Consumer Fetch isn't throwing exception when 409 Exceeded MaxRequestBatch message received

[mtmk]

Observed behavior

// Install NuGet packages `NATS.Net` and `Microsoft.Extensions.Logging.Console`.
using Microsoft.Extensions.Logging;
using NATS.Client.Core;
using NATS.Client.JetStream;
using NATS.Client.JetStream.Models;

using var loggerFactory = LoggerFactory.Create(builder => builder.AddConsole());
await using var nats = new NatsConnection(new NatsOpts { LoggerFactory = loggerFactory });
var js = new NatsJSContext(nats);

var stream = await js.CreateStreamAsync(new StreamConfig("EVENTS", new[] { "events.>" }));

var consumer = await stream.CreateConsumerAsync(new ConsumerConfig("processor") { MaxBatch = 2 });

await foreach (var msg in consumer.FetchAsync<string>(opts: new NatsJSFetchOpts
               {
	               MaxMsgs = 10,
	               NotificationHandler = (notification, token) =>
	               {
		               Console.WriteLine($">>>> {notification.Name}");
		               return Task.CompletedTask;
	               }
               }))
{
}

Output:

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 = NCPYXNOZUU7QDMTVSD6CCLIHR7V2NZN27KIIRACGBPAK6K5EUI5LX46X, Name = NCPYXNOZUU7QDMTVSD6CCLIHR7V2NZN27KIIRACGBPAK6K5EUI5LX46X, Version = 2.10.5, ProtocolVersion = 1, GitCommit = 0883d32, GoVersion = go1.21.4, Host = 0.0.0.0, Port = 4222, HeadersSupported = True, AuthRequired = False, TlsRequired = False, TlsVerify = False, TlsAvailable = False, MaxPayload = 1048576, JetStreamAvailable = True, ClientId = 11, ClientIp = ::1, Nonce = , Cluster = , ClusterDynamic = False, ClientConnectUrls = , WebSocketConnectUrls = , LameDuckMode = False }
info: NATS.Client.Core.NatsConnection[1001]
      Connect succeed NATS .Net Client, NATS nats://localhost:4222
warn: NATS.Client.JetStream.Internal.NatsJSFetch[2005]
      Unhandled protocol message: 409 Exceeded MaxRequestBatch of 2
>>>> Timeout
info: NATS.Client.Core.NatsConnection[1001]
      Disposing connection NATS .Net Client

Expected behavior

consumer.FetchAsync() to throw exception and maybe a notification.

Server and client version

client: 2.0.0
server: 2.10.5

[mtmk]

Also other codes to consider:

• 409 Exceeded MaxRequestExpires of 1s
• 409 Exceeded MaxWaiting
• 409 Exceeded MaxRequestMaxBytes of 3
• 409 Exceeded MaxRequestBatch of 2

Maybe all 409s?

edit: not all 409s are terminal e.g. 409 Server Shutdown

Any thing starts with Exceeded Max:

➜  nats-server git:(release/v2.10.5) grep -e 'sendErr.*Exceeded Max' server/consumer.go
                sendErr(409, fmt.Sprintf("Exceeded MaxRequestBatch of %d", o.cfg.MaxRequestBatch))
                sendErr(409, fmt.Sprintf("Exceeded MaxRequestExpires of %v", o.cfg.MaxRequestExpires))
                sendErr(409, fmt.Sprintf("Exceeded MaxRequestMaxBytes of %v", o.cfg.MaxRequestMaxBytes))
                sendErr(409, "Exceeded MaxWaiting")