copySourceHeader := map[string]string{"X-Amz-Copy-Source": "somewhere"}
	invalidMD5Header := map[string]string{"Content-Md5": "42"}
	invalidStorageClassHeader := map[string]string{xhttp.AmzStorageClass: "INVALID"}

	addCustomHeaders := func(req *http.Request, customHeaders map[string]string) {
		for k, value := range customHeaders {
			req.Header.Set(k, value)
		}
	}

	checksumData := func(b []byte, h hash.Hash) string {