presto-main/src/main/java/io/prestosql/operator/HttpPageBufferClient.java/HttpPageBufferClient/getToken
class HttpPageBufferClient:        private static long getToken(Response response)
        {
            String tokenHeader = response.getHeader(PRESTO_PAGE_TOKEN);
            if (tokenHeader == null) {
                throw new PageTransportErrorException(format("Expected %s header", PRESTO_PAGE_TOKEN));
            }
            return Long.parseLong(tokenHeader);
        }