feat: add HLS manifest cache with TTL-based expiry

internal/playback/handler/manifest_cache.go

@@ -0,0 +1,109 @@
+package handler
+
+import (
+	"container/list"
+	"net/http"
+	"strings"
+	"sync"
+	"time"
+)
+
+const (
+	manifestCacheVODTTL      = 45 * time.Second
+	manifestCacheLiveTTL     = 3 * time.Second
+	manifestCacheMaxEntries  = 256
+	manifestCacheMaxBodySize = 2 << 20
+)
+
+type manifestCacheEntry struct {
+	key       string
+	body      []byte
+	headers   http.Header
+	status    int
+	expiresAt time.Time
+}
+
+type manifestCache struct {
+	mu         sync.Mutex
+	maxEntries int
+	entries    map[string]*list.Element
+	lru        *list.List
+}
+
+func newManifestCache(maxEntries int) *manifestCache {
+	if maxEntries <= 0 {
+		maxEntries = manifestCacheMaxEntries
+	}
+	return &manifestCache{
+		maxEntries: maxEntries,
+		entries:    make(map[string]*list.Element, maxEntries),
+		lru:        list.New(),
+	}
+}
+
+func manifestCacheKey(targetURL string, referer string) string {
+	return targetURL + "\x00" + referer
+}
+
+func (c *manifestCache) get(key string, now time.Time) (manifestCacheEntry, bool) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	el := c.entries[key]
+	if el == nil {
+		return manifestCacheEntry{}, false
+	}
+	entry, ok := el.Value.(manifestCacheEntry)
+	if !ok || !now.Before(entry.expiresAt) {
+		c.remove(el)
+		return manifestCacheEntry{}, false
+	}
+	c.lru.MoveToFront(el)
+	entry.body = append([]byte(nil), entry.body...)
+	entry.headers = entry.headers.Clone()
+	return entry, true
+}
+
+func (c *manifestCache) set(key string, status int, headers http.Header, body []byte, now time.Time) bool {
+	if status < http.StatusOK || status >= http.StatusMultipleChoices || len(body) > manifestCacheMaxBodySize {
+		return false
+	}
+
+	ttl := manifestCacheVODTTL
+	bodyText := string(body)
+	if strings.Contains(bodyText, "#EXTINF") && !strings.Contains(bodyText, "#EXT-X-ENDLIST") {
+		ttl = manifestCacheLiveTTL
+	}
+	entry := manifestCacheEntry{
+		key:       key,
+		body:      append([]byte(nil), body...),
+		headers:   headers.Clone(),
+		status:    status,
+		expiresAt: now.Add(ttl),
+	}
+
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if el := c.entries[key]; el != nil {
+		el.Value = entry
+		c.lru.MoveToFront(el)
+		return true
+	}
+	c.entries[key] = c.lru.PushFront(entry)
+	for len(c.entries) > c.maxEntries {
+		back := c.lru.Back()
+		if back == nil {
+			break
+		}
+		c.remove(back)
+	}
+	return true
+}
+
+func (c *manifestCache) remove(el *list.Element) {
+	entry, ok := el.Value.(manifestCacheEntry)
+	if ok {
+		delete(c.entries, entry.key)
+	}
+	c.lru.Remove(el)
+}