Comment by dgl

Comment by dgl a day ago

The BSD socket API has 3 parameters when creating a socket with socket(), the family (e.g. inet) the kind (datagram in this case) and the protocol (often 0, but IPPROTO_ICMP in this case).

Because when the protocol is 0 it means a UDP socket Rust has called its API for creating any(?) datagram sockets UdpSocket, partly resulting in this confusion.

The kernel patch introducing the API also explains it was partly based on the UDP code, due to obviously sharing a lot of properties with it. https://lwn.net/Articles/420800/

erk__ a day ago

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 a day ago

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

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- erk__ a day ago
  
  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.
  
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stavros a day ago

Thanks, that's quite the misnomer then.

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stingraycharles a day ago

So UdpSocket should really be called DatagramSocket, UDP being the protocol that operates on these datagrams?

Surprising that they got such a fundamental thing wrong.

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krater23 a day ago

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

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- IshKebab a day ago
  
  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.
  
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  Sharlin a day ago
  
  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.
  
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