p2p/discover: add version number to ping packet

The primary motivation for doing this right now is that old PoC 8
nodes and newer PoC 9 nodes keep discovering each other, causing
handshake failures.

p2p/discover/udp.go

@@ -16,11 +16,14 @@ import (
 
 var log = logger.NewLogger("P2P Discovery")
 
+const Version = 3
+
 // Errors
 var (
 	errPacketTooSmall = errors.New("too small")
 	errBadHash        = errors.New("bad hash")
 	errExpired        = errors.New("expired")
+	errBadVersion     = errors.New("version mismatch")
 	errTimeout        = errors.New("RPC timeout")
 	errClosed         = errors.New("socket closed")
 )
@@ -45,6 +48,7 @@ const (
 // RPC request structures
 type (
 	ping struct {
+		Version    uint   // must match Version
 		IP         string // our IP
 		Port       uint16 // our port
 		Expiration uint64
@@ -169,6 +173,7 @@ func (t *udp) ping(e *Node) error {
 	// TODO: maybe check for ReplyTo field in callback to measure RTT
 	errc := t.pending(e.ID, pongPacket, func(interface{}) bool { return true })
 	t.send(e, pingPacket, ping{
+		Version:    Version,
 		IP:         t.self.IP.String(),
 		Port:       uint16(t.self.TCPPort),
 		Expiration: uint64(time.Now().Add(expiration).Unix()),
@@ -371,6 +376,9 @@ func (req *ping) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) er
 	if expired(req.Expiration) {
 		return errExpired
 	}
+	if req.Version != Version {
+		return errBadVersion
+	}
 	t.mutex.Lock()
 	// Note: we're ignoring the provided IP address right now
 	n := t.bumpOrAdd(fromID, from)