Add capability to set TCP ACK Frequency on Windows (#638)

Author: derek-will

src/socket.rs

@@ -2280,6 +2280,14 @@ impl Socket {
             )
         }
     }
+
+    /// On Windows this invokes the `SIO_TCP_SET_ACK_FREQUENCY` IOCTL which
+    /// configures the number of TCP segments that must be received before
+    /// the delayed ACK timer is ignored.
+    #[cfg(all(feature = "all", windows))]
+    pub fn set_tcp_ack_frequency(&self, frequency: u8) -> io::Result<()> {
+        sys::set_tcp_ack_frequency(self.as_raw(), frequency)
+    }
 }
 
 impl Read for Socket {

src/sys/windows.rs

@@ -27,6 +27,12 @@ use windows_sys::Win32::Networking::WinSock::{
     SOCKET_ERROR, WSABUF, WSAEMSGSIZE, WSAESHUTDOWN, WSAPOLLFD, WSAPROTOCOL_INFOW,
     WSA_FLAG_NO_HANDLE_INHERIT, WSA_FLAG_OVERLAPPED, WSA_FLAG_REGISTERED_IO,
 };
+
+#[cfg(feature = "all")]
+use windows_sys::Win32::Networking::WinSock::{
+    SIO_TCP_SET_ACK_FREQUENCY, TCP_ACK_FREQUENCY_PARAMETERS,
+};
+
 #[cfg(feature = "all")]
 use windows_sys::Win32::Networking::WinSock::{
     IP6T_SO_ORIGINAL_DST, SOL_IP, SO_ORIGINAL_DST, SO_PROTOCOL_INFOW,
@@ -798,6 +804,31 @@ pub(crate) fn set_tcp_keepalive(socket: RawSocket, keepalive: &TcpKeepalive) ->
     Ok(())
 }
 
+#[cfg(feature = "all")]
+pub(crate) fn set_tcp_ack_frequency(socket: RawSocket, frequency: u8) -> io::Result<()> {
+    let mut freq_params = TCP_ACK_FREQUENCY_PARAMETERS {
+        TcpDelayedAckFrequency: frequency,
+    };
+
+    let mut out = 0;
+    syscall!(
+        WSAIoctl(
+            socket,
+            SIO_TCP_SET_ACK_FREQUENCY,
+            &mut freq_params as *mut _ as *mut _,
+            size_of::<TCP_ACK_FREQUENCY_PARAMETERS>() as _,
+            ptr::null_mut(),
+            0,
+            &mut out,
+            ptr::null_mut(),
+            None,
+        ),
+        PartialEq::eq,
+        SOCKET_ERROR
+    )
+    .map(|_| ())
+}
+
 /// Caller must ensure `T` is the correct type for `level` and `optname`.
 // NOTE: `optname` is actually `i32`, but all constants are `u32`.
 pub(crate) unsafe fn getsockopt<T>(socket: RawSocket, level: c_int, optname: i32) -> io::Result<T> {

tests/socket.rs

@@ -1824,6 +1824,25 @@ fn tcp_congestion() {
     );
 }
 
+#[test]
+#[cfg(all(feature = "all", windows))]
+fn tcp_set_ack_frequency() {
+    let socket = Socket::new(Domain::IPV4, Type::STREAM, Some(Protocol::TCP)).unwrap();
+    match socket.set_tcp_ack_frequency(1) {
+        Ok(_) => {}
+        Err(err) => panic!("set_tcp_ack_frequency on tcp socket should succeed, error: {err}"),
+    }
+
+    let socket = Socket::new(Domain::IPV4, Type::DGRAM, Some(Protocol::UDP)).unwrap();
+    match socket.set_tcp_ack_frequency(1) {
+        Ok(_) => panic!("set_tcp_ack_frequency on udp socket should fail"),
+        Err(err) => assert_eq!(
+            err.raw_os_error(),
+            Some(windows_sys::Win32::Networking::WinSock::WSAEOPNOTSUPP)
+        ),
+    }
+}
+
 #[test]
 #[ignore = "DCCP support is not enabled in all kernels of majors Linux distros"]
 #[cfg(all(feature = "all", target_os = "linux"))]