List Subjects for a Specific Stream (C# .NET V2)

List Subjects for a Specific Stream in JetStream

All clients have a way to get the list of subjects for any given stream, except it’s not completely obvious how to do this. These examples will show you how to get the list of subjects.

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$ nbe run jetstream/list-subjects/dotnet2

View the source code or learn how to run this example yourself

Code

Install NuGet packages NATS.Net and Microsoft.Extensions.Logging.Console.

using NATS.Client.Core;
using NATS.Client.JetStream;
using NATS.Client.JetStream.Models;

NATS_URL environment variable can be used to pass the locations of the NATS servers.

var url = Environment.GetEnvironmentVariable("NATS_URL") ?? "127.0.0.1:4222";

Connect to NATS server. Since connection is disposable at the end of our scope we should flush our buffers and close connection cleanly.

var opts = new NatsOpts
{
    Url = url,
    Name = "NATS-by-Example",
};
await using var nats = new NatsConnection(opts);
var js = new NatsJSContext(nats);

Stream Setup

var stream = "list-subjects";

Remove the stream first!, so we have a clean starting point.

try
{
    await js.DeleteStreamAsync(stream);
}
catch (NatsJSApiException e) when (e is { Error.Code: 404 })
{
}

Create the stream with a variety of subjects

var streamConfig = new StreamConfig(stream, ["plain", "greater.>", "star.*"])
{
    Storage = StreamConfigStorage.Memory,
};
await js.CreateStreamAsync(streamConfig);

GetStreamAsync with StreamInfoRequest

You can get the subjects of a stream via the GetStreamAsync call. Since this is “state” a subject is not in the state unless there are messages in the subject. To get the subjects map, you must provide a SubjectsFilter Use the > to filter for all subjects

var jsStream = await js.GetStreamAsync(stream, new StreamInfoRequest() { SubjectsFilter = ">" });
Console.WriteLine($"Before publishing any messages, there are 0 subjects: {jsStream.Info.State.Subjects?.Count}");

Publish a message

await js.PublishAsync("plain", "plain-data");

Stream Info contains State, which contains a map, Subjects, of subjects to their count but the server only collects and returns that information if StreamInfoRequest is present with a non-empty subject filter. To get all subjects, set the filter to >

jsStream = await js.GetStreamAsync(stream, new StreamInfoRequest() { SubjectsFilter = ">" });
Console.WriteLine("After publishing a message to a subject, it appears in state:");
if (jsStream.Info.State.Subjects != null)
{
    foreach (var (subject, count) in jsStream.Info.State.Subjects)
    {
        Console.WriteLine($"  Subject '{subject}' has {count} message(s)");
    }
}

Publish some more messages, this time against wildcard subjects

await js.PublishAsync("greater.A", "gtA-1");
await js.PublishAsync("greater.A", "gtA-2");
await js.PublishAsync("greater.A.B", "gtAB-1");
await js.PublishAsync("greater.A.B", "gtAB-2");
await js.PublishAsync("greater.A.B.C", "gtABC");
await js.PublishAsync("greater.B.B.B", "gtBBB");
await js.PublishAsync("star.1", "star1-1");
await js.PublishAsync("star.1", "star1-2");
await js.PublishAsync("star.2", "star2");


jsStream = await js.GetStreamAsync(stream, new StreamInfoRequest() { SubjectsFilter = ">" });
Console.WriteLine("Wildcard subjects show the actual subject, not the template:");
if (jsStream.Info.State.Subjects != null)
{
    foreach (var (subject, count) in jsStream.Info.State.Subjects)
    {
        Console.WriteLine($"  Subject '{subject}' has {count} message(s)");
    }
}

Specific Subject Filtering

You can filter for a more specific subject

jsStream = await js.GetStreamAsync(stream, new StreamInfoRequest() { SubjectsFilter = "greater.>" });
Console.WriteLine("Filtering the subject returns only matching entries ['greater.>']");
if (jsStream.Info.State.Subjects != null)
{
    foreach (var (subject, count) in jsStream.Info.State.Subjects)
    {
        Console.WriteLine($"  Subject '{subject}' has {count} message(s)");
    }
}


jsStream = await js.GetStreamAsync(stream, new StreamInfoRequest() { SubjectsFilter = "greater.A.>" });
Console.WriteLine("Filtering the subject returns only matching entries ['greater.A.>']");
if (jsStream.Info.State.Subjects != null)
{
    foreach (var (subject, count) in jsStream.Info.State.Subjects)
    {
        Console.WriteLine($"  Subject '{subject}' has {count} message(s)");
    }
}

Output

Before publishing any messages, there are 0 subjects: 
After publishing a message to a subject, it appears in state:
  Subject 'plain' has 1 message(s)
Wildcard subjects show the actual subject, not the template:
  Subject 'greater.A' has 2 message(s)
  Subject 'greater.A.B' has 2 message(s)
  Subject 'greater.A.B.C' has 1 message(s)
  Subject 'greater.B.B.B' has 1 message(s)
  Subject 'plain' has 1 message(s)
  Subject 'star.1' has 2 message(s)
  Subject 'star.2' has 1 message(s)
Filtering the subject returns only matching entries ['greater.>']
  Subject 'greater.A' has 2 message(s)
  Subject 'greater.A.B' has 2 message(s)
  Subject 'greater.A.B.C' has 1 message(s)
  Subject 'greater.B.B.B' has 1 message(s)
Filtering the subject returns only matching entries ['greater.A.>']
  Subject 'greater.A.B' has 2 message(s)
  Subject 'greater.A.B.C' has 1 message(s)

Recording

Note, playback is half speed to make it a bit easier to follow.