Adding packet receipt timestamp collection into RecvMeta for linux

Author: recatek

quinn-udp/src/cmsg/mod.rs

@@ -83,7 +83,11 @@ 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!(mem::align_of::<T>() <= mem::align_of::<C>());
-    debug_assert_eq!(cmsg.len(), C::cmsg_len(mem::size_of::<T>()));
+    debug_assert_eq!(
+        cmsg.len(),
+        C::cmsg_len(mem::size_of::<T>()),
+        "cmsg truncated -- you might need to raise the CMSG_LEN constant for this platform"
+    );
     ptr::read(cmsg.cmsg_data() as *const T)
 }
 

quinn-udp/src/fallback.rs

@@ -72,6 +72,8 @@ impl UdpSocketState {
             addr: addr.as_socket().unwrap(),
             ecn: None,
             dst_ip: None,
+            #[cfg(not(wasm_browser))]
+            timestamp: None,
         };
         Ok(1)
     }

quinn-udp/src/lib.rs

@@ -115,6 +115,13 @@ pub struct RecvMeta {
     /// Populated on platforms: Windows, Linux, Android (API level > 25),
     /// FreeBSD, OpenBSD, NetBSD, macOS, and iOS.
     pub dst_ip: Option<IpAddr>,
+    /// A timestamp for when the given packet was received by the operating system.
+    /// Controlled by the `set_recv_timestamping` option on the source socket where available.
+    ///
+    /// Populated on platforms with varying clock sources, as follows:
+    /// - Linux: `CLOCK_REALTIME` (see `SO_TIMESTAMPNS` in `man 7 socket` for more information)
+    #[cfg(not(wasm_browser))]
+    pub timestamp: Option<Duration>,
 }
 
 impl Default for RecvMeta {
@@ -126,6 +133,8 @@ impl Default for RecvMeta {
             stride: 0,
             ecn: None,
             dst_ip: None,
+            #[cfg(not(wasm_browser))]
+            timestamp: None,
         }
     }
 }

quinn-udp/src/unix.rs

@@ -12,6 +12,9 @@ use std::{
     time::Instant,
 };
 
+#[cfg(target_os = "linux")]
+use std::time::Duration;
+
 use socket2::SockRef;
 
 use super::{
@@ -96,6 +99,11 @@ impl UdpSocketState {
                 unsafe { libc::CMSG_SPACE(mem::size_of::<libc::in6_pktinfo>() as _) as usize };
         }
 
+        if cfg!(target_os = "linux") {
+            cmsg_platform_space +=
+                unsafe { libc::CMSG_SPACE(mem::size_of::<libc::timeval>() as _) as usize };
+        }
+
         assert!(
             CMSG_LEN
                 >= unsafe { libc::CMSG_SPACE(mem::size_of::<libc::c_int>() as _) as usize }
@@ -257,6 +265,18 @@ impl UdpSocketState {
         self.may_fragment
     }
 
+    /// Sets the socket to receive packet receipt timestamps from the operating system.
+    /// These can be accessed via [`RecvMeta::timestamp`] on packets when enabled.
+    #[cfg(target_os = "linux")]
+    pub fn set_recv_timestamping(&self, sock: UdpSockRef<'_>, enabled: bool) -> io::Result<()> {
+        let enabled = match enabled {
+            true => OPTION_ON,
+            false => OPTION_OFF,
+        };
+
+        set_socket_option(&*sock.0, libc::SOL_SOCKET, libc::SO_TIMESTAMPNS, enabled)
+    }
+
     /// Returns true if we previously got an EINVAL error from `sendmsg` syscall.
     fn sendmsg_einval(&self) -> bool {
         self.sendmsg_einval.load(Ordering::Relaxed)
@@ -543,7 +563,7 @@ fn recv(io: SockRef<'_>, bufs: &mut [IoSliceMut<'_>], meta: &mut [RecvMeta]) ->
     Ok(1)
 }
 
-const CMSG_LEN: usize = 88;
+const CMSG_LEN: usize = 96;
 
 fn prepare_msg(
     transmit: &Transmit<'_>,
@@ -681,6 +701,8 @@ fn decode_recv(
     let mut dst_ip = None;
     #[allow(unused_mut)] // only mutable on Linux
     let mut stride = len;
+    #[allow(unused_mut)] // only mutable on Linux
+    let mut timestamp = None;
 
     let cmsg_iter = unsafe { cmsg::Iter::new(hdr) };
     for cmsg in cmsg_iter {
@@ -725,6 +747,11 @@ fn decode_recv(
             (libc::SOL_UDP, gro::UDP_GRO) => unsafe {
                 stride = cmsg::decode::<libc::c_int, libc::cmsghdr>(cmsg) as usize;
             },
+            #[cfg(target_os = "linux")]
+            (libc::SOL_SOCKET, libc::SCM_TIMESTAMPNS) => {
+                let tv = unsafe { cmsg::decode::<libc::timespec, libc::cmsghdr>(cmsg) };
+                timestamp = Some(Duration::new(tv.tv_sec as u64, tv.tv_nsec as u32));
+            }
             _ => {}
         }
     }
@@ -759,6 +786,7 @@ fn decode_recv(
         addr,
         ecn: EcnCodepoint::from_bits(ecn_bits),
         dst_ip,
+        timestamp,
     }
 }
 
@@ -907,6 +935,8 @@ fn set_socket_option(
     }
 }
 
+#[allow(dead_code)]
+const OPTION_OFF: libc::c_int = 0;
 const OPTION_ON: libc::c_int = 1;
 
 #[cfg(not(any(target_os = "linux", target_os = "android")))]

quinn-udp/src/windows.rs

@@ -267,6 +267,7 @@ impl UdpSocketState {
             addr: addr.unwrap(),
             ecn: EcnCodepoint::from_bits(ecn_bits as u8),
             dst_ip,
+            timestamp: None,
         };
         Ok(1)
     }

quinn-udp/tests/tests.rs

@@ -186,6 +186,59 @@ fn gso() {
     );
 }
 
+#[test]
+#[cfg(target_os = "linux")]
+fn receive_timestamp() {
+    let send = UdpSocket::bind((Ipv6Addr::LOCALHOST, 0))
+        .or_else(|_| UdpSocket::bind((Ipv4Addr::LOCALHOST, 0)))
+        .unwrap();
+    let recv = UdpSocket::bind((Ipv6Addr::LOCALHOST, 0))
+        .or_else(|_| UdpSocket::bind((Ipv4Addr::LOCALHOST, 0)))
+        .unwrap();
+    let dst_addr = recv.local_addr().unwrap();
+
+    let send_state = UdpSocketState::new((&send).into()).unwrap();
+    let recv_state = UdpSocketState::new((&recv).into()).unwrap();
+
+    if recv_state
+        .set_recv_timestamping((&recv).into(), true)
+        .is_err()
+    {
+        return; // Not supported on this machine -- skip this test
+    }
+
+    // Reverse non-blocking flag set by `UdpSocketState` to make the test non-racy
+    recv.set_nonblocking(false).unwrap();
+
+    let mut buf = [0; u16::MAX as usize];
+    let mut meta = RecvMeta::default();
+
+    send_state
+        .try_send(
+            (&send).into(),
+            &Transmit {
+                destination: dst_addr,
+                ecn: None,
+                contents: b"hello",
+                segment_size: None,
+                src_ip: None,
+            },
+        )
+        .unwrap();
+
+    recv_state
+        .recv(
+            (&recv).into(),
+            &mut [IoSliceMut::new(&mut buf)],
+            slice::from_mut(&mut meta),
+        )
+        .unwrap();
+
+    // We can't really validate the actual value of the timestamp because lots of local factors
+    // can mess with a CLOCK_REALTIME timestamp here, but we should at least have something.
+    assert!(meta.timestamp.is_some());
+}
+
 fn test_send_recv(send: &Socket, recv: &Socket, transmit: Transmit) {
     let send_state = UdpSocketState::new(send.into()).unwrap();
     let recv_state = UdpSocketState::new(recv.into()).unwrap();