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fix(udp): use unaligned cmsg payload access for musl #775

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fix(udp): use unaligned cmsg payload access for musl #775

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10 changes: 5 additions & 5 deletions noq-udp/src/cmsg/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -41,9 +41,7 @@ impl<'a, M: MsgHdr> Encoder<'a, M> {
///
/// # Panics
/// - If insufficient buffer space remains.
/// - If `T` has stricter alignment requirements than `M::ControlMessage`
pub(crate) fn push<T: Copy>(&mut self, level: c_int, ty: c_int, value: T) {
assert!(align_of::<T>() <= align_of::<M::ControlMessage>());
let space = M::ControlMessage::cmsg_space(size_of_val(&value));
assert!(
self.hdr.control_len() >= self.len + space,
Expand All @@ -54,7 +52,8 @@ impl<'a, M: MsgHdr> Encoder<'a, M> {
let cmsg = self.cmsg.take().expect("no control buffer space remaining");
cmsg.set(level, ty, M::ControlMessage::cmsg_len(size_of_val(&value)));
unsafe {
ptr::write(cmsg.cmsg_data() as *const T as *mut T, value);
// Unaligned: `align_of::<M::ControlMessage>()` is 4 on musl.
ptr::write_unaligned(cmsg.cmsg_data() as *const T as *mut T, value);
}
self.len += space;
self.cmsg = unsafe { self.hdr.cmsg_nxt_hdr(cmsg).as_mut() };
Expand All @@ -78,9 +77,10 @@ impl<M: MsgHdr> Drop for Encoder<'_, M> {
///
/// `cmsg` must refer to a native cmsg containing a payload of type `T`
pub(crate) unsafe fn decode<T: Copy, C: CMsgHdr>(cmsg: &impl CMsgHdr) -> T {
assert!(align_of::<T>() <= align_of::<C>());
debug_assert_eq!(cmsg.len(), C::cmsg_len(size_of::<T>()));
unsafe { ptr::read(cmsg.cmsg_data() as *const T) }
// Unaligned: `align_of::<libc::cmsghdr>()` is 4 on musl, but payloads such as
// `libc::timespec` (SCM_TIMESTAMPNS) need 8.
unsafe { ptr::read_unaligned(cmsg.cmsg_data() as *const T) }
}

pub(crate) struct Iter<'a, M: MsgHdr> {
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