assert MsgHdr::with_control with empty buffer which causes error in m…

…acOS

src/lib.rs

@@ -639,8 +639,8 @@ impl<'addr, 'bufs, 'control> MsgHdr<'addr, 'bufs, 'control> {
     /// Corresponds to setting `msg_control` and `msg_controllen` on Unix and
     /// `Control` on Windows.
     pub fn with_control(mut self, buf: &'control [u8]) -> Self {
-        let ptr = buf.as_ptr() as *mut _;
-        sys::set_msghdr_control(&mut self.inner, ptr, buf.len());
+        debug_assert!(!buf.is_empty(), "Empty control buffer might be a programming error");
+        sys::set_msghdr_control(&mut self.inner, buf.as_ptr() as *mut _, buf.len());
         self
     }
 

tests/socket.rs

@@ -755,7 +755,9 @@ fn sendmsg() {
 
     let bufs = &[IoSlice::new(DATA)];
     let addr_b = socket_b.local_addr().unwrap();
-    let msg = socket2::MsgHdr::new().with_addr(&addr_b).with_buffers(bufs);
+    let msg = socket2::MsgHdr::new()
+        .with_addr(&addr_b)
+        .with_buffers(bufs);
     let sent = socket_a.sendmsg(&msg, 0).unwrap();
     assert_eq!(sent, DATA.len());