Reading a Windows Azure Service Bus queue from .NET

This is the second part in a multi part blog post where the previous part is here:

  1. Part 1

We have  a couple of message in the queue. Let’s pull them out. This is the design of these objects we did in the previous post:

postman3

This is simulating a mobile application that can place orders of some kind.

To easily deserialize these into POCOs we create the container classes like this:


Using the same names and structure as the JSON-objects will make the transition very easy for the built-in Javascript deserializer we are going to use.
So, first of all go to the Azure portal and get the connection string to the queue. Click on the link at the bottom saying connection information.
getconnected
In the following popup you click the “copy to clipboard“-icon to the right of the “ACS Connection string” box. There, now you have the connection to the endpoint in your clipboard.

The connection string goes right where it says in the following snippet


Here you get an instance of the NamespaceManager and then use it to check if the queue exists or, otherwise, create it. Orderqueue is the name we chose in the previous sample. Change to whatever your queue is called.

If everything is fine we go ahead and create the QueueClient pointing straight at our queue.

So, that’s all the setup needed.

Let’s go get some object then. Now, remember this example is overly simplified. It’s just blocking forever until a message arrives. It could very well that be you want some timeouts to act upon. The Client.Receive() optionally takes a TimeSpan for specifying the time to wait, just as in the MSMQ counterpart.

You perhaps also would like to check out the Async-methods and see if they better suit your needs. This sample is suitable for a Windows Service or any non-server application where you control the flow. I’m just using one thread for the loop so it’s fine.


A few comments on the code. The BrokeredMessage contains a lot of metadata that you normally would like to extract. I’m just using the EnqueueTime as a sample. One interesting property is DeliveryCount. This is the number of time this message has been picked up for delivery but then just dropped (or at least not completed). SequenceNumber is another one. This can be used to check the ordering of the received messages if that is important in your application.

Ok. We have the message received alright. Since we didn’t go for the xml formatting but used JSON instead, we cannot use just a one-liner for the deserialization. Instead we take the body in the form of a Stream. Remember, the GetBody-method checks for the property “body” in the message
api4
As you see on line 11 we add a property named “body” to hold the user request.

Now with the stream at hand, we wrap it in a StreamReader just so we don’t need to fiddle around with byte arrays but instead just use the nifty ReadToEnd to get the whole payload as a string. This string we then pass into the JavaScript serializer and tell it to deserialize our string to an Order instance. If all this went ok we send a signal to the queue that we are done with the message and it’s ok to delete it. This is done with Complete().

An excerpt from the documentation:

“Completes the receive operation of a message and indicates that the message should be marked as processed and deleted.”

And in our catch we just send it to the deadletter queue where all the garbage ends up. A bit crude but in this sample it is fine.

A few notes at the end:
In the Azure Portal you can set the default behaviour of the queuelike the DeliveryCount I mentioned.
configurequeue
But also, and this is a tip, the lock duration. When you pull the message out of the queue to process it, you have the amount of time specified here at your disposal. After that time has elapsed the message is unlocked and any message.Complete() after that will fail. The DeliveryCount will be increased on the message and it is ready to be retrieved again (by you or another application). I’m mentioning this because during debugging you will probably want to increase this to a very large number to avoid problem.
Another tip to make this work is that you will have to install the Azure SDK to get it to compile. Nowadays this is done  preferably through NuGet.
Right-click on your project, select “Manage NuGet packages…” and search for “service”. There you will find the Azure Service Bus SDK. Click install and you are good to go.
servicebusnuget

Creating a Windows Azure Mobile Services-app with push capabilities (part 1)

Windows Azure Mobile Services (WAMS) has been around for a while by now but the bandwagon has rolled out some significant improvements lately so it’s time to revisit. The perhaps most interesting (and enabling) change is the “Custom API”-feature. Until now, WAMS, was limited to acting as a CRUD-backend to your apps. Now, with Node.js as server language, we can develop “real” applications.

This is me spelunking with these features….

For completeness I’m starting from scratch

Create your WAMS application

Create WAMS

Fill in the form. Sample below:

wamswizard1

Now you should have an application created for you.

wamscreated

Now, the cool thing here is that Microsoft actually will create a boilerplate project for you with all the blanks filled in. Just select technology and download.

wamsdashboard
However, I will not use these boilerplates. I want to play around with the Custom API feature.

Create the Custom API

Just select API in the top menu and then click Create at the bottom. You should see this dialog now:

createcustomapiWe will see the implications of the different permissions later on. Just leave them for now. After finishing this step the api is created and you are presented with the stub below

sampleapicreated

Testing the API

The simplest way to test the new API is through either Fiddler if you are on a Windows box, or with the cross platform Chrome-app Postman. Open a new tab in Chrome and click on “Web store” in the lower right corner. Search for “postman” and download.
In postman you just type your URL for the api where it says “Enter request URL here” and change the verb from GET to POST.
So, I paste my URL https://classon.azure-mobile.net/api/order and change to POST and press Send.
And… I receive a 401 Unauthorized.

unauth
Why? Because as you remember from above the default permissions was “Anybody with the application key” and we didn’t provide one.
So, click on the Headers tab in Postman (top right). And enter X-ZUMO-APPLICATION as the name and paste in your application key as value. Now, when you Send you should get the 200 Hello World response.

x-zumo
Well then, what’s next?
To up the stakes a bit we’ll try to combine other Azure parts as well. Let’s combine this with the Service Bus….

Go to the Service Bus section of the azure management portal and click “Create”. Type in a name of your namespace as it is called. Give it a name and select the same region as you did with the Mobile Service. So, done.
To access this “bus” we need two things; the name and the access key. To get the key you click at the bottom where it says “Connection Information”. A dialog with a lot of connection stuff pops up. Press the copy-icon to the right of “Default key” to copy your key to the clipboard. Paste it somewhere where you can find it as we are going to be needing it when we continue to develop our api.

Connecting Mobile Services to Service Bus

Now, modify the api-script like so:
api4

What is happening here? Well, at line 2 we are using require to get an instance of the azure-sdk for Node.js. Line 3 is actually creating a reference to our Service Bus-namespace (in my case ‘marcus’). Here, as the second parameter, is where your key should go. The rest is kind of self explanatory. CreateQueueIfNotExist does just that. The first time it accessed the queue will be created. At line 9 I’m composing the message I’m going to send to our backend and the at 12 it flies away.
A few caveats: the properties of the message are not arbitrary. The ‘body’-tag will be handled as the actual body of the BrokeredMessage.
More about reading the message in C# in a later post.

Testing the api with a JSON workload

In our previous test we didn’t use any workload. Hence the lack of Content-Type in the headers. So, modify (in Postman) the request like so:

postman3
Edit: Updated payload to contain a collection of items. This way the receiving end will be cooler…

Press send and you receive something like this:
apiresponse

To see that the message didn’t just disappear but really ended up in the queue, go to the Service Bus section again and open your namespace.
You should now have a ‘orderqueue’ with a length other than 0
queuecreated

From here it is just to consume the queue from where ever you prefer.