feat(cache): add memory backend

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

docs/docs/configuration/cache.md

@@ -11,7 +11,7 @@ The cache option is common to all scanners.
 ## Clear Caches
 `trivy clean` subcommand removes caches.
 
-```
+```bash
 $ trivy clean --scan-cache
 ```
 
@@ -31,31 +31,59 @@ See `trivy clean --help` for details.
 ## Cache Directory
 Specify where the cache is stored with `--cache-dir`.
 
-```
+```bash
 $ trivy --cache-dir /tmp/trivy/ image python:3.4-alpine3.9
 ```
 
-## Cache Backend
+## Scan Cache Backend
 !!! warning "EXPERIMENTAL"
     This feature might change without preserving backwards compatibility.
 
-Trivy supports local filesystem and Redis as the cache backend. This option is useful especially for client/server mode.
-
-Two options:
+Trivy utilizes a scan cache to store analysis results, such as package lists.
+It supports three types of backends for this cache: 
 
-- `fs`
-    - the cache path can be specified by `--cache-dir`
-- `redis://`
+- Local File System (`fs`)
+    - The cache path can be specified by `--cache-dir`
+- Memory (`memory`)
+- Redis (`redis://`)
     - `redis://[HOST]:[PORT]`
     - TTL can be configured via `--cache-ttl`
 
+### Local File System
+The local file system backend is the default choice for container and VM image scans.
+When scanning container images, it stores analysis results on a per-layer basis, using layer IDs as keys.
+This approach enables faster scans of the same container image or different images that share layers.
+
+!!! note
+    Internally, this backend uses [BoltDB][boltdb], which has an important limitation: only one process can access the cache at a time.
+    Subsequent processes attempting to access the cache will be locked.
+    For more details on this limitation, refer to the [troubleshooting guide][parallel-run].
+
+### Memory
+The memory backend stores analysis results in memory, which means the cache is discarded when the process ends.
+This makes it useful in scenarios where caching is not required or desired.
+It serves as the default for repository, filesystem and SBOM scans and can also be employed for container image scans when caching is unnecessary.
+
+To use the memory backend for a container image scan, you can use the following command:
+
+```bash
+$ trivy image debian:11 --cache-backend memory
 ```
+
+### Redis
+
+The Redis backend is particularly useful when you need to share the cache across multiple Trivy instances.
+You can set up Trivy to use a Redis backend with a command like this:
+
+```bash
 $ trivy server --cache-backend redis://localhost:6379
 ```
 
+This approach allows for centralized caching, which can be beneficial in distributed or high-concurrency environments.
+
 If you want to use TLS with Redis, you can enable it by specifying the `--redis-tls` flag.
 
-```shell
+```bash
 $ trivy server --cache-backend redis://localhost:6379 --redis-tls
 ```
 
@@ -72,6 +100,8 @@ $ trivy server --cache-backend redis://localhost:6379 \
 [trivy-db]: ./db.md#vulnerability-database
 [trivy-java-db]: ./db.md#java-index-database
 [misconf-checks]: ../scanner/misconfiguration/check/builtin.md
+[boltdb]: https://github.com/etcd-io/bbolt
+[parallel-run]: https://aquasecurity.github.io/trivy/v0.52/docs/references/troubleshooting/#running-in-parallel-takes-same-time-as-series-run
 
 [^1]: Downloaded when scanning for vulnerabilities
 [^2]: Downloaded when scanning `jar/war/par/ear` files

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)
 	}

pkg/cache/memory.go

@@ -0,0 +1,98 @@
+package cache
+
+import (
+	"sync"
+
+	"golang.org/x/xerrors"
+
+	"github.com/aquasecurity/trivy/pkg/fanal/types"
+)
+
+var _ Cache = &MemoryCache{}
+
+type MemoryCache struct {
+	artifacts sync.Map // Map to store artifact information
+	blobs     sync.Map // Map to store blob information
+}
+
+func NewMemoryCache() *MemoryCache {
+	return &MemoryCache{}
+}
+
+// PutArtifact stores the artifact information in the memory cache
+func (c *MemoryCache) PutArtifact(artifactID string, artifactInfo types.ArtifactInfo) error {
+	c.artifacts.Store(artifactID, artifactInfo)
+	return nil
+}
+
+// PutBlob stores the blob information in the memory cache
+func (c *MemoryCache) PutBlob(blobID string, blobInfo types.BlobInfo) error {
+	c.blobs.Store(blobID, blobInfo)
+	return nil
+}
+
+// DeleteBlobs removes the specified blobs from the memory cache
+func (c *MemoryCache) DeleteBlobs(blobIDs []string) error {
+	for _, blobID := range blobIDs {
+		c.blobs.Delete(blobID)
+	}
+	return nil
+}
+
+// GetArtifact retrieves the artifact information from the memory cache
+func (c *MemoryCache) GetArtifact(artifactID string) (types.ArtifactInfo, error) {
+	info, ok := c.artifacts.Load(artifactID)
+	if !ok {
+		return types.ArtifactInfo{}, xerrors.Errorf("artifact (%s) not found in memory cache", artifactID)
+	}
+	artifactInfo, ok := info.(types.ArtifactInfo)
+	if !ok {
+		return types.ArtifactInfo{}, xerrors.Errorf("invalid type for artifact (%s) in memory cache", artifactID)
+	}
+	return artifactInfo, nil
+}
+
+// GetBlob retrieves the blob information from the memory cache
+func (c *MemoryCache) GetBlob(blobID string) (types.BlobInfo, error) {
+	info, ok := c.blobs.Load(blobID)
+	if !ok {
+		return types.BlobInfo{}, xerrors.Errorf("blob (%s) not found in memory cache", blobID)
+	}
+	blobInfo, ok := info.(types.BlobInfo)
+	if !ok {
+		return types.BlobInfo{}, xerrors.Errorf("invalid type for blob (%s) in memory cache", blobID)
+	}
+	return blobInfo, nil
+}
+
+// MissingBlobs determines the missing artifact and blob information in the memory cache
+func (c *MemoryCache) MissingBlobs(artifactID string, blobIDs []string) (bool, []string, error) {
+	var missingArtifact bool
+	var missingBlobIDs []string
+
+	if _, err := c.GetArtifact(artifactID); err != nil {
+		missingArtifact = true
+	}
+
+	for _, blobID := range blobIDs {
+		if _, err := c.GetBlob(blobID); err != nil {
+			missingBlobIDs = append(missingBlobIDs, blobID)
+		}
+	}
+
+	return missingArtifact, missingBlobIDs, nil
+}
+
+// Close clears the artifact and blob information from the memory cache
+func (c *MemoryCache) Close() error {
+	c.artifacts = sync.Map{}
+	c.blobs = sync.Map{}
+	return nil
+}
+
+// Clear clears the artifact and blob information from the memory cache
+func (c *MemoryCache) Clear() error {
+	c.artifacts = sync.Map{}
+	c.blobs = sync.Map{}
+	return nil
+}