Alexa Skills Mediator

Package Version

Build Status	Nuget

Simple mediator implementation for Alexa Skill development in .NET

Installation

Install the package via nuget:

Install-Package Alexa.Net.MediatR

Or via the .Net command line interface

dotnet add package Alexa.Net.MediatR

Setup

After installing the package, there are two delegates that need to be configured, a service factory delegate, which is used to instantiate all the handlers, the pipelines, the request and response interceptors, the exception handlers, the attributes manager, the handler input, and the default handler.

The other delegate that must be configured is the skill request factory, which is used to inject the incoming SkillRequest into the IAttributesManager for request and session attributes.

.Net

The easistet way to set up your skill mediator is to use the Alexa.Net.MediatR.Extensions.Microsoft.DependencyInjection package which includes several IServiceCollection extension methods, which allow you to register all of your custom handlers and configuration from a given assemly or set of assemblies. This package also has a depenency on the Alexa.Net.Lambda package which provides the ability to host your Skill via AWS Lambda with Dependency Injection. An example from the Init method:

protected override void Init(IHostBuilder builder){
    builder.ConfigureServices((context, services) => {
        services.AddSkillMediatorFromAssemblies(context.Configuration, nameof(AlexaSkillOptions), typeof(Function).GetTypeInfo().Assembly);
    })
}

Basics

The Skill Mediator provides the ability to handler request messages for a given Request types. It also provides the ability to intercept those messages and apply changes to the incoming request and the outgoing response.

Request Handling

The base IRequestHandler interface contains two methods, CanHandle and Handle. CanHandle includes the logic to determine if an incoming request can be handled by the handler.

The IRequestHandler<TRequestType> interface is the interface that should be implemented for request handling. The skill mediator will inspect incoming requests to determine the request type, and try and find the appropriate Handler of that type.

public class LaunchRequestHandler : IRequestHandler<LaunchRequest>
{
    public Task<bool> CanHandler(IHandlerInput input, CancellationToken cancellationToken) => Task.FromResult(true);
    
    public Task<SkillResponse> Handle(IHandlerInput input, CancellationToken cancellationToken)
    {
        return input.ResponseBuilder.Tell($"Response from {nameof(LaunchRequestHandler)}", cancellationToken);
    }
}

The above class will handle requests of LaunchRequest type. The IHandlerInput contains references to information that will be needed to process requests, the incoming SkillRequest, the instance of IAttributesManager, and the IResponseBuilder to help generate responses Alexa can understand.

*** Note: unless you add the handlers to the underlying DI container manually, there is no guarantee as to what order they will be registered. As the developer, you are responsible for ensuring that there is no overlap in the handlers CanHandle methods.