Ensure that Server::service will return when the connection terminates

Otherwise the per-connection helper processes used by Capsicum would
never exit.

src/server/controlchan/control_loop.rs

@@ -41,6 +41,7 @@ use tokio::{
         mpsc::{channel, Receiver, Sender},
         Mutex,
     },
+    task::JoinHandle,
 };
 use tokio_util::codec::{Decoder, Framed};
 
@@ -81,7 +82,7 @@ pub(crate) async fn spawn<Storage, User>(
     proxyloop_msg_tx: Option<ProxyLoopSender<Storage, User>>,
     mut shutdown: shutdown::Listener,
     failed_logins: Option<Arc<FailedLoginsCache>>,
-) -> Result<(), ControlChanError>
+) -> Result<JoinHandle<()>, ControlChanError>
 where
     User: UserDetail + 'static,
     Storage: StorageBackend<User> + 'static,
@@ -182,7 +183,7 @@ where
     reply_sink.send(Reply::new(ReplyCode::ServiceReady, config.greeting)).await?;
     reply_sink.flush().await?;
 
-    tokio::spawn(async move {
+    let jh = tokio::spawn(async move {
         // The control channel event loop
         slog::info!(logger, "Starting control loop");
         loop {
@@ -297,7 +298,7 @@ where
         }
     });
 
-    Ok(())
+    Ok(jh)
 }
 
 // gets the reply to be sent to the client and tells if the connection should be closed.

src/server/ftpserver.rs

@@ -756,10 +756,15 @@ where
         let shutdown_listener = shutdown_notifier.subscribe().await;
         slog::debug!(self.logger, "Servicing control connection from");
         let result = controlchan::spawn_loop::<Storage, User>((&options).into(), tcp_stream, None, None, shutdown_listener, failed_logins.clone()).await;
-        if let Err(err) = result {
-            slog::error!(self.logger, "Could not spawn control channel loop: {:?}", err);
-        } else {
-            shutdown_notifier.linger().await;
+        match result {
+            Err(err) => {
+                slog::error!(self.logger, "Could not spawn control channel loop: {:?}", err);
+            }
+            Ok(jh) => {
+                if let Err(e) = jh.await {
+                    slog::error!(self.logger, "Control loop failed to complete: {:?}", e);
+                }
+            }
         }
         Ok(())
     }