Driver: Fix scheduler crash after task closure

A removed audio task could still have one or more driver messages left in its queue, leading to a crash when the id->mixer lookup failed. This removes an unwrap which is invalid under these assumptions and includes an extra cleanup measure for message forwarders under the same circumstances.

This was tested using `cargo make ready`.

src/driver/scheduler/idle.rs

@@ -3,6 +3,7 @@ use std::{collections::HashMap, sync::Arc, time::Duration};
 use flume::{Receiver, Sender};
 use nohash_hasher::{BuildNoHashHasher, IntMap};
 use tokio::time::{Instant as TokInstant, Interval};
+use tracing::warn;
 
 use crate::constants::*;
 
@@ -71,30 +72,32 @@ impl Idle {
             biased;
             msg = self.rx.recv_async() => match msg {
                 Ok(SchedulerMessage::NewMixer(rx, ic, cfg)) => {
-                    let mixer = ParkedMixer::new(rx, ic, cfg);
+                    let mut mixer = ParkedMixer::new(rx, ic, cfg);
                     let id = self.next_id.incr();
 
                     mixer.spawn_forwarder(self.tx.clone(), id);
                     self.tasks.insert(id, mixer);
                     self.stats.add_idle_mixer();
                 },
-                Ok(SchedulerMessage::Demote(id, task)) => {
+                Ok(SchedulerMessage::Demote(id, mut task)) => {
                     task.send_gateway_not_speaking();
 
                     task.spawn_forwarder(self.tx.clone(), id);
                     self.tasks.insert(id, task);
                 },
                 Ok(SchedulerMessage::Do(id, mix_msg)) => {
                     let now_live = mix_msg.is_mixer_now_live();
-                    let task = self.tasks.get_mut(&id).unwrap();
-
-                    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) => {},
-                        Ok(true) | Err(_) => self.to_cull.push(id),
+                    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) => {},
+                            Ok(true) | Err(_) => self.to_cull.push(id),
+                        }
+                    } else {
+                        warn!("Received post-cull message for {id:?}, discarding.");
                     }
                 },
                 Ok(SchedulerMessage::Overspill(worker_id, id, task)) => {
@@ -136,7 +139,9 @@ impl Idle {
         }
 
         for id in self.to_cull.drain(..) {
-            self.tasks.remove(&id);
+            if let Some(tx) = self.tasks.remove(&id).and_then(|t| t.cull_handle) {
+                _ = tx.send_async(()).await;
+            }
         }
 
         true
@@ -292,6 +297,7 @@ mod test {
                 rtp_timestamp: i,
                 park_time: TokInstant::now().into(),
                 last_cost: None,
+                cull_handle: None,
             };
             core.stats.add_idle_mixer();
             core.stats.move_mixer_to_live();

src/driver/scheduler/live.rs

@@ -554,6 +554,7 @@ impl Live {
                 rtp_timestamp: id_0 as u32,
                 park_time: Instant::now(),
                 last_cost: None,
+                cull_handle: None,
             },
             id,
             Instant::now(),
@@ -617,6 +618,7 @@ impl Live {
                     rtp_timestamp,
                     park_time,
                     last_cost: None,
+                    cull_handle: None,
                 },
             )
         })

src/driver/scheduler/task.rs

@@ -75,6 +75,8 @@ pub struct ParkedMixer {
     /// The last known cost of executing this task, if it had to be moved
     /// due to a limit on thread resources.
     pub last_cost: Option<Duration>,
+    /// Handle to any forwarder task, used if this mixer is culled while idle.
+    pub cull_handle: Option<Sender<()>>,
 }
 
 #[allow(missing_docs)]
@@ -88,21 +90,36 @@ impl ParkedMixer {
             rtp_timestamp: random::<u32>(),
             park_time: Instant::now(),
             last_cost: None,
+            cull_handle: None,
         }
     }
 
     /// Spawn a tokio task which forwards any mixer messages to the central `Idle` task pool.
     ///
     /// Any requests which would cause this mixer to become live will terminate
     /// this task.
-    pub fn spawn_forwarder(&self, tx: Sender<SchedulerMessage>, id: TaskId) {
+    pub fn spawn_forwarder(&mut self, tx: Sender<SchedulerMessage>, id: TaskId) {
+        let (kill_tx, kill_rx) = flume::bounded(1);
+        self.cull_handle = Some(kill_tx);
+
         let remote_rx = self.mixer.mix_rx.clone();
         tokio::spawn(async move {
-            while let Ok(msg) = remote_rx.recv_async().await {
-                let exit = msg.is_mixer_now_live();
-                let dead = tx.send_async(SchedulerMessage::Do(id, msg)).await.is_err();
-                if exit || dead {
-                    break;
+            loop {
+                tokio::select! {
+                    biased;
+                    _ = 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();
+                            tx.send_async(SchedulerMessage::Do(id, msg)).await.is_err() || remove_self
+                        } else {
+                            true
+                        };
+
+                        if exit {
+                            break;
+                        }
+                    }
                 }
             }
         });

src/input/sources/http.rs

@@ -13,7 +13,6 @@ use reqwest::{
     header::{HeaderMap, ACCEPT_RANGES, CONTENT_LENGTH, CONTENT_TYPE, RANGE, RETRY_AFTER},
     Client,
 };
-use std::fmt::format;
 use std::{
     io::{Error as IoError, ErrorKind as IoErrorKind, Result as IoResult, SeekFrom},
     pin::Pin,