SendersReceiversWithTopics

Message Senders and Receivers with Service Bus Topics

This sample shows how to interact with a Service Bus Topic via the MessageSender and MessageReceiver clients, as an alternative to the TopicClient and SubscriptionClient class introduced in the basic TopicGettingStarted sample.

The sample is quasi identical to the SendersReceiversWithQueues sample since the API gestures for interacting with queues and topics through those API elements are the same. Showing that is the point of these two samples and in this document we will therefore focus on the few differences.

Prerequisites and Setup

Refer to the main README document for setup instructions. All samples share and require the same setup before they can be run.

Sample Code

The sample is documented inline in the Program.cs C# file.

The send-side of the sample is identical to the SendersReceiversWithQueues sample and therefore shows that queues and topics can be used interchangeably, and that an application's messaging topology can indeed be flexibly adjusted while limiting or avoiding code churn.

The only difference in the sender portion of this sample is that we're passing the name of a topic instead the name of a queue:

    var sender = new MessageSender(connectionString,topicName);

The receive side is also nearly identical. The Run() function passes the name of the subscription in addition to the topic name, and also gets to pass a different console color option for displaying the messages received on that subscription.

    async Task ReceiveMessagesAsync(string connectionString, string topicName, string subscriptionName, 
                                    CancellationToken cancellationToken, ConsoleColor color)
    {
        ... create factory ...

The only truly noteworthy difference is that we are constructing the MessageReceiver not over the path of the main entity as we do with queues, but first format a path to the subscription from the topic and subscription names, and then construct the MessageReceiver using the composite path. From the MessageReceiver perspective, the resulting path is completely interchangeable with any queue's path.

The static helper method SubscriptionClient.FormatSubscriptionPath() returns a path of the form {topic-name}/Subscription/{subscription-name}

>       var subscriptionPath = SubscriptionClient.FormatSubscriptionPath(topicName, subscriptionName);
        var receiver = new MessageReceiver(connectionString,subscriptionPath, ReceiveMode.PeekLock);

Generally, If you want to retain flexibility for your application's messaging topology, you will manage the path from which you receive messages for a component or service separately, likely in configuration.

You can obviously also easily create a SubscriptionClient through the MessagingFactory as follows and in a single line:

    var receiver = new SubscriptionClient(topicName, subscriptionName);

The SubscriptionClient class differs from the regular receiver in that it has specific support for managing subscription rules at runtime. More on this in the TopicFilters sample.

Run()

The Run() method that is invoked by the common sample entry point first sends a few messages and kicks off the receivers for three subscriptions in parallel. The messages received from the subscriptions will differ in color, depending on which subscription they were received from.

The cancellation token passed to the receiver method is being triggered when the user presses any key sometime after sender and receiver have been kicked off.

    public async Task Run(string connectionString, string topicName, string sendToken)
    {
        var cts = new CancellationTokenSource();

        await this.SendMessagesAsync(connectionString, topicName, sendToken);

        var allReceives = Task.WhenAll(
            this.ReceiveMessagesAsync(connectionString, topicName, "Subscription1", receiveToken, cts.Token, ConsoleColor.Cyan),
            this.ReceiveMessagesAsync(connectionString, topicName, "Subscription2", receiveToken, cts.Token, ConsoleColor.Green),
            this.ReceiveMessagesAsync(connectionString, topicName, "Subscription3", receiveToken, cts.Token, ConsoleColor.Yellow));
        Console.WriteLine("\nEnd of scenario, press any key to exit.");
        Console.ReadKey();

        cts.Cancel();
        await allReceives;
    }

Running the sample

You can run the application from Visual Studio or on the command line from the sample's root directory by starting bin/debug/SendersReceiversWithTopics.exe