return 0, SizeTooLarge{Want: r.expectedMax, Got: r.bytesRead}
			}
		}

		if r.sha256 != nil {
			if sum := r.sha256.Sum(nil); !bytes.Equal(r.contentSHA256, sum) {
				return n, SHA256Mismatch{
					ExpectedSHA256:   hex.EncodeToString(r.contentSHA256),
					CalculatedSHA256: hex.EncodeToString(sum),
				}
			}
		}
		if r.contentHasher != nil {
			if r.contentHash.Type.Trailing() {
				var err error

// so far. Reading more content changes the MD5
// checksum. Therefore, calling ETag multiple
// times may return different results.
func (r *Reader) ETag() ETag {
	sum := r.md5.Sum(nil)
	return ETag(sum)
}

// VerifyError is an error signaling that a
// computed ETag does not match an expected
// ETag.
type VerifyError struct {
	Expected ETag
	Computed ETag
}