Driver: Fix transition to Live on connect (serenity-rs#222)

This PR fixes a case where a call which changes channel or gracefully
reconnects would have been stuck in the Idle state. SetConn events will
now allow a transition straight back to Live if any tracks are found
attached to a mixer.

src/driver/scheduler/idle.rs

@@ -86,12 +86,18 @@ impl Idle {
                     self.tasks.insert(id, task);
                 },
                 Ok(SchedulerMessage::Do(id, mix_msg)) => {
-                    let now_live = mix_msg.is_mixer_now_live();
+                    let maybe_live = mix_msg.is_mixer_maybe_live();
                     if let Some(task) = self.tasks.get_mut(&id) {
                         match task.handle_message(mix_msg) {
-                            Ok(false) if now_live => {
-                                let task = self.tasks.remove(&id).unwrap();
-                                self.schedule_mixer(task, id, None);
+                            Ok(false) if maybe_live => {
+                                if task.mixer.tracks.is_empty() {
+                                    // No tracks, likely due to SetConn.
+                                    // Recreate message forwarding task.
+                                    task.spawn_forwarder(self.tx.clone(), id);
+                                } else {
+                                    let task = self.tasks.remove(&id).unwrap();
+                                    self.schedule_mixer(task, id, None);
+                                }
                             },
                             Ok(false) => {},
                             Ok(true) | Err(()) => self.to_cull.push(id),

src/driver/scheduler/task.rs

@@ -116,7 +116,7 @@ impl ParkedMixer {
                     _ = kill_rx.recv_async() => break,
                     msg = remote_rx.recv_async() => {
                         let exit = if let Ok(msg) = msg {
-                            let remove_self = msg.is_mixer_now_live();
+                            let remove_self = msg.is_mixer_maybe_live();
                             tx.send_async(SchedulerMessage::Do(id, msg)).await.is_err() || remove_self
                         } else {
                             true
@@ -135,7 +135,8 @@ impl ParkedMixer {
     pub fn handle_message(&mut self, msg: MixerMessage) -> Result<bool, ()> {
         match msg {
             MixerMessage::SetConn(conn, ssrc) => {
-                // Overridden because
+                // Overridden because payload-specific fields are carried
+                // externally on `ParkedMixer`.
                 self.ssrc = ssrc;
                 self.rtp_sequence = random::<u16>();
                 self.rtp_timestamp = random::<u32>();

src/driver/tasks/message/mixer.rs

@@ -40,8 +40,11 @@ pub enum MixerMessage {
 }
 
 impl MixerMessage {
-    pub fn is_mixer_now_live(&self) -> bool {
-        matches!(self, Self::AddTrack(_) | Self::SetTrack(Some(_)))
+    pub fn is_mixer_maybe_live(&self) -> bool {
+        matches!(
+            self,
+            Self::AddTrack(_) | Self::SetTrack(Some(_)) | Self::SetConn(..)
+        )
     }
 }
 

src/driver/tasks/udp_rx/ssrc_state.rs

@@ -141,7 +141,7 @@ impl SsrcState {
             let mut out = vec![0; self.decode_size.len()];
 
             for _ in 0..missed_packets {
-                let missing_frame: Option<OpusPacket> = None;
+                let missing_frame: Option<OpusPacket<'_>> = None;
                 let dest_samples = (&mut out[..])
                     .try_into()
                     .expect("Decode logic will cap decode buffer size at i32::MAX.");