Only request justifications from available peers (#1586)

substrate/core/network/src/sync.rs

@@ -92,8 +92,8 @@ impl<B: BlockT> PendingJustifications<B> {
 		}
 
 		let mut available_peers = peers.iter().filter_map(|(peer, sync)| {
-			// don't request to any peers that already have pending requests
-			if self.peer_requests.contains_key(&peer) {
+			// don't request to any peers that already have pending requests or are unavailable
+			if sync.state != PeerSyncState::Available || self.peer_requests.contains_key(&peer) {
 				None
 			} else {
 				Some((*peer, sync.best_number))
@@ -152,6 +152,7 @@ impl<B: BlockT> PendingJustifications<B> {
 				.expect("peer was is taken from available_peers; available_peers is a subset of peers; qed")
 				.state = PeerSyncState::DownloadingJustification(request.0);
 
+			trace!(target: "sync", "Requesting justification for block #{} from {}", request.0, peer);
 			let request = message::generic::BlockRequest {
 				id: 0,
 				fields: message::BlockAttributes::JUSTIFICATION,