Make the heartbeat task call the server's tick() method regularly.

The plumbing to get the tick task a reference to a server handle is a bit ugly;
some of the server methods should probably move to the handle impl instead.

src/net/server.rs

@@ -1,10 +1,11 @@
 use super::*;
 use anyhow::{Context, Error, Result};
+use future::{abortable, AbortHandle};
 use futures::{channel::mpsc::*, future::try_join, lock::Mutex, prelude::*};
 use serde_json::json;
 use std::sync::Arc;
 use stream::iter;
-use future::{AbortHandle, abortable};
+use tokio::time::{interval, Instant};
 
 /// There is a point at which a client falls far enough behind
 /// that it's probably not worth trying to catch them up; for now,
@@ -56,11 +57,13 @@ impl Server {
         }
     }
 
-    pub fn process_message(&mut self, player: usize, msg: ClientMessage) {
-        debug!("Client#{} message: {:?}", player, &msg);
-    }
-
-    pub async fn add_player(&mut self, mut sender: Sender<ServerMessage>) -> Result<PlayerId> {
+    /// connect a client to this server
+    /// TODO: currently needs to be passed a handle to this server instance, which feels flakey.
+    pub async fn add_player(
+        &mut self,
+        mut sender: Sender<ServerMessage>,
+        handle: &Handle,
+    ) -> Result<PlayerId> {
         // TODO: limit total number of players
 
         // allot player ID
@@ -79,17 +82,28 @@ impl Server {
         info!("Client#{} connected", player_id);
 
         // ensure server task is running
-        self.spinup();
+        self.spinup(handle);
 
         Ok(player_id)
     }
 
+    pub fn process_message(&mut self, player: usize, msg: ClientMessage) {
+        trace!("Client#{} message: {:?}", player, &msg);
+    }
+
+    fn tick(&mut self, tick: Instant) {
+        trace!("Tick {:?}", tick)
+    }
+
     pub fn remove_player(&mut self, player_id: PlayerId) {
         if player_id < self.players.len() && self.players[player_id].is_some() {
             self.players[player_id] = None;
             info!("Client#{} disconnected", player_id);
         } else {
-            error!("Tried to disconnect Client#{} but there was no record for them", player_id);
+            error!(
+                "Tried to disconnect Client#{} but there was no record for them",
+                player_id
+            );
         }
 
         // check if no players left
@@ -99,13 +113,22 @@ impl Server {
     }
 
     /// Start the heartbeat task, if it's not running
-    fn spinup(&mut self) {
+    /// TODO: currently needs to be passed a handle to this server instance, which feels flakey.
+    fn spinup(&mut self, server_handle: &Handle) {
         if let None = self.heartbeat_task {
             info!("Starting heartbeat task");
-            let (task, handle) = abortable(async {
+            // Take a reference to the server so the server tick task can access its state + send messages;
+            // A strong reference is fine, because we manually abort (& drop) this task when
+            // no more players are connected.
+            let server_handle = server_handle.clone();
+            let (task, abort_handle) = abortable(async move {
                 info!("Heartbeat task started");
+                let mut ticks = interval(TICK_LENGTH);
+                while let Some(tick) = ticks.next().await {
+                    server_handle.server.lock().await.tick(tick);
+                }
             });
-            self.heartbeat_task = Some(handle);
+            self.heartbeat_task = Some(abort_handle);
             tokio::spawn(task);
         }
     }
@@ -127,7 +150,7 @@ pub async fn run_client(
     let (sender, receiver) = channel(CHANNEL_BUFFER);
 
     // register player
-    let player_id = handle.server.lock().await.add_player(sender).await?;
+    let player_id = handle.server.lock().await.add_player(sender, &handle).await?;
 
     let (output_task, output_handle) = abortable(receiver.map(Ok).forward(sink));
 
@@ -137,15 +160,14 @@ pub async fn run_client(
                 Some(msg) => handle.server.lock().await.process_message(player_id, msg),
                 None => break,
             }
-        };
+        }
         // stop the sink so it won't error
         output_handle.abort();
         Ok(())
     };
 
     // intentional aborting is not a reportable error
-    let output_task = output_task
-        .map(|result| result.unwrap_or(Ok(())));
+    let output_task = output_task.map(|result| result.unwrap_or(Ok(())));
 
     let result = try_join(output_task, input_task).await.map(|((), ())| ());