Azure Web PubSub client library for .NET - version 1.0.0

Web PubSub is an Azure-managed service that helps developers easily build web applications with real-time features and publish-subscribe patterns. Any scenario that requires real-time publish-subscribe messaging between server and clients or among clients can use Web PubSub. Traditional real-time features that often require polling from the server or submitting HTTP requests can also use Web PubSub.

You can use this library on your client side to manage the WebSocket client connections, as shown in the below diagram:


Use this library to:

  • Send messages to groups
  • Send events to the server
  • Join and leave groups
  • Listen messages from groups and servers

Details about the terms used here are described in Key concepts section.

Source code | API reference documentation | Product documentation |

Getting started

Install the package

Install the client library from NuGet:

dotnet add package Azure.Messaging.WebPubSub.Client


Authenticate the client

A Client uses a Client Access URL to connect and authenticate with the service. The Uri follow the patten as wss://<service_name><hub_name>?access_token=<token>. There're multiple ways to get a Client Access URL. As a quick start, you can copy and paste from Azure Portal, and for production, you usually need a negotiation server to generate the Uri.

Use Client Access URL from Azure Portal

As a quick start, you can go to the Portal and copy the Client Access URL from Key blade.


As shown in the diagram, the client will be granted permission of sending messages to the specific group and joining the specific group. Learn more about client permission, see permissions

var client = new WebPubSubClient(new Uri("<client-access-uri>"));

Use negotiation server to generate Client Access URL

In production, a client usually fetches the Client Access URL from a negotiation server. The server holds the connection string and generates the Client Access URL through WebPubSubServiceClient. As a sample, the code snippet below just demonstrates how to generate the Client Access URL inside a single process.

var client = new WebPubSubClient(new WebPubSubClientCredential(token =>
    // In common practice, you will have a negotiation server for generating token. Client should fetch token from it.
    return FetchClientAccessTokenFromServerAsync(token);
public async ValueTask<Uri> FetchClientAccessTokenFromServerAsync(CancellationToken token)
    var serviceClient = new WebPubSubServiceClient("<< Connection String >>", "hub");
    return await serviceClient.GetClientAccessUriAsync();

Features to differentiate WebPubSubClient and WebPubSubServiceClient.

Class Name WebPubSubClient WebPubSubServiceClient
Nuget Package Name Azure.Messaging.WebPubSub.Client Azure.Messaging.WebPubSub
Features Usually used on client side. Publish messages and subscribe to messages. Usually used on server side. Generate Client Access Uri and manage clients

Find more details in Azure.Messaging.WebPubSub

Key concepts


A connection, also known as a client connection, represents an individual WebSocket connection connected to the Web PubSub. When successfully connected, the Web PubSub assigns the connection a unique connection ID. Each WebPubSubClient creates its own exclusive connection.


If a client using reliable protocols disconnects, a new WebSocket tries to establish using the connection ID of the lost connection. If the new WebSocket connection is successfully connected, the connection is recovered. Throughout the time a client is disconnected, the service retains the client's context as well as all messages that the client was subscribed to, and when the client recovers, the service will send these messages to the client. If the service returns WebSocket error code 1008 or the recovery attempt lasts more than 30 seconds, the recovery fails.


Reconnection happens when the client connection drops and fails to recover. Reconnection starts a new connection and the new connection has a new connection ID. Unlike recovery, the service treats the reconnected client as a new client connection. The client connection needs to rejoin groups. By default, the client library rejoins groups after reconnection.


A hub is a logical concept representing a collection of client connections. Usually, you use one hub for one purpose: for example, a chat hub, or a notification hub. When a client connection is created, it connects to a hub, and during its lifetime, it is bound to that hub. Different applications can share one Web PubSub by using different hub names.


A group is a subset of connections to the hub. You can add and remove connections from a group at any time. For example, a chat room can be considered a group. When clients join and leave the room, they are added and removed from the group. A connection can belong to multiple groups, and a group can contain multiple connections.


Connections to Web PubSub can belong to one user. A user might have multiple connections, for example when a single user is connected across multiple devices or browser tabs.

Client Lifetime

Each of the Web PubSub clients is safe to cache and use as a singleton for the lifetime of the application. The registered event callbacks share the same lifetime with the client. This means you can add or remove callbacks at any time and the registration status won't change after reconnection or even stopping the client.


Specify subprotocol

You can specify the subprotocol to be used by the client. By default, the client uses You can choose to use or as shown below.

var client = new WebPubSubClient(new Uri("<client-access-uri>"), new WebPubSubClientOptions
    Protocol = new WebPubSubJsonProtocol()
var client = new WebPubSubClient(new Uri("<client-access-uri>"), new WebPubSubClientOptions
    Protocol = new WebPubSubJsonReliableProtocol()

Consume messages from the server and groups

A client can add callbacks to consume messages from the server and groups. Please note, clients can only receive group messages that it has joined.

client.ServerMessageReceived += eventArgs =>
    Console.WriteLine($"Receive message: {eventArgs.Message.Data}");
    return Task.CompletedTask;
client.GroupMessageReceived += eventArgs =>
    Console.WriteLine($"Receive group message from {eventArgs.Message.Group}: {eventArgs.Message.Data}");
    return Task.CompletedTask;

Add callbacks for connected, disconnected, and stopped events

When a client connection is connected to the service, the Connected event is triggered once it received the connected message from the service.

client.Connected += eventArgs =>
    Console.WriteLine($"Connection {eventArgs.ConnectionId} is connected");
    return Task.CompletedTask;

When a client connection is disconnected and fails to recover, the Disconnected event is triggered.

client.Disconnected += eventArgs =>
    Console.WriteLine($"Connection is disconnected");
    return Task.CompletedTask;

When a client is stopped, which means the client connection is disconnected and the client stops trying to reconnect, the Stopped event will be triggered. This usually happens after the client.StopAsync() is called, or disabled AutoReconnect. If you want to restart the client, you can call client.StartAsync() in the Stopped event.

client.Stopped += eventArgs =>
    Console.WriteLine($"Client is stopped");
    return Task.CompletedTask;

Auto rejoin groups and handle rejoin failure

When a client connection has dropped and fails to recover, all group contexts will be cleaned up on the service side. That means when the client reconnects, it needs to rejoin groups. By default, the client enabled AutoRejoinGroups options. However, this feature has limitations. The client can only rejoin groups that it's originally joined by the client rather than joined by the server side. And rejoin group operations may fail due to various reasons, e.g. the client doesn't have permission to join groups. In such cases, users need to add a callback to handle the failure.

client.RejoinGroupFailed += eventArgs =>
    Console.WriteLine($"Restore group failed");
    return Task.CompletedTask;

Operation and retry

By default, the operation such as client.JoinGroupAsync(), client.LeaveGroupAsync(), client.SendToGroupAsync(), client.SendEventAsync() has three reties. You can use WebPubSubClientOptions.MessageRetryOptions to change. If all retries have failed, an error will be thrown. You can keep retrying by passing in the same ackId as previous retries, thus the service can help to deduplicate the operation with the same ackId

// Send message to group "testGroup"
    await client.JoinGroupAsync("testGroup");
catch (SendMessageFailedException ex)
    if (ex.AckId != null)
        await client.JoinGroupAsync("testGroup", ackId: ex.AckId);


Setting up console logging

You can also enable console logging if you want to dig deeper into the requests you're making against the service.

Next steps

You can also find more samples here.


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