[client] Persist sync response via pluggable store (disk on iOS) (#6331)

* Persist sync response via pluggable store (disk on iOS)

The latest Management sync response (which carries the network map) was
kept in memory for debug bundle generation. On memory-constrained
platforms like iOS the network map can be large enough to matter.

Introduce a syncstore package with a Store interface and two backends:
a memory backend (the previous behavior) and a disk backend that
serializes the response to a file in the state directory. The backend
is selected per-platform at build time: disk on iOS, memory elsewhere.

The disk store clears any leftover file on construction so a fresh
store never reads stale data from an earlier run (e.g. another
profile's network map).

In the engine, drop the separate persistSyncResponse bool: the store is
only instantiated while persistence is enabled, and its presence is
what marks persistence as active. The store is also cleared on engine
close so the file does not linger on disk.

* syncstore: silence nilnil linter on "nothing stored" returns

Get returns (nil, nil) to signal that nothing is stored, which is part
of the Store contract and preserves the original behaviour. Annotate
both backends with //nolint:nilnil so golangci-lint does not flag it.

* syncstore: hold syncRespMux for the whole store Set/Get

Both handleSync and GetLatestSyncResponse snapshotted e.syncStore under
the read lock and then released it before calling Set/Get. That allowed
SetSyncResponsePersistence(false) or engine close to clear the store
mid-call. In particular a concurrent Clear()+nil followed by a late
Set could re-create the file that was just removed, defeating the
leak/lingering protection.

Hold syncRespMux for the duration of the store operation in both spots
so the store cannot be cleared while a Set/Get is in flight.

* syncstore: avoid StateDir "." when state path is empty

On mobile the state path may be empty (the engine tolerates a missing
state file). filepath.Dir("") returns ".", which would make a
disk-backed syncstore write into the working directory instead of
letting NewDiskStore fall back to os.TempDir().

Only set engineConfig.StateDir when path is non-empty.

client/internal/engine.go

@@ -22,7 +22,6 @@ import (
 	log "github.com/sirupsen/logrus"
 	"golang.zx2c4.com/wireguard/tun/netstack"
 	"golang.zx2c4.com/wireguard/wgctrl/wgtypes"
-	"google.golang.org/protobuf/proto"
 
 	nberrors "github.com/netbirdio/netbird/client/errors"
 	"github.com/netbirdio/netbird/client/firewall"
@@ -56,6 +55,7 @@ import (
 	"github.com/netbirdio/netbird/client/internal/routemanager"
 	"github.com/netbirdio/netbird/client/internal/routemanager/systemops"
 	"github.com/netbirdio/netbird/client/internal/statemanager"
+	"github.com/netbirdio/netbird/client/internal/syncstore"
 	"github.com/netbirdio/netbird/client/internal/updater"
 	"github.com/netbirdio/netbird/client/jobexec"
 	cProto "github.com/netbirdio/netbird/client/proto"
@@ -148,6 +148,10 @@ type EngineConfig struct {
 
 	LogPath string
 	TempDir string
+
+	// StateDir is the directory holding the state file. The sync response
+	// (network map) is serialized here on platforms that persist it to disk.
+	StateDir string
 }
 
 // EngineServices holds the external service dependencies required by the Engine.
@@ -226,10 +230,15 @@ type Engine struct {
 
 	afpacketCapture *capture.AFPacketCapture
 
-	// Sync response persistence (protected by syncRespMux)
-	syncRespMux         sync.RWMutex
-	persistSyncResponse bool
-	latestSyncResponse  *mgmProto.SyncResponse
+	// Sync response persistence (protected by syncRespMux).
+	// syncStore is nil unless persistence has been enabled; its presence is
+	// what marks persistence as active. The backend (disk or memory) is
+	// selected per-platform; see the syncstore package. syncStoreDir is where
+	// a disk-backed store serializes to.
+	syncRespMux  sync.RWMutex
+	syncStore    syncstore.Store
+	syncStoreDir string
+
 	flowManager         nftypes.FlowManager
 
 	// auto-update
@@ -292,6 +301,7 @@ func NewEngine(
 		jobExecutor:        jobexec.NewExecutor(),
 		clientMetrics:      services.ClientMetrics,
 		updateManager:      services.UpdateManager,
+		syncStoreDir:       config.StateDir,
 	}
 
 	log.Infof("I am: %s", config.WgPrivateKey.PublicKey().String())
@@ -913,19 +923,18 @@ func (e *Engine) handleSync(update *mgmProto.SyncResponse) error {
 	}
 
 	// Persist sync response under the dedicated lock (syncRespMux), not under syncMsgMux.
-	// Read the storage-enabled flag under the syncRespMux too.
+	// A non-nil syncStore is what marks persistence as enabled. Hold the lock for
+	// the whole Set so the store cannot be cleared (disabled / engine close)
+	// mid-call and have this write resurrect a file that was just removed.
 	e.syncRespMux.RLock()
-	enabled := e.persistSyncResponse
-	e.syncRespMux.RUnlock()
-
-	// Store sync response if persistence is enabled
-	if enabled {
-		e.syncRespMux.Lock()
-		e.latestSyncResponse = update
-		e.syncRespMux.Unlock()
-
-		log.Debugf("sync response persisted with serial %d", nm.GetSerial())
+	if e.syncStore != nil {
+		if err := e.syncStore.Set(update); err != nil {
+			log.Errorf("failed to persist sync response: %v", err)
+		} else {
+			log.Debugf("sync response persisted with serial %d", nm.GetSerial())
+		}
 	}
+	e.syncRespMux.RUnlock()
 
 	// only apply new changes and ignore old ones
 	if err := e.updateNetworkMap(nm); err != nil {
@@ -1813,6 +1822,18 @@ func (e *Engine) close() {
 	if err := e.portForwardManager.GracefullyStop(ctx); err != nil {
 		log.Warnf("failed to gracefully stop port forwarding manager: %s", err)
 	}
+
+	// Drop any persisted sync response so its network map does not linger on
+	// disk after the engine stops (and cannot leak into a later run).
+	e.syncRespMux.Lock()
+	store := e.syncStore
+	e.syncStore = nil
+	e.syncRespMux.Unlock()
+	if store != nil {
+		if err := store.Clear(); err != nil {
+			log.Warnf("failed to clear persisted sync response on close: %v", err)
+		}
+	}
 }
 
 func (e *Engine) readInitialSettings() ([]*route.Route, *nbdns.Config, bool, error) {
@@ -2142,45 +2163,42 @@ func (e *Engine) stopDNSServer() {
 	e.statusRecorder.UpdateDNSStates(nsGroupStates)
 }
 
-// SetSyncResponsePersistence enables or disables sync response persistence
+// SetSyncResponsePersistence enables or disables sync response persistence.
+// The store is only instantiated while persistence is enabled; construction
+// itself drops any stale data left over from an earlier run (see syncstore).
 func (e *Engine) SetSyncResponsePersistence(enabled bool) {
 	e.syncRespMux.Lock()
 	defer e.syncRespMux.Unlock()
 
-	if enabled == e.persistSyncResponse {
+	if enabled == (e.syncStore != nil) {
 		return
 	}
-	e.persistSyncResponse = enabled
 	log.Debugf("Sync response persistence is set to %t", enabled)
 
 	if !enabled {
-		e.latestSyncResponse = nil
+		if err := e.syncStore.Clear(); err != nil {
+			log.Warnf("failed to clear persisted sync response: %v", err)
+		}
+		e.syncStore = nil
+		return
 	}
+
+	e.syncStore = syncstore.New(e.syncStoreDir)
 }
 
 // GetLatestSyncResponse returns the stored sync response if persistence is enabled
 func (e *Engine) GetLatestSyncResponse() (*mgmProto.SyncResponse, error) {
+	// Hold the lock for the whole Get so the store cannot be cleared
+	// (disabled / engine close) mid-call.
 	e.syncRespMux.RLock()
-	enabled := e.persistSyncResponse
-	latest := e.latestSyncResponse
-	e.syncRespMux.RUnlock()
+	defer e.syncRespMux.RUnlock()
 
-	if !enabled {
+	if e.syncStore == nil {
 		return nil, errors.New("sync response persistence is disabled")
 	}
 
-	if latest == nil {
-		//nolint:nilnil
-		return nil, nil
-	}
-
-	log.Debugf("Retrieving latest sync response with size %d bytes", proto.Size(latest))
-	sr, ok := proto.Clone(latest).(*mgmProto.SyncResponse)
-	if !ok {
-		return nil, fmt.Errorf("failed to clone sync response")
-	}
-
-	return sr, nil
+	//nolint:nilnil
+	return e.syncStore.Get()
 }
 
 // GetWgAddr returns the wireguard address