chunked: store compressed digest if validated

if the compressed digest was validated, as it happens when
'pull_options = {convert_images = "true"}' is set, then store it as
well so that reusing the blob by its compressed digest works.

Previously, when an image converted to zstd:chunked was pulled a
second time, it would not be recognized by its compressed digest,
resulting in the need to re-pull the image again.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

drivers/driver.go

@@ -193,6 +193,7 @@ type DriverWithDifferOutput struct {
 	UIDs               []uint32
 	GIDs               []uint32
 	UncompressedDigest digest.Digest
+	CompressedDigest   digest.Digest
 	Metadata           string
 	BigData            map[string][]byte
 	TarSplit           []byte

layers.go

@@ -2529,6 +2529,7 @@ func (r *layerStore) applyDiffFromStagingDirectory(id string, diffOutput *driver
 	layer.GIDs = diffOutput.GIDs
 	updateDigestMap(&r.byuncompressedsum, layer.UncompressedDigest, diffOutput.UncompressedDigest, layer.ID)
 	layer.UncompressedDigest = diffOutput.UncompressedDigest
+	layer.CompressedDigest = diffOutput.CompressedDigest
 	updateDigestMap(&r.bytocsum, diffOutput.TOCDigest, diffOutput.TOCDigest, layer.ID)
 	layer.TOCDigest = diffOutput.TOCDigest
 	layer.UncompressedSize = diffOutput.Size

pkg/chunked/storage_linux.go

@@ -1122,6 +1122,7 @@ func (c *chunkedDiffer) ApplyDiff(dest string, options *archive.TarOptions, diff
 	// stream to use for reading the zstd:chunked or Estargz file.
 	stream := c.stream
 
+	var compressedDigest digest.Digest
 	var uncompressedDigest digest.Digest
 	var convertedBlobSize int64
 
@@ -1138,7 +1139,7 @@ func (c *chunkedDiffer) ApplyDiff(dest string, options *archive.TarOptions, diff
 		}()
 
 		// calculate the checksum before accessing the file.
-		compressedDigest, err := c.copyAllBlobToFile(blobFile)
+		compressedDigest, err = c.copyAllBlobToFile(blobFile)
 		if err != nil {
 			return graphdriver.DriverWithDifferOutput{}, err
 		}
@@ -1224,6 +1225,7 @@ func (c *chunkedDiffer) ApplyDiff(dest string, options *archive.TarOptions, diff
 		},
 		TOCDigest:          c.tocDigest,
 		UncompressedDigest: uncompressedDigest,
+		CompressedDigest:   compressedDigest,
 	}
 
 	// When the hard links deduplication is used, file attributes are ignored because setting them