Ability to serialize to a stream

[CrustyAuklet]

Presuming that radio.cfg_ is a structure that I have appropriately configured for glaze with meta information I can make a pretty nice set function in my embedded device REPL.

Something like:

Result<void> RadioTask::ConfigTree::on_set(std::string_view path, std::string_view data) {
    if(glz::read_as_json(radio.cfg_, path, data)) {
        radio->commit();
        return success();
    }
    return Error::BadArgument;
}

But a get function is a little harder. I don't see a way to write to a stream, so I have to resort to some arbitrarily large static buffer

Result<void> RadioTask::ConfigTree::on_get(std::string_view path, io::OutDevice& os) {
    // static std::array<char, 128> b;  // couldn't actually get std::array to work!
    static char b[256];
    memset(b, 0, 256);
    if(glz::write_as_json(radio.cfg_, path, b)) {
        os.write(to_bytes(b, strlen(b)));
        return success();
    }
    return Error::BadArgument;
}

I tried wrapping our custom io::OutDevice class (just a UART virtual interface) with a simple output iterator but glaze concepts want either a "range" (defined by having begin and end) or a raw buffer.

Let me know if this is out of scope, since I know streams are not the most performant solution. But on small embedded platforms a stream is often the best solution to limit RAM use and stack size.

[stephenberry]

Thanks so much for sharing your use case. We initially had streaming support, but it made the code much more complicated. We'll probably add it back at some point, but I don't expect it to be in the near future.

I would recommend sharing your buffer as much as possible so that you don't end up with multiple large buffers in your code. Using static here was a good choice.

I plan to look more at using std::pmr with a stack buffer (e.g. std::pmr::string) for some of these kinds of use case. You might find this worth looking into. A benefit here is that it could eliminate the need to call strlen, which should improve performance.

I'll make an issue about std::array<char... not working, since it should.