bugfix: cache empty layer for docker schema1 image

fuweid · fuweid · commit 57d79e1b49c8 · 2018-09-28T15:45:59.000+08:00
containerd should cache empty label for docker schema1 image.

if not, the original empty layer will be non-empty layer and the image
config will be changed too. in this case, the image ID will be changed.

check the blob empty label to avoid changing image ID when repull docker
schema1 image.

Signed-off-by: Wei Fu &lt;fuweid89@gmail.com&gt;
diff --git a/remotes/docker/schema1/converter.go b/remotes/docker/schema1/converter.go
@@ -24,6 +24,7 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
+	"strconv"
 	"strings"
 	"sync"
 	"time"
@@ -42,7 +43,10 @@ import (
 	"github.com/pkg/errors"
 )
 
-const manifestSizeLimit = 8e6 // 8MB
+const (
+	manifestSizeLimit            = 8e6 // 8MB
+	labelDockerSchema1EmptyLayer = "containerd.io/docker.schema1.empty.layer"
+)
 
 type blobState struct {
 	diffID digest.Digest
@@ -353,10 +357,11 @@ func (c *Converter) fetchBlob(ctx context.Context, desc ocispec.Descriptor) erro
 		Digest: desc.Digest,
 		Labels: map[string]string{
 			"containerd.io/uncompressed": state.diffID.String(),
+			labelDockerSchema1EmptyLayer: strconv.FormatBool(state.empty),
 		},
 	}
 
-	if _, err := c.contentStore.Update(ctx, cinfo, "labels.containerd.io/uncompressed"); err != nil {
+	if _, err := c.contentStore.Update(ctx, cinfo, "labels.containerd.io/uncompressed", fmt.Sprintf("labels.%s", labelDockerSchema1EmptyLayer)); err != nil {
 		return errors.Wrap(err, "failed to update uncompressed label")
 	}
 
@@ -380,7 +385,18 @@ func (c *Converter) reuseLabelBlobState(ctx context.Context, desc ocispec.Descri
 		return false, nil
 	}
 
-	bState := blobState{empty: false}
+	emptyVal, ok := cinfo.Labels[labelDockerSchema1EmptyLayer]
+	if !ok {
+		return false, nil
+	}
+
+	isEmpty, err := strconv.ParseBool(emptyVal)
+	if err != nil {
+		log.G(ctx).WithField("id", desc.Digest).Warnf("failed to parse bool from label %s: %v", labelDockerSchema1EmptyLayer, isEmpty)
+		return false, nil
+	}
+
+	bState := blobState{empty: isEmpty}
 
 	if bState.diffID, err = digest.Parse(diffID); err != nil {
 		log.G(ctx).WithField("id", desc.Digest).Warnf("failed to parse digest from label containerd.io/uncompressed: %v", diffID)
