les: limit LES peer count and improve peer configuration logic (#16010)

* les: limit number of LES connections

* eth, cmd/utils: light vs max peer configuration logic

4 files changed, 16 insertions, 4 deletions

diff --git a/les/backend.go b/les/backend.go
index 798e44e85..6a324cb04 100644
--- a/les/backend.go
+++ b/les/backend.go
@@ -46,6 +46,8 @@ import (
 )
 
 type LightEthereum struct {
+	config *eth.Config
+
 	odr         *LesOdr
 	relay       *LesTxRelay
 	chainConfig *params.ChainConfig
@@ -92,6 +94,7 @@ func New(ctx *node.ServiceContext, config *eth.Config) (*LightEthereum, error) {
 	quitSync := make(chan struct{})
 
 	leth := &LightEthereum{
+		config:           config,
 		chainConfig:      chainConfig,
 		chainDb:          chainDb,
 		eventMux:         ctx.EventMux,
@@ -224,7 +227,7 @@ func (s *LightEthereum) Start(srvr *p2p.Server) error {
 	// clients are searching for the first advertised protocol in the list
 	protocolVersion := AdvertiseProtocolVersions[0]
 	s.serverPool.start(srvr, lesTopic(s.blockchain.Genesis().Hash(), protocolVersion))
-	s.protocolManager.Start()
+	s.protocolManager.Start(s.config.LightPeers)
 	return nil
 }
 
diff --git a/les/handler.go b/les/handler.go
index ad2e8058f..8cd37c7ab 100644
--- a/les/handler.go
+++ b/les/handler.go
@@ -109,6 +109,7 @@ type ProtocolManager struct {
 	downloader *downloader.Downloader
 	fetcher    *lightFetcher
 	peers      *peerSet
+	maxPeers   int
 
 	SubProtocols []p2p.Protocol
 
@@ -216,7 +217,9 @@ func (pm *ProtocolManager) removePeer(id string) {
 	pm.peers.Unregister(id)
 }
 
-func (pm *ProtocolManager) Start() {
+func (pm *ProtocolManager) Start(maxPeers int) {
+	pm.maxPeers = maxPeers
+
 	if pm.lightSync {
 		go pm.syncer()
 	} else {
@@ -257,6 +260,10 @@ func (pm *ProtocolManager) newPeer(pv int, nv uint64, p *p2p.Peer, rw p2p.MsgRea
 // handle is the callback invoked to manage the life cycle of a les peer. When
 // this function terminates, the peer is disconnected.
 func (pm *ProtocolManager) handle(p *peer) error {
+	if pm.peers.Len() >= pm.maxPeers {
+		return p2p.DiscTooManyPeers
+	}
+
 	p.Log().Debug("Light Ethereum peer connected", "name", p.Name())
 
 	// Execute the LES handshake
diff --git a/les/helper_test.go b/les/helper_test.go
index 57e693996..1c1de64ad 100644
--- a/les/helper_test.go
+++ b/les/helper_test.go
@@ -176,7 +176,7 @@ func newTestProtocolManager(lightSync bool, blocks int, generator func(int, *cor
 		srv.fcManager = flowcontrol.NewClientManager(50, 10, 1000000000)
 		srv.fcCostStats = newCostStats(nil)
 	}
-	pm.Start()
+	pm.Start(1000)
 	return pm, nil
 }
 
diff --git a/les/server.go b/les/server.go
index ec2e44fec..85ebbf898 100644
--- a/les/server.go
+++ b/les/server.go
@@ -38,6 +38,7 @@ import (
 )
 
 type LesServer struct {
+	config          *eth.Config
 	protocolManager *ProtocolManager
 	fcManager       *flowcontrol.ClientManager // nil if our node is client only
 	fcCostStats     *requestCostStats
@@ -62,6 +63,7 @@ func NewLesServer(eth *eth.Ethereum, config *eth.Config) (*LesServer, error) {
 	}
 
 	srv := &LesServer{
+		config:           config,
 		protocolManager:  pm,
 		quitSync:         quitSync,
 		lesTopics:        lesTopics,
@@ -108,7 +110,7 @@ func (s *LesServer) Protocols() []p2p.Protocol {
 
 // Start starts the LES server
 func (s *LesServer) Start(srvr *p2p.Server) {
-	s.protocolManager.Start()
+	s.protocolManager.Start(s.config.LightPeers)
 	for _, topic := range s.lesTopics {
 		topic := topic
 		go func() {