feat: add memory cache backend (#7048)

Signed-off-by: knqyf263 <knqyf263@gmail.com>

pkg/cache/client.go

@@ -5,12 +5,15 @@ import (
 	"time"
 
 	"golang.org/x/xerrors"
+
+	"github.com/aquasecurity/trivy/pkg/log"
 )
 
 const (
 	TypeUnknown Type = "unknown"
 	TypeFS      Type = "fs"
 	TypeRedis   Type = "redis"
+	TypeMemory  Type = "memory"
 )
 
 type Type string
@@ -33,6 +36,8 @@ func NewType(backend string) Type {
 		return TypeRedis
 	case backend == "fs", backend == "":
 		return TypeFS
+	case backend == "memory":
+		return TypeMemory
 	default:
 		return TypeUnknown
 	}
@@ -44,6 +49,7 @@ func New(opts Options) (Cache, func(), error) {
 
 	var cache Cache
 	t := NewType(opts.Backend)
+	log.Debug("Initializing scan cache...", log.String("type", string(t)))
 	switch t {
 	case TypeRedis:
 		redisCache, err := NewRedisCache(opts.Backend, opts.RedisCACert, opts.RedisCert, opts.RedisKey, opts.RedisTLS, opts.TTL)
@@ -58,6 +64,8 @@ func New(opts Options) (Cache, func(), error) {
 			return nil, cleanup, xerrors.Errorf("unable to initialize fs cache: %w", err)
 		}
 		cache = fsCache
+	case TypeMemory:
+		cache = NewMemoryCache()
 	default:
 		return nil, cleanup, xerrors.Errorf("unknown cache type: %s", t)
 	}