Only obtain the zstd:chunked TOC digest once

Make it structually clear that the code is all using the same value,
making it less likely for the verifier and other uses to get out of sync.

Also avoids some redundant parsing and error paths.
The conversion path looks longer, but that's just moving the parsing
from the called function (which is redundant for other callers).

Should not change behavior.

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

storage/pkg/chunked/compression_linux.go

@@ -135,7 +135,7 @@ func readEstargzChunkedManifest(blobStream ImageSourceSeekable, blobSize int64,
 // readZstdChunkedManifest reads the zstd:chunked manifest from the seekable stream blobStream.  The blob total size must
 // be specified.
 // This function uses the io.github.containers.zstd-chunked. annotations when specified.
-func readZstdChunkedManifest(blobStream ImageSourceSeekable, blobSize int64, annotations map[string]string) ([]byte, []byte, int64, error) {
+func readZstdChunkedManifest(blobStream ImageSourceSeekable, blobSize int64, tocDigest digest.Digest, annotations map[string]string) ([]byte, []byte, int64, error) {
 	footerSize := int64(internal.FooterSizeSupported)
 	if blobSize <= footerSize {
 		return nil, nil, 0, errors.New("blob too small")
@@ -145,7 +145,7 @@ func readZstdChunkedManifest(blobStream ImageSourceSeekable, blobSize int64, ann
 
 	if offsetMetadata := annotations[internal.ManifestInfoKey]; offsetMetadata != "" {
 		var err error
-		footerData, err = internal.ReadFooterDataFromAnnotations(annotations)
+		footerData, err = internal.ReadFooterDataFromAnnotations(tocDigest, annotations)
 		if err != nil {
 			return nil, nil, 0, err
 		}

storage/pkg/chunked/internal/compression.go

@@ -231,13 +231,10 @@ func footerDataToBlob(footer ZstdChunkedFooterData) []byte {
 }
 
 // ReadFooterDataFromAnnotations reads the zstd:chunked footer data from the given annotations.
-func ReadFooterDataFromAnnotations(annotations map[string]string) (ZstdChunkedFooterData, error) {
+func ReadFooterDataFromAnnotations(tocDigest digest.Digest, annotations map[string]string) (ZstdChunkedFooterData, error) {
 	var footerData ZstdChunkedFooterData
 
-	footerData.ChecksumAnnotation = annotations[ManifestChecksumKey]
-	if footerData.ChecksumAnnotation == "" {
-		return footerData, fmt.Errorf("manifest checksum annotation %q not found", ManifestChecksumKey)
-	}
+	footerData.ChecksumAnnotation = tocDigest.String()
 
 	offsetMetadata := annotations[ManifestInfoKey]
 

storage/pkg/chunked/storage_linux.go

@@ -25,6 +25,7 @@ import (
 	"github.com/containers/storage/pkg/archive"
 	"github.com/containers/storage/pkg/chunked/compressor"
 	"github.com/containers/storage/pkg/chunked/internal"
+	"github.com/containers/storage/pkg/chunked/toc"
 	"github.com/containers/storage/pkg/fsverity"
 	"github.com/containers/storage/pkg/idtools"
 	"github.com/containers/storage/pkg/system"
@@ -264,7 +265,7 @@ func GetDiffer(ctx context.Context, store storage.Store, blobDigest digest.Diges
 		return nil, errors.New("enable_partial_images not configured")
 	}
 
-	_, hasZstdChunkedTOC := annotations[internal.ManifestChecksumKey]
+	zstdChunkedTOCDigestString, hasZstdChunkedTOC := annotations[internal.ManifestChecksumKey]
 	estargzTOCDigestString, hasEstargzTOC := annotations[estargz.TOCJSONDigestAnnotation]
 
 	if hasZstdChunkedTOC && hasEstargzTOC {
@@ -272,7 +273,11 @@ func GetDiffer(ctx context.Context, store storage.Store, blobDigest digest.Diges
 	}
 
 	if hasZstdChunkedTOC {
-		return makeZstdChunkedDiffer(ctx, store, blobSize, annotations, iss, &storeOpts)
+		zstdChunkedTOCDigest, err := digest.Parse(zstdChunkedTOCDigestString)
+		if err != nil {
+			return nil, fmt.Errorf("parsing zstd:chunked TOC digest %q: %w", zstdChunkedTOCDigestString, err)
+		}
+		return makeZstdChunkedDiffer(ctx, store, blobSize, zstdChunkedTOCDigest, annotations, iss, &storeOpts)
 	}
 	if hasEstargzTOC {
 		estargzTOCDigest, err := digest.Parse(estargzTOCDigestString)
@@ -307,8 +312,8 @@ func makeConvertFromRawDiffer(ctx context.Context, store storage.Store, blobDige
 	}, nil
 }
 
-func makeZstdChunkedDiffer(ctx context.Context, store storage.Store, blobSize int64, annotations map[string]string, iss ImageSourceSeekable, storeOpts *types.StoreOptions) (*chunkedDiffer, error) {
-	manifest, tarSplit, tocOffset, err := readZstdChunkedManifest(iss, blobSize, annotations)
+func makeZstdChunkedDiffer(ctx context.Context, store storage.Store, blobSize int64, tocDigest digest.Digest, annotations map[string]string, iss ImageSourceSeekable, storeOpts *types.StoreOptions) (*chunkedDiffer, error) {
+	manifest, tarSplit, tocOffset, err := readZstdChunkedManifest(iss, blobSize, tocDigest, annotations)
 	if err != nil {
 		return nil, fmt.Errorf("read zstd:chunked manifest: %w", err)
 	}
@@ -317,11 +322,6 @@ func makeZstdChunkedDiffer(ctx context.Context, store storage.Store, blobSize in
 		return nil, err
 	}
 
-	tocDigest, err := digest.Parse(annotations[internal.ManifestChecksumKey])
-	if err != nil {
-		return nil, fmt.Errorf("parse TOC digest %q: %w", annotations[internal.ManifestChecksumKey], err)
-	}
-
 	return &chunkedDiffer{
 		fsVerityDigests: make(map[string]string),
 		blobSize:        blobSize,
@@ -1691,7 +1691,14 @@ func (c *chunkedDiffer) ApplyDiff(dest string, options *archive.TarOptions, diff
 		blobFile.Close()
 		blobFile = nil
 
-		manifest, tarSplit, tocOffset, err := readZstdChunkedManifest(fileSource, c.blobSize, annotations)
+		tocDigest, err := toc.GetTOCDigest(annotations)
+		if err != nil {
+			return graphdriver.DriverWithDifferOutput{}, fmt.Errorf("internal error: parsing just-created zstd:chunked TOC digest: %w", err)
+		}
+		if tocDigest == nil {
+			return graphdriver.DriverWithDifferOutput{}, fmt.Errorf("internal error: just-created zstd:chunked missing TOC digest")
+		}
+		manifest, tarSplit, tocOffset, err := readZstdChunkedManifest(fileSource, c.blobSize, *tocDigest, annotations)
 		if err != nil {
 			return graphdriver.DriverWithDifferOutput{}, fmt.Errorf("read zstd:chunked manifest: %w", err)
 		}

storage/pkg/chunked/zstdchunked_test.go

@@ -12,8 +12,10 @@ import (
 	"testing"
 
 	"github.com/containers/storage/pkg/chunked/internal"
+	"github.com/containers/storage/pkg/chunked/toc"
 	"github.com/klauspost/compress/zstd"
 	"github.com/opencontainers/go-digest"
+	"github.com/stretchr/testify/require"
 )
 
 type seekable struct {
@@ -148,7 +150,10 @@ func TestGenerateAndParseManifest(t *testing.T) {
 		t:            t,
 	}
 
-	manifest, _, _, err := readZstdChunkedManifest(s, 8192, annotations)
+	tocDigest, err := toc.GetTOCDigest(annotations)
+	require.NoError(t, err)
+	require.NotNil(t, tocDigest)
+	manifest, _, _, err := readZstdChunkedManifest(s, 8192, *tocDigest, annotations)
 	if err != nil {
 		t.Error(err)
 	}