chore: improve engine api event handling (#9682)

crates/engine/tree/src/chain.rs

@@ -112,7 +112,7 @@ where
             match this.handler.poll(cx) {
                 Poll::Ready(handler_event) => {
                     match handler_event {
-                        HandlerEvent::BackfillSync(action) => {
+                        HandlerEvent::BackfillAction(action) => {
                             // forward action to backfill_sync
                             this.backfill_sync.on_action(action);
                             continue 'outer
@@ -169,7 +169,7 @@ pub enum ChainEvent<T> {
 ///
 /// The [`ChainOrchestrator`] is responsible for advancing this handler through
 /// [`ChainHandler::poll`] and handling the emitted events, for example
-/// [`HandlerEvent::BackfillSync`] to start a backfill sync. Events from the [`ChainOrchestrator`]
+/// [`HandlerEvent::BackfillAction`] to start a backfill sync. Events from the [`ChainOrchestrator`]
 /// are passed to the handler via [`ChainHandler::on_event`], e.g.
 /// [`FromOrchestrator::BackfillSyncStarted`] once the backfill sync started or finished.
 pub trait ChainHandler: Send + Sync {
@@ -187,7 +187,7 @@ pub trait ChainHandler: Send + Sync {
 #[derive(Clone, Debug)]
 pub enum HandlerEvent<T> {
     /// Request an action to backfill sync
-    BackfillSync(BackfillAction),
+    BackfillAction(BackfillAction),
     /// Other event emitted by the handler
     Event(T),
 }

crates/engine/tree/src/engine.rs

@@ -1,9 +1,9 @@
 //! An engine API handler for the chain.
 
 use crate::{
+    backfill::BackfillAction,
     chain::{ChainHandler, FromOrchestrator, HandlerEvent},
     download::{BlockDownloader, DownloadAction, DownloadOutcome},
-    tree::TreeEvent,
 };
 use futures::{Stream, StreamExt};
 use reth_beacon_consensus::{BeaconConsensusEngineEvent, BeaconEngineMessage};
@@ -75,10 +75,10 @@ where
                 match ev {
                     RequestHandlerEvent::HandlerEvent(ev) => {
                         return match ev {
-                            HandlerEvent::BackfillSync(target) => {
+                            HandlerEvent::BackfillAction(target) => {
                                 // bubble up backfill sync request request
                                 self.downloader.on_action(DownloadAction::Clear);
-                                Poll::Ready(HandlerEvent::BackfillSync(target))
+                                Poll::Ready(HandlerEvent::BackfillAction(target))
                             }
                             HandlerEvent::Event(ev) => {
                                 // bubble up the event
@@ -191,16 +191,10 @@ where
             EngineApiEvent::BeaconConsensus(ev) => {
                 RequestHandlerEvent::HandlerEvent(HandlerEvent::Event(ev))
             }
-            EngineApiEvent::FromTree(ev) => match ev {
-                TreeEvent::BackfillAction(target) => {
-                    RequestHandlerEvent::HandlerEvent(HandlerEvent::BackfillSync(target))
-                }
-                TreeEvent::Download(download) => RequestHandlerEvent::Download(download),
-                TreeEvent::TreeAction(ev) => {
-                    // TODO revise this
-                    return Poll::Pending
-                }
-            },
+            EngineApiEvent::BackfillAction(action) => {
+                RequestHandlerEvent::HandlerEvent(HandlerEvent::BackfillAction(action))
+            }
+            EngineApiEvent::Download(action) => RequestHandlerEvent::Download(action),
         };
         Poll::Ready(ev)
     }
@@ -212,8 +206,10 @@ pub enum EngineApiEvent {
     /// Event from the consensus engine.
     // TODO(mattsse): find a more appropriate name for this variant, consider phasing it out.
     BeaconConsensus(BeaconConsensusEngineEvent),
-    /// Bubbled from tree.
-    FromTree(TreeEvent),
+    /// Backfill action is needed.
+    BackfillAction(BackfillAction),
+    /// Block download is needed.
+    Download(DownloadRequest),
 }
 
 impl From<BeaconConsensusEngineEvent> for EngineApiEvent {

crates/engine/tree/src/tree/mod.rs

@@ -404,9 +404,7 @@ where
                 },
                 FromEngine::DownloadedBlocks(blocks) => {
                     if let Some(event) = self.on_downloaded(blocks) {
-                        if let Err(err) = self.outgoing.send(EngineApiEvent::FromTree(event)) {
-                            error!("Failed to send event: {err:?}");
-                        }
+                        self.on_tree_event(event);
                     }
                 }
             }
@@ -439,6 +437,21 @@ where
         }
     }
 
+    /// Handles a tree event.
+    fn on_tree_event(&self, event: TreeEvent) {
+        match event {
+            TreeEvent::TreeAction(action) => {
+                // TODO: handle
+            }
+            TreeEvent::BackfillAction(action) => {
+                self.emit_event(EngineApiEvent::BackfillAction(action));
+            }
+            TreeEvent::Download(action) => {
+                self.emit_event(EngineApiEvent::Download(action));
+            }
+        }
+    }
+
     /// Emits an outgoing event to the engine.
     fn emit_event(&self, event: impl Into<EngineApiEvent>) {
         let _ = self