Merge pull request #418 from longfin/bugfix/skip-preload

Skip PreloadAsync when there is no suitable peer

CHANGES.md

@@ -91,6 +91,8 @@ To be released.
     when the connection had reset by a remote peer.  [[#414]]
  -  Fixed a bug that `Swarm<T>` had hung forever after a remote peer had
     disconnected while receiving.  [[#416]]
+ -  Fixed a bug that `Swarm<T>.PreloadAsync()` had been processed even if there
+    is no appropriate peer. [[#418]]
 
 [#319]: https://github.com/planetarium/libplanet/issues/319
 [#343]: https://github.com/planetarium/libplanet/pull/343
@@ -119,6 +121,7 @@ To be released.
 [#414]: https://github.com/planetarium/libplanet/pull/414
 [#416]: https://github.com/planetarium/libplanet/pull/416
 [#417]: https://github.com/planetarium/libplanet/pull/417
+[#418]: https://github.com/planetarium/libplanet/pull/418
 [LiteDB #1268]: https://github.com/mbdavid/LiteDB/issues/1268
 
 

Libplanet/Net/Swarm.cs

@@ -576,6 +576,17 @@ internal async Task PreloadAsync(
                 trustedStateValidators = ImmutableHashSet<Address>.Empty;
             }
 
+            IList<(Peer, long? TipIndex)> peersWithHeight =
+                await DialToExistingPeers(cancellationToken).Select(pp =>
+                    (pp.Item1, pp.Item2.TipIndex)
+                ).ToListAsync(cancellationToken);
+
+            if (!peersWithHeight.Any())
+            {
+                _logger.Information("There is no appropriate peer for preloading.");
+                return;
+            }
+
             Block<T> initialTip = _blockChain.Tip;
 
             // As preloading takes long, the blockchain data can corrupt if a program suddenly
@@ -587,10 +598,6 @@ internal async Task PreloadAsync(
                 ? _blockChain.Fork(tip.Hash)
                 : new BlockChain<T>(_blockChain.Policy, _blockChain.Store, Guid.NewGuid());
 
-            IList<(Peer, long? TipIndex)> peersWithHeight =
-                await DialToExistingPeers(cancellationToken).Select(pp =>
-                    (pp.Item1, pp.Item2.TipIndex)
-                ).ToListAsync(cancellationToken);
             await SyncBehindsBlocksFromPeersAsync(
                 workspace,
                 peersWithHeight,