# Azure Service Bus

Microsoft Azure Service Bus is a fully managed enterprise integration message broker. Service Bus is most commonly used to decouple applications and services from each other, and is a reliable and secure platform for asynchronous data and state transfer. 

Azure services can be used in CAP as a message transporter. 

## Configuration

!!! warning "Requirement"
    For the Service Bus pricing layer, CAP requires "standard" or "advanced" to support Topic functionality.

To use Azure Service Bus as a message transport, you need to install the following package from NuGet:

```powershell
PM> Install-Package DotNetCore.CAP.AzureServiceBus
```
Next, add configuration items to the `ConfigureServices` method of `Startup.cs`:

```csharp

public void ConfigureServices(IServiceCollection services)
{
    // ...

    services.AddCap(x =>
    {
        x.UseAzureServiceBus(opt=>
        {
            //AzureServiceBusOptions
        });
        // x.UseXXX ...
    });
}

```

#### AzureServiceBus Options

The AzureServiceBus configuration options provided directly by the CAP:

NAME | DESCRIPTION | TYPE | DEFAULT
:---|:---|---|:---
ConnectionString | Endpoint address | string | 
EnableSessions | Enable [Service bus sessions](https://docs.microsoft.com/en-us/azure/service-bus-messaging/message-sessions) | bool | false 
TopicPath | Topic entity path | string | cap
ManagementTokenProvider | Token provider | ITokenProvider | null

#### Sessions

When sessions are enabled (see `EnableSessions` option above), every message sent will have a session id. To control the session id, include
an extra header with name `AzureServiceBusHeaders.SessionId` when publishing events:

```csharp
ICapPublisher capBus = ...;
string yourEventName = ...;
YourEventType yourEvent = ...;

Dictionary<string, string> extraHeaders = new Dictionary<string, string>();
extraHeaders.Add(AzureServiceBusHeaders.SessionId, <your-session-id>);

capBus.Publish(yourEventName, yourEvent, extraHeaders);
```

If no session id header is present, the message id will be used as the session id.