[client] Fix slow wg operations (#6633)

* [iface] Drop redundant device dump in kernel configure()

wgctrl.ConfigureDevice already returns an error when the interface is
missing, so the preceding wg.Device() existence check is redundant. That
check dumps the entire device (all peers) on every configure() call,
making it O(peers) per call and turning bulk peer insertion into
O(peers^2): inserting N peers one by one re-parsed the whole growing peer
list N times. Removing it keeps each peer write constant-time regardless
of how many peers are already configured.

* [iface] Cache WireGuard stats to collapse per-peer device dumps

Each peer runs a WGWatcher that polls GetStats(), and every call dumps
the whole device, so with N peers the watchers perform O(N) full dumps
per poll cycle (O(N^2) work) while each keeps only its own peer's entry.

Wrap the kernel and userspace configurer GetStats() in a short-TTL cache
with singleflight: the staggered per-peer calls share a single device
dump per window and concurrent misses collapse into one dump. The kernel
and userspace WireGuard APIs have no per-peer stats query (a get always
returns the whole device), so a shared cached snapshot avoids the
repeated full dumps.

* Ignore .claude directory

.gitignore

@@ -1,3 +1,4 @@
+.claude
 .idea
 .run
 *.iml

client/iface/configurer/kernel_unix.go

@@ -17,12 +17,15 @@ import (
 
 type KernelConfigurer struct {
 	deviceName string
+	statsCache *statsCache
 }
 
 func NewKernelConfigurer(deviceName string) *KernelConfigurer {
-	return &KernelConfigurer{
+	c := &KernelConfigurer{
 		deviceName: deviceName,
 	}
+	c.statsCache = newStatsCache(statsCacheTTL, c.fetchStats)
+	return c
 }
 
 func (c *KernelConfigurer) ConfigureInterface(privateKey string, port int) error {
@@ -246,12 +249,6 @@ func (c *KernelConfigurer) configure(config wgtypes.Config) error {
 		}
 	}()
 
-	// validate if device with name exists
-	_, err = wg.Device(c.deviceName)
-	if err != nil {
-		return err
-	}
-
 	return wg.ConfigureDevice(c.deviceName, config)
 }
 
@@ -300,6 +297,14 @@ func (c *KernelConfigurer) FullStats() (*Stats, error) {
 }
 
 func (c *KernelConfigurer) GetStats() (map[string]WGStats, error) {
+	return c.statsCache.get()
+}
+
+func (c *KernelConfigurer) LastActivities() map[string]monotime.Time {
+	return nil
+}
+
+func (c *KernelConfigurer) fetchStats() (map[string]WGStats, error) {
 	stats := make(map[string]WGStats)
 	wg, err := wgctrl.New()
 	if err != nil {
@@ -326,7 +331,3 @@ func (c *KernelConfigurer) GetStats() (map[string]WGStats, error) {
 	}
 	return stats, nil
 }
-
-func (c *KernelConfigurer) LastActivities() map[string]monotime.Time {
-	return nil
-}

client/iface/configurer/stats_cache.go

@@ -0,0 +1,52 @@
+package configurer
+
+import (
+	"sync"
+	"time"
+
+	"golang.org/x/sync/singleflight"
+)
+
+const statsCacheTTL = 1 * time.Second
+
+type statsCache struct {
+	ttl   time.Duration
+	fetch func() (map[string]WGStats, error)
+
+	mu       sync.RWMutex
+	value    map[string]WGStats
+	expireAt time.Time
+
+	sf singleflight.Group
+}
+
+func newStatsCache(ttl time.Duration, fetch func() (map[string]WGStats, error)) *statsCache {
+	return &statsCache{ttl: ttl, fetch: fetch}
+}
+
+func (c *statsCache) get() (map[string]WGStats, error) {
+	c.mu.RLock()
+	if c.value != nil && time.Now().Before(c.expireAt) {
+		value := c.value
+		c.mu.RUnlock()
+		return value, nil
+	}
+	c.mu.RUnlock()
+
+	value, err, _ := c.sf.Do("stats", func() (interface{}, error) {
+		res, err := c.fetch()
+		if err != nil {
+			return nil, err
+		}
+
+		c.mu.Lock()
+		c.value = res
+		c.expireAt = time.Now().Add(c.ttl)
+		c.mu.Unlock()
+		return res, nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	return value.(map[string]WGStats), nil
+}

client/iface/configurer/stats_cache_test.go

@@ -0,0 +1,70 @@
+package configurer
+
+import (
+	"errors"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestStatsCache_CachesWithinTTL(t *testing.T) {
+	var calls atomic.Int64
+	c := newStatsCache(50*time.Millisecond, func() (map[string]WGStats, error) {
+		calls.Add(1)
+		return map[string]WGStats{"p": {}}, nil
+	})
+
+	for i := 0; i < 10; i++ {
+		_, err := c.get()
+		require.NoError(t, err)
+	}
+	require.Equal(t, int64(1), calls.Load(), "within TTL only one underlying fetch")
+
+	time.Sleep(60 * time.Millisecond)
+	_, err := c.get()
+	require.NoError(t, err)
+	require.Equal(t, int64(2), calls.Load(), "after TTL expiry a fresh fetch happens")
+}
+
+func TestStatsCache_SingleFlight(t *testing.T) {
+	var calls atomic.Int64
+	release := make(chan struct{})
+	c := newStatsCache(time.Minute, func() (map[string]WGStats, error) {
+		calls.Add(1)
+		<-release
+		return map[string]WGStats{}, nil
+	})
+
+	const n = 50
+	var wg sync.WaitGroup
+	wg.Add(n)
+	for i := 0; i < n; i++ {
+		go func() {
+			defer wg.Done()
+			_, _ = c.get()
+		}()
+	}
+	time.Sleep(20 * time.Millisecond)
+	close(release)
+	wg.Wait()
+
+	require.Equal(t, int64(1), calls.Load(), "concurrent misses collapse into one fetch")
+}
+
+func TestStatsCache_ErrorNotCached(t *testing.T) {
+	var calls atomic.Int64
+	wantErr := errors.New("dump failed")
+	c := newStatsCache(time.Minute, func() (map[string]WGStats, error) {
+		calls.Add(1)
+		return nil, wantErr
+	})
+
+	_, err := c.get()
+	require.ErrorIs(t, err, wantErr)
+	_, err = c.get()
+	require.ErrorIs(t, err, wantErr)
+	require.Equal(t, int64(2), calls.Load(), "errors are not cached; each call retries")
+}

client/iface/configurer/usp.go

@@ -40,6 +40,7 @@ type WGUSPConfigurer struct {
 	device           *device.Device
 	deviceName       string
 	activityRecorder *bind.ActivityRecorder
+	statsCache       *statsCache
 
 	uapiListener net.Listener
 }
@@ -50,16 +51,19 @@ func NewUSPConfigurer(device *device.Device, deviceName string, activityRecorder
 		deviceName:       deviceName,
 		activityRecorder: activityRecorder,
 	}
+	wgCfg.statsCache = newStatsCache(statsCacheTTL, wgCfg.fetchStats)
 	wgCfg.startUAPI()
 	return wgCfg
 }
 
 func NewUSPConfigurerNoUAPI(device *device.Device, deviceName string, activityRecorder *bind.ActivityRecorder) *WGUSPConfigurer {
-	return &WGUSPConfigurer{
+	wgCfg := &WGUSPConfigurer{
 		device:           device,
 		deviceName:       deviceName,
 		activityRecorder: activityRecorder,
 	}
+	wgCfg.statsCache = newStatsCache(statsCacheTTL, wgCfg.fetchStats)
+	return wgCfg
 }
 
 func (c *WGUSPConfigurer) ConfigureInterface(privateKey string, port int) error {
@@ -348,6 +352,10 @@ func (t *WGUSPConfigurer) Close() {
 }
 
 func (t *WGUSPConfigurer) GetStats() (map[string]WGStats, error) {
+	return t.statsCache.get()
+}
+
+func (t *WGUSPConfigurer) fetchStats() (map[string]WGStats, error) {
 	ipc, err := t.device.IpcGet()
 	if err != nil {
 		return nil, fmt.Errorf("ipc get: %w", err)