Refactor - now wireguard based. (#7)

peer/multicast/broadcaster.go

@@ -0,0 +1,62 @@
+package multicast
+
+import (
+	"log"
+	"net"
+	"net/netip"
+	"time"
+
+	"golang.zx2c4.com/wireguard/wgctrl/wgtypes"
+)
+
+var addr = net.UDPAddrFromAddrPort(netip.AddrPortFrom(
+	netip.AddrFrom4([4]byte{224, 0, 0, 157}),
+	4560))
+
+func Broadcast(
+	selfVPNIP netip.Addr,
+	pubKey wgtypes.Key,
+	wgPort uint16,
+	signKey *[64]byte,
+) {
+	for {
+		broadcastInner(selfVPNIP, pubKey, wgPort, signKey)
+		time.Sleep(errorTimeout)
+	}
+}
+
+func broadcastInner(selfVPNIP netip.Addr, pubKey wgtypes.Key, wgPort uint16, signKey *[64]byte) {
+	conn, err := net.ListenMulticastUDP("udp", nil, addr)
+	if err != nil {
+		log.Printf("[MCBroadcast] bind: %v", err)
+		return
+	}
+	defer conn.Close()
+
+	buf := make([]byte, BufferSize)
+	packet := Packet{
+		PeerIP:   selfVPNIP.As4()[3],
+		WGPubKey: pubKey,
+		WGPort:   wgPort,
+	}
+
+	// Re-sign on each send so the timestamp is fresh; a stale timestamp would be
+	// dropped by receivers' freshness gate.
+	send := func() error {
+		packet.Timestamp = time.Now().Unix()
+		payload := packet.Marshal(buf, signKey)
+		_, err := conn.WriteToUDP(payload, addr)
+		return err
+	}
+
+	if err := send(); err != nil {
+		log.Printf("[MCBroadcast] write: %v", err)
+	}
+
+	for range time.Tick(broadcastInterval) {
+		if err := send(); err != nil {
+			log.Printf("[MCBroadcast] write: %v", err)
+			return
+		}
+	}
+}