Fix wrong highest block number in snapshot sync

ethcore/sync/src/chain/mod.rs

@@ -548,7 +548,7 @@ impl ChainSync {
 		// Make sure the snapshot block is not too far away from best block and network best block and
 		// that it is higher than fork detection block
 		let our_best_block = io.chain().chain_info().best_block_number;
-		let fork_block = self.fork_block.as_ref().map(|&(n, _)| n).unwrap_or(0);
+		let fork_block = self.fork_block.map_or(0, |(n, _)| n);
 
 		let (best_hash, max_peers, snapshot_peers) = {
 			let expected_warp_block = match self.warp_sync {
@@ -558,10 +558,16 @@ impl ChainSync {
 			//collect snapshot infos from peers
 			let snapshots = self.peers.iter()
 				.filter(|&(_, p)| p.is_allowed() && p.snapshot_number.map_or(false, |sn|
+					// Snapshot must be old enough that it's usefull to sync with it
 					our_best_block < sn && (sn - our_best_block) > SNAPSHOT_RESTORE_THRESHOLD &&
+					// Snapshot must have been taken after the Fork
 					sn > fork_block &&
+					// Snapshot must be greater than the warp barrier if any
 					sn > expected_warp_block &&
-					self.highest_block.map_or(true, |highest| highest >= sn && (highest - sn) <= SNAPSHOT_RESTORE_THRESHOLD)
+					// If we know a highest block, snapshot must be recent enough
+					self.highest_block.map_or(true, |highest| {
+						highest < sn || (highest - sn) <= SNAPSHOT_RESTORE_THRESHOLD
+					})
 				))
 				.filter_map(|(p, peer)| peer.snapshot_hash.map(|hash| (p, hash.clone())))
 				.filter(|&(_, ref hash)| !self.snapshot.is_known_bad(hash));