added minimal image checker

app/maindb/blob.go

@@ -59,6 +59,23 @@ func (db *Database) GetBlobByNameDigest(ctx context.Context, name, digest string
 	return exists, res, err
 }
 
+func (db *Database) GetBlobByNameRefDigest(ctx context.Context, name, reference, digest string) (bool, descr.Blob, error) {
+	var err error
+	blobs := make([]descr.Blob, 0)
+	res := descr.Blob{}
+	exists := false
+	request := `SELECT * FROM blobs WHERE name = $1 AND reference = $2 AND digest = $3 LIMIT 1`
+	err = db.db.Select(&blobs, request, name, reference, digest)
+	if err != nil {
+		return exists, res, err
+	}
+	if len(blobs) > 0 {
+		res = blobs[0]
+		exists = true
+	}
+	return exists, res, err
+}
+
 func (db *Database) ListAllBlobs(ctx context.Context) ([]descr.Blob, error) {
 	var err error
 	blobs := make([]descr.Blob, 0)