Add UpdateListener::timeout_hint

src/dispatching/update_listeners.rs

@@ -141,6 +141,11 @@ pub trait UpdateListener<E>: for<'a> AsUpdateStream<'a, E> {
     /// updates as soon as possible and return `None` from the update stream as
     /// soon as all cached updates are returned.
     fn stop(&mut self);
+
+    /// Timeout duration hint.
+    fn timeout_hint(&self) -> Option<Duration> {
+        None
+    }
 }
 
 /// [`UpdateListener`]'s supertrait/extension.
@@ -313,11 +318,9 @@ where
         .flatten()
     }
 
-    let timeout = timeout.map(|t| t.as_secs().try_into().expect("timeout is too big"));
-
     let state = State {
         bot: requester,
-        timeout,
+        timeout: timeout.map(|t| t.as_secs().try_into().expect("timeout is too big")),
         limit,
         allowed_updates,
         offset: 0,
@@ -325,11 +328,11 @@ where
         fetched: None,
     };
 
-    let stop = assert_stop_fn(|st: &mut State<_>| {
-        st.run_state = RunningState::Stopping;
-    });
+    let stop = Some(|st: &mut State<_>| st.run_state = RunningState::Stopping);
 
-    StatefulListner { state, stream, stop }
+    let timeout_hint = Some(move |_: &State<_>| timeout);
+
+    StatefulListner { state, stream, stop, timeout_hint }
 }
 
 async fn delete_webhook_if_setup<R>(requester: &R)
@@ -354,7 +357,7 @@ where
 }
 
 /// A listner created from `state` and `stream`/`stop` functions.
-struct StatefulListner<St, Sf, F> {
+struct StatefulListner<St, Assf, Sf, Thf> {
     /// The state of the listner.
     state: St,
 
@@ -362,18 +365,24 @@ struct StatefulListner<St, Sf, F> {
     ///
     /// Must be of type `for<'a> &'a mut St -> impl Stream + 'a` and callable by
     /// `&mut`.
-    stream: Sf,
+    stream: Assf,
 
     /// Function used as `UpdateListner::stop`.
     ///
     /// Must be of type `for<'a> &'a mut St`.
-    stop: Option<F>,
+    stop: Option<Sf>,
+
+    /// Function used as `UpdateListner::timeout_hint`.
+    ///
+    /// Must be of type `for<'a> &'a St -> Option<Duration>` and callable by
+    /// `&`.
+    timeout_hint: Option<Thf>,
 }
 
-impl<'a, St, Sf, F, Strm, E> AsUpdateStream<'a, E> for StatefulListner<St, Sf, F>
+impl<'a, St, Assf, Sf, Thf, Strm, E> AsUpdateStream<'a, E> for StatefulListner<St, Assf, Sf, Thf>
 where
     (St, Strm): 'a,
-    Sf: FnMut(&'a mut St) -> Strm,
+    Assf: FnMut(&'a mut St) -> Strm,
     Strm: Stream<Item = Result<Update, E>>,
 {
     type Stream = Strm;
@@ -383,21 +392,17 @@ where
     }
 }
 
-impl<St, Sf, F, E> UpdateListener<E> for StatefulListner<St, Sf, F>
+impl<St, Assf, Sf, Thf, E> UpdateListener<E> for StatefulListner<St, Assf, Sf, Thf>
 where
     Self: for<'a> AsUpdateStream<'a, E>,
-    F: FnOnce(&mut St),
+    Sf: FnOnce(&mut St),
+    Thf: Fn(&St) -> Option<Duration>,
 {
     fn stop(&mut self) {
         self.stop.take().map(|stop| stop(&mut self.state));
     }
-}
 
-/// Assert (at compile tume) that `f` is fine as a stop-function (closure
-/// lifetime inference workaround).
-fn assert_stop_fn<F, St>(f: F) -> Option<F>
-where
-    F: FnOnce(&mut St),
-{
-    Some(f)
+    fn timeout_hint(&self) -> Option<Duration> {
+        self.timeout_hint.as_ref().and_then(|f| f(&self.state))
+    }
 }