Azure Web PubSub client library for .NET

Note

Details about the terms used here are described in key concepts article.

The client-side SDK aims to speed up developer's workflow; more specifically,

• simplifies managing client connections
• simplifies sending messages among clients
• automatically retries after unintended drops of client connection
• reliably deliveries messages in number and in order after recovering from connection drops

As shown in the diagram, your clients establish WebSocket connections with your Web PubSub resource.

Getting started

Install the package

Install the client library from NuGet:

dotnet add package Azure.Messaging.WebPubSub.Client --prerelease

Prerequisites

• An Azure subscription
• An existing Web PubSub instance

Authenticate the client

A Client uses a Client Access URL to connect and authenticate with the service. Client Access URL follows the pattern as wss://<service_name>.webpubsub.azure.com/client/hubs/<hub_name>?access_token=<token>. There are 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 Client Access URL. See details.

Use Client Access URL from Azure portal

As a quick start, you can go to Azure portal and copy the Client Access URL from Keys blade.

As shown in the diagram, the client is granted permission of sending messages to specific groups and joining specific groups. 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 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	Used on client side. Publish messages and subscribe to messages.	Used on server side. Generate Client Access Uri and manage clients

Examples

Consume messages from the server and groups

A client can add callbacks to consume messages from the server and groups. 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 is 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 are 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, for example, the client doesn't have permission to join groups. In such cases, users need to add a callback to handle such 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 is 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"
try
{
    await client.JoinGroupAsync("testGroup");
}
catch (SendMessageFailedException ex)
{
    if (ex.AckId != null)
    {
        await client.JoinGroupAsync("testGroup", ackId: ex.AckId);
    }
}

Troubleshooting

Enable logs

You can set the following environment variable to get the debug logs when using this library.

export AZURE_LOG_LEVEL=verbose

For more detailed instructions on how to enable logs, you can look at the @azure/logger package docs.

Live Trace

Use Live Trace tool from Azure portal to inspect live message traffic through your Web PubSub resource.