type ObjectLayer interface {
	// Locking operations on object.
	NewNSLock(bucket string, objects ...string) RWLocker

	// Storage operations.
	Shutdown(context.Context) error
	NSScanner(ctx context.Context, updates chan<- DataUsageInfo, wantCycle uint32, scanMode madmin.HealScanMode) error
	BackendInfo() madmin.BackendInfo
	Legacy() bool // Only returns true for deployments which use CRCMOD as its object distribution algorithm.

	// object also has an ETag that is the MD5 of its part ETags.
	// The fact the in case of encryption the ETag of a part is
	// not the MD5 of the part content does not change that.
	var completeETags []etag.ETag
	for _, part := range complMultipartUpload.Parts {
		ETag, err := etag.Parse(part.ETag)
		if err != nil {
			continue
		}

func getCpObjMetadataFromHeader(ctx context.Context, r *http.Request, userMeta map[string]string) (map[string]string, error) {
	// Make a copy of the supplied metadata to avoid
	// to change the original one.
	defaultMeta := make(map[string]string, len(userMeta))
	for k, v := range userMeta {
		// skip tier metadata when copying metadata from source object
		switch k {