I can’t send objects to stream, it gives an error.

[oneprofittips]

I have this piece of code, and it works if I pass an int string, but if I start passing objects, then an error occurs.

using NATS.Client.Core;
using NATS.Client.Hosting;

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddNats();

var app = builder.Build();

app.MapGet("/subscribe", (INatsConnection command, CancellationToken ct) =>
{
    _ = Task.Run(async () =>
    {
        await foreach (var msg in command.SubscribeAsync<object>("foo"))
        {
            Console.WriteLine($"Recived: {msg.Data}");
        }
    });

    return Task.CompletedTask;
});

app.MapGet("/publish", async (INatsConnection command) =>
    {
        try
        {
            var t = new Test();
            await command.PublishAsync<object>("foo", t);
            Console.WriteLine($"Publish: {t}");

        }catch (Exception ex)
        {
            Console.WriteLine(ex.ToString());
        }
    }
);

app.Run();

public class Test
{
    public string Id {  get; set; }
    public Test()
    {
        Id = Guid.NewGuid().ToString("N");
    }
    public override string ToString()
    {
        return $"{Id}";
    }
}

I get this error

info: NATS.Client.Core.NatsConnection[1001]
      Try to connect NATS nats://localhost:4222
info: NATS.Client.Core.Internal.NatsReadProtocolProcessor[1005]
      Received server info: ServerInfo { Id = NAAT6SWIJVMB6RYFT6VN54KAA3APNDC5KYRNXBLQZGGEFMXDI5N3IWKJ, Name = NAAT6SWIJVMB6RYFT6VN54KAA3APNDC5KYRNXBLQZGGEFMXDI5N3IWKJ, Version = 2.10.3, ProtocolVersion = 1, GitCommit = 1528434, GoVersion = go1.21.3, Host = 0.0.0.0, Port = 4222, HeadersSupported = True, AuthRequired = False, TlsRequired = False, TlsVerify = False, TlsAvailable = False, MaxPayload = 1048576, JetStreamAvailable = True, ClientId = 5, ClientIp = 172.19.0.1, Nonce = , Cluster = , ClusterDynamic = False, ClientConnectUrls = , WebSocketConnectUrls = , LameDuckMode = False }
info: NATS.Client.Core.NatsConnection[1001]
      Connect succeed NATS .Net Client, NATS nats://localhost:4222
Publish: d8010b89c4d34fa6b0624f2be36e2acb
fail: NATS.Client.Core.Internal.NatsPipeliningWriteProtocolProcessor[0]
      Internal error occured on WriteLoop.
      NATS.Client.Core.NatsException: Can't serialize System.Object
         at NATS.Client.Core.NatsUtf8PrimitivesSerializer`1.Serialize(IBufferWriter`1 bufferWriter, T value)
         at NATS.Client.Core.NatsRawSerializer`1.Serialize(IBufferWriter`1 bufferWriter, T value)
         at NATS.Client.Core.Commands.ProtocolWriter.WritePublish[T](String subject, String replyTo, NatsHeaders headers, T value, INatsSerialize`1 serializer)
         at NATS.Client.Core.Commands.PublishCommand`1.Write(ProtocolWriter writer)
         at NATS.Client.Core.Internal.NatsPipeliningWriteProtocolProcessor.WriteLoopAsync()

What am I doing wrong?

[mtmk]

By default AOT friendly serializers are used so it won't work with custom objects. You need define contexts for your objects or use JSON serializer with reflection:

Add this Nuget package first:

$ dotnet add package NATS.Client.Serializers.Json

then change the default serializer:

var natsOpts = NatsOpts.Default with { SerializerRegistry = NatsJsonSerializerRegistry.Default };

await using var nats = new NatsConnection(natsOpts);

see also https://nats-io.github.io/nats.net.v2/documentation/serialization.html#using-json-serialization-with-reflection

[mtmk]

I haven't tried it but I think you can pass opts to builder.Services.AddNats(). did explanation above solved the issue?