From d0634a78291a8d7702ba7a9ab3385739fb8d0293 Mon Sep 17 00:00:00 2001
From: Roman Khimov <roman@nspcc.ru>
Date: Fri, 26 Mar 2021 12:26:45 +0300
Subject: [PATCH 1/2] network: don't attempt to connect to the same node twice

We can have multiple copies of the same address in the pool and we should only
proceed to connect once per attempt.
---
 pkg/network/discovery.go | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/pkg/network/discovery.go b/pkg/network/discovery.go
index 9d7073226..25da5a5ba 100644
--- a/pkg/network/discovery.go
+++ b/pkg/network/discovery.go
@@ -45,6 +45,7 @@ type DefaultDiscovery struct {
 	connectedAddrs   map[string]bool
 	goodAddrs        map[string]capability.Capabilities
 	unconnectedAddrs map[string]int
+	attempted        map[string]bool
 	isDead           bool
 	requestCh        chan int
 	pool             chan string
@@ -60,6 +61,7 @@ func NewDefaultDiscovery(addrs []string, dt time.Duration, ts Transporter) *Defa
 		connectedAddrs:   make(map[string]bool),
 		goodAddrs:        make(map[string]capability.Capabilities),
 		unconnectedAddrs: make(map[string]int),
+		attempted:        make(map[string]bool),
 		requestCh:        make(chan int),
 		pool:             make(chan string, maxPoolSize),
 	}
@@ -189,7 +191,11 @@ func (d *DefaultDiscovery) RegisterConnectedAddr(addr string) {
 }
 
 func (d *DefaultDiscovery) tryAddress(addr string) {
-	if err := d.transport.Dial(addr, d.dialTimeout); err != nil {
+	err := d.transport.Dial(addr, d.dialTimeout)
+	d.lock.Lock()
+	delete(d.attempted, addr)
+	d.lock.Unlock()
+	if err != nil {
 		d.RegisterBadAddr(addr)
 		d.RequestRemote(1)
 	}
@@ -225,14 +231,14 @@ func (d *DefaultDiscovery) run() {
 					requested = r
 				}
 			case addr := <-d.pool:
-				d.lock.RLock()
-				addrIsConnected := d.connectedAddrs[addr]
-				d.lock.RUnlock()
 				updatePoolCountMetric(d.PoolCount())
-				if !addrIsConnected {
+				d.lock.Lock()
+				if !d.connectedAddrs[addr] && !d.attempted[addr] {
+					d.attempted[addr] = true
 					go d.tryAddress(addr)
 					requested--
 				}
+				d.lock.Unlock()
 			default: // Empty pool
 				var added int
 				d.lock.Lock()

From fa4380c9da0041083db4bd863eca846819c62968 Mon Sep 17 00:00:00 2001
From: Roman Khimov <roman@nspcc.ru>
Date: Fri, 26 Mar 2021 12:31:07 +0300
Subject: [PATCH 2/2] network: prevent putting duplicate addresses into pool
 from peer's data

It can't be trusted.
---
 pkg/network/server.go | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/pkg/network/server.go b/pkg/network/server.go
index e7272da9e..af5287cd1 100644
--- a/pkg/network/server.go
+++ b/pkg/network/server.go
@@ -916,9 +916,11 @@ func (s *Server) handleAddrCmd(p Peer, addrs *payload.AddressList) error {
 	if !p.CanProcessAddr() {
 		return errors.New("unexpected addr received")
 	}
+	dups := make(map[string]bool)
 	for _, a := range addrs.Addrs {
 		addr, err := a.GetTCPAddress()
-		if err == nil {
+		if err == nil && !dups[addr] {
+			dups[addr] = true
 			s.discovery.BackFill(addr)
 		}
 	}