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NATS - .NET C# Client

A C# .NET client for the NATS messaging system multi targetting .NET4.6+ and .NETStandard1.6.

This NATS Maintainer supported client parallels the NATS GO Client.

License Apache 2.0 API Documentation Build Status NuGet

Getting started

The easiest and recommended way to start using NATS in your .NET projects, is to use the NuGet package. For examples on how to use the client, see below or in any of the included sample projects.

Get up and running with the source code

First, download the source code:

git clone

Project files

The repository contains several projects, all located under src\

  • NATS - The NATS.Client assembly
  • Tests
    • IntegrationTests - XUnit tests, verifying the client integration with nats-server.exe (ensure you have nats-server.exe in your path to run these).
    • UnitTests - XUnit tests that requires no dependencies
  • Samples
    • Publish Subscribe
      • Publish - A sample publisher.
      • Subscribe - A sample subscriber.
    • QueueGroup - An example queue group subscriber.
    • Request Reply
      • Requestor - A requestor sample.
      • Replier - A sample replier for the Requestor application.

All examples provide statistics for benchmarking.


.NET Core SDK style projects are used, so ensure your environment (command line, VSCode, Visual Studio, etc) supports the targetted .NET Core SDK in src\global.json as well as .NET Framework 4.6 or greater.

Visual Studio

The recommendation is to load src\NATS.sln into Visual Studio 2019 (Visual Studio 2017 works as well). .NET Core SDK style projects are used to multitarget different frameworks, so when working with the source code (debugging, running tets etc) you might need to mind the "context" of the current framework.

XML documentation is generated (in Release), so code completion, context help, etc, will be available in the editor.

Command line

Since .NET Core SDK style projects are used, you can use the .NET SDK to build, run tests, pack etc.

E.g. to build:

dotnet build src\NATS.sln -c Release

This will build the respective NATS.Client.dll, examples etc in Release mode, with only requiring the .NET Core SDK and the .NET Platform.

Building the API Documentation

Doxygen is used for building the API documentation. To build the API documentation, change directories to documentation and run the following command:


Doxygen will build the NATS .NET Client API documentation, placing it in the documentation\NATS.Client\html directory. Doxygen is required to be installed and in the PATH. Version 1.8 is known to work.

Current API Documentation

Version Notes

Version 1.0.1 Consumer Create

This release by default will use a new JetStream consumer create API when interacting with nats-server version 2.9.0 or higher. This changes the subjects used by the client to create consumers, which might in some cases require changes in access and import/export configuration. The developer can opt out of using this feature by using a custom JetStreamOptions and using it when creating JetStream, Key Value and Object Store regular and management contexts.

JetStreamOptions jso = JetStreamOptions.Builder().WithOptOut290ConsumerCreate(true).Build();

IJetStream js = connection.CreateJetStreamContext(jso);
IJetStreamManagement jsm = connection.CreateJetStreamManagementContext(jso);
IKeyValue kv = connection.CreateKeyValueContext("bucket", KeyValueOptions.Builder(jso).Build());
IKeyValueManagement kvm = connection.CreateKeyValueManagementContext(KeyValueOptions.Builder(jso).Build());
IObjectStore os = connection.CreateObjectStoreContext("bucket", ObjectStoreOptions.Builder(jso).Build());
IObjectStoreManagement osm = connection.CreateObjectStoreManagementContext(ObjectStoreOptions.Builder(jso).Build());

Basic Usage

NATS .NET C# Client uses interfaces to reference most NATS client objects, and delegates for all types of events.

Creating a NATS .NET Application

First, reference the NATS.Client assembly so you can use it in your code. Be sure to add a reference in your project or if compiling via command line, compile with the /r:NATS.Client.DLL parameter. While the NATS client is written in C#, any .NET langage can use it.

Below is some code demonstrating basic API usage. Note that this is example code, not functional as a whole (e.g. requests will fail without a subscriber to reply).

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

// Reference the NATS client.
using NATS.Client;

Here are example snippets of using the API to create a connection, subscribe, publish, and request data.

            // Create a new connection factory to create
            // a connection.
            ConnectionFactory cf = new ConnectionFactory();

            // Creates a live connection to the default
            // NATS Server running locally
            IConnection c = cf.CreateConnection();

            // Setup an event handler to process incoming messages.
            // An anonymous delegate function is used for brevity.
            EventHandler<MsgHandlerEventArgs> h = (sender, args) =>
                // print the message

                // Here are some of the accessible properties from
                // the message:
                // args.Message.Data;
                // args.Message.Reply;
                // args.Message.Subject;
                // args.Message.ArrivalSubcription.Subject;
                // args.Message.ArrivalSubcription.QueuedMessageCount;
                // args.Message.ArrivalSubcription.Queue;

                // Unsubscribing from within the delegate function is supported.

            // The simple way to create an asynchronous subscriber
            // is to simply pass the event in.  Messages will start
            // arriving immediately.
            IAsyncSubscription s = c.SubscribeAsync("foo", h);

            // Alternatively, create an asynchronous subscriber on subject foo,
            // assign a message handler, then start the subscriber.   When
            // multicasting delegates, this allows all message handlers
            // to be setup before messages start arriving.
            IAsyncSubscription sAsync = c.SubscribeAsync("foo");
            sAsync.MessageHandler += h;

            // Simple synchronous subscriber
            ISyncSubscription sSync = c.SubscribeSync("foo");

            // Using a synchronous subscriber, gets the first message available,
            // waiting up to 1000 milliseconds (1 second)
            Msg m = sSync.NextMessage(1000);

            c.Publish("foo", Encoding.UTF8.GetBytes("hello world"));

            // Unsubscribing

            // Publish requests to the given reply subject:
            c.Publish("foo", "bar", Encoding.UTF8.GetBytes("help!"));

            // Sends a request (internally creates an inbox) and Auto-Unsubscribe the
            // internal subscriber, which means that the subscriber is unsubscribed
            // when receiving the first response from potentially many repliers.
            // This call will wait for the reply for up to 1000 milliseconds (1 second).
            m = c.Request("foo", Encoding.UTF8.GetBytes("help"), 1000);

            // Draining and closing a connection

            // Closing a connection

RX Usage

Importing the namespace NATS.Client.Rx you will be able to use an extension method connection.Observe(subject) to turn the connection to an observable. If you have a more advanced IAsyncSubscription, you can use asyncSubscription.ToObservable().

You can now import the namespace NATS.Client.Rx.Ops. After this you get builtin support for:

  • Subscribe
  • SubscribeSafe (will not fail an observer if it misbehaves)
  • Where
  • Select

If you want, you could instead take an external dependency on System.Reactive and use that instead of NATS.RX.Ops.

using System;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using NATS.Client;
using NATS.Client.Rx;
using NATS.Client.Rx.Ops; //Can be replaced with using System.Reactive.Linq;

namespace RxSample
    class Program
        static void Main(string[] args)
            using (var cn = new ConnectionFactory().CreateConnection())
                var temperatures =
                        .Where(m => m.Data?.Any() == true)
                        .Select(m => BitConverter.ToInt32(m.Data, 0));

                temperatures.Subscribe(t => Console.WriteLine($"{t}C"));

                temperatures.Subscribe(t => Console.WriteLine($"{(t * 9 / 5) + 32}F"));

                var cts = new CancellationTokenSource();

                Task.Run(async () =>
                    var rnd = new Random();

                    while (!cts.IsCancellationRequested)
                        cn.Publish("temperatures", BitConverter.GetBytes(rnd.Next(-10, 40)));

                        await Task.Delay(1000, cts.Token);
                }, cts.Token);


Basic Encoded Usage

The .NET NATS client mirrors go encoding through serialization and deserialization. Simply create an encoded connection and publish objects, and receive objects through an asynchronous subscription using the encoded message event handler. The .NET 4.6 client has a default formatter serializing objects using the BinaryFormatter, but methods used to serialize and deserialize objects can be overridden. The NATS core version does not have serialization defaults and they must be specified.

        using (IEncodedConnection c = new ConnectionFactory().CreateEncodedConnection())
            EventHandler<EncodedMessageEventArgs> eh = (sender, args) =>
                // Here, obj is an instance of the object published to
                // this subscriber.  Retrieve it through the
                // ReceivedObject property of the arguments.
                MyObject obj = (MyObject)args.ReceivedObject;

                System.Console.WriteLine("Company: " + obj.Company);

            // Subscribe using the encoded message event handler
            IAsyncSubscription s = c.SubscribeAsync("foo", eh);

            MyObject obj = new MyObject();
            obj.Company = "MyCompany";

            // To publish an instance of your object, simply
            // call the IEncodedConnection publish API and pass
            // your object.
            c.Publish("foo", obj);

Other Types of Serialization

Optionally, one can override serialization. Depending on the level of support or third party packages used, objects can be serialized to JSON, SOAP, or a custom scheme. XML was chosen as the example here as it is natively supported by .NET 4.6.

        // Example XML serialization.
        byte[] serializeToXML(Object obj)
            MemoryStream  ms = new MemoryStream();
            XmlSerializer x = new XmlSerializer(((SerializationTestObj)obj).GetType());

            x.Serialize(ms, obj);

            byte[] content = new byte[ms.Position];
            Array.Copy(ms.GetBuffer(), content, ms.Position);

            return content;

        Object deserializeFromXML(byte[] data)
            XmlSerializer x = new XmlSerializer(new SerializationTestObj().GetType());
            MemoryStream ms = new MemoryStream(data);
            return x.Deserialize(ms);


        // Create an encoded connection and override the OnSerialize and
        // OnDeserialize delegates.
        IEncodedConnection c = new ConnectionFactory().CreateEncodedConnection();
        c.OnDeserialize = deserializeFromXML;
        c.OnSerialize = serializeToXML;

        // From here on, the connection will use the custom delegates
        // for serialization.

One can also use Data Contract to serialize objects. Below are simple example overrides that work with .NET core:

public class JsonObject
    public string Value = "";

internal object jsonDeserializer(byte[] buffer)
    using (MemoryStream stream = new MemoryStream())
        var serializer = new DataContractJsonSerializer(typeof(JsonObject));
        stream.Write(buffer, 0, buffer.Length);
        stream.Position = 0;
        return serializer.ReadObject(stream);

internal byte[] jsonSerializer(object obj)
    if (obj == null)
        return null;

    var serializer = new DataContractJsonSerializer(typeof(JsonObject));

    using (MemoryStream stream = new MemoryStream())
        serializer.WriteObject(stream, obj);
        return stream.ToArray();


// Create an encoded connection and override the OnSerialize and
// OnDeserialize delegates.
IEncodedConnection c = new ConnectionFactory().CreateEncodedConnection();
c.OnDeserialize = jsonDeserializer;
c.OnSerialize = jsonSerializer;

// From here on, the connection will use the custom delegates
// for serialization.

Wildcard Subscriptions

The * wildcard matches any token, at any level of the subject:

IAsyncSubscription s = c.SubscribeAsync("foo.*.baz");

This subscriber would receive messages sent to:

  • foo.a.baz
  • etc...

It would not, however, receive messages on:

  • foo.baz
  • etc...

The > wildcard matches any length of the tail of a subject, and can only be the last token.

IAsyncSubscription s = c.SubscribeAsync("foo.>");

This subscriber would receive any message sent to:

  • etc...

However, it would not receive messages sent on:

  • foo
  • etc...

Publishing on this subject would cause the two above subscriber to receive the message:

c.Publish("", null);

Queue Groups

All subscriptions with the same queue name will form a queue group. Each message will be delivered to only one subscriber per queue group, using queue sematics. You can have as many queue groups as you wish. Normal subscribers will continue to work as expected.

ISyncSubscription s1 = c.SubscribeSync("foo", "job_workers");


IAsyncSubscription s = c.SubscribeAsync("foo", "job_workers", myHandler);

To unsubscribe, call the ISubscriber Unsubscribe method:


When finished with NATS, close the connection.


Advanced Usage

Connection and Subscriber objects implement IDisposable and can be created in a using statement. Here is all the code required to connect to a default server, receive ten messages, and clean up, unsubcribing and closing the connection when finished.

            using (IConnection c = new ConnectionFactory().CreateConnection())
                using (ISyncSubscription s = c.SubscribeSync("foo"))
                    for (int i = 0; i < 10; i++)
                        Msg m = s.NextMessage();
                        System.Console.WriteLine("Received: " + m);

Or to publish ten messages:

            using (IConnection c = new ConnectionFactory().CreateConnection())
                for (int i = 0; i < 10; i++)
                    c.Publish("foo", Encoding.UTF8.GetBytes("hello"));

Flush a connection to the server - this call returns when all messages have been processed. Optionally, a timeout in milliseconds can be passed.



Setup a subscriber to auto-unsubscribe after ten messsages.

        IAsyncSubscription s = c.SubscribeAsync("foo");
        s.MessageHandler += (sender, args) =>
           Console.WriteLine("Received: " + args.Message);


Note that an anonymous function was used. This is for brevity here - in practice, delegate functions can be used as well.

Other events can be assigned delegate methods through the options object.

            Options opts = ConnectionFactory.GetDefaultOptions();

            opts.AsyncErrorEventHandler += (sender, args) =>
                Console.WriteLine("Error: ");
                Console.WriteLine("   Server: " + args.Conn.ConnectedUrl);
                Console.WriteLine("   Message: " + args.Error);
                Console.WriteLine("   Subject: " + args.Subscription.Subject);

            opts.ServerDiscoveredEventHandler += (sender, args) =>
                Console.WriteLine("A new server has joined the cluster:");
                Console.WriteLine("    " + String.Join(", ", args.Conn.DiscoveredServers));

            opts.ClosedEventHandler += (sender, args) =>
                Console.WriteLine("Connection Closed: ");
                Console.WriteLine("   Server: " + args.Conn.ConnectedUrl);

            opts.DisconnectedEventHandler += (sender, args) =>
                Console.WriteLine("Connection Disconnected: ");
                Console.WriteLine("   Server: " + args.Conn.ConnectedUrl);

            IConnection c = new ConnectionFactory().CreateConnection(opts);

After version 0.5.0, the C# .NET client supports async Requests.

public async void MyRequestDataMethod(IConnection c)
    var m = await c.RequestAsync("foo", null);

    m = c.RequestAsync("foo", null);
    // do some work
    await m;

    // cancellation tokens are supported.
    var cts = new CancellationTokenSource();

    var msg = c.RequestAsync("foo", null, cts.Token);
    // do stuff
    if (requestIsNowIrrevelant())

    await msg;
    // be sure to handle OperationCancelled Exception.

The NATS .NET client supports the cluster discovery protocol. The list of servers known to a connection is automatically updated when a connection is established, and afterword in realtime as cluster changes occur. A current list of known servers in a cluster can be obtained using the IConnection.Servers property; this list will be used if the client needs to reconnect to the cluster.

Clustered Usage

            string[] servers = new string[] {

            Options opts = ConnectionFactory.GetDefaultOptions();
            opts.MaxReconnect = 2;
            opts.ReconnectWait = 1000;
            opts.Servers = servers;

            IConnection c = new ConnectionFactory().CreateConnection(opts);


The NATS .NET client supports TLS 1.2. Set the secure option, add the certificate, and connect. Note that .NET requires both the private key and certificate to be present in the same certificate file.

In addition to the code found here, please refer to the sample code at TlsVariationsExample

        Options opts = ConnectionFactory.GetDefaultOptions();
        opts.Secure = true;

        // .NET requires the private key and cert in the
        //  same file. 'client.pfx' is generated from:
        // openssl pkcs12 -export -out client.pfx
        //    -inkey client-key.pem -in client-cert.pem
        X509Certificate2 cert = new X509Certificate2("client.pfx", "password");


        // Some connections like those with OCSP 
        // require CheckCertificateRevocation
        opts.CheckCertificateRevocation = true;
        IConnection c = new ConnectionFactory().CreateConnection(opts);

Many times, it is useful when developing an application (or necessary when using self-signed certificates) to override server certificate validation. This is achieved by overriding the remove certificate validation callback through the NATS client options.

    private bool verifyServerCert(object sender,
        X509Certificate certificate, X509Chain chain,
                SslPolicyErrors sslPolicyErrors)
            if (sslPolicyErrors == SslPolicyErrors.None)
                return true;

            // Do what is necessary to achieve the level of
            // security you need given a policy error.


        Options opts = ConnectionFactory.GetDefaultOptions();
        opts.Secure = true;
        opts.TLSRemoteCertificationValidationCallback = verifyServerCert;

        IConnection c = new ConnectionFactory().CreateConnection(opts);

The NATS server default cipher suites may not be supported by the Microsoft .NET framework. Please refer to nats-server --help_tls usage and configure the NATS server to include the most secure cipher suites supported by the .NET framework.

NATS 2.0 Authentication (Nkeys and User Credentials)

This requires server with version >= 2.0.0

NATS servers have a new security and authentication mechanism to authenticate with user credentials and Nkeys. The simplest form is to use the helper method UserCredentials(credsFilepath).

IConnection c = new ConnectionFactory().CreateConnection("nats://", "user.creds")

The helper methods creates two callback handlers to present the user JWT and sign the nonce challenge from the server. The core client library never has direct access to your private key and simply performs the callback for signing the server challenge. The helper will load and wipe and erase memory it uses for each connect or reconnect.

The helper also can take two entries, one for the JWT and one for the NKey seed file.

IConnection c = new ConnectionFactory().CreateConnection("nats://", "user.jwt", "user.nk");

You can also set the event handlers directly and manage challenge signing directly.

EventHandler<UserJWTEventArgs> jwtEh = (sender, args) =>
    // Obtain a user JWT...
    string jwt = getMyUserJWT();

    // You must set the JWT in the args to hand off
    // to the client library.
    args.JWT = jwt;

EventHandler<UserSignatureEventArgs> sigEh = (sender, args) =>
    // get a private key seed from your environment.
    string seed = getMyUserSeed();

    // Generate a NkeyPair
    NkeyPair kp = NKeys.FromSeed(seed);

    // Sign the nonce and return the result in the SignedNonce
    // args property.  This must be set.
    args.SignedNonce = kp.Sign(args.ServerNonce)
Options opts = ConnectionFactory.GetDefaultOptions();
opts.SetUserCredentialHandlers(jwtEh, sigEh);

IConnection c = new ConnectionFactory().CreateConnection(opts));

Bare Nkeys are also supported. The nkey seed should be in a read only file, e.g. seed.txt

> cat seed.txt

This is a helper function which will load and decode and do the proper signing for the server nonce. It will clear memory in between invocations. You can choose to use the low level option and provide the public key and a signature callback on your own.

Options opts = ConnectionFactory.GetDefaultOptions();

// Direct
IConnection c = new ConnectionFactory().CreateConnection(opts));

Message Headers

The NATS.Client version 0.11.0 and NATS server version 2.2 support message headers. Message headers are represented as a string name value pair just as HTTP headers are.

Setting Message Headers

IConnection c = new new ConnectionFactory().CreateConnection();

Msg m = new Msg();
m.Header["Content-Type"] = "json";
m.Subject = "foo";

Getting Message Headers

IConnection c = new new ConnectionFactory().CreateConnection();
var s = c.SubscribeSync("foo")

Msg m = s.NextMessage();
string contentType = m.Header["Content-Type"];


The NATS .NET client can throw the following exceptions:

  • NATSException - The generic NATS exception, and base class for all other NATS exception.
  • NATSConnectionException - The exception that is thrown when there is a connection error.
  • NATSProtocolException - This exception that is thrown when there is an internal error with the NATS protocol.
  • NATSNoServersException - The exception that is thrown when a connection cannot be made to any server.
  • NATSSecureConnRequiredException - The exception that is thrown when a secure connection is required.
  • NATSConnectionClosedException - The exception that is thrown when an operation is performed on a connection that is closed.
  • NATSSlowConsumerException - The exception that is thrown when a consumer (subscription) is slow.
  • NATSStaleConnectionException - The exception that is thrown when an operation occurs on a connection that has been determined to be stale.
  • NATSMaxPayloadException - The exception that is thrown when a message payload exceeds what the maximum configured.
  • NATSBadSubscriptionException - The exception that is thrown when a subscriber operation is performed on an invalid subscriber.
  • NATSTimeoutException - The exception that is thrown when a NATS operation times out.


Publishing and subscribing to JetStream enabled servers is straightforward. A JetStream enabled application will connect to a server, establish a JetStream context, and then publish or subscribe. This can be mixed and matched with standard NATS subject, and JetStream subscribers, depending on configuration, receive messages from both streams and directly from other NATS producers.

The JetStream Context

After establishing a connection as described above, create a JetStream Context.

IJetStream js = c.CreateJetStreamContext();

You can pass options to configure the JetStream client, although the defaults should suffice for most users. See the JetStreamOptions class.

There is no limit to the number of contexts used, although normally one would only require a single context. Contexts may be prefixed to be used in conjunction with NATS authorization.


To publish messages, use the IJetStream.Publish(...) API. A stream must be established before publishing. You can publish in either a synchronous or asynchronous manner.


       // create a typical NATS message
       Msg msg = new Msg("foo", Encoding.UTF8.GetBytes("hello"));
       PublishAck pa = js.Publish(msg);

See JetStreamPublish in the JetStream samples for a detailed and runnable sample.

If there is a problem an exception will be thrown, and the message may not have been persisted. Otherwise, the stream name and sequence number is returned in the publish acknowledgement.

There are a variety of publish options that can be set when publishing. When duplicate checking has been enabled on the stream, a message ID should be set. One set of options are expectations. You can set a publish expectation such as a particular stream name, previous message ID, or previous sequence number. These are hints to the server that it should reject messages where these are not met, primarily for enforcing your ordering or ensuring messages are not stored on the wrong stream.

The PublishOptions are immutable, but the builder can be re-used for expectations by clearing the expected.

For example:

      PublishOptions.PublishOptionsBuilder builder = PublishOptions.Builder()

      PublishAck pa = js.Publish("foo", null, builder.Build());
      pa = js.Publish("foo", null,;

See JetStreamPublishWithOptionsUseCases in the JetStream samples for a detailed and runnable sample.


      IList<Task<PublishAck>> tasks = new new List<Task<PublishAck>>();
      for (int x = 1; x < roundCount; x++) {
          // create a typical NATS message
          Msg msg = new Msg("foo", Encoding.UTF8.GetBytes("hello"));

          // Publish a message

     foreach (Task<PublishAck> task in tasks) {
         ... process the task

See the JetStreamPublishAsync in the JetStream samples for a detailed and runnable sample.

ReplyTo When Publishing

The Message object allows you to set a replyTo, but in publish requests, the replyTo is reserved for internal use as the address for the server to respond to the client with the PublishAck.


There are three methods of subscribing, Push Async, Push Sync and Pull with each variety having its own set of options and abilities.

Push subscriptions can be synchronous or asynchronous. The server pushes messages to the client.

Push Async Subscribing

        void MyHandler(object sender, MsgHandlerEventArgs args)
            // Process the message.
            // Ack the message depending on the ack model

        PushSubscribeOptions pso = PushSubscribeOptions.Builder()
        boolean autoAck = ...
        // Subscribe using the handler
        IJetStreamPushAsyncSubscription sub = 
            js.PushSubscribeAsync("subject", MyHandler, false, pso);

See the JetStreamPushSubcribeBasicAsync in the JetStream samples for a detailed and runnable sample.

Push Sync Subscribing

        PushSubscribeOptions pso = PushSubscribeOptions.Builder()
        // Subscribe 
        IJetStreamPushSyncSubscription sub = 
                js.PushSubscribeSync("subject", pso);

See JetStreamPushSubcribeSync in the JetStream samples for a detailed and runnable sample.

Pull Subscribing

Pull subscriptions are always synchronous. The server organizes messages into a batch which it sends when requested.

        PullSubscribeOptions options = PullSubscribeOptions.Builder()

        IJetStreamPullSubscription sub = js.PullSubscribe("subject", options);


        List<Msg> message = sub.Fetch(100, 1000); // 100 messages, 1000 millis timeout
        for (Msg m : messages) {
            // process message

The fetch pull is a macro pull that uses advanced pulls under the covers to return a list of messages. The list may be empty or contain at most the batch size. All status messages are handled for you. The client can provide a timeout to wait for the first message in a batch. The fetch call returns when the batch is ready. The timeout may be exceeded if the server sent messages very near the end of the timeout period.

See JetStreamPullSubFetch and JetStreamPullSubFetchUseCases in the JetStream samples for a detailed and runnable sample.

Batch Size:

        sub.Pull(100); // 100 messages
        Msg m = sub.NextMessage(1000);

An advanced version of pull specifies a batch size. When asked, the server will send whatever messages it has up to the batch size. If it has no messages it will wait until it has some to send. The client may time out before that time. If there are less than the batch size available, you can ask for more later. Once the entire batch size has been filled, you must make another pull request.

See JetStreamPullSubBatchSize and JetStreamPullSubBatchSizeUseCases in the JetStream samples for detailed and runnable samples.

No Wait and Batch Size:

        sub.PullNoWait(100); // 100 messages
        Msg m = sub.NextMessage(1000);

An advanced version of pull also specifies a batch size. When asked, the server will send whatever messages it has up to the batch size, but will never wait for the batch to fill and the client will return immediately. If there are less than the batch size available, you will get what is available and a 404 status message indicating the server did not have enough messages. You must make a pull request every time. This is an advanced api

See the JetStreamPullSubNoWaitUseCases in the JetStream samples for a detailed and runnable sample.

Expires In and Batch Size:

        sub.PullExpiresIn(100, 3000); // 100 messages, expires in 3000 millis
        Msg m = sub.NextMessage(4000);

Another advanced version of pull specifies a maximum time to wait for the batch to fill. The server returns messages when either the batch is filled or the time expires. It's important to set your client's timeout to be longer than the time you've asked the server to expire in. You must make a pull request every time. In subsequent pulls, you will receive multiple 408 status messages, one for each message the previous batch was short. You can just ignore these. This is an advanced api

See JetStreamPullSubExpiresIn and JetStreamPullSubExpiresInUseCases in the JetStream samples for detailed and runnable samples.

Client Error Messages

In addition to some generic validation messages for values in builders, there are also additional grouped and numbered client error messages:

  • Subscription building and creation
  • Consumer creation
  • Object Store operations
Name Group Code Description
JsSoDurableMismatch SO 90101 Builder durable must match the consumer configuration durable if both are provided.
JsSoDeliverGroupMismatch SO 90102 Builder deliver group must match the consumer configuration deliver group if both are provided.
JsSoDeliverSubjectMismatch SO 90103 Builder deliver subject must match the consumer configuration deliver subject if both are provided.
JsSoOrderedNotAllowedWithBind SO 90104 Bind is not allowed with an ordered consumer.
JsSoOrderedNotAllowedWithDeliverGroup SO 90105 Deliver group is not allowed with an ordered consumer.
JsSoOrderedNotAllowedWithDurable SO 90106 Durable is not allowed with an ordered consumer.
JsSoOrderedNotAllowedWithDeliverSubject SO 90107 Deliver subject is not allowed with an ordered consumer.
JsSoOrderedRequiresAckPolicyNone SO 90108 Ordered consumer requires Ack Policy None.
JsSoOrderedRequiresMaxDeliver SO 90109 Max deliver is limited to 1 with an ordered consumer.
JsSoNameMismatch SO 90110 Builder name must match the consumer configuration name if both are provided.
JsSoOrderedMemStorageNotSuppliedOrTrue SO 90111 Mem Storage must be true if supplied.
JsSoOrderedReplicasNotSuppliedOrOne SO 90112 Replicas must be 1 if supplied.
JsSubPullCantHaveDeliverGroup SUB 90001 Pull subscriptions can't have a deliver group.
JsSubPullCantHaveDeliverSubject SUB 90002 Pull subscriptions can't have a deliver subject.
JsSubPushCantHaveMaxPullWaiting SUB 90003 Push subscriptions cannot supply max pull waiting.
JsSubQueueDeliverGroupMismatch SUB 90004 Queue / deliver group mismatch.
JsSubFcHbNotValidPull SUB 90005 Flow Control and/or heartbeat is not valid with a pull subscription.
JsSubFcHbNotValidQueue SUB 90006 Flow Control and/or heartbeat is not valid in queue mode.
JsSubNoMatchingStreamForSubject SUB 90007 No matching streams for subject.
JsSubConsumerAlreadyConfiguredAsPush SUB 90008 Consumer is already configured as a push consumer.
JsSubConsumerAlreadyConfiguredAsPull SUB 90009 Consumer is already configured as a pull consumer.
removed SUB 90010
JsSubSubjectDoesNotMatchFilter SUB 90011 Subject does not match consumer configuration filter.
JsSubConsumerAlreadyBound SUB 90012 Consumer is already bound to a subscription.
JsSubExistingConsumerNotQueue SUB 90013 Existing consumer is not configured as a queue / deliver group.
JsSubExistingConsumerIsQueue SUB 90014 Existing consumer is configured as a queue / deliver group.
JsSubExistingQueueDoesNotMatchRequestedQueue SUB 90015 Existing consumer deliver group does not match requested queue / deliver group.
JsSubExistingConsumerCannotBeModified SUB 90016 Existing consumer cannot be modified.
JsSubConsumerNotFoundRequiredInBind SUB 90017 Consumer not found, required in bind mode.
JsSubOrderedNotAllowOnQueues SUB 90018 Ordered consumer not allowed on queues.
JsSubPushCantHaveMaxBatch SUB 90019 Push subscriptions cannot supply max batch.
JsSubPushCantHaveMaxBytes SUB 90020 Push subscriptions cannot supply max bytes.
JsConsumerCreate290NotAvailable CON 90301 Name field not valid when v2.9.0 consumer create api is not available.
JsConsumerNameDurableMismatch CON 90302 Name must match durable if both are supplied.
OsObjectNotFound OS 90201 The object was not found.
OsObjectIsDeleted OS 90202 The object is deleted.
OsObjectAlreadyExists OS 90203 An object with that name already exists.
OsCantLinkToLink OS 90204 A link cannot link to another link.
OsGetDigestMismatch OS 90205 Digest does not match meta data.
OsGetChunksMismatch OS 90206 Number of chunks does not match meta data.
OsGetSizeMismatch OS 90207 Total size does not match meta data.
OsGetLinkToBucket OS 90208 Cannot get object, it is a link to a bucket.
OsLinkNotAllowOnPut OS 90209 Link not allowed in metadata when putting an object.

Message Acknowledgements

There are multiple types of acknowledgements in JetStream:

  • Msg.Ack(): Acknowledges a message.
  • Msg.AckSync(timeout): Acknowledges a message and waits for a confirmation. When used with deduplications this creates exactly once delivery guarantees (within the deduplication window). This may significantly impact performance of the system.
  • Msg.Nak(): A negative acknowledgment indicating processing failed and the message should be resent later.
  • Msg.Term(): Never send this message again, regardless of configuration.
  • Msg.InProgress(): The message is being processed and reset the redelivery timer in the server. The message must be acknowledged later when processing is complete.

Note that exactly once delivery guarantee can be achieved by using a consumer with explicit ack mode attached to stream setup with a deduplication window and using the ackSync to acknowledge messages. The guarantee is only valid for the duration of the deduplication window.

Benchmarking the NATS .NET Client

Benchmarking the NATS .NET Client is simple - run the benchmark application with a default NATS server running. Tests can be customized, run benchmark -h for more details. In order to get the best out of your test, update the priority of the benchmark application and the NATS server:

start /B /REALTIME nats-server.exe

And the benchmark:

start /B /REALTIME benchmark.exe

The benchmarks include:

  • PubOnly - publish only
  • PubSub - publish and subscribe
  • ReqReply - request/reply
  • Lat - latency.

Note, kb/s is solely payload, excluding the NATS message protocol. Latency is measure in microseconds.

Here is some sample output, from a VM running on a Macbook Pro, simulating a cloud environment. Running the benchmarks in your environment is highly recommended; these numbers below should reflect the low end of performance numbers.

PubOnlyNo	  10000000	   4715384 msgs/s	       0 kb/s
PubOnly8b	  10000000	   4058182 msgs/s	   31704 kb/s
PubOnly32b	  10000000	   3044199 msgs/s	   95131 kb/s
PubOnly256b	  10000000	    408034 msgs/s	  102008 kb/s
PubOnly512b	  10000000	    203681 msgs/s	  101840 kb/s
PubOnly1k	   1000000	     94106 msgs/s	   94106 kb/s
PubOnly4k	    500000	     52653 msgs/s	  210612 kb/s
PubOnly8k	    100000	      8552 msgs/s	   68416 kb/s
PubSubNo	  10000000	   1101135 msgs/s	       0 kb/s
PubSub8b	  10000000	   1075814 msgs/s	    8404 kb/s
PubSub32b	  10000000	    990223 msgs/s	   30944 kb/s
PubSub256b	  10000000	    391208 msgs/s	   97802 kb/s
PubSub512b	    500000	    190811 msgs/s	   95405 kb/s
PubSub1k	    500000	     97392 msgs/s	   97392 kb/s
PubSub4k	    500000	     23714 msgs/s	   94856 kb/s
PubSub8k	    100000	     11870 msgs/s	   94960 kb/s
ReqReplNo	     20000	      3245 msgs/s	       0 kb/s
ReqRepl8b	     10000	      3237 msgs/s	      25 kb/s
ReqRepl32b	     10000	      3076 msgs/s	      96 kb/s
ReqRepl256b	      5000	      2446 msgs/s	     611 kb/s
ReqRepl512b	      5000	      2530 msgs/s	    1265 kb/s
ReqRepl1k	      5000	      2973 msgs/s	    2973 kb/s
ReqRepl4k	      5000	      1944 msgs/s	    7776 kb/s
ReqRepl8k	      5000	      1394 msgs/s	   11152 kb/s
LatNo (us)	500 msgs, 141.74 avg, 86.00 min, 600.40 max, 23.28 stddev
Lat8b (us)	500 msgs, 141.52 avg, 70.30 min, 307.00 max, 26.77 stddev
Lat32b (us)	500 msgs, 139.64 avg, 93.70 min, 304.20 max, 15.88 stddev
Lat256b (us)	500 msgs, 175.55 avg, 101.80 min, 323.90 max, 14.93 stddev
Lat512b (us)	500 msgs, 182.56 avg, 103.00 min, 1982.00 max, 81.50 stddev
Lat1k (us)	500 msgs, 193.15 avg, 86.20 min, 28705.20 max, 1277.13 stddev
Lat4k (us)	500 msgs, 291.09 avg, 99.70 min, 43679.10 max, 2047.67 stddev
Lat8k (us)	500 msgs, 363.56 avg, 131.50 min, 39428.50 max, 1990.81 stddev

About the code and contributing

A note: The NATS C# .NET client was originally developed with the idea in mind that it would support the .NET 4.0 code base for increased adoption, and closely parallel the GO client (internally) for maintenance purposes. So, some of the nice .NET APIs/features were intentionally left out. While this has certainly paid off, after consideration, and some maturation of the NATS C# library, the NATS C# code will move toward more idiomatic .NET coding style where it makes sense.

To that end, with any contributions, certainly feel free to code in a more .NET idiomatic style than what you see. PRs are always welcome!


  • Key Value
  • Ordered Consumer
  • Object Store
  • JetStream
  • Another performance pass - look at stream directly over socket, contention, fastpath optimizations, rw locks.
  • Rx API (unified over NATS Streaming?)
  • Allow configuration for performance tuning (buffer sizes), defaults based on plaform.
  • Azure Service Bus Connector
  • Visual Studio Starter Kit
  • Expand Unit Tests to test internals (namely Parsing)
  • Travis CI (Used AppVeyor instead)
  • .NET Core compatibility, TLS required.
  • Convert unit tests to xunit
  • Comprehensive benchmarking
  • TLS
  • Encoding (Serialization/Deserialization)
  • Update delegates from traditional model to custom
  • NuGet package
  • Strong name the assembly

Any suggestions and/or contributions are welcome!