if err != nil {
		return nil, BadDigest{ // TODO(aead): Return an error that indicates that an invalid ETag has been specified
			ExpectedMD5:   md5Hex,
			CalculatedMD5: "",
		}
	}
	SHA256, err := hex.DecodeString(sha256Hex)
	if err != nil {
		return nil, SHA256Mismatch{ // TODO(aead): Return an error that indicates that an invalid Content-SHA256 has been specified
			ExpectedSHA256:   sha256Hex,

// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//

// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//

		return nil
	}
	return r.Tagger.ETag()
}

// Wrap returns an io.Reader that reads from the wrapped
// io.Reader and implements the Tagger interaface.
//
// If content implements Tagger then the returned Reader
// returns ETag of the content. Otherwise, it returns
// nil as ETag.
//
// Wrap provides an adapter for io.Reader implementations
// that don't implement the Tagger interface.