fix panic on async task cancellation (#570)

sctp/src/association/mod.rs

@@ -488,7 +488,7 @@ impl Association {
         let done = Arc::new(AtomicBool::new(false));
         let name = Arc::new(name);
 
-        while !done.load(Ordering::Relaxed) {
+        'outer: while !done.load(Ordering::Relaxed) {
             //log::debug!("[{}] gather_outbound begin", name);
             let (packets, continue_loop) = {
                 let mut ai = association_internal.lock().await;
@@ -512,9 +512,8 @@ impl Association {
                 // Doing it this way, tokio schedules this work on a dedicated blocking thread, this future is suspended, and the read_loop can make progress
                 match tokio::task::spawn_blocking(move || raw.marshal_to(&mut buf).map(|_| buf))
                     .await
-                    .unwrap()
                 {
-                    Ok(mut buf) => {
+                    Ok(Ok(mut buf)) => {
                         let raw = buf.as_ref();
                         if let Err(err) = net_conn.send(raw.as_ref()).await {
                             log::warn!("[{}] failed to write packets on net_conn: {}", name2, err);
@@ -527,9 +526,21 @@ impl Association {
                         buf.clear();
                         buffer = Some(buf);
                     }
-                    Err(err) => {
+                    Ok(Err(err)) => {
                         log::warn!("[{}] failed to serialize a packet: {:?}", name2, err);
                     }
+                    Err(err) => {
+                        if err.is_cancelled() {
+                            log::debug!(
+                                "[{}] task cancelled while serializing a packet: {:?}",
+                                name,
+                                err
+                            );
+                            break 'outer;
+                        } else {
+                            log::error!("[{}] panic while serializing a packet: {:?}", name, err);
+                        }
+                    }
                 }
                 //log::debug!("[{}] sending {} bytes done", name, raw.len());
             }