Add support for TCP_CONGESTION socketopt

Co-authored-by: Campbell He <kp.campbell.he@duskmoon314.com>

src/sys/unix.rs

@@ -204,6 +204,10 @@ const MAX_BUF_LEN: usize = ssize_t::MAX as usize;
 #[cfg(target_vendor = "apple")]
 const MAX_BUF_LEN: usize = c_int::MAX as usize - 1;
 
+// TCP_CA_NAME_MAX isn't defined in user space include files(not in libc)
+#[cfg(all(feature = "all", any(target_os = "freebsd", target_os = "linux")))]
+const TCP_CA_NAME_MAX: usize = 16;
+
 #[cfg(any(
     all(
         target_os = "linux",
@@ -2154,6 +2158,55 @@ impl crate::Socket {
             )
         }
     }
+
+    /// Get the value of the `TCP_CONGESTION` option for this socket.
+    ///
+    /// For more information about this option, see [`set_tcp_congestion`].
+    ///
+    /// [`set_tcp_congestion`]: Socket::set_tcp_congestion
+    #[cfg(all(feature = "all", any(target_os = "freebsd", target_os = "linux")))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(all(feature = "all", any(target_os = "freebsd", target_os = "linux"))))
+    )]
+    pub fn tcp_congestion(&self) -> io::Result<Vec<u8>> {
+        let mut payload: [u8; TCP_CA_NAME_MAX] = [0; TCP_CA_NAME_MAX];
+        let mut len = payload.len() as libc::socklen_t;
+        syscall!(getsockopt(
+            self.as_raw(),
+            IPPROTO_TCP,
+            libc::TCP_CONGESTION,
+            payload.as_mut_ptr().cast(),
+            &mut len,
+        ))
+        .map(|_| {
+            let buf = &payload[..len as usize];
+            // TODO: use `MaybeUninit::slice_assume_init_ref` once stable.
+            unsafe { &*(buf as *const [_] as *const [u8]) }.into()
+        })
+    }
+
+    /// Set the value of the `TCP_CONGESTION` option for this socket.
+    ///
+    /// Specifies the TCP congestion control algorithm to use for this socket.
+    ///
+    /// The value must be a valid TCP congestion control algorithm name of the
+    /// platform. For example, Linux may supports "reno", "cubic".
+    #[cfg(all(feature = "all", any(target_os = "freebsd", target_os = "linux")))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(all(feature = "all", any(target_os = "freebsd", target_os = "linux"))))
+    )]
+    pub fn set_tcp_congestion(&self, tcp_ca_name: &[u8]) -> io::Result<()> {
+        syscall!(setsockopt(
+            self.as_raw(),
+            IPPROTO_TCP,
+            libc::TCP_CONGESTION,
+            tcp_ca_name.as_ptr() as *const _,
+            tcp_ca_name.len() as libc::socklen_t,
+        ))
+        .map(|_| ())
+    }
 }
 
 #[cfg_attr(docsrs, doc(cfg(unix)))]

tests/socket.rs

@@ -1341,3 +1341,49 @@ fn original_dst_ipv6() {
         Err(err) => assert_eq!(err.raw_os_error(), Some(libc::EOPNOTSUPP)),
     }
 }
+
+#[test]
+#[cfg(all(feature = "all", any(target_os = "freebsd", target_os = "linux")))]
+fn tcp_congestion() {
+    let socket: Socket = Socket::new(Domain::IPV4, Type::STREAM, None).unwrap();
+    // Get and set current tcp_ca
+    let origin_tcp_ca = socket
+        .tcp_congestion()
+        .expect("failed to get tcp congestion algorithm");
+    socket
+        .set_tcp_congestion(&origin_tcp_ca)
+        .expect("failed to set tcp congestion algorithm");
+    // Return a Err when set a non-exist tcp_ca
+    socket
+        .set_tcp_congestion(b"tcp_congestion_does_not_exist")
+        .unwrap_err();
+    let cur_tcp_ca = socket.tcp_congestion().unwrap();
+    assert_eq!(
+        cur_tcp_ca, origin_tcp_ca,
+        "expected {origin_tcp_ca:?} but get {cur_tcp_ca:?}"
+    );
+    let cur_tcp_ca = cur_tcp_ca.splitn(2, |num| *num == 0).next().unwrap();
+    const OPTIONS: [&[u8]; 2] = [
+        b"cubic",
+        #[cfg(target_os = "linux")] // or Android.
+        b"reno",
+        #[cfg(target_os = "freebsd")]
+        b"newreno",
+    ];
+    // Set a new tcp ca
+    #[cfg(target_os = "linux")]
+    let new_tcp_ca = if cur_tcp_ca == OPTIONS[0] {
+        OPTIONS[1]
+    } else {
+        OPTIONS[0]
+    };
+    #[cfg(target_os = "freebsd")]
+    let new_tcp_ca = OPTIONS[1];
+    socket.set_tcp_congestion(new_tcp_ca).unwrap();
+    // Check if new tcp ca is successfully set
+    let cur_tcp_ca = socket.tcp_congestion().unwrap();
+    assert_eq!(
+        cur_tcp_ca.splitn(2, |num| *num == 0).next().unwrap(),
+        new_tcp_ca,
+    );
+}