The std api can only create UdpSockets, the trick here is that you use Socket2 which allows more kinds of sockets and then you tell UdpSocket that some raw file descriptor is a upd socket through a unsafe api with no checks and I guess it works because they use the same api on posix.

Edit: It is possible in safe rust as well, see child comment.

The macro used by socket2: https://docs.rs/socket2/0.6.1/src/socket2/lib.rs.html#108

The FromRawFd trait: https://doc.rust-lang.org/stable/std/os/fd/trait.FromRawFd.h...

From/Into conversion via OwnedFd is the safe API, RawFd is the older and lower-level one.

Ahh I guess that means that its possible in safe rust to cast a file descriptor to a different type. I was just looking at how socket2 did it and forgot to have a proper look.

Thanks, that's quite the misnomer then.

That happens when someones learning project ("I rewrite a library in the new language I want to learn") ends up in productive code.

This is in the standard library; it's not a learning project. And it also isn't even incorrect - see erk__'s comment.

Rust is an excellent language and fully capable of production use.

It's not, it's the `socket2` library. The standard sockets don't allow (ab)using actual `UdpSocket`s as a different kind of datagram socket.

Sure it does.

    let f = std::fs::File::open("/dev/null").unwrap();
    let f: std::os::fd::OwnedFd = f.into();
    let socket: std::net::UdpSocket = f.into();

This is really no different. In this example it's not even a socket.

We're talking about UdpSocket: https://doc.rust-lang.org/stable/std/net/struct.UdpSocket.ht...

Yes, I know, but the point is that the standard UdpSocket is correctly named as it doesn’t represent any other datagram socket. Uh, we’re pribably in agreement here actually.

Yeah exactly! :-D