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//! Utilities for dealing with message headers.
//!
//! These take closures rather than returning a `c::msghdr` directly because
//! the message headers may reference stack-local data.
#![allow(unsafe_code)]
use crate::backend::c;
use crate::backend::net::write_sockaddr::{encode_sockaddr_v4, encode_sockaddr_v6};
use crate::io::{self, IoSlice, IoSliceMut};
use crate::net::{RecvAncillaryBuffer, SendAncillaryBuffer, SocketAddrV4, SocketAddrV6};
use crate::utils::as_ptr;
use core::mem::{size_of, zeroed, MaybeUninit};
use core::ptr::null_mut;
fn msg_iov_len(len: usize) -> c::size_t {
// This cast cannot overflow.
len as c::size_t
}
pub(crate) fn msg_control_len(len: usize) -> c::size_t {
// Same as above.
len as c::size_t
}
/// Create a message header intended to receive a datagram.
pub(crate) fn with_recv_msghdr<R>(
name: &mut MaybeUninit<c::sockaddr_storage>,
iov: &mut [IoSliceMut<'_>],
control: &mut RecvAncillaryBuffer<'_>,
f: impl FnOnce(&mut c::msghdr) -> io::Result<R>,
) -> io::Result<R> {
control.clear();
let namelen = size_of::<c::sockaddr_storage>() as c::c_int;
let mut msghdr = c::msghdr {
msg_name: name.as_mut_ptr().cast(),
msg_namelen: namelen,
msg_iov: iov.as_mut_ptr().cast(),
msg_iovlen: msg_iov_len(iov.len()),
msg_control: control.as_control_ptr().cast(),
msg_controllen: msg_control_len(control.control_len()),
// Zero-initialize any padding bytes.
..unsafe { zeroed() }
};
let res = f(&mut msghdr);
// Reset the control length.
if res.is_ok() {
unsafe {
control.set_control_len(msghdr.msg_controllen.try_into().unwrap_or(usize::MAX));
}
}
res
}
/// Create a message header intended to send without an address.
pub(crate) fn with_noaddr_msghdr<R>(
iov: &[IoSlice<'_>],
control: &mut SendAncillaryBuffer<'_, '_, '_>,
f: impl FnOnce(c::msghdr) -> R,
) -> R {
f(c::msghdr {
msg_name: null_mut(),
msg_namelen: 0,
msg_iov: iov.as_ptr() as _,
msg_iovlen: msg_iov_len(iov.len()),
msg_control: control.as_control_ptr().cast(),
msg_controllen: msg_control_len(control.control_len()),
// Zero-initialize any padding bytes.
..unsafe { zeroed() }
})
}
/// Create a message header intended to send with an IPv4 address.
pub(crate) fn with_v4_msghdr<R>(
addr: &SocketAddrV4,
iov: &[IoSlice<'_>],
control: &mut SendAncillaryBuffer<'_, '_, '_>,
f: impl FnOnce(c::msghdr) -> R,
) -> R {
let encoded = unsafe { encode_sockaddr_v4(addr) };
f(c::msghdr {
msg_name: as_ptr(&encoded) as _,
msg_namelen: size_of::<SocketAddrV4>() as _,
msg_iov: iov.as_ptr() as _,
msg_iovlen: msg_iov_len(iov.len()),
msg_control: control.as_control_ptr().cast(),
msg_controllen: msg_control_len(control.control_len()),
// Zero-initialize any padding bytes.
..unsafe { zeroed() }
})
}
/// Create a message header intended to send with an IPv6 address.
pub(crate) fn with_v6_msghdr<R>(
addr: &SocketAddrV6,
iov: &[IoSlice<'_>],
control: &mut SendAncillaryBuffer<'_, '_, '_>,
f: impl FnOnce(c::msghdr) -> R,
) -> R {
let encoded = unsafe { encode_sockaddr_v6(addr) };
f(c::msghdr {
msg_name: as_ptr(&encoded) as _,
msg_namelen: size_of::<SocketAddrV6>() as _,
msg_iov: iov.as_ptr() as _,
msg_iovlen: msg_iov_len(iov.len()),
msg_control: control.as_control_ptr().cast(),
msg_controllen: msg_control_len(control.control_len()),
// Zero-initialize any padding bytes.
..unsafe { zeroed() }
})
}
/// Create a message header intended to send with a Unix address.
pub(crate) fn with_unix_msghdr<R>(
addr: &crate::net::SocketAddrUnix,
iov: &[IoSlice<'_>],
control: &mut SendAncillaryBuffer<'_, '_, '_>,
f: impl FnOnce(c::msghdr) -> R,
) -> R {
f(c::msghdr {
msg_name: as_ptr(addr) as _,
msg_namelen: addr.addr_len() as _,
msg_iov: iov.as_ptr() as _,
msg_iovlen: msg_iov_len(iov.len()),
msg_control: control.as_control_ptr().cast(),
msg_controllen: msg_control_len(control.control_len()),
// Zero-initialize any padding bytes.
..unsafe { zeroed() }
})
}
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