feat: add LocalWriter

We add LocalWriter to wrap writer in the content store to
make sure not to write any labels in boltdb.
In that case, we can make gc work well with the lease.

Signed-off-by: Yadong Ding <ding_yadong@foxmail.com>

pkg/content/content.go

@@ -126,6 +126,9 @@ func (content *Content) Info(ctx context.Context, dgst digest.Digest) (content.I
 }
 
 func (content *Content) Update(ctx context.Context, info content.Info, fieldpaths ...string) (content.Info, error) {
+	if info.Labels != nil {
+		info.Labels = nil
+	}
 	return content.store.Update(ctx, info, fieldpaths...)
 }
 
@@ -158,5 +161,37 @@ func (content *Content) Abort(ctx context.Context, ref string) error {
 }
 
 func (content *Content) Writer(ctx context.Context, opts ...content.WriterOpt) (content.Writer, error) {
-	return content.store.Writer(ctx, opts...)
+	writer, err := content.store.Writer(ctx, opts...)
+	return &LocalWriter{
+		writer: writer,
+	}, err
+}
+
+type LocalWriter struct {
+	writer content.Writer
+}
+
+func (localWriter *LocalWriter) Close() error {
+	return localWriter.writer.Close()
+}
+
+func (localWriter *LocalWriter) Write(p []byte) (int, error) {
+	return localWriter.writer.Write(p)
+}
+
+func (localWriter *LocalWriter) Digest() digest.Digest {
+	return localWriter.writer.Digest()
+}
+
+func (localWriter *LocalWriter) Truncate(size int64) error {
+	return localWriter.writer.Truncate(size)
+}
+
+func (localWriter *LocalWriter) Commit(ctx context.Context, size int64, expected digest.Digest, opts ...content.Opt) error {
+	// we don't write any lables, drop the opts
+	return localWriter.writer.Commit(ctx, size, expected)
+}
+
+func (localWriter *LocalWriter) Status() (st content.Status, err error) {
+	return localWriter.writer.Status()
 }