Fix unused servers cleanup (#2826)

The cleanup loop did not manage those situations well when a connection failed or 
the connection success but the code did not add a peer connection to it yet.

- in the cleanup loop check if a connection failed to a server
- after adding a foreign server connection force to keep it a minimum 5 sec

relay/client/manager.go

@@ -16,6 +16,7 @@ import (
 
 var (
 	relayCleanupInterval = 60 * time.Second
+	keepUnusedServerTime = 5 * time.Second
 
 	ErrRelayClientNotConnected = fmt.Errorf("relay client not connected")
 )
@@ -27,10 +28,13 @@ type RelayTrack struct {
 	sync.RWMutex
 	relayClient *Client
 	err         error
+	created     time.Time
 }
 
 func NewRelayTrack() *RelayTrack {
-	return &RelayTrack{}
+	return &RelayTrack{
+		created: time.Now(),
+	}
 }
 
 type OnServerCloseListener func()
@@ -302,6 +306,18 @@ func (m *Manager) cleanUpUnusedRelays() {
 
 	for addr, rt := range m.relayClients {
 		rt.Lock()
+		// if the connection failed to the server the relay client will be nil
+		// but the instance will be kept in the relayClients until the next locking
+		if rt.err != nil {
+			rt.Unlock()
+			continue
+		}
+
+		if time.Since(rt.created) <= keepUnusedServerTime {
+			rt.Unlock()
+			continue
+		}
+
 		if rt.relayClient.HasConns() {
 			rt.Unlock()
 			continue

relay/client/manager_test.go

@@ -288,8 +288,9 @@ func TestForeginAutoClose(t *testing.T) {
 		t.Fatalf("failed to close connection: %s", err)
 	}
 
-	t.Logf("waiting for relay cleanup: %s", relayCleanupInterval+1*time.Second)
+	timeout := relayCleanupInterval + keepUnusedServerTime + 1*time.Second
-	time.Sleep(relayCleanupInterval + 1*time.Second)
+	t.Logf("waiting for relay cleanup: %s", timeout)
+	time.Sleep(timeout)
 	if len(mgr.relayClients) != 0 {
 		t.Errorf("expected 0, got %d", len(mgr.relayClients))
 	}

relay/client/picker_test.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"errors"
 	"testing"
-	"time"
 )
 
 func TestServerPicker_UnavailableServers(t *testing.T) {
@@ -13,7 +12,7 @@ func TestServerPicker_UnavailableServers(t *testing.T) {
 		PeerID:     "test",
 	}
 
-	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	ctx, cancel := context.WithTimeout(context.Background(), connectionTimeout+1)
 	defer cancel()
 
 	go func() {