Bindings

Creating a binding component requires just a few basic steps.

Add bindings namespaces

Add using statements for the bindings related namespaces.

using Dapr.PluggableComponents.Components;
using Dapr.PluggableComponents.Components.Bindings;

Input bindings: Implement IInputBinding

Create a class that implements the IInputBinding interface.

internal sealed class MyBinding : IInputBinding
{
    public Task InitAsync(MetadataRequest request, CancellationToken cancellationToken = default)
    {
        // Called to initialize the component with its configured metadata...
    }
    public async Task ReadAsync(MessageDeliveryHandler<InputBindingReadRequest, InputBindingReadResponse> deliveryHandler, CancellationToken cancellationToken = default)
    {
        // Until canceled, check the underlying store for messages and deliver them to the Dapr runtime...
    }
}

Calls to the ReadAsync() method are “long-lived”, in that the method is not expected to return until canceled (for example, via the cancellationToken). As messages are read from the underlying store of the component, they are delivered to the Dapr runtime via the deliveryHandler callback. Delivery allows the component to receive notification if/when the application (served by the Dapr runtime) acknowledges processing of the message.

    public async Task ReadAsync(MessageDeliveryHandler<InputBindingReadRequest, InputBindingReadResponse> deliveryHandler, CancellationToken cancellationToken = default)
    {
        TimeSpan pollInterval = // Polling interval (e.g. from initalization metadata)...
        // Poll the underlying store until canceled...
        while (!cancellationToken.IsCancellationRequested)
        {
            var messages = // Poll underlying store for messages...
            foreach (var message in messages)
            {
                // Deliver the message to the Dapr runtime...
                await deliveryHandler(
                    new InputBindingReadResponse
                    {
                        // Set the message content...
                    },
                    // Callback invoked when application acknowledges the message...
                    async request =>
                    {
                        // Process response data or error message...
                    })
            }
            // Wait for the next poll (or cancellation)...
            await Task.Delay(pollInterval, cancellationToken);
        }
    }

Output bindings: Implement IOutputBinding

Create a class that implements the IOutputBinding interface.

internal sealed class MyBinding : IOutputBinding
{
    public Task InitAsync(MetadataRequest request, CancellationToken cancellationToken = default)
    {
        // Called to initialize the component with its configured metadata...
    }
    public Task<OutputBindingInvokeResponse> InvokeAsync(OutputBindingInvokeRequest request, CancellationToken cancellationToken = default)
    {
        // Called to invoke a specific operation...
    }
    public Task<string[]> ListOperationsAsync(CancellationToken cancellationToken = default)
    {
        // Called to list the operations that can be invoked.
    }
}

Input and output binding components

A component can be both an input and output binding, simply by implementing both interfaces.

internal sealed class MyBinding : IInputBinding, IOutputBinding
{
    // IInputBinding Implementation...
    // IOutputBinding Implementation...
}

Register binding component

In the main program file (for example, Program.cs), register the binding component in an application service.

using Dapr.PluggableComponents;
var app = DaprPluggableComponentsApplication.Create();
app.RegisterService(
    "<socket name>",
    serviceBuilder =>
    {
        serviceBuilder.RegisterBinding<MyBinding>();
    });
app.Run();

Note

A component that implements both IInputBinding and IOutputBinding will be registered as both an input and output binding.