func init() {
	if runtime.GOARCH == "amd64" {
		// On amd64 we have assembly and can use stronger compression.
		compressOpts = append(compressOpts, s2.WriterBetterCompression())
	}
}

// newS2CompressReader will read data from r, compress it and return the compressed data as a Reader.
// Use Close to ensure resources are released on incomplete streams.
//
// input 'on' is always recommended such that this function works

	// Compress only if the compression is enabled during initial multipart.
	var idxCb func() []byte
	if isCompressed {
		wantEncryption := crypto.Requested(r.Header) || isEncrypted
		s2c, cb := newS2CompressReader(reader, actualPartSize, wantEncryption)
		idxCb = cb
		defer s2c.Close()
		reader = etag.Wrap(s2c, reader)
		length = -1
	}

	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			buf := make([]byte, 100) // make small buffer to ensure multiple reads are required for large case

			r, idxCB := newS2CompressReader(bytes.NewReader(tt.data), int64(len(tt.data)), false)
			defer r.Close()

			var rdrBuf bytes.Buffer
			_, err := io.CopyBuffer(&rdrBuf, r, buf)
			if err != nil {
				t.Fatal(err)
			}
			r.Close()

		compressMetadata[ReservedMetadataPrefix+"actual-size"] = strconv.FormatInt(actualSize, 10)

		reader = etag.NewReader(ctx, reader, nil, nil)
		wantEncryption := crypto.Requested(r.Header)
		s2c, cb := newS2CompressReader(reader, actualSize, wantEncryption)
		dstOpts.IndexCB = cb
		defer s2c.Close()
		reader = etag.Wrap(s2c, reader)
		length = -1
	} else {