Fix handling of heartbeat gateway event (#3105)

Author: DPlayer234

src/gateway/shard.rs

@@ -309,30 +309,6 @@ impl Shard {
         None
     }
 
-    #[instrument(skip(self))]
-    fn handle_heartbeat_event(&mut self, s: u64) -> ShardAction {
-        info!("[{:?}] Received shard heartbeat", self.shard_info);
-
-        // Received seq is off -- attempt to resume.
-        if s > self.seq + 1 {
-            info!(
-                "[{:?}] Received off sequence (them: {}; us: {}); resuming",
-                self.shard_info, s, self.seq
-            );
-
-            if self.stage == ConnectionStage::Handshake {
-                self.stage = ConnectionStage::Identifying;
-
-                return ShardAction::Identify;
-            }
-            warn!("[{:?}] Heartbeat during non-Handshake; auto-reconnecting", self.shard_info);
-
-            return ShardAction::Reconnect(self.reconnection_type());
-        }
-
-        ShardAction::Heartbeat
-    }
-
     #[instrument(skip(self))]
     fn handle_gateway_closed(
         &mut self,
@@ -442,7 +418,11 @@ impl Shard {
     pub fn handle_event(&mut self, event: &Result<GatewayEvent>) -> Result<Option<ShardAction>> {
         match event {
             Ok(GatewayEvent::Dispatch(seq, event)) => Ok(self.handle_gateway_dispatch(*seq, event)),
-            Ok(GatewayEvent::Heartbeat(s)) => Ok(Some(self.handle_heartbeat_event(*s))),
+            Ok(GatewayEvent::Heartbeat(..)) => {
+                info!("[{:?}] Received shard heartbeat", self.shard_info);
+
+                Ok(Some(ShardAction::Heartbeat))
+            },
             Ok(GatewayEvent::HeartbeatAck) => {
                 self.last_heartbeat_ack = Some(Instant::now());
                 self.last_heartbeat_acknowledged = true;

src/model/event.rs

@@ -1098,7 +1098,7 @@ pub struct MessagePollVoteRemoveEvent {
 #[serde(untagged)]
 pub enum GatewayEvent {
     Dispatch(u64, Event),
-    Heartbeat(u64),
+    Heartbeat(#[deprecated = "always 0 because it is never provided by the gateway"] u64),
     Reconnect,
     /// Whether the session can be resumed.
     InvalidateSession(bool),
@@ -1118,7 +1118,9 @@ impl<'de> Deserialize<'de> for GatewayEvent {
                 deserialize_val(Value::from(map))?,
             ),
             Opcode::Heartbeat => {
-                GatewayEvent::Heartbeat(seq.ok_or_else(|| DeError::missing_field("s"))?)
+                // Placeholder value. Discord expects the last Dispatch
+                // sequence number and doesn't send it with the heartbeat.
+                GatewayEvent::Heartbeat(0)
             },
             Opcode::InvalidSession => {
                 GatewayEvent::InvalidateSession(remove_from_map(&mut map, "d")?)