func diffLayer(store storage.Store, layerID string) (rc io.ReadCloser, n int64, err error) {
layer, err := store.GetLayer(layerID)
if err != nil {
return nil, -1, err
}
layerMeta := storageLayerMetadata{
CompressedSize: -1,
}
if layer.Metadata != "" {
if err := json.Unmarshal([]byte(layer.Metadata), &layerMeta); err != nil {
return nil, -1, errors.Wrapf(err, "error decoding metadata for layer %q", layerID)
}
}
if layerMeta.CompressedSize <= 0 {
n = -1
} else {
n = layerMeta.CompressedSize
}
diff, err := store.Diff("", layer.ID)
if err != nil {
return nil, -1, err
}
return diff, n, nil
}
