Creating an UDP server is cumbersome

[Geod24]

Creating a TCP server is rather straightforward and documented.
However, as I tried to create an UDP server, I hit a few issues:

• Low documentation: I could only find https://github.com/vibe-d/vibe.d/blob/1f830a8241041c39c61bbdcde37fe4bc40c13432/examples/udp/source/app.d in Vibe.d
• No way to set up a server mode: listenTCP allows passing a callback. UDP only seems to have recv, which will throw on timeout.

[Geod24]

Additionally, calling listenUDP before the event loop is running results in an invalidHandle error.
I had the following code:

    if (cmdline_args.dns)
    {
        auto udp = listenUDP(53);
        runTask({
                while (true) {
                    auto pack = udp.recv();
                    logInfo("Got packet: %s", pack);
                }
            });
    }

    return runEventLoop();

And got an error. Moving the listenUDP inside runTask cleared it.
To be precise, it seems like the UDP handle's validationCounter stays at 0 while the common is 1.

[mkykadir]

I've tried this recently and it seems to be working properly now.

[dushibaiyu]

you shoud use listenUDP on run Task.
like this:

    if (cmdline_args.dns)
    {
        runTask({
               auto udp = listenUDP(53);
               ubyte[] buffer = cast(ubyte[]) Mallocator.instance.allocate(2048);
                scope(exit) Mallocator.instance.deallocate(cast(void[]) buffer);
                while (true) {
                    auto pack = udp.recv(buffer,null);
                    logInfo("Got packet: %s", pack);
                }
            });
    }

    return runEventLoop();

[Geod24]

If the fiber is in the same thread it should not make a difference. Also in this case I think we were saving the listener somewhere so we could shut it down when the user pressed Ctrl+C, so it wasn't actually an option.