//	   if err != nil {
//	   }
//	}
//	ETag = ETag.Format()
func (e ETag) Format() ETag {
	if !e.IsEncrypted() {
		return e
	}
	return e[len(e)-16:]
}

var _ Tagger = ETag{} // compiler check

// ETag returns the ETag itself.
//
// By providing this method ETag implements
// the Tagger interface.
func (e ETag) ETag() ETag { return e }

	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
}

func (v VerifyError) Error() string {
	return fmt.Sprintf("etag: expected ETag %q does not match computed ETag %q", v.Expected, v.Computed)
}

// UUIDHash - use uuid to make md5sum

		{[]CompletePart{{ETag: "wrong-md5-hash-string"}}, "0deb8cb07527b4b2669c861cb9653607-1", ""},

		// Single CompletePart with valid MD5 hash string.
		{[]CompletePart{{ETag: "cf1f738a5924e645913c984e0fe3d708"}}, "10dc1617fbcf0bd0858048cb96e6bd77-1", ""},

		// Multiple CompletePart with valid MD5 hash string.

var stringTests = []struct {
	ETag   ETag
	String string
}{
	{ETag: ETag{59, 131, 239, 150, 56, 127, 20, 101}, String: "3b83ef96387f1465"},                                                                  // 0
	{ETag: ETag{59, 131, 239, 150, 56, 127, 20, 101, 95, 200, 84, 221, 195, 198, 189, 87}, String: "3b83ef96387f14655fc854ddc3c6bd57"},             // 1

	// We must not use the http.Header().Set method here because some (broken)
	// clients expect the ETag header key to be literally "ETag" - not "Etag" (case-sensitive).
	// Therefore, we have to set the ETag directly as map entry.
	if objInfo.ETag != "" && !del {
		w.Header()[xhttp.ETag] = []string{`"` + objInfo.ETag + `"`}
	}

	// Set the relevant version ID as part of the response header.

		12: {bucketName: bucket, objName: object, inputData: []byte("ijkl"), inputMeta: map[string]string{"etag": "09a0877d04abf8759f99adec02baf579"}, inputDataSize: int64(len("ijkl"))},

		ETag:       "",
		ShouldFail: true, // ETag prefix is not a valid hex value
	},
	{
		ObjectKey:  [32]byte{},
		ObjectInfo: ObjectInfo{ETag: "16516b396f0f4d4f2a0e7177557bec4-1-2"},
		ETag:       "",
		ShouldFail: true, // ETag contains multiple: -
	},
}

func TestDecryptETag(t *testing.T) {
	for i, test := range decryptETagTests {

		etag = commonETag(etags, quorum)

		if etag != "" { // allow this fallback only if a non-empty etag is found.
			for index, e := range etags {
				if partsMetadata[index].IsValid() && e == etag {
					onlineDisks[index] = disks[index]
				} else {
					onlineDisks[index] = nil
				}
			}
			return onlineDisks, modTime, etag
		}
	}

		// This should fail even without quorum issues, but with quorum failure
		// we can't verify the ETag at all.
		opts := ObjectOptions{
			UserDefined: map[string]string{
				xhttp.IfMatch: "wrong-etag-12345",
			},
			HasIfMatch: true,
			CheckPrecondFn: func(oi ObjectInfo) bool {
				// Precondition fails if ETags don't match
				return oi.ETag != "wrong-etag-12345"
			},
		}

	return partKey
}

// SealETag seals the etag using the object key.
// It does not encrypt empty ETags because such ETags indicate
// that the S3 client hasn't sent an ETag = MD5(object) and
// the backend can pick an ETag value.
func (key ObjectKey) SealETag(etag []byte) []byte {
	if len(etag) == 0 { // don't encrypt empty ETag - only if client sent ETag = MD5(object)
		return etag
	}
	var buffer bytes.Buffer