Fix issue when theres nothing new to learn from a peer

consensus/src/sync/light/sync_requests.rs

@@ -24,7 +24,7 @@ use crate::{
             sync::{EpochIds, PeerMacroRequests},
             LightMacroSync,
         },
-        syncer::MacroSync,
+        syncer::{MacroSync, MacroSyncReturn},
     },
 };
 
@@ -180,7 +180,7 @@ impl<TNetwork: Network> LightMacroSync<TNetwork> {
     pub(crate) fn request_macro_headers(
         &mut self,
         mut epoch_ids: EpochIds<TNetwork::PeerId>,
-    ) -> Option<TNetwork::PeerId> {
+    ) -> Option<MacroSyncReturn<TNetwork::PeerId>> {
         // Read our current blockchain state.
         let (our_epoch_id, our_epoch_number, our_block_number) = {
             let blockchain = self.blockchain.read();
@@ -204,7 +204,7 @@ impl<TNetwork: Network> LightMacroSync<TNetwork> {
                     peer = %epoch_ids.sender,
                     "Peer is behind"
                 );
-                return Some(epoch_ids.sender);
+                return Some(MacroSyncReturn::Outdated(epoch_ids.sender));
             } else {
                 // Check that the epoch_id sent by the peer at our current epoch number corresponds to
                 // our accepted state. If it doesn't, the peer is on a "permanent" fork, so we ban it.
@@ -219,7 +219,7 @@ impl<TNetwork: Network> LightMacroSync<TNetwork> {
                         peer = %epoch_ids.sender,
                         "Peer is on a different chain"
                     );
-                    return Some(epoch_ids.sender);
+                    return Some(MacroSyncReturn::Outdated(epoch_ids.sender));
                 }
 
                 epoch_ids.ids = epoch_ids
@@ -236,6 +236,13 @@ impl<TNetwork: Network> LightMacroSync<TNetwork> {
             }
         }
 
+        // After discarding all epoch_ids & checkpoint prior to our current state
+        // It could happen that we don't have anything new to learn from this peer
+        if epoch_ids.ids.is_empty() && epoch_ids.checkpoint.is_none() {
+            log::debug!("Nothing new to learn from this peer, emit it as good");
+            return Some(MacroSyncReturn::Good(epoch_ids.sender));
+        }
+
         let mut peer_requests = PeerMacroRequests::new();
 
         log::trace!(%epoch_ids.sender,

consensus/src/sync/light/sync_stream.rs

@@ -261,9 +261,26 @@ impl<TNetwork: Network> LightMacroSync<TNetwork> {
                 }
             }
 
-            // If the macro header process deems a peer useless, it is returned here and we emit it.
-            if let Some(agent) = self.request_macro_headers(epoch_ids) {
-                return Poll::Ready(Some(MacroSyncReturn::Outdated(agent)));
+            // Request the macro headers from the peer or emit it accordingly
+            if let Some(macro_sync_return) = self.request_macro_headers(epoch_ids) {
+                match macro_sync_return {
+                    MacroSyncReturn::Good(peer_id) => {
+                        // We are synced with this peer.
+                        debug!(?peer_id, "Finished macro syncing with peer");
+
+                        if self.blockchain.read().can_enforce_validity_window() {
+                            // We can enforce the validity window, so we are done.
+                            return Poll::Ready(Some(MacroSyncReturn::Good(peer_id)));
+                        } else {
+                            #[cfg(feature = "full")]
+                            self.start_validity_synchronization(peer_id);
+                        }
+                    }
+                    _ => {
+                        // Propagate any other sync result (outdated is the only one that can be emitted by the macro headers process)
+                        return Poll::Ready(Some(macro_sync_return));
+                    }
+                }
             }
         }