index = opts.IndexCB()
	}

	actualSize := data.ActualSize()
	if actualSize < 0 {
		_, encrypted := crypto.IsEncrypted(fi.Metadata)
		compressed := fi.IsCompressed()
		switch {
		case compressed:
			// ... nothing changes for compressed stream.
			// if actualSize is -1 we have no known way to
			// determine what is the actualSize.
		case encrypted:
			decSize, err := sio.DecryptedSize(uint64(n))

		modTime = UTCNow()
	}

	kind, encrypted := crypto.IsEncrypted(userDefined)
	actualSize := data.ActualSize()
	if actualSize < 0 {
		compressed := fi.IsCompressed()
		switch {
		case compressed:
			// ... nothing changes for compressed stream.
			// if actualSize is -1 we have no known way to
			// determine what is the actualSize.
		case encrypted:
			decSize, err := sio.DecryptedSize(uint64(n))

			writeErrorResponse(ctx, w, toAPIError(ctx, err), r.URL)
			return
		}
	}

	var compressMetadata map[string]string
	// No need to compress for remote etcd calls
	// Pass the decompressed stream to such calls.
	isDstCompressed := isCompressible(r.Header, dstObject) &&
		length > minCompressibleSize &&
		!isRemoteCopyRequired(ctx, srcBucket, dstBucket, objectAPI)

	// Read compression metadata preserved in the init multipart for the decision.
	_, isCompressed := mi.UserDefined[ReservedMetadataPrefix+"compression"]
	// 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)