private static void addContentEncodingHeaderIfMissing(HttpServletResponse response, boolean wantsGzip) {
        if (!wantsGzip) {
            response.setHeader(CONTENT_ENCODING, GZIP);
        }
    }
Checks if the HTTP request/response accepts and wants GZIP and i that case wraps the response output stream in a
{@link java.util.zip.GZIPOutputStream}.

@param httpRequest        the HTTP servlet request.
@param httpResponse       the HTTP servlet response.
@param requireWantsHeader if wants header is required
@return if accepted and wanted a {@link java.util.zip.GZIPOutputStream} otherwise the unchanged response
output stream.
@throws IOException in case of IO error.
src/main/java/spark/utils/GzipUtils.java