if this is not the last buffer.
bool more = true;
If this is true and data is nullptr,
the error http::need_buffer
will be returned from http::serializer::get
This field is not used during parsing.
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)