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...

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the8472 4 hours ago | parent [-]

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

	▲	erk__ 4 hours ago \| parent [-]
		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.