Deserializing ServiceBus content in Azure Logic App

This is caused by how the message is placed on the ServiceBus, specifically in the C# code. I was using the following code to add a new message:

var json = JsonConvert.SerializeObject(item);
var message = new BrokeredMessage(json);
await TopicClient.SendAsync(message);

This code looks fine, and works between different C# services no problem. The problem is caused by the way the BrokeredMessage(Object) constructor serializes the payload given to it:

Initializes a new instance of the BrokeredMessage class from a given object by using DataContractSerializer with a binary XmlDictionaryWriter.

That means the content is serialized as binary XML, which explains the prefix and the unrecognizable characters. This is hidden by the C# implementation when deserializing, and it returns the object you were expecting, but it becomes apparent when using a different library (such as the one used by Azure Logic Apps).

There are two alternatives to handle this problem:

• Make sure the receiver can handle messages in binary XML format
• Make sure the sender actually uses the format we want, e.g. JSON.

Paco de la Cruz's answer handles the first case, using substring, indexOf and lastIndexOf:

@json(substring(base64ToString(triggerBody()?['ContentData']), indexof(base64ToString(triggerBody()?['ContentData']), '{'), add(1, sub(lastindexof(base64ToString(triggerBody()?['ContentData']), '}'), indexof(base64ToString(triggerBody()?['ContentData']), '}')))))

As for the second case, fixing the problem at the source simply involves using the BrokeredMessage(Stream) constructor instead. That way, we have direct control over the content:

var json = JsonConvert.SerializeObject(item);
var bytes = Encoding.UTF8.GetBytes(json);
var stream = new MemoryStream(bytes);
var message = new BrokeredMessage(stream, true);
await TopicClient.SendAsync(message);

You can use the substring function together with indexOf and lastIndexOf to get only the JSON substring.

Unfortunately, it's rather complex, but it should look something like this:

@json(substring(base64ToString(triggerBody()?['ContentData']), indexof(base64ToString(triggerBody()?['ContentData']), '{'), add(1, sub(lastindexof(base64ToString(triggerBody()?['ContentData']), '}'), indexof(base64ToString(triggerBody()?['ContentData']), '}')))))

More info on how to use these functions here.

HTH