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

p2p/server.go

@@ -40,11 +40,10 @@ const (
 	refreshPeersInterval    = 30 * time.Second
 	staticPeerCheckInterval = 15 * time.Second
 
-	// Maximum number of concurrently handshaking inbound connections.
-	maxAcceptConns = 50
-
-	// Maximum number of concurrently dialing outbound connections.
+	// Connectivity defaults.
 	maxActiveDialTasks     = 16
+	defaultMaxPendingPeers = 50
+	defaultDialRatio       = 3
 
 	// Maximum time allowed for reading a complete message.
 	// This is effectively the amount of time a connection can be idle.
@@ -70,6 +69,11 @@ type Config struct {
 	// Zero defaults to preset values.
 	MaxPendingPeers int `toml:",omitempty"`
 
+	// DialRatio controls the ratio of inbound to dialed connections.
+	// Example: a DialRatio of 2 allows 1/2 of connections to be dialed.
+	// Setting DialRatio to zero defaults it to 3.
+	DialRatio int `toml:",omitempty"`
+
 	// NoDiscovery can be used to disable the peer discovery mechanism.
 	// Disabling is useful for protocol debugging (manual topology).
 	NoDiscovery bool
@@ -476,10 +480,7 @@ func (srv *Server) Start() (err error) {
 		srv.DiscV5 = ntab
 	}
 
-	dynPeers := (srv.MaxPeers + 1) / 2
-	if srv.NoDiscovery {
-		dynPeers = 0
-	}
+	dynPeers := srv.maxDialedConns()
 	dialer := newDialState(srv.StaticNodes, srv.BootstrapNodes, srv.ntab, dynPeers, srv.NetRestrict)
 
 	// handshake
@@ -536,6 +537,7 @@ func (srv *Server) run(dialstate dialer) {
 	defer srv.loopWG.Done()
 	var (
 		peers        = make(map[discover.NodeID]*Peer)
+		inboundCount = 0
 		trusted      = make(map[discover.NodeID]bool, len(srv.TrustedNodes))
 		taskdone     = make(chan task, maxActiveDialTasks)
 		runningTasks []task
@@ -621,14 +623,14 @@ running:
 			}
 			// TODO: track in-progress inbound node IDs (pre-Peer) to avoid dialing them.
 			select {
-			case c.cont <- srv.encHandshakeChecks(peers, c):
+			case c.cont <- srv.encHandshakeChecks(peers, inboundCount, c):
 			case <-srv.quit:
 				break running
 			}
 		case c := <-srv.addpeer:
 			// At this point the connection is past the protocol handshake.
 			// Its capabilities are known and the remote identity is verified.
-			err := srv.protoHandshakeChecks(peers, c)
+			err := srv.protoHandshakeChecks(peers, inboundCount, c)
 			if err == nil {
 				// The handshakes are done and it passed all checks.
 				p := newPeer(c, srv.Protocols)
@@ -639,8 +641,11 @@ running:
 				}
 				name := truncateName(c.name)
 				srv.log.Debug("Adding p2p peer", "name", name, "addr", c.fd.RemoteAddr(), "peers", len(peers)+1)
-				peers[c.id] = p
 				go srv.runPeer(p)
+				peers[c.id] = p
+				if p.Inbound() {
+					inboundCount++
+				}
 			}
 			// The dialer logic relies on the assumption that
 			// dial tasks complete after the peer has been added or
@@ -655,6 +660,9 @@ running:
 			d := common.PrettyDuration(mclock.Now() - pd.created)
 			pd.log.Debug("Removing p2p peer", "duration", d, "peers", len(peers)-1, "req", pd.requested, "err", pd.err)
 			delete(peers, pd.ID())
+			if pd.Inbound() {
+				inboundCount--
+			}
 		}
 	}
 
@@ -681,20 +689,22 @@ running:
 	}
 }
 
-func (srv *Server) protoHandshakeChecks(peers map[discover.NodeID]*Peer, c *conn) error {
+func (srv *Server) protoHandshakeChecks(peers map[discover.NodeID]*Peer, inboundCount int, c *conn) error {
 	// Drop connections with no matching protocols.
 	if len(srv.Protocols) > 0 && countMatchingProtocols(srv.Protocols, c.caps) == 0 {
 		return DiscUselessPeer
 	}
 	// Repeat the encryption handshake checks because the
 	// peer set might have changed between the handshakes.
-	return srv.encHandshakeChecks(peers, c)
+	return srv.encHandshakeChecks(peers, inboundCount, c)
 }
 
-func (srv *Server) encHandshakeChecks(peers map[discover.NodeID]*Peer, c *conn) error {
+func (srv *Server) encHandshakeChecks(peers map[discover.NodeID]*Peer, inboundCount int, c *conn) error {
 	switch {
 	case !c.is(trustedConn|staticDialedConn) && len(peers) >= srv.MaxPeers:
 		return DiscTooManyPeers
+	case !c.is(trustedConn) && c.is(inboundConn) && inboundCount >= srv.maxInboundConns():
+		return DiscTooManyPeers
 	case peers[c.id] != nil:
 		return DiscAlreadyConnected
 	case c.id == srv.Self().ID:
@@ -704,6 +714,21 @@ func (srv *Server) encHandshakeChecks(peers map[discover.NodeID]*Peer, c *conn)
 	}
 }
 
+func (srv *Server) maxInboundConns() int {
+	return srv.MaxPeers - srv.maxDialedConns()
+}
+
+func (srv *Server) maxDialedConns() int {
+	if srv.NoDiscovery || srv.NoDial {
+		return 0
+	}
+	r := srv.DialRatio
+	if r == 0 {
+		r = defaultDialRatio
+	}
+	return srv.MaxPeers / r
+}
+
 type tempError interface {
 	Temporary() bool
 }
@@ -714,10 +739,7 @@ func (srv *Server) listenLoop() {
 	defer srv.loopWG.Done()
 	srv.log.Info("RLPx listener up", "self", srv.makeSelf(srv.listener, srv.ntab))
 
-	// This channel acts as a semaphore limiting
-	// active inbound connections that are lingering pre-handshake.
-	// If all slots are taken, no further connections are accepted.
-	tokens := maxAcceptConns
+	tokens := defaultMaxPendingPeers
 	if srv.MaxPendingPeers > 0 {
 		tokens = srv.MaxPendingPeers
 	}
@@ -758,9 +780,6 @@ func (srv *Server) listenLoop() {
 
 		fd = newMeteredConn(fd, true)
 		srv.log.Trace("Accepted connection", "addr", fd.RemoteAddr())
-
-		// Spawn the handler. It will give the slot back when the connection
-		// has been established.
 		go func() {
 			srv.SetupConn(fd, inboundConn, nil)
 			slots <- struct{}{}