alt Hacker NewsThis is interesting, but falls just short of explaining what's going on. Why does UDP work for ICMP? What does the final packet look like, and how is ICMP different from UDP? None of that is explained, it's just "do you want ICMP? Just use UDP" and that's it.
It would have been OK if it were posted as a short reference to something common people might wonder about, but I don't know how often people try to reimplement rootless ping.
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The semantic wrappers around file descriptors (File, UdpSocket, PidFd, PipeReader, etc.) are advisory and generally interconvertible. Since there's no dedicated IcmpSocket they're using UdpSocket which happens to provide the right functions to invoke the syscalls they need.
ICMP is just different protocol from UDP. There's field "Protocol" in IP packet. 0x01 = ICMP, 0x06 = TCP, 0x11 = UDP.
I think that this article gets terminology wrong. It's not UDP socket that gets created here, but Datagram socket. Seems to be bad API naming in Rust library.
So in fairness, this doesn't actually use UDP at all (SOCK_DGRAM does not mean UDP!).
The actual protocol in use, and what's supported, it matched by all of the address family (IPV4), the socket type (DGRAM), and the protocol (ICMP). The match structure for IPV4 is here in Linux at least: https://elixir.bootlin.com/linux/v6.18/source/net/ipv4/af_in...
So ultimately, it's not even UDP, it's just creating a standard ICMP socket.
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/