feat(client): add Linux ancillary receive metadata
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Nils Andreas Svee committed
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@@ -0,0 +1,278 @@
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use std::{
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io, mem,
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net::{SocketAddr, UdpSocket},
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os::fd::AsRawFd,
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ptr,
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};
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use crate::{metadata::ReceiveMeta, receive::ReceivedDatagram, timing::ClientTimestamp};
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const CONTROL_LEN: usize = 64;
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pub(crate) fn configure_receive_metadata(socket: &UdpSocket, remote: SocketAddr) -> io::Result<()> {
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let socket = socket2::SockRef::from(socket);
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if remote.is_ipv4() {
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socket.set_recv_tos(true)
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} else {
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socket.set_recv_tclass_v6(true)
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}
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}
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pub(crate) fn recv_datagram(
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socket: &UdpSocket,
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buf: &mut [u8],
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) -> Result<ReceivedDatagram, io::Error> {
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let mut control = ControlBuffer::new();
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let mut iov = libc::iovec {
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iov_base: buf.as_mut_ptr().cast(),
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iov_len: buf.len(),
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};
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let mut msg: libc::msghdr = unsafe { mem::zeroed() };
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msg.msg_iov = &mut iov;
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msg.msg_iovlen = 1;
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msg.msg_control = control.as_mut_ptr().cast();
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msg.msg_controllen = control.len();
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let len = unsafe {
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// SAFETY: `msg` points to one writable iovec backed by `buf`, and the
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// control buffer is writable and lives until `recvmsg` returns. The
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// socket file descriptor is borrowed from a valid `UdpSocket`.
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libc::recvmsg(socket.as_raw_fd(), &mut msg, 0)
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};
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if len < 0 {
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return Err(io::Error::last_os_error());
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}
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let received_at = ClientTimestamp::now();
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let meta = unsafe {
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// SAFETY: `msg` was initialized by a successful `recvmsg` call. The
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// parser only reads cmsghdr entries within `msg_controllen` and ignores
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// short or unrelated control messages.
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parse_receive_meta(&msg)
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};
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Ok(ReceivedDatagram {
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len: len as usize,
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received_at,
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meta,
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})
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}
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unsafe fn parse_receive_meta(msg: &libc::msghdr) -> ReceiveMeta {
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let mut meta = ReceiveMeta::default();
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let mut cmsg = libc::CMSG_FIRSTHDR(msg);
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while !cmsg.is_null() {
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let cmsg_ref = &*cmsg;
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if cmsg_ref.cmsg_len >= libc::CMSG_LEN(0) as usize {
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let data_len = cmsg_ref.cmsg_len - libc::CMSG_LEN(0) as usize;
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if is_traffic_class_cmsg(cmsg_ref) {
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meta.traffic_class = read_int_cmsg_low_byte(cmsg, data_len);
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}
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}
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cmsg = libc::CMSG_NXTHDR(msg, cmsg);
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}
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meta
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}
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fn is_traffic_class_cmsg(cmsg: &libc::cmsghdr) -> bool {
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(cmsg.cmsg_level == libc::IPPROTO_IP && cmsg.cmsg_type == libc::IP_TOS)
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|| (cmsg.cmsg_level == libc::IPPROTO_IPV6 && cmsg.cmsg_type == libc::IPV6_TCLASS)
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}
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unsafe fn read_u8_cmsg(cmsg: *mut libc::cmsghdr, data_len: usize) -> Option<u8> {
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if data_len >= mem::size_of::<u8>() {
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Some(*libc::CMSG_DATA(cmsg).cast::<u8>())
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} else {
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None
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}
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}
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unsafe fn read_int_cmsg_low_byte(cmsg: *mut libc::cmsghdr, data_len: usize) -> Option<u8> {
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if data_len >= mem::size_of::<libc::c_int>() {
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let value = ptr::read_unaligned(libc::CMSG_DATA(cmsg).cast::<libc::c_int>());
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Some((value & 0xff) as u8)
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} else {
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read_u8_cmsg(cmsg, data_len)
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}
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}
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#[repr(align(8))]
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struct ControlBuffer([u8; CONTROL_LEN]);
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impl ControlBuffer {
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fn new() -> Self {
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Self([0; CONTROL_LEN])
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}
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fn as_mut_ptr(&mut self) -> *mut u8 {
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self.0.as_mut_ptr()
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}
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fn len(&self) -> usize {
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self.0.len()
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}
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}
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#[cfg(test)]
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mod tests {
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use std::{
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io,
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net::{SocketAddr, UdpSocket},
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time::Duration,
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};
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use crate::{
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event::PacketMeta,
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receive::{configure_receive_metadata, recv_datagram},
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socket_options::apply_dscp_to_socket,
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timing::ClientTimestamp,
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};
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fn connected_ipv4_loopback_pair() -> (UdpSocket, UdpSocket) {
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let a = UdpSocket::bind(SocketAddr::from(([127, 0, 0, 1], 0))).unwrap();
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let b = UdpSocket::bind(SocketAddr::from(([127, 0, 0, 1], 0))).unwrap();
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a.connect(b.local_addr().unwrap()).unwrap();
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b.connect(a.local_addr().unwrap()).unwrap();
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a.set_read_timeout(Some(Duration::from_millis(200)))
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.unwrap();
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b.set_read_timeout(Some(Duration::from_millis(200)))
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.unwrap();
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(a, b)
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}
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fn connected_ipv6_loopback_pair() -> Option<(UdpSocket, UdpSocket)> {
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let bind_addr = SocketAddr::from(([0, 0, 0, 0, 0, 0, 0, 1], 0));
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let a = match UdpSocket::bind(bind_addr) {
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Ok(socket) => socket,
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Err(error) if is_unavailable_ipv6_loopback(&error) => {
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eprintln!(
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"skipping IPv6 ancillary receive test: IPv6 loopback unavailable: {error}"
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);
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return None;
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}
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Err(error) => panic!("{error}"),
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};
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let b = match UdpSocket::bind(bind_addr) {
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Ok(socket) => socket,
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Err(error) if is_unavailable_ipv6_loopback(&error) => {
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eprintln!(
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"skipping IPv6 ancillary receive test: IPv6 loopback unavailable: {error}"
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);
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return None;
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}
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Err(error) => panic!("{error}"),
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};
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match a.connect(b.local_addr().unwrap()) {
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Ok(()) => {}
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Err(error) if is_unavailable_ipv6_loopback(&error) => {
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eprintln!(
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"skipping IPv6 ancillary receive test: IPv6 loopback unavailable: {error}"
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);
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return None;
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}
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Err(error) => panic!("{error}"),
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}
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match b.connect(a.local_addr().unwrap()) {
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Ok(()) => {}
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Err(error) if is_unavailable_ipv6_loopback(&error) => {
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eprintln!(
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"skipping IPv6 ancillary receive test: IPv6 loopback unavailable: {error}"
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);
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return None;
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}
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Err(error) => panic!("{error}"),
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}
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a.set_read_timeout(Some(Duration::from_millis(200)))
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.unwrap();
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b.set_read_timeout(Some(Duration::from_millis(200)))
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.unwrap();
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Some((a, b))
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}
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#[test]
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fn recvmsg_receive_returns_length_payload_and_timestamp() {
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let (sender, receiver) = connected_ipv4_loopback_pair();
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configure_receive_metadata(&receiver, sender.local_addr().unwrap()).unwrap();
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sender.send(b"hello").unwrap();
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let before = ClientTimestamp::now();
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let mut buf = [0_u8; 16];
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let datagram = recv_datagram(&receiver, &mut buf).unwrap();
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let after = ClientTimestamp::now();
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assert_eq!(datagram.len, 5);
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assert_eq!(&buf[..datagram.len], b"hello");
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assert!(datagram.received_at.mono >= before.mono);
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assert!(datagram.received_at.mono <= after.mono);
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}
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#[test]
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fn ipv4_traffic_class_metadata_is_observed_when_kernel_provides_it() {
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let (sender, receiver) = connected_ipv4_loopback_pair();
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configure_receive_metadata(&receiver, sender.local_addr().unwrap()).unwrap();
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apply_dscp_to_socket(&sender, receiver.local_addr().unwrap(), 46).unwrap();
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sender.send(b"dscp").unwrap();
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let mut buf = [0_u8; 16];
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let datagram = recv_datagram(&receiver, &mut buf).unwrap();
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let Some(traffic_class) = datagram.meta.traffic_class else {
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eprintln!("skipping IPv4 ancillary metadata assertion: kernel did not provide IP_TOS");
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return;
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};
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let packet_meta = PacketMeta::from(datagram.meta);
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assert_eq!(traffic_class & 0xfc, 184);
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assert_eq!(packet_meta.dscp, Some(46));
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assert_eq!(packet_meta.ecn, Some(0));
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}
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#[test]
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fn ipv6_traffic_class_metadata_is_observed_when_kernel_provides_it() {
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let Some((sender, receiver)) = connected_ipv6_loopback_pair() else {
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return;
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};
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configure_receive_metadata(&receiver, sender.local_addr().unwrap()).unwrap();
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apply_dscp_to_socket(&sender, receiver.local_addr().unwrap(), 46).unwrap();
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sender.send(b"dscp").unwrap();
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let mut buf = [0_u8; 16];
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let datagram = recv_datagram(&receiver, &mut buf).unwrap();
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let Some(traffic_class) = datagram.meta.traffic_class else {
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eprintln!(
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"skipping IPv6 ancillary metadata assertion: kernel did not provide IPV6_TCLASS"
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);
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return;
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};
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let packet_meta = PacketMeta::from(datagram.meta);
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assert_eq!(traffic_class & 0xfc, 184);
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assert_eq!(packet_meta.dscp, Some(46));
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assert_eq!(packet_meta.ecn, Some(0));
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}
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#[test]
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fn observed_zero_traffic_class_preserves_some_zero() {
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let (sender, receiver) = connected_ipv4_loopback_pair();
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configure_receive_metadata(&receiver, sender.local_addr().unwrap()).unwrap();
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sender.send(b"zero").unwrap();
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let mut buf = [0_u8; 16];
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let datagram = recv_datagram(&receiver, &mut buf).unwrap();
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let Some(traffic_class) = datagram.meta.traffic_class else {
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eprintln!("skipping observed-zero assertion: kernel did not provide IP_TOS");
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return;
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};
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let packet_meta = PacketMeta::from(datagram.meta);
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assert_eq!(traffic_class, 0);
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assert_eq!(packet_meta.traffic_class, Some(0));
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assert_eq!(packet_meta.dscp, Some(0));
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assert_eq!(packet_meta.ecn, Some(0));
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}
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fn is_unavailable_ipv6_loopback(error: &io::Error) -> bool {
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matches!(
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error.kind(),
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io::ErrorKind::AddrNotAvailable | io::ErrorKind::Unsupported
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)
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}
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}
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