p2p, p2p/discover, p2p/discv5: implement UDP port sharing (#15200)

This commit affects p2p/discv5 "topic discovery" by running it on
the same UDP port where the old discovery works. This is realized
by giving an "unhandled" packet channel to the old v4 discovery
packet handler where all invalid packets are sent. These packets
are then processed by v5. v5 packets are always invalid when
interpreted by v4 and vice versa. This is ensured by adding one
to the first byte of the packet hash in v5 packets.

DiscoveryV5Bootnodes is also changed to point to new bootnodes
that are implementing the changed packet format with modified
hash. Existing and new v5 bootnodes are both running on different
ports ATM.

2 files changed, 22 insertions, 25 deletions

diff --git a/p2p/discover/udp.go b/p2p/discover/udp.go
index f9eb99ee3..60436952d 100644
--- a/p2p/discover/udp.go
+++ b/p2p/discover/udp.go
@@ -210,17 +210,15 @@ type reply struct {
 	matched chan<- bool
 }
 
+// ReadPacket is sent to the unhandled channel when it could not be processed
+type ReadPacket struct {
+	Data []byte
+	Addr *net.UDPAddr
+}
+
 // ListenUDP returns a new table that listens for UDP packets on laddr.
-func ListenUDP(priv *ecdsa.PrivateKey, laddr string, natm nat.Interface, nodeDBPath string, netrestrict *netutil.Netlist) (*Table, error) {
-	addr, err := net.ResolveUDPAddr("udp", laddr)
-	if err != nil {
-		return nil, err
-	}
-	conn, err := net.ListenUDP("udp", addr)
-	if err != nil {
-		return nil, err
-	}
-	tab, _, err := newUDP(priv, conn, natm, nodeDBPath, netrestrict)
+func ListenUDP(priv *ecdsa.PrivateKey, conn conn, realaddr *net.UDPAddr, unhandled chan ReadPacket, nodeDBPath string, netrestrict *netutil.Netlist) (*Table, error) {
+	tab, _, err := newUDP(priv, conn, realaddr, unhandled, nodeDBPath, netrestrict)
 	if err != nil {
 		return nil, err
 	}
@@ -228,7 +226,7 @@ func ListenUDP(priv *ecdsa.PrivateKey, laddr string, natm nat.Interface, nodeDBP
 	return tab, nil
 }
 
-func newUDP(priv *ecdsa.PrivateKey, c conn, natm nat.Interface, nodeDBPath string, netrestrict *netutil.Netlist) (*Table, *udp, error) {
+func newUDP(priv *ecdsa.PrivateKey, c conn, realaddr *net.UDPAddr, unhandled chan ReadPacket, nodeDBPath string, netrestrict *netutil.Netlist) (*Table, *udp, error) {
 	udp := &udp{
 		conn:        c,
 		priv:        priv,
@@ -237,16 +235,6 @@ func newUDP(priv *ecdsa.PrivateKey, c conn, natm nat.Interface, nodeDBPath strin
 		gotreply:    make(chan reply),
 		addpending:  make(chan *pending),
 	}
-	realaddr := c.LocalAddr().(*net.UDPAddr)
-	if natm != nil {
-		if !realaddr.IP.IsLoopback() {
-			go nat.Map(natm, udp.closing, "udp", realaddr.Port, realaddr.Port, "ethereum discovery")
-		}
-		// TODO: react to external IP changes over time.
-		if ext, err := natm.ExternalIP(); err == nil {
-			realaddr = &net.UDPAddr{IP: ext, Port: realaddr.Port}
-		}
-	}
 	// TODO: separate TCP port
 	udp.ourEndpoint = makeEndpoint(realaddr, uint16(realaddr.Port))
 	tab, err := newTable(udp, PubkeyID(&priv.PublicKey), realaddr, nodeDBPath)
@@ -256,7 +244,7 @@ func newUDP(priv *ecdsa.PrivateKey, c conn, natm nat.Interface, nodeDBPath strin
 	udp.Table = tab
 
 	go udp.loop()
-	go udp.readLoop()
+	go udp.readLoop(unhandled)
 	return udp.Table, udp, nil
 }
 
@@ -492,8 +480,11 @@ func encodePacket(priv *ecdsa.PrivateKey, ptype byte, req interface{}) ([]byte,
 }
 
 // readLoop runs in its own goroutine. it handles incoming UDP packets.
-func (t *udp) readLoop() {
+func (t *udp) readLoop(unhandled chan ReadPacket) {
 	defer t.conn.Close()
+	if unhandled != nil {
+		defer close(unhandled)
+	}
 	// Discovery packets are defined to be no larger than 1280 bytes.
 	// Packets larger than this size will be cut at the end and treated
 	// as invalid because their hash won't match.
@@ -509,7 +500,12 @@ func (t *udp) readLoop() {
 			log.Debug("UDP read error", "err", err)
 			return
 		}
-		t.handlePacket(from, buf[:nbytes])
+		if t.handlePacket(from, buf[:nbytes]) != nil && unhandled != nil {
+			select {
+			case unhandled <- ReadPacket{buf[:nbytes], from}:
+			default:
+			}
+		}
 	}
 }
 
diff --git a/p2p/discover/udp_test.go b/p2p/discover/udp_test.go
index 21e8b561d..b81caf839 100644
--- a/p2p/discover/udp_test.go
+++ b/p2p/discover/udp_test.go
@@ -70,7 +70,8 @@ func newUDPTest(t *testing.T) *udpTest {
 		remotekey:  newkey(),
 		remoteaddr: &net.UDPAddr{IP: net.IP{10, 0, 1, 99}, Port: 30303},
 	}
-	test.table, test.udp, _ = newUDP(test.localkey, test.pipe, nil, "", nil)
+	realaddr := test.pipe.LocalAddr().(*net.UDPAddr)
+	test.table, test.udp, _ = newUDP(test.localkey, test.pipe, realaddr, nil, "", nil)
 	return test
 }