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Calculate cmsg buffer size statically

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Although generic const fn max hasn't been stabilized yet[1], it's possible
to write a concrete impl for usize.

Follow-up to #178 and #225.

[1] https://github.com/rust-lang/rust/issues/92391
This commit is contained in:
WGH 2025-09-06 05:41:20 +03:00
parent 9bdfd76819
commit 4a11c6adc7
1 changed files with 9 additions and 7 deletions
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16
phantun/src/utils.rs
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@ -62,13 +62,11 @@ pub async fn udp_recv_pktinfo(
buf: &mut [u8],
) -> std::io::Result<(usize, SocketAddr, IpAddr)> {
sock.async_io(Interest::READABLE, || {
// according to documented struct definition in RFC 3542,
// sizeof(in6_pktinfo) should always be larger than sizeof(in_pktinfo),
// this assert just double checks that. The goal is to avoid
// a heap allocation with Vec at runtime.
assert!(cmsg_space::<nix::libc::in6_pktinfo>() >= cmsg_space::<nix::libc::in_pktinfo>());
let mut control_message_buffer = [0u8; cmsg_space::<nix::libc::in6_pktinfo>()];
const CONTROL_MESSAGE_BUFFER_SIZE: usize = max_usize(
cmsg_space::<nix::libc::in_pktinfo>(),
cmsg_space::<nix::libc::in6_pktinfo>(),
);
let mut control_message_buffer = [0u8; CONTROL_MESSAGE_BUFFER_SIZE];
let iov = &mut [std::io::IoSliceMut::new(buf)];
let res = nix::sys::socket::recvmsg::<SockaddrStorage>(
sock.as_raw_fd(),
@ -151,3 +149,7 @@ pub fn assign_ipv6_address(device_name: &str, local: Ipv6Addr, peer: Ipv6Addr) {
.unwrap();
rtnl.send(&nl_header).unwrap();
}
const fn max_usize(a: usize, b: usize) -> usize {
if a > b { a } else { b }
}