fix(container): serve cached images when upstream is unavailable

docs/architecture.md

@@ -353,6 +353,7 @@ Eviction can be implemented as:
 - Fresh data - new versions visible immediately
 - Metadata is small, upstream fetch is fast
 - Set `cache_metadata: true` or use the mirror command to enable metadata caching for offline use via the `metadata_cache` table
+- OCI manifests are the exception: they are cached automatically so previously fetched images remain pullable when the registry or token service is unavailable
 
 **Why stream artifacts?**
 - Memory efficient - don't load large files into RAM

docs/configuration.md

@@ -246,6 +246,8 @@ Note: Hex cooldown requires disabling registry signature verification since the
 
 By default the proxy fetches metadata fresh from upstream on every request. Enable `cache_metadata` to store metadata responses in the database and storage backend for offline fallback. When upstream is unreachable, the proxy serves the last cached copy. ETag-based revalidation avoids re-downloading unchanged metadata.
 
+OCI manifests are always cached because cached image blobs cannot be pulled without their manifests. Digest-addressed manifests are immutable and served directly from cache. Tag-addressed manifests follow `metadata_ttl`, revalidate when stale, and fall back to the last cached response when the registry is unavailable.
+
 ```yaml
 cache_metadata: true
 ```

internal/database/metadata_cache_test.go

@@ -30,8 +30,12 @@ func TestUpsertAndGetMetadataCache(t *testing.T) {
 		StoragePath: "_metadata/npm/lodash/metadata",
 		ETag:        sql.NullString{String: `"abc123"`, Valid: true},
 		ContentType: sql.NullString{String: "application/json", Valid: true},
-		Size:        sql.NullInt64{Int64: 1024, Valid: true},
-		FetchedAt:   sql.NullTime{Time: time.Now(), Valid: true},
+		ContentDigest: sql.NullString{
+			String: "sha256:0123456789abcdef",
+			Valid:  true,
+		},
+		Size:      sql.NullInt64{Int64: 1024, Valid: true},
+		FetchedAt: sql.NullTime{Time: time.Now(), Valid: true},
 	}
 
 	err := db.UpsertMetadataCache(entry)
@@ -62,6 +66,9 @@ func TestUpsertAndGetMetadataCache(t *testing.T) {
 	if !got.ContentType.Valid || got.ContentType.String != "application/json" {
 		t.Errorf("content_type = %v, want %q", got.ContentType, "application/json")
 	}
+	if !got.ContentDigest.Valid || got.ContentDigest.String != "sha256:0123456789abcdef" {
+		t.Errorf("content_digest = %v, want %q", got.ContentDigest, "sha256:0123456789abcdef")
+	}
 	if !got.Size.Valid || got.Size.Int64 != 1024 {
 		t.Errorf("size = %v, want 1024", got.Size)
 	}
@@ -178,3 +185,47 @@ func TestMetadataCacheTableCreatedByMigration(t *testing.T) {
 		t.Error("metadata_cache table should exist after migration")
 	}
 }
+
+func TestMetadataCacheContentDigestMigrationPreservesExistingRows(t *testing.T) {
+	dbPath := filepath.Join(t.TempDir(), "test.db")
+	db, err := Create(dbPath)
+	if err != nil {
+		t.Fatalf("Create failed: %v", err)
+	}
+	defer func() { _ = db.Close() }()
+
+	if _, err := db.Exec("ALTER TABLE metadata_cache DROP COLUMN content_digest"); err != nil {
+		t.Fatalf("dropping content_digest: %v", err)
+	}
+	if _, err := db.Exec("DELETE FROM migrations WHERE name = ?", "006_add_metadata_content_digest"); err != nil {
+		t.Fatalf("resetting digest migration: %v", err)
+	}
+	if _, err := db.Exec(`
+		INSERT INTO metadata_cache (ecosystem, name, storage_path, content_type, size, fetched_at, created_at, updated_at)
+		VALUES (?, ?, ?, ?, ?, ?, ?, ?)
+	`, "oci-manifest", "cache-key", "_metadata/oci-manifest/cache-key/metadata", "application/json", 2, time.Now(), time.Now(), time.Now()); err != nil {
+		t.Fatalf("inserting legacy cache row: %v", err)
+	}
+
+	if err := db.MigrateSchema(); err != nil {
+		t.Fatalf("MigrateSchema() error = %v", err)
+	}
+	hasDigest, err := db.HasColumn("metadata_cache", "content_digest")
+	if err != nil {
+		t.Fatalf("HasColumn() error = %v", err)
+	}
+	if !hasDigest {
+		t.Fatal("metadata_cache.content_digest was not added")
+	}
+
+	entry, err := db.GetMetadataCache("oci-manifest", "cache-key")
+	if err != nil {
+		t.Fatalf("GetMetadataCache() error = %v", err)
+	}
+	if entry == nil || entry.StoragePath != "_metadata/oci-manifest/cache-key/metadata" {
+		t.Fatalf("existing metadata cache row was not preserved: %#v", entry)
+	}
+	if entry.ContentDigest.Valid {
+		t.Errorf("legacy content digest = %q, want NULL", entry.ContentDigest.String)
+	}
+}

internal/database/queries.go

@@ -894,7 +894,7 @@ func (db *DB) GetMetadataCache(ecosystem, name string) (*MetadataCacheEntry, err
 	var entry MetadataCacheEntry
 	query := db.Rebind(`
 		SELECT id, ecosystem, name, storage_path, etag, content_type,
-		       size, last_modified, fetched_at, created_at, updated_at
+		       content_digest, size, last_modified, fetched_at, created_at, updated_at
 		FROM metadata_cache WHERE ecosystem = ? AND name = ?
 	`)
 	err := db.Get(&entry, query, ecosystem, name)
@@ -914,12 +914,13 @@ func (db *DB) UpsertMetadataCache(entry *MetadataCacheEntry) error {
 	if db.dialect == DialectPostgres {
 		query = `
 			INSERT INTO metadata_cache (ecosystem, name, storage_path, etag, content_type,
-			                            size, last_modified, fetched_at, created_at, updated_at)
-			VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10)
+			                            content_digest, size, last_modified, fetched_at, created_at, updated_at)
+			VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11)
 			ON CONFLICT(ecosystem, name) DO UPDATE SET
 				storage_path = EXCLUDED.storage_path,
 				etag = EXCLUDED.etag,
 				content_type = EXCLUDED.content_type,
+				content_digest = EXCLUDED.content_digest,
 				size = EXCLUDED.size,
 				last_modified = EXCLUDED.last_modified,
 				fetched_at = EXCLUDED.fetched_at,
@@ -928,12 +929,13 @@ func (db *DB) UpsertMetadataCache(entry *MetadataCacheEntry) error {
 	} else {
 		query = `
 			INSERT INTO metadata_cache (ecosystem, name, storage_path, etag, content_type,
-			                            size, last_modified, fetched_at, created_at, updated_at)
-			VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+			                            content_digest, size, last_modified, fetched_at, created_at, updated_at)
+			VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
 			ON CONFLICT(ecosystem, name) DO UPDATE SET
 				storage_path = excluded.storage_path,
 				etag = excluded.etag,
 				content_type = excluded.content_type,
+				content_digest = excluded.content_digest,
 				size = excluded.size,
 				last_modified = excluded.last_modified,
 				fetched_at = excluded.fetched_at,
@@ -943,7 +945,7 @@ func (db *DB) UpsertMetadataCache(entry *MetadataCacheEntry) error {
 
 	_, err := db.Exec(query,
 		entry.Ecosystem, entry.Name, entry.StoragePath, entry.ETag,
-		entry.ContentType, entry.Size, entry.LastModified, entry.FetchedAt, now, now,
+		entry.ContentType, entry.ContentDigest, entry.Size, entry.LastModified, entry.FetchedAt, now, now,
 	)
 	if err != nil {
 		return fmt.Errorf("upserting metadata cache: %w", err)

internal/database/schema.go

@@ -102,6 +102,7 @@ CREATE TABLE IF NOT EXISTS metadata_cache (
 	storage_path TEXT NOT NULL,
 	etag TEXT,
 	content_type TEXT,
+	content_digest TEXT,
 	size INTEGER,
 	last_modified DATETIME,
 	fetched_at DATETIME,
@@ -202,6 +203,7 @@ CREATE TABLE IF NOT EXISTS metadata_cache (
 	storage_path TEXT NOT NULL,
 	etag TEXT,
 	content_type TEXT,
+	content_digest TEXT,
 	size BIGINT,
 	last_modified TIMESTAMP,
 	fetched_at TIMESTAMP,
@@ -359,6 +361,7 @@ var migrations = []migration{
 	{"003_ensure_artifacts_table", migrateEnsureArtifactsTable},
 	{"004_ensure_vulnerabilities_table", migrateEnsureVulnerabilitiesTable},
 	{"005_ensure_metadata_cache_table", migrateEnsureMetadataCacheTable},
+	{"006_add_metadata_content_digest", migrateAddMetadataContentDigest},
 }
 
 // isTableNotFound returns true if the error indicates a missing table.
@@ -581,6 +584,20 @@ func migrateEnsureMetadataCacheTable(db *DB) error {
 	return db.EnsureMetadataCacheTable()
 }
 
+func migrateAddMetadataContentDigest(db *DB) error {
+	hasColumn, err := db.HasColumn("metadata_cache", "content_digest")
+	if err != nil {
+		return fmt.Errorf("checking metadata_cache content_digest column: %w", err)
+	}
+	if hasColumn {
+		return nil
+	}
+	if _, err := db.Exec("ALTER TABLE metadata_cache ADD COLUMN content_digest TEXT"); err != nil {
+		return fmt.Errorf("adding metadata_cache content_digest column: %w", err)
+	}
+	return nil
+}
+
 // EnsureMetadataCacheTable creates the metadata_cache table if it doesn't exist.
 func (db *DB) EnsureMetadataCacheTable() error {
 	has, err := db.HasTable("metadata_cache")
@@ -601,6 +618,7 @@ func (db *DB) EnsureMetadataCacheTable() error {
 				storage_path TEXT NOT NULL,
 				etag TEXT,
 				content_type TEXT,
+				content_digest TEXT,
 				size BIGINT,
 				last_modified TIMESTAMP,
 				fetched_at TIMESTAMP,
@@ -618,6 +636,7 @@ func (db *DB) EnsureMetadataCacheTable() error {
 				storage_path TEXT NOT NULL,
 				etag TEXT,
 				content_type TEXT,
+				content_digest TEXT,
 				size INTEGER,
 				last_modified DATETIME,
 				fetched_at DATETIME,

internal/database/types.go

@@ -78,17 +78,18 @@ func (a *Artifact) IsCached() bool {
 
 // MetadataCacheEntry represents a cached metadata blob for offline serving.
 type MetadataCacheEntry struct {
-	ID           int64          `db:"id" json:"id"`
-	Ecosystem    string         `db:"ecosystem" json:"ecosystem"`
-	Name         string         `db:"name" json:"name"`
-	StoragePath  string         `db:"storage_path" json:"storage_path"`
-	ETag         sql.NullString `db:"etag" json:"etag,omitempty"`
-	ContentType  sql.NullString `db:"content_type" json:"content_type,omitempty"`
-	Size         sql.NullInt64  `db:"size" json:"size,omitempty"`
-	LastModified sql.NullTime   `db:"last_modified" json:"last_modified,omitempty"`
-	FetchedAt    sql.NullTime   `db:"fetched_at" json:"fetched_at,omitempty"`
-	CreatedAt    time.Time      `db:"created_at" json:"created_at"`
-	UpdatedAt    time.Time      `db:"updated_at" json:"updated_at"`
+	ID            int64          `db:"id" json:"id"`
+	Ecosystem     string         `db:"ecosystem" json:"ecosystem"`
+	Name          string         `db:"name" json:"name"`
+	StoragePath   string         `db:"storage_path" json:"storage_path"`
+	ETag          sql.NullString `db:"etag" json:"etag,omitempty"`
+	ContentType   sql.NullString `db:"content_type" json:"content_type,omitempty"`
+	ContentDigest sql.NullString `db:"content_digest" json:"content_digest,omitempty"`
+	Size          sql.NullInt64  `db:"size" json:"size,omitempty"`
+	LastModified  sql.NullTime   `db:"last_modified" json:"last_modified,omitempty"`
+	FetchedAt     sql.NullTime   `db:"fetched_at" json:"fetched_at,omitempty"`
+	CreatedAt     time.Time      `db:"created_at" json:"created_at"`
+	UpdatedAt     time.Time      `db:"updated_at" json:"updated_at"`
 }
 
 // Vulnerability represents a cached vulnerability record.