p2p: limit the number of incoming connections

to p2p.max_num_inbound_peers + len(p2p.unconditional_peer_ids)

node/node.go

@@ -467,6 +467,11 @@ func createTransport(
 	}
 
 	p2p.MultiplexTransportConnFilters(connFilters...)(transport)
+
+	// Limit the number of incoming connections.
+	max := config.P2P.MaxNumInboundPeers + len(splitAndTrimEmpty(config.P2P.UnconditionalPeerIDs, ",", " "))
+	p2p.MultiplexTransportMaxIncomingConnections(max)(transport)
+
 	return transport, peerFilters
 }
 

p2p/transport.go

@@ -7,6 +7,7 @@ import (
 	"time"
 
 	"github.com/pkg/errors"
+	"golang.org/x/net/netutil"
 
 	"github.com/tendermint/tendermint/crypto"
 	"github.com/tendermint/tendermint/p2p/conn"
@@ -122,11 +123,18 @@ func MultiplexTransportResolver(resolver IPResolver) MultiplexTransportOption {
 	return func(mt *MultiplexTransport) { mt.resolver = resolver }
 }
 
+// MultiplexTransportMaxIncomingConnections sets the maximum number of
+// simultaneous connections (incoming). Default: 0 (unlimited)
+func MultiplexTransportMaxIncomingConnections(n int) MultiplexTransportOption {
+	return func(mt *MultiplexTransport) { mt.maxIncomingConnections = n }
+}
+
 // MultiplexTransport accepts and dials tcp connections and upgrades them to
 // multiplexed peers.
 type MultiplexTransport struct {
-	netAddr  NetAddress
-	listener net.Listener
+	netAddr                NetAddress
+	listener               net.Listener
+	maxIncomingConnections int // see MaxIncomingConnections
 
 	acceptc chan accept
 	closec  chan struct{}
@@ -240,6 +248,10 @@ func (mt *MultiplexTransport) Listen(addr NetAddress) error {
 		return err
 	}
 
+	if mt.maxIncomingConnections > 0 {
+		ln = netutil.LimitListener(ln, mt.maxIncomingConnections)
+	}
+
 	mt.netAddr = addr
 	mt.listener = ln
 

p2p/transport_test.go

@@ -5,6 +5,7 @@ import (
 	"math/rand"
 	"net"
 	"reflect"
+	"strings"
 	"testing"
 	"time"
 
@@ -134,6 +135,50 @@ func TestTransportMultiplexConnFilterTimeout(t *testing.T) {
 	}
 }
 
+func TestTransportMultiplexMaxIncomingConnections(t *testing.T) {
+	mt := newMultiplexTransport(
+		emptyNodeInfo(),
+		NodeKey{
+			PrivKey: ed25519.GenPrivKey(),
+		},
+	)
+	id := mt.nodeKey.ID()
+
+	MultiplexTransportMaxIncomingConnections(0)(mt)
+
+	addr, err := NewNetAddressString(IDAddressString(id, "127.0.0.1:0"))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if err := mt.Listen(*addr); err != nil {
+		t.Fatal(err)
+	}
+
+	errc := make(chan error)
+
+	go func() {
+		addr := NewNetAddress(id, mt.listener.Addr())
+
+		_, err := addr.Dial()
+		if err != nil {
+			errc <- err
+			return
+		}
+
+		close(errc)
+	}()
+
+	if err := <-errc; err != nil {
+		t.Errorf("connection failed: %v", err)
+	}
+
+	_, err = mt.Accept(peerConfig{})
+	if err == nil || !strings.Contains(err.Error(), "connection reset by peer") {
+		t.Errorf("expected connection reset by peer error, got %v", err)
+	}
+}
+
 func TestTransportMultiplexAcceptMultiple(t *testing.T) {
 	mt := testSetupMultiplexTransport(t)
 	laddr := NewNetAddress(mt.nodeKey.ID(), mt.listener.Addr())