Add the UtunIfname sockopt (UTUN_OPT_IFNAME) (nix-rust#2325)

changelog/2325.added.md

@@ -0,0 +1 @@
+Add socket option UtunIfname.

src/sys/socket/sockopt.rs

@@ -1065,6 +1065,17 @@ sockopt_impl!(
     libc::IPV6_DONTFRAG,
     bool
 );
+#[cfg(apple_targets)]
+#[cfg(feature = "net")]
+sockopt_impl!(
+    /// Get the utun interface name.
+    UtunIfname,
+    GetOnly,
+    libc::SYSPROTO_CONTROL,
+    libc::UTUN_OPT_IFNAME,
+    OsString,
+    GetOsString<[u8; libc::IFNAMSIZ]>
+);
 
 #[allow(missing_docs)]
 // Not documented by Linux!

test/sys/test_sockopt.rs

@@ -828,3 +828,34 @@ fn test_ktls() {
         Err(err) => panic!("{err:?}"),
     }
 }
+
+#[test]
+#[cfg(apple_targets)]
+fn test_utun_ifname() {
+    use nix::sys::socket::connect;
+    use nix::sys::socket::SysControlAddr;
+
+    let fd = socket(
+        AddressFamily::System,
+        SockType::Datagram,
+        SockFlag::empty(),
+        SockProtocol::KextControl,
+    )
+    .unwrap();
+
+    let unit = 123;
+    let addr = SysControlAddr::from_name(
+        fd.as_raw_fd(),
+        "com.apple.net.utun_control",
+        unit,
+    )
+    .unwrap();
+
+    connect(fd.as_raw_fd(), &addr).unwrap();
+
+    let name = getsockopt(&fd, sockopt::UtunIfname)
+        .expect("getting UTUN_OPT_IFNAME on a utun interface should succeed");
+
+    let expected_name = format!("utun{}\0", unit - 1);
+    assert_eq!(name.into_string(), Ok(expected_name));
+}