fix: block downloader polling

crates/engine/tree/src/download.rs

@@ -194,10 +194,6 @@ where
 
     /// Advances the download process.
     fn poll(&mut self, cx: &mut Context<'_>) -> Poll<DownloadOutcome> {
-        if let Some(pending_event) = self.pop_pending_event() {
-            return Poll::Ready(pending_event);
-        }
-
         // advance all full block requests
         for idx in (0..self.inflight_full_block_requests.len()).rev() {
             let mut request = self.inflight_full_block_requests.swap_remove(idx);
@@ -235,25 +231,33 @@ where
 
         self.update_block_download_metrics();
 
-        if self.set_buffered_blocks.is_empty() {
-            return Poll::Pending;
+        if !self.set_buffered_blocks.is_empty() {
+            // drain all unique element of the block buffer if there are any
+            let mut downloaded_blocks: Vec<SealedBlockWithSenders> =
+                Vec::with_capacity(self.set_buffered_blocks.len());
+            while let Some(block) = self.set_buffered_blocks.pop() {
+                // peek ahead and pop duplicates
+                while let Some(peek) = self.set_buffered_blocks.peek_mut() {
+                    if peek.0 .0.hash() == block.0 .0.hash() {
+                        PeekMut::pop(peek);
+                    } else {
+                        break
+                    }
+                }
+                downloaded_blocks.push(block.0.into());
+            }
+
+            self.push_pending_event(DownloadOutcome::Blocks(downloaded_blocks));
         }
 
-        // drain all unique element of the block buffer if there are any
-        let mut downloaded_blocks: Vec<SealedBlockWithSenders> =
-            Vec::with_capacity(self.set_buffered_blocks.len());
-        while let Some(block) = self.set_buffered_blocks.pop() {
-            // peek ahead and pop duplicates
-            while let Some(peek) = self.set_buffered_blocks.peek_mut() {
-                if peek.0 .0.hash() == block.0 .0.hash() {
-                    PeekMut::pop(peek);
-                } else {
-                    break
-                }
+        if let Some(pending_event) = self.pop_pending_event() {
+            if !self.pending_events.is_empty() {
+                cx.waker().wake_by_ref();
             }
-            downloaded_blocks.push(block.0.into());
+            return Poll::Ready(pending_event);
         }
-        Poll::Ready(DownloadOutcome::Blocks(downloaded_blocks))
+
+        Poll::Pending
     }
 }