cpp-neltib (and Boost) default string type in windows

Question

I want to be able to get HTTP request header values that contain utf8 characters in a server built with cpp-netlib. I understand that there are two kind of wrapper classes for requests and responses depending on the used string type - request_header_narrow and request_header_wide, but while browsing the code to understand how this is actually decided i came down to:

template <class Tag>
    struct request_header
    : mpl::if_<
        is_default_string<Tag>,
        request_header_narrow,
        typename mpl::if_<
            is_default_wstring<Tag>,
            request_header_wide,
            unsupported_tag<Tag>
        >::type
    >
    {};

and

namespace boost { namespace network {

    template <class Tag, class Enable = void>
    struct is_default_string : mpl::false_ {};

    template <class Tag>
    struct is_default_string<Tag, typename enable_if<typename Tag::is_default_string>::type> : mpl::true_ {};

} // namespace network

} // namespace boost

and

namespace boost { namespace network {

    template <class Tag, class Enable = void>
    struct is_default_wstring : mpl::false_ {};

    template <class Tag>
    struct is_default_wstring<Tag, typename enable_if<typename Tag::is_default_wstring>::type> : mpl::true_ {};

} // namespace network

} // namespace boost

Since i'm not too experienced with the template meta programming stuff i did not quite understand the Boosts mpl::if_ logic and how is the default string type actually determined if both have mpl::false_ as a default value? Can anyone either clear this or explain how to make cpp-netlib use std::wstring as default string type?

Answer 1

Seems I found at least one solution, not sure if it's the best so comments are welcome, but seems that at least one way to do this is define a new server tag set an then pass these tags to the server base class:

namespace boost { namespace network { namespace http { namespace tags {

    typedef mpl::vector<http, simple, async, pod, default_wstring, server> http_async_wstring_server_tags;

    BOOST_NETWORK_DEFINE_TAG(http_async_wstring_server);

} /* tags */

} /* http */

} /* network */

} /* boost */

namespace http = boost::network::http;
...
typedef http::server_base<http::tags::http_async_wstring_server, CHTTPRequestHandler>::type async_server;