feat: Add function to check if cache contains a key

bigcache.go

@@ -233,6 +233,13 @@ func (c *BigCache) Iterator() *EntryInfoIterator {
 	return newIterator(c)
 }
 
+// Contains returns whether the given key exists in cache
+func (c *BigCache) Contains(key string) bool {
+	hashedKey := c.hash.Sum64(key)
+	shard := c.getShard(hashedKey)
+	return shard.contains(key, hashedKey)
+}
+
 func (c *BigCache) onEvict(oldestEntry []byte, currentTimestamp uint64, evict func(reason RemoveReason) error) bool {
 	oldestTimestamp := readTimestampFromEntry(oldestEntry)
 	if currentTimestamp < oldestTimestamp {

bigcache_test.go

@@ -1388,3 +1388,31 @@ func TestRemoveNonExpiredData(t *testing.T) {
 		noError(t, err)
 	}
 }
+
+func TestContainsExists(t *testing.T) {
+	t.Parallel()
+
+	// given
+	cache, _ := New(context.Background(), DefaultConfig(5*time.Second))
+	value := []byte("value")
+
+	// when
+	cache.Set("key", value)
+	exists := cache.Contains("key")
+
+	// then
+	assertEqual(t, true, exists)
+}
+
+func TestContainsNotExists(t *testing.T) {
+	t.Parallel()
+
+	// given
+	cache, _ := New(context.Background(), DefaultConfig(5*time.Second))
+
+	// when
+	exists := cache.Contains("key")
+
+	// then
+	assertEqual(t, false, exists)
+}

shard.go

@@ -117,6 +117,18 @@ func (s *cacheShard) getValidWrapEntry(key string, hashedKey uint64) ([]byte, er
 	return wrappedEntry, nil
 }
 
+func (s *cacheShard) contains(key string, hashedKey uint64) bool {
+	s.lock.RLock()
+	wrappedEntry, err := s.getWrappedEntry(hashedKey)
+	if err != nil {
+		s.lock.RUnlock()
+		return false
+	}
+	entryKey := readKeyFromEntry(wrappedEntry)
+	s.lock.RUnlock()
+	return key == entryKey
+}
+
 func (s *cacheShard) set(key string, hashedKey uint64, entry []byte) error {
 	currentTimestamp := uint64(s.clock.Epoch())