core/network/sync: Ask for block from all peers if none provided

When requesting an explicit fork sync, try to sync from all known peers,
when no specific peers were provided.

core/network/src/protocol/sync.rs

@@ -456,14 +456,20 @@ impl<B: BlockT> ChainSync<B> {
 
 	/// Request syncing for the given block from given set of peers.
 	// The implementation is similar to on_block_announce with unknown parent hash.
-	pub fn set_sync_fork_request(&mut self, peers: Vec<PeerId>, hash: &B::Hash, number: NumberFor<B>) {
+	pub fn set_sync_fork_request(&mut self, mut peers: Vec<PeerId>, hash: &B::Hash, number: NumberFor<B>) {
 		if peers.is_empty() {
-			if let Some(_) = self.fork_targets.remove(hash) {
-				debug!(target: "sync", "Cleared sync request for block {:?} with {:?}", hash, peers);
-			}
-			return;
+			debug!(
+				target: "sync",
+				"Explicit sync request for block {:?} with no peers specified. \
+				 Syncing from all connected peers {:?} instead.",
+				hash, peers,
+			);
+
+			peers = self.peers.iter().map(|(id, _)| id.clone()).collect();
+		} else {
+			debug!(target: "sync", "Explicit sync request for block {:?} with {:?}", hash, peers);
 		}
-		debug!(target: "sync", "Explicit sync request for block {:?} with {:?}", hash, peers);
+
 		if self.is_known(&hash) {
 			debug!(target: "sync", "Refusing to sync known hash {:?}", hash);
 			return;