fix(server): memory leak in cache warmer (#4095)

* Prevent cache warmer memory leak when cache disabled

* refactor(tests): replace disabledCache with mockFileCache in CacheWarmer tests

Signed-off-by: Deluan <deluan@navidrome.org>

* test(cache): enhance CacheWarmer tests for initialization, buffer management, and error handling

Signed-off-by: Deluan <deluan@navidrome.org>

---------

Signed-off-by: Deluan <deluan@navidrome.org>

core/artwork/cache_warmer.go

@@ -31,6 +31,12 @@ func NewCacheWarmer(artwork Artwork, cache cache.FileCache) CacheWarmer {
 		return &noopCacheWarmer{}
 	}
 
+	// If the file cache is disabled, return a NOOP implementation
+	if cache.Disabled(context.Background()) {
+		log.Debug("Image cache disabled. Cache warmer will not run")
+		return &noopCacheWarmer{}
+	}
+
 	a := &cacheWarmer{
 		artwork:    artwork,
 		cache:      cache,
@@ -53,6 +59,9 @@ type cacheWarmer struct {
 }
 
 func (a *cacheWarmer) PreCache(artID model.ArtworkID) {
+	if a.cache.Disabled(context.Background()) {
+		return
+	}
 	a.mutex.Lock()
 	defer a.mutex.Unlock()
 	a.buffer[artID] = struct{}{}
@@ -74,6 +83,17 @@ func (a *cacheWarmer) run(ctx context.Context) {
 			break
 		}
 
+		if a.cache.Disabled(ctx) {
+			a.mutex.Lock()
+			pending := len(a.buffer)
+			a.buffer = make(map[model.ArtworkID]struct{})
+			a.mutex.Unlock()
+			if pending > 0 {
+				log.Trace(ctx, "Cache disabled, discarding precache buffer", "bufferLen", pending)
+			}
+			return
+		}
+
 		// If cache not available, keep waiting
 		if !a.cache.Available(ctx) {
 			if len(a.buffer) > 0 {

core/artwork/cache_warmer_test.go

@@ -0,0 +1,216 @@
+package artwork
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"strings"
+	"sync/atomic"
+	"time"
+
+	"github.com/navidrome/navidrome/conf"
+	"github.com/navidrome/navidrome/conf/configtest"
+	"github.com/navidrome/navidrome/model"
+	"github.com/navidrome/navidrome/utils/cache"
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("CacheWarmer", func() {
+	var (
+		fc *mockFileCache
+		aw *mockArtwork
+	)
+
+	BeforeEach(func() {
+		DeferCleanup(configtest.SetupConfig())
+		fc = &mockFileCache{}
+		aw = &mockArtwork{}
+	})
+
+	Context("initialization", func() {
+		It("returns noop when cache is disabled", func() {
+			fc.SetDisabled(true)
+			cw := NewCacheWarmer(aw, fc)
+			_, ok := cw.(*noopCacheWarmer)
+			Expect(ok).To(BeTrue())
+		})
+
+		It("returns noop when ImageCacheSize is 0", func() {
+			conf.Server.ImageCacheSize = "0"
+			cw := NewCacheWarmer(aw, fc)
+			_, ok := cw.(*noopCacheWarmer)
+			Expect(ok).To(BeTrue())
+		})
+
+		It("returns noop when EnableArtworkPrecache is false", func() {
+			conf.Server.EnableArtworkPrecache = false
+			cw := NewCacheWarmer(aw, fc)
+			_, ok := cw.(*noopCacheWarmer)
+			Expect(ok).To(BeTrue())
+		})
+
+		It("returns real implementation when properly configured", func() {
+			conf.Server.ImageCacheSize = "100MB"
+			conf.Server.EnableArtworkPrecache = true
+			fc.SetDisabled(false)
+			cw := NewCacheWarmer(aw, fc)
+			_, ok := cw.(*cacheWarmer)
+			Expect(ok).To(BeTrue())
+		})
+	})
+
+	Context("buffer management", func() {
+		BeforeEach(func() {
+			conf.Server.ImageCacheSize = "100MB"
+			conf.Server.EnableArtworkPrecache = true
+			fc.SetDisabled(false)
+		})
+
+		It("drops buffered items when cache becomes disabled", func() {
+			cw := NewCacheWarmer(aw, fc).(*cacheWarmer)
+			cw.PreCache(model.MustParseArtworkID("al-test"))
+			fc.SetDisabled(true)
+			Eventually(func() int {
+				cw.mutex.Lock()
+				defer cw.mutex.Unlock()
+				return len(cw.buffer)
+			}).Should(Equal(0))
+		})
+
+		It("adds multiple items to buffer", func() {
+			cw := NewCacheWarmer(aw, fc).(*cacheWarmer)
+			cw.PreCache(model.MustParseArtworkID("al-1"))
+			cw.PreCache(model.MustParseArtworkID("al-2"))
+			cw.mutex.Lock()
+			defer cw.mutex.Unlock()
+			Expect(len(cw.buffer)).To(Equal(2))
+		})
+
+		It("deduplicates items in buffer", func() {
+			cw := NewCacheWarmer(aw, fc).(*cacheWarmer)
+			cw.PreCache(model.MustParseArtworkID("al-1"))
+			cw.PreCache(model.MustParseArtworkID("al-1"))
+			cw.mutex.Lock()
+			defer cw.mutex.Unlock()
+			Expect(len(cw.buffer)).To(Equal(1))
+		})
+	})
+
+	Context("error handling", func() {
+		BeforeEach(func() {
+			conf.Server.ImageCacheSize = "100MB"
+			conf.Server.EnableArtworkPrecache = true
+			fc.SetDisabled(false)
+		})
+
+		It("continues processing after artwork retrieval error", func() {
+			aw.err = errors.New("artwork error")
+			cw := NewCacheWarmer(aw, fc).(*cacheWarmer)
+			cw.PreCache(model.MustParseArtworkID("al-error"))
+			cw.PreCache(model.MustParseArtworkID("al-1"))
+
+			Eventually(func() int {
+				cw.mutex.Lock()
+				defer cw.mutex.Unlock()
+				return len(cw.buffer)
+			}).Should(Equal(0))
+		})
+
+		It("continues processing after cache error", func() {
+			fc.err = errors.New("cache error")
+			cw := NewCacheWarmer(aw, fc).(*cacheWarmer)
+			cw.PreCache(model.MustParseArtworkID("al-error"))
+			cw.PreCache(model.MustParseArtworkID("al-1"))
+
+			Eventually(func() int {
+				cw.mutex.Lock()
+				defer cw.mutex.Unlock()
+				return len(cw.buffer)
+			}).Should(Equal(0))
+		})
+	})
+
+	Context("background processing", func() {
+		BeforeEach(func() {
+			conf.Server.ImageCacheSize = "100MB"
+			conf.Server.EnableArtworkPrecache = true
+			fc.SetDisabled(false)
+		})
+
+		It("processes items in batches", func() {
+			cw := NewCacheWarmer(aw, fc).(*cacheWarmer)
+			for i := 0; i < 5; i++ {
+				cw.PreCache(model.MustParseArtworkID(fmt.Sprintf("al-%d", i)))
+			}
+
+			Eventually(func() int {
+				cw.mutex.Lock()
+				defer cw.mutex.Unlock()
+				return len(cw.buffer)
+			}).Should(Equal(0))
+		})
+
+		It("wakes up on new items", func() {
+			cw := NewCacheWarmer(aw, fc).(*cacheWarmer)
+
+			// Add first batch
+			cw.PreCache(model.MustParseArtworkID("al-1"))
+			Eventually(func() int {
+				cw.mutex.Lock()
+				defer cw.mutex.Unlock()
+				return len(cw.buffer)
+			}).Should(Equal(0))
+
+			// Add second batch
+			cw.PreCache(model.MustParseArtworkID("al-2"))
+			Eventually(func() int {
+				cw.mutex.Lock()
+				defer cw.mutex.Unlock()
+				return len(cw.buffer)
+			}).Should(Equal(0))
+		})
+	})
+})
+
+type mockArtwork struct {
+	err error
+}
+
+func (m *mockArtwork) Get(ctx context.Context, artID model.ArtworkID, size int, square bool) (io.ReadCloser, time.Time, error) {
+	if m.err != nil {
+		return nil, time.Time{}, m.err
+	}
+	return io.NopCloser(strings.NewReader("test")), time.Now(), nil
+}
+
+func (m *mockArtwork) GetOrPlaceholder(ctx context.Context, id string, size int, square bool) (io.ReadCloser, time.Time, error) {
+	return m.Get(ctx, model.ArtworkID{}, size, square)
+}
+
+type mockFileCache struct {
+	disabled atomic.Bool
+	ready    atomic.Bool
+	err      error
+}
+
+func (f *mockFileCache) Get(ctx context.Context, item cache.Item) (*cache.CachedStream, error) {
+	if f.err != nil {
+		return nil, f.err
+	}
+	return &cache.CachedStream{Reader: io.NopCloser(strings.NewReader("cached"))}, nil
+}
+
+func (f *mockFileCache) Available(ctx context.Context) bool {
+	return f.ready.Load() && !f.disabled.Load()
+}
+
+func (f *mockFileCache) Disabled(ctx context.Context) bool {
+	return f.disabled.Load()
+}
+
+func (f *mockFileCache) SetDisabled(v bool) {
+	f.disabled.Store(v)
+	f.ready.Store(true)
+}

utils/cache/file_caches.go

@@ -54,6 +54,9 @@ type FileCache interface {
 
 	// Available checks if the cache is available
 	Available(ctx context.Context) bool
+
+	// Disabled reports if the cache has been permanently disabled
+	Disabled(ctx context.Context) bool
 }
 
 // NewFileCache creates a new FileCache. This function initializes the cache and starts it in the background.
@@ -119,6 +122,13 @@ func (fc *fileCache) Available(_ context.Context) bool {
 	return fc.ready.Load() && !fc.disabled
 }
 
+func (fc *fileCache) Disabled(_ context.Context) bool {
+	fc.mutex.RLock()
+	defer fc.mutex.RUnlock()
+
+	return fc.disabled
+}
+
 func (fc *fileCache) invalidate(ctx context.Context, key string) error {
 	if !fc.Available(ctx) {
 		log.Debug(ctx, "Cache not initialized yet. Cannot invalidate key", "cache", fc.name, "key", key)

utils/cache/file_caches_test.go

@@ -50,6 +50,13 @@ var _ = Describe("File Caches", func() {
 			Expect(fc.cache).To(BeNil())
 			Expect(fc.disabled).To(BeTrue())
 		})
+
+		It("reports when cache is disabled", func() {
+			fc := callNewFileCache("test", "0", "test", 0, nil)
+			Expect(fc.Disabled(context.Background())).To(BeTrue())
+			fc = callNewFileCache("test", "1KB", "test", 0, nil)
+			Expect(fc.Disabled(context.Background())).To(BeFalse())
+		})
 	})
 
 	Describe("FileCache", func() {