skypjack/uvw

Header-only, event based, tiny and easy to use libuv wrapper in modern C++

smalls12

@smalls12

I should provide more context
I am trying to integrate a 3rdparty library with libuv / uvw similar to how I would use boost::asio
basically I just want the libuv event loop to tell me when there is something to read or write and hand that off to the 3rdparty library

Michele Caini

@skypjack

This doesn't really add much :slight_smile: the documentation for a poll handle in libuv is here, with uvw it's just a matter of invoking a member function rather than a free function

You pass a file descriptor to the constructor and invoke start, that's it

Events are sent when something relevant happens, you can listen to them with a callback

All this stuff is described in the readme file though and it's literally the same for all classes

How you obtain a file descriptor doesn't depende on libuv nor uvw, so it's up to you

smalls12

@smalls12

I'll post the code I have tried when I get back infront of it

smalls12

@smalls12

I'm back looking at this now
this is the code I have tried, it is seg faulting on me

auto loop = uvw::Loop::getDefault();

    auto poller = loop->resource<uvw::PollHandle>(fd);
    poller->on<uvw::PollEvent>(
    [](const auto &, auto &req)
    {
        std::cout << "poller - some event?\n";
    });

    if(poller->init())
    {
        std::cout << "poller - initialized?\n";
        poller->start(uvw::PollHandle::Event::READABLE);
    }
    else
    {
        std::cerr << "poller - error?\n";
    }

    loop->run();

is this what you expected?

fd is the file descriptor from the other library

Michele Caini

@skypjack

No, it's not expected but it's hard to tell what the problem is without a reproducible example. From what I can see, it can be in uvw, it can be in the other library, it can be elsewhere in the middle...

smalls12

@smalls12

ok the fd was actually -1

doh

now it is working

but I do not see any events indicating something is available to read

smalls12

@smalls12

ok that was my problem again

I think I did something wrong with the ::on call

the event is being spammed now with some poll event

instead of only indicating when there is data to read

smalls12

@smalls12

trying to get some more information from the event

poller->on<uvw::PollEvent>(
    [](const uvw::PollEvent& event, uvw::PollHandle& handle)
    {

    });

is there anything to be obtained from event or handle?

Michele Caini

@skypjack

You can look at the documentation of either uvw or libuv, because the event wraps the underlying event (if any) and the handle does the same with a libuv's poll handle

That is, uvw is a layer on top of libuv and makes you available what is exposed by the underlying library

smalls12

@smalls12

I was able to solve it.

Would you accept a PR showing how to use the poller? Since it is not explicitly captured in an example?

Michele Caini

@skypjack

Sure thing, PRs are always welcome :slight_smile:

Stefano Fiorentino

@stefanofiorentino

Sorry to be absent from this room so far ;)

Michele Caini

@skypjack

No worries man, it's a very low traffic one

KartikAiyer

@KartikAiyer

Hi folks, I have a question about best practices and design choices
I've written up a small mDNS library with service discovery and querying being the key use cases. I using uvw which means I don't have to deal with sockets and can get a good set of platform agnostic APIs like ntohs etc. My question is what is the best way to post callbacks given that everything is async. e.g
I have the following API which performs a discovery query and the API accepts callbacks

  void discover(discovery_response_f fn,
                std::function<void(const uvw::ErrorEvent&)> error_fn);

where discovery_response_f is a client supplied function pointer which receives a parsed response. In the implementation, those are called in the listeners for UDPDataEvent and ErrorEvent. I'm wondering if the more idiomatic way would be have my classes inherit from Emitter and provide similar Events that client can listen on. Looking at uvw, its obvious it would need a good dose of template wizardry, but I'm just what would others recommend ? No rush here. Just looking for wisdom :)

Michele Caini

@skypjack

@KartikAiyer not sure I get why you want to inherit from the emitter (granted, 11PM here, probably the problem is on this side of the keyboard :sweat_smile:). Using a callback as you did already is literally the way uwv works and is meant to work.

KartikAiyer

@KartikAiyer

Got it. Definitely don't think the problem is on your end. I kind of wanted to get an idea of how you intended clients of uvw to handle their own async jobs. The listener and publisher APIs that uvw has are really very nice and I was wondering if clients using uvw should also aspire to using a similar approach to provide async notifications.

Michele Caini

@skypjack

Oh, well, yeah, emitter is publicly available because you can make the same api leak to the user codebase

Though, I've not a strong opinion about it, I think it's more a matter of tastes

skebanga

@skebanga_gitlab

Hi all. Does uvw support SSL and/or HTTP and/or websockets? If not, are there any recommended libraries which build on top of it which offer these things?

Michele Caini

@skypjack

Hi @skebanga_gitlab no, there is not actually, uvw wraps libuv and only offers what the latter offers, that is, no http nor ssl support

skebanga

@skebanga_gitlab

@skypjack ok, thanks for the response!

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