[client] Feature/lazy connection (#3379)

With the lazy connection feature, the peer will connect to target peers on-demand. The trigger can be any IP traffic.

This feature can be enabled with the NB_ENABLE_EXPERIMENTAL_LAZY_CONN environment variable.

When the engine receives a network map, it binds a free UDP port for every remote peer, and the system configures WireGuard endpoints for these ports. When traffic appears on a UDP socket, the system removes this listener and starts the peer connection procedure immediately.

Key changes
Fix slow netbird status -d command
Move from engine.go file to conn_mgr.go the peer connection related code
Refactor the iface interface usage and moved interface file next to the engine code
Add new command line flag and UI option to enable feature
The peer.Conn struct is reusable after it has been closed.
Change connection states
Connection states
Idle: The peer is not attempting to establish a connection. This typically means it's in a lazy state or the remote peer is expired.

Connecting: The peer is actively trying to establish a connection. This occurs when the peer has entered an active state and is continuously attempting to reach the remote peer.

Connected: A successful peer-to-peer connection has been established and communication is active.

client/iface/configurer/usp.go

@@ -1,6 +1,7 @@
 package configurer
 
 import (
+	"encoding/base64"
 	"encoding/hex"
 	"fmt"
 	"net"
@@ -17,6 +18,13 @@ import (
 	nbnet "github.com/netbirdio/netbird/util/net"
 )
 
+const (
+	ipcKeyLastHandshakeTimeSec  = "last_handshake_time_sec"
+	ipcKeyLastHandshakeTimeNsec = "last_handshake_time_nsec"
+	ipcKeyTxBytes               = "tx_bytes"
+	ipcKeyRxBytes               = "rx_bytes"
+)
+
 var ErrAllowedIPNotFound = fmt.Errorf("allowed IP not found")
 
 type WGUSPConfigurer struct {
@@ -217,91 +225,75 @@ func (t *WGUSPConfigurer) Close() {
 	}
 }
 
-func (t *WGUSPConfigurer) GetStats(peerKey string) (WGStats, error) {
+func (t *WGUSPConfigurer) GetStats() (map[string]WGStats, error) {
 	ipc, err := t.device.IpcGet()
 	if err != nil {
-		return WGStats{}, fmt.Errorf("ipc get: %w", err)
+		return nil, fmt.Errorf("ipc get: %w", err)
 	}
 
-	stats, err := findPeerInfo(ipc, peerKey, []string{
-		"last_handshake_time_sec",
-		"last_handshake_time_nsec",
-		"tx_bytes",
-		"rx_bytes",
-	})
-	if err != nil {
-		return WGStats{}, fmt.Errorf("find peer info: %w", err)
-	}
-
-	sec, err := strconv.ParseInt(stats["last_handshake_time_sec"], 10, 64)
-	if err != nil {
-		return WGStats{}, fmt.Errorf("parse handshake sec: %w", err)
-	}
-	nsec, err := strconv.ParseInt(stats["last_handshake_time_nsec"], 10, 64)
-	if err != nil {
-		return WGStats{}, fmt.Errorf("parse handshake nsec: %w", err)
-	}
-	txBytes, err := strconv.ParseInt(stats["tx_bytes"], 10, 64)
-	if err != nil {
-		return WGStats{}, fmt.Errorf("parse tx_bytes: %w", err)
-	}
-	rxBytes, err := strconv.ParseInt(stats["rx_bytes"], 10, 64)
-	if err != nil {
-		return WGStats{}, fmt.Errorf("parse rx_bytes: %w", err)
-	}
-
-	return WGStats{
-		LastHandshake: time.Unix(sec, nsec),
-		TxBytes:       txBytes,
-		RxBytes:       rxBytes,
-	}, nil
+	return parseTransfers(ipc)
 }
 
-func findPeerInfo(ipcInput string, peerKey string, searchConfigKeys []string) (map[string]string, error) {
-	peerKeyParsed, err := wgtypes.ParseKey(peerKey)
-	if err != nil {
-		return nil, fmt.Errorf("parse key: %w", err)
-	}
-
-	hexKey := hex.EncodeToString(peerKeyParsed[:])
-
-	lines := strings.Split(ipcInput, "\n")
-
-	configFound := map[string]string{}
-	foundPeer := false
+func parseTransfers(ipc string) (map[string]WGStats, error) {
+	stats := make(map[string]WGStats)
+	var (
+		currentKey   string
+		currentStats WGStats
+		hasPeer      bool
+	)
+	lines := strings.Split(ipc, "\n")
 	for _, line := range lines {
 		line = strings.TrimSpace(line)
 
 		// If we're within the details of the found peer and encounter another public key,
 		// this means we're starting another peer's details. So, stop.
-		if strings.HasPrefix(line, "public_key=") && foundPeer {
-			break
-		}
-
-		// Identify the peer with the specific public key
-		if line == fmt.Sprintf("public_key=%s", hexKey) {
-			foundPeer = true
-		}
-
-		for _, key := range searchConfigKeys {
-			if foundPeer && strings.HasPrefix(line, key+"=") {
-				v := strings.SplitN(line, "=", 2)
-				configFound[v[0]] = v[1]
+		if strings.HasPrefix(line, "public_key=") {
+			peerID := strings.TrimPrefix(line, "public_key=")
+			h, err := hex.DecodeString(peerID)
+			if err != nil {
+				return nil, fmt.Errorf("decode peerID: %w", err)
 			}
+			currentKey = base64.StdEncoding.EncodeToString(h)
+			currentStats = WGStats{} // Reset stats for the new peer
+			hasPeer = true
+			stats[currentKey] = currentStats
+			continue
+		}
+
+		if !hasPeer {
+			continue
+		}
+
+		key := strings.SplitN(line, "=", 2)
+		if len(key) != 2 {
+			continue
+		}
+		switch key[0] {
+		case ipcKeyLastHandshakeTimeSec:
+			hs, err := toLastHandshake(key[1])
+			if err != nil {
+				return nil, err
+			}
+			currentStats.LastHandshake = hs
+			stats[currentKey] = currentStats
+		case ipcKeyRxBytes:
+			rxBytes, err := toBytes(key[1])
+			if err != nil {
+				return nil, fmt.Errorf("parse rx_bytes: %w", err)
+			}
+			currentStats.RxBytes = rxBytes
+			stats[currentKey] = currentStats
+		case ipcKeyTxBytes:
+			TxBytes, err := toBytes(key[1])
+			if err != nil {
+				return nil, fmt.Errorf("parse tx_bytes: %w", err)
+			}
+			currentStats.TxBytes = TxBytes
+			stats[currentKey] = currentStats
 		}
 	}
 
-	// todo: use multierr
-	for _, key := range searchConfigKeys {
-		if _, ok := configFound[key]; !ok {
-			return configFound, fmt.Errorf("config key not found: %s", key)
-		}
-	}
-	if !foundPeer {
-		return nil, fmt.Errorf("%w: %s", ErrPeerNotFound, peerKey)
-	}
-
-	return configFound, nil
+	return stats, nil
 }
 
 func toWgUserspaceString(wgCfg wgtypes.Config) string {
@@ -355,6 +347,18 @@ func toWgUserspaceString(wgCfg wgtypes.Config) string {
 	return sb.String()
 }
 
+func toLastHandshake(stringVar string) (time.Time, error) {
+	sec, err := strconv.ParseInt(stringVar, 10, 64)
+	if err != nil {
+		return time.Time{}, fmt.Errorf("parse handshake sec: %w", err)
+	}
+	return time.Unix(sec, 0), nil
+}
+
+func toBytes(s string) (int64, error) {
+	return strconv.ParseInt(s, 10, 64)
+}
+
 func getFwmark() int {
 	if nbnet.AdvancedRouting() {
 		return nbnet.ControlPlaneMark