p2p: add configuration for direct peers (#4769)

direct peers are not pruned, and node will always try to establish connections with them
regardless of the current number of connections.

configuration is in p2p section, same format for address as bootnodes
```json
"p2p": {
    "direct": []
}
```

p2p/dhtdiscovery/discovery.go

@@ -54,6 +54,12 @@ func WithBackup(backup []peer.AddrInfo) Opt {
 	}
 }
 
+func WithDirect(direct []peer.AddrInfo) Opt {
+	return func(d *Discovery) {
+		d.direct = direct
+	}
+}
+
 func WithLogger(logger *zap.Logger) Opt {
 	return func(d *Discovery) {
 		d.logger = logger
@@ -121,10 +127,10 @@ type Discovery struct {
 	// how often to check if we have enough peers
 	period time.Duration
 	// timeout used for connections
-	timeout           time.Duration
-	bootstrapDuration time.Duration
-	minPeers          int
-	backup, bootnodes []peer.AddrInfo
+	timeout                   time.Duration
+	bootstrapDuration         time.Duration
+	minPeers                  int
+	direct, backup, bootnodes []peer.AddrInfo
 }
 
 func (d *Discovery) Start() {
@@ -151,6 +157,8 @@ func (d *Discovery) Start() {
 			case <-ticker.C:
 			case <-disconnected:
 			}
+			// ensure we are always connected with direct peers
+			d.connect(&connEg, d.direct)
 			if connected := len(d.h.Network().Peers()); connected >= d.minPeers {
 				d.backup = nil // once got enough peers no need to keep backup, they are either already connected or unavailable
 				d.logger.Debug("node is connected with required number of peers. skipping bootstrap",

p2p/host.go

@@ -63,6 +63,7 @@ type Config struct {
 	Flood                  bool        `mapstructure:"flood"`
 	Listen                 string      `mapstructure:"listen"`
 	Bootnodes              []string    `mapstructure:"bootnodes"`
+	Direct                 []string    `mapstructure:"direct"`
 	MinPeers               int         `mapstructure:"min-peers"`
 	LowPeers               int         `mapstructure:"low-peers"`
 	HighPeers              int         `mapstructure:"high-peers"`

p2p/upgrade.go

@@ -93,6 +93,13 @@ func Upgrade(h host.Host, opts ...Opt) (*Host, error) {
 	if err != nil {
 		return nil, err
 	}
+	direct, err := parseIntoAddr(fh.cfg.Bootnodes)
+	if err != nil {
+		return nil, err
+	}
+	for _, peer := range direct {
+		h.ConnManager().Protect(peer.ID, "direct")
+	}
 	if fh.PubSub, err = pubsub.New(fh.ctx, fh.logger, h, pubsub.Config{
 		Flood:          cfg.Flood,
 		IsBootnode:     cfg.Bootnode,
@@ -117,6 +124,7 @@ func Upgrade(h host.Host, opts ...Opt) (*Host, error) {
 	dopts := []discovery.Opt{
 		discovery.WithDir(cfg.DataDir),
 		discovery.WithBootnodes(bootnodes),
+		discovery.WithDirect(direct),
 		discovery.WithLogger(fh.logger.Zap()),
 	}
 	if cfg.PrivateNetwork {