Writing snapshot entry so that it can be deserialized by entry.DeserializeFromJsonAsync()

[RyanTT]

Hello,

I am trying to implement a simple state machine with a snapshot builder.

What I'd to do is write JSON values. For this purpose, I am utilizing CreateJsonLogEntry + ReplicateAsync to distribute non-snapshot entries. This appears to work fine. However, when it comes to writing the Snapshot as an entry, I always get very strange inconsistent results that I cannot explain to myself:

1. Inside my CustomSnapshotBuilder : IncrementalSnapshotBuilder WriteToAsync<TWriter>, I use the following lines to write my desired snapshot data:

var chars = JsonSerializer.Serialize(Snapshot);

await writer.WriteStringAsync(chars.AsMemory(), new DotNext.Text.EncodingContext(Encoding.UTF8, true), DotNext.IO.LengthFormat.PlainLittleEndian, token);

This appears to write fine.

2. Inside my RaftMemoryBasedStateMachine : MemoryBasedStateMachine ApplyAsync method, I then check each arriving LogEntry for its IsSnapshot property, and deserialize the LogEntry the following way:

EntryBase value = default;

if (entry.IsSnapshot)
{
    var jsonStr = await entry.GetReader().ReadStringAsync(DotNext.IO.LengthFormat.PlainLittleEndian, new DotNext.Text.DecodingContext(Encoding.UTF8, true));

    value = JsonSerializer.Deserialize<ApplicationStateSnapshot>(jsonStr);
}
else
{
    value = await entry.DeserializeFromJsonAsync() as EntryBase;
}

Now there are two scenarios:
If one node in a cluster size = 1 becomes leader and writes entries to it's log, a second node joins the cluster by utilizing AddMember on the leader, the log's between the nodes replicate fine.

However, if one node in a cluster size = 1 becomes leader, writes entries to it's log to the point of causing a snapshot to be created, and THEN a second node joins the cluster by utilizing AddMember on the leader, then the following error appears on the newly joined node inside the RaftMemoryBasedStateMachine : MemoryBasedStateMachine ApplyAsync method when an entry has IsSnapshot = false and my code tries to execute await entry.DeserializeFromJsonAsync() as EntryBase;. It errors out with

System.IO.FileNotFoundException: Could not load file or assembly 'YASP☻, Culture=neutral, PublicKeyToken=null'. Das System kann die angegebene Datei nicht finden.
      File name: 'YASP☻, Culture=neutral, PublicKeyToken=null'
         at System.RuntimeTypeHandle.GetTypeByName(String name, Boolean throwOnError, Boolean ignoreCase, StackCrawlMarkHandle stackMark, ObjectHandleOnStack assemblyLoadContext, ObjectHandleOnStack type, ObjectHandleOnStack keepalive)
         at System.RuntimeTypeHandle.GetTypeByName(String name, Boolean throwOnError, Boolean ignoreCase, StackCrawlMark& stackMark, AssemblyLoadContext assemblyLoadContext)
         at System.RuntimeType.GetType(String typeName, Boolean throwOnError, Boolean ignoreCase, StackCrawlMark& stackMark)
         at System.Type.GetType(String typeName, Boolean throwOnError)
         at DotNext.Net.Cluster.Consensus.Raft.JsonLogEntry.LoadType(String typeId, Func`2 typeLoader) in /_/src/cluster/DotNext.Net.Cluster/Net/Cluster/Consensus/Raft/JsonLogEntry.cs:line 19
         at DotNext.Net.Cluster.Consensus.Raft.JsonLogEntry.Deserialize(SequenceReader input, Func`2 typeLoader, JsonSerializerOptions options) in /_/src/cluster/DotNext.Net.Cluster/Net/Cluster/Consensus/Raft/JsonLogEntry.cs:line 77
         at DotNext.Net.Cluster.Consensus.Raft.PersistentState.LogEntry.DeserializeSlowAsync(Func`2 typeLoader, JsonSerializerOptions options, CancellationToken token) in /_/src/cluster/DotNext.Net.Cluster/Net/Cluster/Consensus/Raft/PersistentState.LogEntry.cs:line 247
         at YASP.Server.Application.Clustering.Raft.RaftMemoryBasedStateMachine.<>c__DisplayClass14_0.<<ApplyAsync>b__2>d.MoveNext() in G:\Dev\Personal_Private\YASP\src\YASP.Server.Application\Clustering\Raft\RaftMemoryBasedStateMachine.cs:line 80

Das System kann die angegebene Datei nicht finden. means The System cannot find the specified file. As you can see, the string it is trying to load is not correct (as my assemblies name surely does not contain a smiley) Could not load file or assembly 'YASP☻, Culture=neutral, PublicKeyToken=null'.

I am really confused about what I'm doing wrong. I tried to look at an older discussion about a similiar topic, however sadly the library seems to have changed a bit since then and the example is not applicable 1-to-1 anymore.

I'd be really glad if you were able to push me into a direction!

Thank you very much in advance!

[sakno]

Hi @RyanTT , there is a known issue with snapshot building process in some circumstances. I've fixed this yesterday. Could you please test your code using develop branch?

[RyanTT]

Thank you for your quick response!

I have downloaded the latest develop branch and tried the exact same scenario again but with your newer codebase and it seems to work flawlessly. I will notify you if any (de)serialization issues arise again. Tyvm!

PS: Do you plan on providing a development nuget package or a beta/alpha nuget package through nuget.org any time soon? And if not, is there a rough estimate when a new nuget version will be provided?

[sakno]

Estimated time-to-marked is the end of this month.