WIP

peer/mcwriter.go

@@ -1,54 +1,43 @@
 package peer
 
 import (
+	"encoding/binary"
+	"fmt"
 	"log"
 	"net"
 	"time"
-
-	"golang.org/x/crypto/nacl/sign"
 )
 
-func createLocalDiscoveryPacket(localIP byte, signingKey []byte) []byte {
-	h := Header{
-		SourceIP: localIP,
-		DestIP:   255,
-	}
-	buf := make([]byte, headerSize)
-	h.Marshal(buf)
-	out := make([]byte, headerSize+signingOverhead)
-	return sign.Sign(out[:0], buf, (*[64]byte)(signingKey))
-}
-
-func headerFromLocalDiscoveryPacket(pkt []byte) (h Header, ok bool) {
-	if len(pkt) != headerSize+signingOverhead {
-		return
-	}
-
-	h.Parse(pkt[signingOverhead:])
-	ok = true
-	return
-}
-
-func verifyLocalDiscoveryPacket(pkt, buf []byte, pubSignKey []byte) bool {
-	_, ok := sign.Open(buf[:0], pkt, (*[32]byte)(pubSignKey))
-	return ok
-}
-
-// ----------------------------------------------------------------------------
-
-func RunMCWriter(localIP byte, signingKey []byte) {
-	discoveryPacket := createLocalDiscoveryPacket(localIP, signingKey)
+const beaconLen = 35 // 1 VPN IP byte + 32 WG pubkey + 2 WG listen port
 
+func RunMCWriter(g Globals) {
 	conn, err := net.ListenMulticastUDP("udp", nil, multicastAddr)
 	if err != nil {
-		log.Fatalf("[MCWriter] Failed to bind to multicast address: %v", err)
+		log.Fatalf("[MCWriter] bind: %v", err)
 	}
 
 	for range time.Tick(broadcastInterval) {
-		log.Printf("[MCWriter] Broadcasting on %v...", multicastAddr)
-		_, err := conn.WriteToUDP(discoveryPacket, multicastAddr)
+		beacon, err := buildBeacon(g)
 		if err != nil {
-			log.Printf("[MCWriter] Failed to write multicast: %v", err)
+			log.Printf("[MCWriter] build beacon: %v", err)
+			continue
+		}
+		log.Printf("[MCWriter] Broadcasting on %v...", multicastAddr)
+		if _, err := conn.WriteToUDP(beacon, multicastAddr); err != nil {
+			log.Printf("[MCWriter] write: %v", err)
 		}
 	}
 }
+
+func buildBeacon(g Globals) ([]byte, error) {
+	dev, err := g.WGClient.Device(g.WGDevName)
+	if err != nil {
+		return nil, fmt.Errorf("get WG device: %w", err)
+	}
+	beacon := make([]byte, beaconLen)
+	beacon[0] = g.LocalPeerIP
+	pubKey := g.WGPrivKey.PublicKey()
+	copy(beacon[1:33], pubKey[:])
+	binary.BigEndian.PutUint16(beacon[33:35], uint16(dev.ListenPort))
+	return beacon, nil
+}