Move the canFallback logic from make...Differ into read...Manifest

That's a logically better place, it pairs the getBlobAt
calls with the ErrBadRequest types specific to those call sites.

We will, also, add more fallback reasons.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

pkg/chunked/compression_linux.go

@@ -44,6 +44,8 @@ func typeToTarType(t string) (byte, error) {
 	return r, nil
 }
 
+// readEstargzChunkedManifest reads the estargz manifest from the seekable stream blobStream.
+// It may return an error matching ErrFallbackToOrdinaryLayerDownload.
 func readEstargzChunkedManifest(blobStream ImageSourceSeekable, blobSize int64, tocDigest digest.Digest) ([]byte, int64, error) {
 	// information on the format here https://github.com/containerd/stargz-snapshotter/blob/main/docs/stargz-estargz.md
 	footerSize := int64(51)
@@ -54,6 +56,10 @@ func readEstargzChunkedManifest(blobStream ImageSourceSeekable, blobSize int64,
 	footer := make([]byte, footerSize)
 	streamsOrErrors, err := getBlobAt(blobStream, ImageSourceChunk{Offset: uint64(blobSize - footerSize), Length: uint64(footerSize)})
 	if err != nil {
+		var badRequestErr ErrBadRequest
+		if errors.As(err, &badRequestErr) {
+			err = newErrFallbackToOrdinaryLayerDownload(err)
+		}
 		return nil, 0, err
 	}
 
@@ -89,6 +95,10 @@ func readEstargzChunkedManifest(blobStream ImageSourceSeekable, blobSize int64,
 
 	streamsOrErrors, err = getBlobAt(blobStream, ImageSourceChunk{Offset: uint64(tocOffset), Length: uint64(size)})
 	if err != nil {
+		var badRequestErr ErrBadRequest
+		if errors.As(err, &badRequestErr) {
+			err = newErrFallbackToOrdinaryLayerDownload(err)
+		}
 		return nil, 0, err
 	}
 
@@ -148,6 +158,7 @@ func readEstargzChunkedManifest(blobStream ImageSourceSeekable, blobSize int64,
 
 // readZstdChunkedManifest reads the zstd:chunked manifest from the seekable stream blobStream.
 // Returns (manifest blob, parsed manifest, tar-split blob or nil, manifest offset).
+// It may return an error matching ErrFallbackToOrdinaryLayerDownload.
 func readZstdChunkedManifest(blobStream ImageSourceSeekable, tocDigest digest.Digest, annotations map[string]string) (_ []byte, _ *minimal.TOC, _ []byte, _ int64, retErr error) {
 	offsetMetadata := annotations[minimal.ManifestInfoKey]
 	if offsetMetadata == "" {
@@ -186,6 +197,10 @@ func readZstdChunkedManifest(blobStream ImageSourceSeekable, tocDigest digest.Di
 
 	streamsOrErrors, err := getBlobAt(blobStream, chunks...)
 	if err != nil {
+		var badRequestErr ErrBadRequest
+		if errors.As(err, &badRequestErr) {
+			err = newErrFallbackToOrdinaryLayerDownload(err)
+		}
 		return nil, nil, nil, 0, err
 	}
 

pkg/chunked/storage_linux.go

@@ -304,11 +304,7 @@ func makeConvertFromRawDiffer(store storage.Store, blobDigest digest.Digest, blo
 // It may return an error matching ErrFallbackToOrdinaryLayerDownload.
 func makeZstdChunkedDiffer(store storage.Store, blobSize int64, tocDigest digest.Digest, annotations map[string]string, iss ImageSourceSeekable, pullOptions pullOptions) (*chunkedDiffer, error) {
 	manifest, toc, tarSplit, tocOffset, err := readZstdChunkedManifest(iss, tocDigest, annotations)
-	if err != nil {
-		var badRequestErr ErrBadRequest
-		if errors.As(err, &badRequestErr) {
-			err = newErrFallbackToOrdinaryLayerDownload(err)
-		}
+	if err != nil { // May be ErrFallbackToOrdinaryLayerDownload
 		return nil, fmt.Errorf("read zstd:chunked manifest: %w", err)
 	}
 
@@ -355,11 +351,7 @@ func makeEstargzChunkedDiffer(store storage.Store, blobSize int64, tocDigest dig
 	}
 
 	manifest, tocOffset, err := readEstargzChunkedManifest(iss, blobSize, tocDigest)
-	if err != nil {
-		var badRequestErr ErrBadRequest
-		if errors.As(err, &badRequestErr) {
-			err = newErrFallbackToOrdinaryLayerDownload(err)
-		}
+	if err != nil { // May be ErrFallbackToOrdinaryLayerDownload
 		return nil, fmt.Errorf("read zstd:chunked manifest: %w", err)
 	}
 	layersCache, err := getLayersCache(store)