Added changelog entry and test for LocalPeerPid

CHANGELOG.md

@@ -13,6 +13,7 @@ This project adheres to [Semantic Versioning](https://semver.org/).
   ([#1912](https://github.com/nix-rust/nix/pull/1912))
 - Added `mq_timedreceive` to `::nix::mqueue`.
   ([#1966])(https://github.com/nix-rust/nix/pull/1966)
+- Added `LocalPeerPid` to `nix::sys::socket::sockopt` for macOS. ([#1967](https://github.com/nix-rust/nix/pull/1967))
 
 ### Changed
 

test/sys/test_sockopt.rs

@@ -54,6 +54,22 @@ pub fn test_local_peercred_stream() {
     assert_eq!(Gid::from_raw(xucred.groups()[0]), Gid::current());
 }
 
+#[cfg(target_os = "macos")]
+#[test]
+pub fn test_local_peer_pid() {
+    use nix::sys::socket::socketpair;
+
+    let (fd1, _fd2) = socketpair(
+        AddressFamily::Unix,
+        SockType::Stream,
+        None,
+        SockFlag::empty(),
+    )
+    .unwrap();
+    let pid = getsockopt(fd1, sockopt::LocalPeerPid).unwrap();
+    assert_eq!(pid, std::process::id() as _);
+}
+
 #[cfg(target_os = "linux")]
 #[test]
 fn is_so_mark_functional() {