write_json(msg, boost::beast::flat_buffer)

[akm76]

Is there a good technical reason I can't
write_json(msg, boost::beast::flat_buffer)
directly?

[stephenberry]

Glaze requires this concept to pass:

template <class Buffer>
concept output_buffer = range<Buffer> && (sizeof(range_value_t<Buffer>) == sizeof(char)) && non_const_buffer<Buffer>;

You'd have to look into why [flat_buffer](boost::beast::flat_buffer) seems to fail the range concept.

template <class T>
concept range = requires(T& t) {
  requires !std::same_as<void, decltype(t.begin())>;
  requires !std::same_as<void, decltype(t.end())>;
  requires std::input_iterator<decltype(t.begin())>;
};

[akm76]

I think I got it, to get glz::read_json parse beast::flat_buffer

    beast::flat_buffer beast_buff(/*omitted for brevity*/);
    response_message_type msg;
    auto buff = beast_buff.data().data(); // rather unsightly 
    // first data() to get asio::const_buffer from beast::flat_buffer, 
    // second to get void* from asio::const_buffer.
    auto glz_buff = static_cast<char *>(buff);
    auto ec = glz::read_json(msg, glz_buff);

not entirely sure of the rationale, except some provision for multi-buffer sequence is being made in asio/beast and some abstraction layer does provide begin() and end() iterators, just not the flat_buffer itself.

[stephenberry]

If you can get a size from the buffer I would recommend passing in a std::string_view, so that Glaze can know the size.