Add the ListenQLimit sockopt (SO_LISTENQLIMIT) (#2263)

changelog/2263.added.md

@@ -0,0 +1 @@
+Added the `SO_LISTENQLIMIT` sockopt.

src/sys/socket/sockopt.rs

@@ -522,6 +522,17 @@ sockopt_impl!(
     libc::SO_PEERCRED,
     super::UnixCredentials
 );
+#[cfg(target_os = "freebsd")]
+#[cfg(feature = "net")]
+sockopt_impl!(
+    #[cfg_attr(docsrs, doc(cfg(feature = "net")))]
+    /// Get backlog limit of the socket
+    ListenQLimit,
+    GetOnly,
+    libc::SOL_SOCKET,
+    libc::SO_LISTENQLIMIT,
+    u32
+);
 #[cfg(apple_targets)]
 #[cfg(feature = "net")]
 sockopt_impl!(

test/sys/test_sockopt.rs

@@ -103,6 +103,31 @@ fn test_so_buf() {
     assert!(actual >= bufsize);
 }
 
+#[cfg(target_os = "freebsd")]
+#[test]
+fn test_so_listen_q_limit() {
+    use nix::sys::socket::{bind, listen, SockaddrIn};
+    use std::net::SocketAddrV4;
+    use std::str::FromStr;
+
+    let std_sa = SocketAddrV4::from_str("127.0.0.1:4004").unwrap();
+    let sock_addr = SockaddrIn::from(std_sa);
+
+    let rsock = socket(
+        AddressFamily::Inet,
+        SockType::Stream,
+        SockFlag::empty(),
+        SockProtocol::Tcp,
+    )
+    .unwrap();
+    bind(rsock.as_raw_fd(), &sock_addr).unwrap();
+    let pre_limit = getsockopt(&rsock, sockopt::ListenQLimit).unwrap();
+    assert_eq!(pre_limit, 0);
+    listen(&rsock, 42).unwrap();
+    let post_limit = getsockopt(&rsock, sockopt::ListenQLimit).unwrap();
+    assert_eq!(post_limit, 42);
+}
+
 #[test]
 fn test_so_tcp_maxseg() {
     use nix::sys::socket::{accept, bind, connect, listen, SockaddrIn};