p2p, p2p/discover: misc connectivity improvements (#16069)

* p2p: add DialRatio for configuration of inbound vs. dialed connections

* p2p: add connection flags to PeerInfo

* p2p/netutil: add SameNet, DistinctNetSet

* p2p/discover: improve revalidation and seeding

This changes node revalidation to be periodic instead of on-demand. This
should prevent issues where dead nodes get stuck in closer buckets
because no other node will ever come along to replace them.

Every 5 seconds (on average), the last node in a random bucket is
checked and moved to the front of the bucket if it is still responding.
If revalidation fails, the last node is replaced by an entry of the
'replacement list' containing recently-seen nodes.

Most close buckets are removed because it's very unlikely we'll ever
encounter a node that would fall into any of those buckets.

Table seeding is also improved: we now require a few minutes of table
membership before considering a node as a potential seed node. This
should make it less likely to store short-lived nodes as potential
seeds.

* p2p/discover: fix nits in UDP transport

We would skip sending neighbors replies if there were fewer than
maxNeighbors results and CheckRelayIP returned an error for the last
one. While here, also resolve a TODO about pong reply tokens.

p2p/discover/udp_test.go

@@ -70,14 +70,15 @@ func newUDPTest(t *testing.T) *udpTest {
 		remotekey:  newkey(),
 		remoteaddr: &net.UDPAddr{IP: net.IP{10, 0, 1, 99}, Port: 30303},
 	}
-	realaddr := test.pipe.LocalAddr().(*net.UDPAddr)
-	test.table, test.udp, _ = newUDP(test.localkey, test.pipe, realaddr, nil, "", nil)
+	test.table, test.udp, _ = newUDP(test.pipe, Config{PrivateKey: test.localkey})
+	// Wait for initial refresh so the table doesn't send unexpected findnode.
+	<-test.table.initDone
 	return test
 }
 
 // handles a packet as if it had been sent to the transport.
 func (test *udpTest) packetIn(wantError error, ptype byte, data packet) error {
-	enc, err := encodePacket(test.remotekey, ptype, data)
+	enc, _, err := encodePacket(test.remotekey, ptype, data)
 	if err != nil {
 		return test.errorf("packet (%d) encode error: %v", ptype, err)
 	}
@@ -90,19 +91,19 @@ func (test *udpTest) packetIn(wantError error, ptype byte, data packet) error {
 
 // waits for a packet to be sent by the transport.
 // validate should have type func(*udpTest, X) error, where X is a packet type.
-func (test *udpTest) waitPacketOut(validate interface{}) error {
+func (test *udpTest) waitPacketOut(validate interface{}) ([]byte, error) {
 	dgram := test.pipe.waitPacketOut()
-	p, _, _, err := decodePacket(dgram)
+	p, _, hash, err := decodePacket(dgram)
 	if err != nil {
-		return test.errorf("sent packet decode error: %v", err)
+		return hash, test.errorf("sent packet decode error: %v", err)
 	}
 	fn := reflect.ValueOf(validate)
 	exptype := fn.Type().In(0)
 	if reflect.TypeOf(p) != exptype {
-		return test.errorf("sent packet type mismatch, got: %v, want: %v", reflect.TypeOf(p), exptype)
+		return hash, test.errorf("sent packet type mismatch, got: %v, want: %v", reflect.TypeOf(p), exptype)
 	}
 	fn.Call([]reflect.Value{reflect.ValueOf(p)})
-	return nil
+	return hash, nil
 }
 
 func (test *udpTest) errorf(format string, args ...interface{}) error {
@@ -351,7 +352,7 @@ func TestUDP_successfulPing(t *testing.T) {
 	})
 
 	// remote is unknown, the table pings back.
-	test.waitPacketOut(func(p *ping) error {
+	hash, _ := test.waitPacketOut(func(p *ping) error {
 		if !reflect.DeepEqual(p.From, test.udp.ourEndpoint) {
 			t.Errorf("got ping.From %v, want %v", p.From, test.udp.ourEndpoint)
 		}
@@ -365,7 +366,7 @@ func TestUDP_successfulPing(t *testing.T) {
 		}
 		return nil
 	})
-	test.packetIn(nil, pongPacket, &pong{Expiration: futureExp})
+	test.packetIn(nil, pongPacket, &pong{ReplyTok: hash, Expiration: futureExp})
 
 	// the node should be added to the table shortly after getting the
 	// pong packet.