feat: add lru+ttl subtitle cache

internal/playback/handler/handler.go

@@ -5,11 +5,12 @@ import (
 	"io"
 	"mal/internal/domain"
 	"mal/pkg/net/proxytransport"
+	"mal/pkg/net/useragent"
 	"maps"
 	"net/http"
 	"strconv"
 	"strings"
-	"sync"
+	"time"
 
 	"github.com/gin-gonic/gin"
 )
@@ -20,7 +21,7 @@ type PlaybackHandler struct {
 
 	proxyClient     *http.Client
 	streamingClient *http.Client
-	subtitleCache   sync.Map
+	subtitleCache   *subtitleCache
 }
 
 func NewPlaybackHandler(svc domain.PlaybackService, animeSvc domain.AnimeService) *PlaybackHandler {
@@ -29,6 +30,7 @@ func NewPlaybackHandler(svc domain.PlaybackService, animeSvc domain.AnimeService
 		animeSvc:        animeSvc,
 		proxyClient:     proxytransport.NewClient(),
 		streamingClient: proxytransport.NewStreamingClient(),
+		subtitleCache:   newSubtitleCache(10*time.Minute, 256),
 	}
 }
 
@@ -268,7 +270,7 @@ func (h *PlaybackHandler) HandleProxyStream(c *gin.Context) {
 	if ifRangeHeader := c.GetHeader("If-Range"); ifRangeHeader != "" {
 		req.Header.Set("If-Range", ifRangeHeader)
 	}
-	req.Header.Set("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/121.0")
+	req.Header.Set("User-Agent", useragent.Firefox121)
 
 	resp, err := h.streamingClient.Do(req)
 	if err != nil {
@@ -284,11 +286,6 @@ func (h *PlaybackHandler) HandleProxyStream(c *gin.Context) {
 	_, _ = io.Copy(c.Writer, resp.Body)
 }
 
-type cachedSubtitle struct {
-	data        []byte
-	contentType string
-}
-
 func (h *PlaybackHandler) HandleProxySubtitle(c *gin.Context) {
 	token := c.Query("token")
 	if token == "" {
@@ -302,9 +299,8 @@ func (h *PlaybackHandler) HandleProxySubtitle(c *gin.Context) {
 		return
 	}
 
-	if cached, ok := h.subtitleCache.Load(targetURL); ok {
-		entry := cached.(cachedSubtitle)
-		c.Data(http.StatusOK, entry.contentType, entry.data)
+	if data, contentType, ok := h.subtitleCache.Get(targetURL, time.Now()); ok {
+		c.Data(http.StatusOK, contentType, data)
 		return
 	}
 
@@ -316,7 +312,7 @@ func (h *PlaybackHandler) HandleProxySubtitle(c *gin.Context) {
 	if referer != "" {
 		req.Header.Set("Referer", referer)
 	}
-	req.Header.Set("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/121.0")
+	req.Header.Set("User-Agent", useragent.Firefox121)
 
 	resp, err := h.proxyClient.Do(req)
 	if err != nil {
@@ -336,7 +332,7 @@ func (h *PlaybackHandler) HandleProxySubtitle(c *gin.Context) {
 		contentType = detectSubtitleType(targetURL)
 	}
 
-	h.subtitleCache.Store(targetURL, cachedSubtitle{data: body, contentType: contentType})
+	h.subtitleCache.Set(targetURL, body, contentType, time.Now())
 
 	c.Data(http.StatusOK, contentType, body)
 }

internal/playback/handler/subtitle_cache.go

@@ -0,0 +1,95 @@
+package handler
+
+import (
+	"container/list"
+	"sync"
+	"time"
+)
+
+type subtitleCacheEntry struct {
+	key         string
+	data        []byte
+	contentType string
+	expiresAt   time.Time
+}
+
+// subtitleCache is a small TTL+LRU cache to avoid unbounded memory usage when
+// proxying subtitles.
+type subtitleCache struct {
+	mu         sync.Mutex
+	ttl        time.Duration
+	maxEntries int
+
+	entries map[string]*list.Element
+	lru     *list.List
+}
+
+func newSubtitleCache(ttl time.Duration, maxEntries int) *subtitleCache {
+	if ttl <= 0 {
+		ttl = 10 * time.Minute
+	}
+	if maxEntries <= 0 {
+		maxEntries = 256
+	}
+	return &subtitleCache{
+		ttl:        ttl,
+		maxEntries: maxEntries,
+		entries:    make(map[string]*list.Element, maxEntries),
+		lru:        list.New(),
+	}
+}
+
+func (c *subtitleCache) Get(key string, now time.Time) (data []byte, contentType string, ok bool) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	el := c.entries[key]
+	if el == nil {
+		return nil, "", false
+	}
+	entry := el.Value.(subtitleCacheEntry)
+	if !entry.expiresAt.IsZero() && now.After(entry.expiresAt) {
+		c.removeElement(el)
+		return nil, "", false
+	}
+	c.lru.MoveToFront(el)
+	return entry.data, entry.contentType, true
+}
+
+func (c *subtitleCache) Set(key string, data []byte, contentType string, now time.Time) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	if el := c.entries[key]; el != nil {
+		entry := el.Value.(subtitleCacheEntry)
+		entry.data = data
+		entry.contentType = contentType
+		entry.expiresAt = now.Add(c.ttl)
+		el.Value = entry
+		c.lru.MoveToFront(el)
+		return
+	}
+
+	entry := subtitleCacheEntry{
+		key:         key,
+		data:        data,
+		contentType: contentType,
+		expiresAt:   now.Add(c.ttl),
+	}
+	el := c.lru.PushFront(entry)
+	c.entries[key] = el
+
+	for len(c.entries) > c.maxEntries {
+		back := c.lru.Back()
+		if back == nil {
+			break
+		}
+		c.removeElement(back)
+	}
+}
+
+func (c *subtitleCache) removeElement(el *list.Element) {
+	entry := el.Value.(subtitleCacheEntry)
+	delete(c.entries, entry.key)
+	c.lru.Remove(el)
+}

internal/playback/handler/subtitle_cache_test.go

@@ -0,0 +1,46 @@
+package handler
+
+import (
+	"testing"
+	"time"
+)
+
+func TestSubtitleCache_TTLExpiry(t *testing.T) {
+	c := newSubtitleCache(50*time.Millisecond, 10)
+	now := time.Unix(100, 0)
+
+	c.Set("k", []byte("v"), "text/plain", now)
+
+	if _, _, ok := c.Get("k", now.Add(49*time.Millisecond)); !ok {
+		t.Fatalf("expected cache hit before expiry")
+	}
+	if _, _, ok := c.Get("k", now.Add(51*time.Millisecond)); ok {
+		t.Fatalf("expected cache miss after expiry")
+	}
+}
+
+func TestSubtitleCache_LRUEviction(t *testing.T) {
+	c := newSubtitleCache(time.Minute, 2)
+	now := time.Unix(200, 0)
+
+	c.Set("a", []byte("a"), "text/plain", now)
+	c.Set("b", []byte("b"), "text/plain", now)
+
+	// Make "a" most recently used; "b" should be evicted next.
+	if _, _, ok := c.Get("a", now); !ok {
+		t.Fatalf("expected hit for a")
+	}
+
+	c.Set("c", []byte("c"), "text/plain", now)
+
+	if _, _, ok := c.Get("b", now); ok {
+		t.Fatalf("expected b to be evicted")
+	}
+	if _, _, ok := c.Get("a", now); !ok {
+		t.Fatalf("expected a to remain")
+	}
+	if _, _, ok := c.Get("c", now); !ok {
+		t.Fatalf("expected c to exist")
+	}
+}
+