perf(storage): add config caching and shared HTTP connection pool

- Implement thread-safe local config caching with a 5s TTL check.
- Reuse backend client singletons in storage.Active and storage.ForDriver.
- Reset in-memory config cache on configuration saves and updates.
- Create internal/httppool package to manage shared HTTP transports.
- Configure WebDAV client and CDN retrieval to reuse the shared pool.
- Add unit tests for httppool and storage caching behaviors.

internal/apps/admin/system_config/routers.go

@@ -246,6 +246,10 @@ func UpdateSystemConfig(c *gin.Context) {
 		return
 	}
 
+	if key == model.ConfigKeyStorageConfig {
+		storage.ResetCache()
+	}
+
 	c.JSON(http.StatusOK, util.OKNil())
 }
 

internal/httppool/httppool.go

@@ -0,0 +1,66 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+// Package httppool manages shared, optimized HTTP transports to reuse TCP connections.
+package httppool
+
+import (
+	"crypto/tls"
+	"net"
+	"net/http"
+	"sync"
+	"time"
+
+	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
+)
+
+const (
+	dialTimeout           = 30 * time.Second
+	dialKeepAlive         = 30 * time.Second
+	maxIdleConns          = 200
+	maxIdleConnsPerHost   = 32
+	idleConnTimeout       = 90 * time.Second
+	tlsHandshakeTimeout   = 10 * time.Second
+	expectContinueTimeout = 1 * time.Second
+	tlsSessionCacheSize   = 100
+)
+
+var (
+	defaultTransport http.RoundTripper
+	once             sync.Once
+)
+
+// DefaultTransport returns a globally shared, optimized http.RoundTripper
+// with OTel instrumentation. It maintains a pool of idle TCP connections
+// across hosts.
+func DefaultTransport() http.RoundTripper {
+	once.Do(func() {
+		transport := &http.Transport{
+			Proxy: http.ProxyFromEnvironment,
+			DialContext: (&net.Dialer{
+				Timeout:   dialTimeout,
+				KeepAlive: dialKeepAlive,
+			}).DialContext,
+			ForceAttemptHTTP2:     true,
+			MaxIdleConns:          maxIdleConns,
+			MaxIdleConnsPerHost:   maxIdleConnsPerHost,
+			IdleConnTimeout:       idleConnTimeout,
+			TLSHandshakeTimeout:   tlsHandshakeTimeout,
+			ExpectContinueTimeout: expectContinueTimeout,
+			TLSClientConfig: &tls.Config{
+				ClientSessionCache: tls.NewLRUClientSessionCache(tlsSessionCacheSize),
+			},
+		}
+		defaultTransport = otelhttp.NewTransport(transport)
+	})
+	return defaultTransport
+}
+
+// NewClient returns a new http.Client that shares the global connection pool
+// but has its own timeout configuration.
+func NewClient(timeout time.Duration) *http.Client {
+	return &http.Client{
+		Timeout:   timeout,
+		Transport: DefaultTransport(),
+	}
+}

internal/httppool/httppool_test.go

@@ -0,0 +1,37 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package httppool
+
+import (
+	"testing"
+	"time"
+)
+
+func TestDefaultTransport(t *testing.T) {
+	tr1 := DefaultTransport()
+	if tr1 == nil {
+		t.Fatal("DefaultTransport() returned nil")
+	}
+
+	tr2 := DefaultTransport()
+	if tr1 != tr2 {
+		t.Error("DefaultTransport() did not return a singleton instance")
+	}
+}
+
+func TestNewClient(t *testing.T) {
+	timeout := 15 * time.Second
+	client := NewClient(timeout)
+	if client == nil {
+		t.Fatal("NewClient() returned nil")
+	}
+
+	if client.Timeout != timeout {
+		t.Errorf("NewClient() timeout = %v, want %v", client.Timeout, timeout)
+	}
+
+	if client.Transport != DefaultTransport() {
+		t.Error("NewClient() is not configured with the default transport")
+	}
+}

internal/storage/config.go

@@ -10,6 +10,7 @@ import (
 	"errors"
 	"fmt"
 	"strings"
+	"time"
 
 	"github.com/Rain-kl/Wavelet/internal/db"
 	"github.com/Rain-kl/Wavelet/internal/model"
@@ -87,6 +88,21 @@ func DefaultConfig() Config {
 
 // LoadConfig loads the active storage configuration.
 func LoadConfig(ctx context.Context) (Config, error) {
+	cacheMutex.RLock()
+	isCacheValid := time.Since(lastChecked) < 5*time.Second && activeConfigJSON != ""
+	configJSON := activeConfigJSON
+	cacheMutex.RUnlock()
+
+	if isCacheValid {
+		cfg := DefaultConfig()
+		if strings.TrimSpace(configJSON) != "" {
+			if err := json.Unmarshal([]byte(configJSON), &cfg); err != nil {
+				return Config{}, fmt.Errorf("parse storage config from cache: %w", err)
+			}
+		}
+		return cfg, nil
+	}
+
 	return loadConfigByKey(ctx, model.ConfigKeyStorageConfig, DefaultConfig())
 }
 
@@ -163,9 +179,13 @@ func SaveActiveConfig(ctx context.Context, cfg Config) error {
 }
 
 func saveSystemConfig(ctx context.Context, key string, value any, description string) error {
-	return db.DB(ctx).Transaction(func(tx *gorm.DB) error {
+	err := db.DB(ctx).Transaction(func(tx *gorm.DB) error {
 		return upsertSystemConfig(ctx, tx, key, value, description)
 	})
+	if err == nil && key == model.ConfigKeyStorageConfig {
+		ResetCache()
+	}
+	return err
 }
 
 func upsertSystemConfig(ctx context.Context, tx *gorm.DB, key string, value any, description string) error {

internal/storage/http.go

@@ -8,6 +8,9 @@ import (
 	"fmt"
 	"net/http"
 	"net/url"
+	"time"
+
+	"github.com/Rain-kl/Wavelet/internal/httppool"
 )
 
 func getHTTPObject(ctx context.Context, baseURL, key string) (*Object, error) {
@@ -19,7 +22,9 @@ func getHTTPObject(ctx context.Context, baseURL, key string) (*Object, error) {
 	if err != nil {
 		return nil, fmt.Errorf("create CDN request: %w", err)
 	}
-	response, err := http.DefaultClient.Do(request)
+	const cdnRequestTimeout = 30 * time.Second
+	client := httppool.NewClient(cdnRequestTimeout)
+	response, err := client.Do(request)
 	if err != nil {
 		return nil, fmt.Errorf("get CDN object: %w", err)
 	}

internal/storage/storage.go

@@ -5,8 +5,16 @@ package storage
 
 import (
 	"context"
+	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/Rain-kl/Wavelet/internal/model"
+	"gorm.io/gorm"
 )
 
 const (
@@ -35,26 +43,88 @@ var (
 	// IsEnabledFunc preserves the legacy S3 test hook while tests migrate to backend injection.
 	IsEnabledFunc = func() bool { return false }
 	mockBackend   Backend
+
+	activeBackend    Backend
+	activeDriver     Driver
+	activeConfigJSON string
+	lastChecked      time.Time
+	cacheMutex       sync.RWMutex
 )
 
-// Active returns the configured active driver and backend.
+// ResetCache clears the local cache for storage configuration and client singletons.
+func ResetCache() {
+	cacheMutex.Lock()
+	defer cacheMutex.Unlock()
+	activeBackend = nil
+	activeDriver = ""
+	activeConfigJSON = ""
+	lastChecked = time.Time{}
+}
+
+// Active returns the configured active driver and backend, using an in-memory cache with 5s TTL.
 func Active(ctx context.Context) (Driver, Backend, error) {
 	if IsEnabledFunc() && mockBackend != nil {
 		return DriverS3, mockBackend, nil
 	}
-	cfg, err := LoadConfig(ctx)
+
+	cacheMutex.RLock()
+	isCacheValid := time.Since(lastChecked) < 5*time.Second && activeBackend != nil
+	if isCacheValid {
+		d, b := activeDriver, activeBackend
+		cacheMutex.RUnlock()
+		return d, b, nil
+	}
+	cacheMutex.RUnlock()
+
+	cacheMutex.Lock()
+	defer cacheMutex.Unlock()
+
+	// Double-check under write lock
+	if time.Since(lastChecked) < 5*time.Second && activeBackend != nil {
+		return activeDriver, activeBackend, nil
+	}
+
+	var sc model.SystemConfig
+	err := sc.GetByKey(ctx, model.ConfigKeyStorageConfig)
+	if err != nil && !errors.Is(err, gorm.ErrRecordNotFound) {
+		return "", nil, err
+	}
+
+	lastChecked = time.Now()
+
+	// Reuse existing backend client singleton if configuration JSON matches
+	if sc.Value == activeConfigJSON && activeBackend != nil {
+		return activeDriver, activeBackend, nil
+	}
+
+	cfg := DefaultConfig()
+	if strings.TrimSpace(sc.Value) != "" {
+		if err := json.Unmarshal([]byte(sc.Value), &cfg); err != nil {
+			return "", nil, fmt.Errorf("parse storage config: %w", err)
+		}
+	}
+
+	backend, err := NewBackend(ctx, cfg, cfg.Driver)
 	if err != nil {
 		return "", nil, err
 	}
-	backend, err := NewBackend(ctx, cfg, cfg.Driver)
+
-	return cfg.Driver, backend, err
+	activeDriver = cfg.Driver
+	activeBackend = backend
+	activeConfigJSON = sc.Value
+
+	return activeDriver, activeBackend, nil
 }
 
-// ForDriver returns the active or pending backend for an upload record.
+// ForDriver returns the active or pending backend for an upload record, reusing the active singleton if matched.
 func ForDriver(ctx context.Context, driver Driver) (Backend, error) {
 	if driver == DriverS3 && mockBackend != nil {
 		return mockBackend, nil
 	}
+	activeDrv, activeBnd, err := Active(ctx)
+	if err == nil && activeDrv == driver {
+		return activeBnd, nil
+	}
 	cfg, err := LoadConfig(ctx)
 	if err != nil {
 		return nil, err

internal/storage/storage_test.go

@@ -0,0 +1,82 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package storage
+
+import (
+	"context"
+	"encoding/json"
+	"io"
+	"testing"
+	"time"
+)
+
+func TestStorageCache(t *testing.T) {
+	// 1. Reset cache
+	ResetCache()
+
+	if activeConfigJSON != "" || activeDriver != "" || activeBackend != nil || !lastChecked.IsZero() {
+		t.Fatal("ResetCache did not clear cache variables")
+	}
+
+	// 2. Set up cache manually
+	expectedConfig := Config{
+		Driver: DriverLocal,
+		Local:  LocalConfig{Root: "/tmp/wavelet-test"},
+	}
+	cfgJSON, err := json.Marshal(expectedConfig)
+	if err != nil {
+		t.Fatalf("Marshal config failed: %v", err)
+	}
+
+	cacheMutex.Lock()
+	activeConfigJSON = string(cfgJSON)
+	lastChecked = time.Now()
+	cacheMutex.Unlock()
+
+	// 3. Call LoadConfig and verify it loads from cache (doesn't hit database, which would fail/panic because DB is not initialized)
+	ctx := context.Background()
+	loadedCfg, err := LoadConfig(ctx)
+	if err != nil {
+		t.Fatalf("LoadConfig failed: %v", err)
+	}
+
+	if loadedCfg.Driver != expectedConfig.Driver || loadedCfg.Local.Root != expectedConfig.Local.Root {
+		t.Errorf("Loaded config %+v, expected %+v", loadedCfg, expectedConfig)
+	}
+
+	// 4. Test Active() returns cached driver and backend
+	mockBnd := &functionBackend{
+		put:    func(context.Context, string, io.Reader, int64, string) error { return nil },
+		get:    func(context.Context, string) (*Object, error) { return nil, nil },
+		delete: func(context.Context, string) error { return nil },
+	}
+
+	cacheMutex.Lock()
+	activeBackend = mockBnd
+	activeDriver = DriverLocal
+	cacheMutex.Unlock()
+
+	drv, bnd, err := Active(ctx)
+	if err != nil {
+		t.Fatalf("Active failed: %v", err)
+	}
+	if drv != DriverLocal || bnd != mockBnd {
+		t.Errorf("Active returned driver %v, backend %v; expected %v, %v", drv, bnd, DriverLocal, mockBnd)
+	}
+
+	// 5. Test ForDriver returns cached backend
+	bnd2, err := ForDriver(ctx, DriverLocal)
+	if err != nil {
+		t.Fatalf("ForDriver failed: %v", err)
+	}
+	if bnd2 != mockBnd {
+		t.Errorf("ForDriver returned backend %v, expected %v", bnd2, mockBnd)
+	}
+
+	// 6. Test ResetCache again
+	ResetCache()
+	if activeConfigJSON != "" || activeDriver != "" || activeBackend != nil || !lastChecked.IsZero() {
+		t.Fatal("ResetCache did not clear cache variables after setting them")
+	}
+}

internal/storage/webdav.go

@@ -10,6 +10,7 @@ import (
 	"path"
 	"strings"
 
+	"github.com/Rain-kl/Wavelet/internal/httppool"
 	"github.com/studio-b12/gowebdav"
 )
 
@@ -19,8 +20,10 @@ type webDAVBackend struct {
 }
 
 func newWebDAVBackend(cfg WebDAVConfig) (*webDAVBackend, error) {
+	client := gowebdav.NewClient(strings.TrimRight(cfg.Endpoint, "/"), cfg.Username, cfg.Password)
+	client.SetTransport(httppool.DefaultTransport())
 	return &webDAVBackend{
-		client:   gowebdav.NewClient(strings.TrimRight(cfg.Endpoint, "/"), cfg.Username, cfg.Password),
+		client:   client,
 		basePath: strings.Trim(cfg.BasePath, "/"),
 	}, nil
 }