98 lines
2.9 KiB
Go
98 lines
2.9 KiB
Go
// Package cache wraps Redis with the small surface the gateway needs.
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//
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// Every cached value is scoped to an Emby user id, because "what's on the home screen"
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// is per-user. Mutations (favourite, watched, playback stopped) drop that user's keys
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// so the next request re-reads Emby rather than serving a stale row.
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package cache
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import (
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"context"
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"errors"
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"fmt"
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"time"
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"github.com/redis/go-redis/v9"
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)
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// ErrMiss means the key was absent — an ordinary outcome, not a failure.
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var ErrMiss = errors.New("cache: miss")
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type Cache struct {
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rdb *redis.Client
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}
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func Open(redisURL string) (*Cache, error) {
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opts, err := redis.ParseURL(redisURL)
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if err != nil {
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return nil, fmt.Errorf("cache: parse url: %w", err)
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}
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return &Cache{rdb: redis.NewClient(opts)}, nil
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}
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func (c *Cache) Close() error { return c.rdb.Close() }
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func (c *Cache) Ping(ctx context.Context) error { return c.rdb.Ping(ctx).Err() }
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func (c *Cache) Get(ctx context.Context, key string) ([]byte, error) {
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b, err := c.rdb.Get(ctx, key).Bytes()
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if errors.Is(err, redis.Nil) {
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return nil, ErrMiss
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}
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if err != nil {
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return nil, err
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}
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return b, nil
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}
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func (c *Cache) Set(ctx context.Context, key string, value []byte, ttl time.Duration) error {
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return c.rdb.Set(ctx, key, value, ttl).Err()
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}
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func (c *Cache) Delete(ctx context.Context, keys ...string) error {
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if len(keys) == 0 {
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return nil
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}
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return c.rdb.Del(ctx, keys...).Err()
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}
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// InvalidateUser drops every cached view belonging to one Emby user.
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//
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// SCAN rather than KEYS so a large keyspace never blocks Redis; the key count here is
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// small, but the habit costs nothing.
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func (c *Cache) InvalidateUser(ctx context.Context, userID string) error {
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pattern := fmt.Sprintf("u:%s:*", userID)
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var cursor uint64
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for {
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keys, next, err := c.rdb.Scan(ctx, cursor, pattern, 200).Result()
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if err != nil {
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return err
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}
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if len(keys) > 0 {
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if err := c.rdb.Del(ctx, keys...).Err(); err != nil {
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return err
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}
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}
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if next == 0 {
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return nil
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}
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cursor = next
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}
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}
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// UserKey builds the namespaced key used by everything user-scoped.
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func UserKey(userID, view string) string { return fmt.Sprintf("u:%s:%s", userID, view) }
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// RecommendationsKey sits in its own `r:` namespace on purpose.
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//
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// Recommendations cost several Emby queries to build, so they must survive the cache
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// wipe that every favourite toggle triggers. Only a genuine change in viewing history
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// — a finished playback — retires them, via [Cache.InvalidateRecommendations].
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func RecommendationsKey(userID string) string { return fmt.Sprintf("r:%s:rows:v3", userID) }
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func (c *Cache) InvalidateRecommendations(ctx context.Context, userID string) error {
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return c.Delete(ctx, RecommendationsKey(userID))
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}
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// SessionKey caches a token→session lookup, keyed by token hash (never the token).
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func SessionKey(tokenHashHex string) string { return "sess:" + tokenHashHex }
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