Fix issue tracking some warnings as errors (#1563)

Signed-off-by: Sergio Castaño Arteaga <tegioz@icloud.com>

internal/repo/manager.go

@@ -365,6 +365,9 @@ func (m *Manager) GetMetadata(mdFile string) (*hub.RepositoryMetadata, error) {
 		defer cancel()
 		ref := fmt.Sprintf("%s:%s", strings.TrimPrefix(mdFile, hub.RepositoryOCIPrefix), artifacthubTag)
 		_, data, err = util.OCIPullLayer(ctx, ref, MetadataLayerMediaType, "", "")
+		if errors.Is(err, util.ErrArtifactNotFound) || errors.Is(err, util.ErrLayerNotFound) {
+			err = ErrMetadataNotFound
+		}
 	} else {
 		// Remote HTTP url / local file path
 		for _, extension := range []string{".yml", ".yaml"} {

internal/tracker/source/helm/helm.go

@@ -319,6 +319,9 @@ func (s *TrackerSource) chartHasProvenanceFile(chartURL *url.URL) (bool, error)
 			s.i.Repository.AuthPass,
 		)
 		if err != nil {
+			if errors.Is(err, util.ErrLayerNotFound) {
+				return false, nil
+			}
 			return false, fmt.Errorf("error pulling provenance layer: %w", err)
 		}
 	default:

internal/util/oci.go

@@ -3,6 +3,7 @@ package util
 import (
 	"context"
 	"errors"
+	"strings"
 
 	"github.com/containerd/containerd/remotes/docker"
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
@@ -12,13 +13,17 @@ import (
 )
 
 var (
+	// ErrArtifactNotFound indicates that the requested artifact was not found
+	// in the registry.
+	ErrArtifactNotFound = errors.New("artifact not found")
+
 	// ErrLayerNotFound indicates that the requested layer was not found in the
-	// OCI image provided.
+	// OCI artifact provided.
 	ErrLayerNotFound = errors.New("layer not found")
 )
 
 // OCIPullLayer pulls the first layer of the media type provided from the OCI
-// image at the given reference.
+// artifact at the given reference.
 func OCIPullLayer(
 	ctx context.Context,
 	ref,
@@ -45,6 +50,9 @@ func OCIPullLayer(
 		oras.WithAllowedMediaTypes([]string{mediaType}),
 	)
 	if err != nil {
+		if strings.HasSuffix(err.Error(), "not found") { // TODO: https://github.com/oras-project/oras-go/blob/a3ccc872651aac656c04c9a231423161f98e2f64/pkg/content/multireader.go#L55
+			err = ErrArtifactNotFound
+		}
 		return ocispec.Descriptor{}, nil, err
 	}