// MD5 sum once the r returns io.EOF.
func NewReader(ctx context.Context, r io.Reader, etag ETag, forceMD5 []byte) *Reader {
	if er, ok := r.(*Reader); ok {
		if er.readN == 0 && Equal(etag, er.checksum) {
			return er
		}
	}
	if len(forceMD5) != 0 {
		return &Reader{
			src:      r,
			md5:      NewUUIDHash(forceMD5),
			checksum: etag,
		}
	}
	return &Reader{
		src:      r,
		md5:      md5.New(),

		if !disableMD5 {
			if _, ok := src.(etag.Tagger); !ok {
				src = etag.NewReader(ctx, r, MD5, forceMD5)
			} else {
				src = etag.Wrap(r, src)
			}
		} else {
			src = r
		}
	} else if _, ok := src.(etag.Tagger); !ok {
		if !disableMD5 {
			src = etag.NewReader(ctx, src, MD5, forceMD5)
		}
	}
	var h hash.Hash
	if len(SHA256) != 0 {
		h = sha256.New()
	}
	return &Reader{

		return
	}

	var forceMD5 []byte
	// Optimization: If SSE-KMS and SSE-C did not request Content-Md5. Use uuid as etag. Optionally enable this also
	// for server that is started with `--no-compat`.
	kind, _ := crypto.IsRequested(formValues)
	if !etag.ContentMD5Requested(formValues) && (kind == crypto.SSEC || kind == crypto.S3KMS || !globalServerCtxt.StrictS3Compat) {
		forceMD5 = mustGetUUIDBytes()
	}