7 +118,7 @@ func setupInterface() {
 		panic(err)
 	}
 
-	if err := exec.Command("ip", "addr", "add", internalIP.String()+"/24", "dev", IFACE_NAME).Run(); err != nil {
+	if err := exec.Command("ip", "addr", "add", internalIP.String()+"/32", "dev", IFACE_NAME).Run(); err != nil {
 		panic(err)
 	}
 	if err := exec.Command("ip", "link", "set", "dev", IFACE_NAME, "up").Run(); err != nil {
diff --git a/server/main.go b/server/main.go
index 594985a..c02a93e 100644
--- a/server/main.go
+++ b/server/main.go
@@ -1,11 +1,13 @@
 // TODO: slice bounds checking
 // TODO: authentication
 // TODO: encryption
+// TODO: somehow persist IPs
+// TODO: handle multiple peers behind one NAT
 package main
 
 import (
+	"crypto/rand"
 	"encoding/binary"
-	"fmt"
 	"log"
 	"net"
 	"os"
@@ -22,7 +24,6 @@ type Peer struct {
 var (
 	peers      = map[string]*Peer{}
 	peersMutex sync.Mutex
-	nextIP     = 3
 	conn       *net.UDPConn
 )
 
@@ -83,8 +84,7 @@ func receivePacket(pkt []byte, addr *net.UDPAddr) {
 		peersMutex.Lock()
 		defer peersMutex.Unlock()
 
-		// TODO
-		internalIP := fmt.Sprintf("10.1.0.%d", nextIP)
+		internalIP := randomIP().String()
 
 		if destPeer, ok := peers[addr.IP.String()]; ok {
 			internalIP = destPeer.InternalIP
@@ -93,10 +93,9 @@ func receivePacket(pkt []byte, addr *net.UDPAddr) {
 				RealAddr:   addr,
 				InternalIP: internalIP,
 			}
-			nextIP++
 		}
 
-		resp := shared.BuildPkt(shared.RESP_REGISTER, net.ParseIP(internalIP).To4())
+		resp := shared.BuildPkt(shared.RESP_REGISTER, net.ParseIP(internalIP))
 		sendTo(addr, resp)
 	case shared.REQ_DATA:
 		frame := pkt[4:]
@@ -104,22 +103,20 @@ func receivePacket(pkt []byte, addr *net.UDPAddr) {
 		payload := frame[14:]
 
 		switch etherType {
-		case 0x0800: // IPv4
-			destIP := net.IP(payload[16:20]).String()
-			if destPeer := getPeerByInternalIP(destIP); destPeer != nil {
+		case 0x86dd: // IPv6
+			rawDestIP := payload[24:40]
+			destIP := net.IP(rawDestIP).String()
+			resp := shared.BuildPkt(shared.RESP_DATA, frame)
+
+			if rawDestIP[0] == 0xff { // multicast
+				log.Println(peer.InternalIP + " -> " + destIP + " (*)")
+				broadcast(resp, peer.InternalIP)
+			} else if destPeer := getPeerByInternalIP(destIP); destPeer != nil {
 				log.Println(peer.InternalIP + " -> " + destIP)
-				resp := shared.BuildPkt(shared.RESP_DATA, frame)
-				sendTo(peer.RealAddr, resp)
+				sendTo(destPeer.RealAddr, resp)
 			} else {
 				log.Println(peer.InternalIP + " -/> " + destIP + " (unrecognized IP)")
 			}
-		case 0x0806: // ARP
-			log.Println(peer.InternalIP + " -> *")
-			resp := shared.BuildPkt(shared.RESP_DATA, frame)
-			broadcast(resp, peer.InternalIP)
-		case 0x86dd: // IPv6
-			destIP := net.IP(payload[24:40]).String()
-			log.Println(peer.InternalIP + " -/> " + destIP + " (IPv6)") // TODO
 		default:
 			log.Printf("unhandled EtherType: 0x%x\n", etherType)
 		}
@@ -132,7 +129,7 @@ func broadcast(pkt []byte, except string) {
 	peersMutex.Lock()
 	defer peersMutex.Unlock()
 	for _, p := range peers {
-		if p.RealAddr.IP.String() == except {
+		if p.InternalIP == except {
 			continue
 		}
 		sendTo(p.RealAddr, pkt)
@@ -155,3 +152,16 @@ func getPeerByInternalIP(internalIP string) *Peer {
 	}
 	return nil
 }
+
+// fd00:baa1::/32
+func randomIP() net.IP {
+	ip := make(net.IP, 16)
+	ip[0] = 0xfd
+	ip[1] = 0x00
+	ip[2] = 0xba
+	ip[3] = 0xa1
+	if _, err := rand.Read(ip[4:]); err != nil {
+		panic(err)
+	}
+	return ip
+}