MSL.Dialogue.Pipeline 1.0.27

Dialogue

Dialogue is a request pipeline that supports middleware delegates and classes. It provides configuration, dependency injection, and middleware pipeline services for AWS Lambda functions or Azure functions.

References

Dialogue is based this article: How is the ASP.NET Core Middleware Pipeline Built - Steve Gorden, July 2020

Getting Started

If you're not familiar with middleware pipelines, Microsoft has a good primer on how middleware works in ASP.NET Core.

Installing

To install, use the following command: dotnet add package MSL.Dialogue.Pipeline

Usage

1. Create an IRequestHandlerBuilder<TRequest, TResponse> by calling one of the static RequestHandlerBuilder.New methods.
2. Builder adds configuration providers for appsettings files, environment variables, command line args, and user secrets by default.
3. Handle additional configuration scenarios through the IConfigurationManager Configuration property on the builder.
4. Register services with the IServiceCollection Servics property.
5. Use the Build method to create an IRequestRequestDelegate<TRequest, TResponse> instance.
6. Configure the request delegate pipeline by calling the Use methods on the request handler.
7. Call the Prepare method on the request handler to compile the pipeline. If you don't call Prepare, the pipeline will be compiled when the first request is processed.
8. Call the InvokeAsync method on the request handler to forward the request to the pipeline.
9. Within your middleware delegates, or IMiddleware implementations, always invoke Next to pass the request context to the next delegate in the pipeline.
10. Always call context.CancelationToken.ThrowIfCancellationRequested() to check for cancellation requests before processing the request or invoking Next.
11. To terminate, or "short circuit", the pipeline don't invoke Next.
12. In your terminal delegate, set the response value in the request context.

Samples

Projects

AWS Lambda (SQS)

• Dialogue.Samples.Lambda.SQS
• Dialogue.Samples.Lambda.SQS.Tests
• Dialogue.Samples.Lambda.APIGateway
• Dialogue.Samples.Lambda.APIGateway.Tests

Simplest Example - no config, no services, no middleware

In this sample, we create a request handler that does nothing with no configuration, no service registration, and no user-defined middleware. This is the simplest possible example.

var request = "Hello, World!";

var handler = RequestHandlerBuilder
    .New<string, string>()
    .Build();

var response = await handler.InvokeAsync(request);

Assert.True(String.IsNullOrEmpty(response));

Middleware Delegate Example

In this sample, we create a request handler with user-defined middleware that converts the request to uppercase.

var request = "Hello, World!";

var handler = RequestHandlerBuilder.New<string, string>()
    .Build()
    .Use(async (context, next) =>
    {
        context.CancelationToken.ThrowIfCancellationRequested();
        context.Response = context.Request.ToUpperInvariant();
        await next(context); // call next to pass the request context to next delegate in the pipeline
    })
    .Prepare();

var response = await handler.InvokeAsync(request);

Assert.Equal(request.ToUpperInvariant(), response);

Middleware Class Example

In this sample, we create a request handler with a user-defined IMiddleware implementation that converts the request to lowercase.

First, we define the middleware class, which receives the next middleware delegate in the pipeline in its constructor. The middleware is responsible for calling the next delegate unless the middleware needs to short-circuiting the pipeline. An example short-circuit scenario might be a request validation middleware that returns an error response if the request is invalid.

IMiddleware implementations support constructor-based dependency injection. The next delegate must be the first argument in the contstructor.

internal sealed class ToLowerMiddleware(RequestMiddleware<string, string> next)
    : IMiddleware<string, string>
{
    private readonly RequestMiddleware<string, string> next = next
        ?? throw new ArgumentNullException(nameof(next));

    public Task InvokeAsync(Context<string, string> context)
    {
        context.CancelationToken.ThrowIfCancellationRequested();
        context.Response = context.Request.ToLowerInvariant();
        return next(context); // call next to pass the request context to next delegate in the pipeline
    }
}

Then we register it with the request handler.

var request = "Hello, World!";

var handler = RequestHandlerBuilder.New<string, string>()
    .Build()
    .Use<ToLowerMiddleware>()
    .Prepare();

var response = await handler.InvokeAsync(request);

Assert.Equal(request.ToLowerInvariant(), response);

Builder Configure Example

Call the Configure method on the builder to load configuration from appsettings.json, environment variables, user secrets, etc. Call Configure before calling ConfigureServices.

var builder = RequestHandlerBuilder.New<string, string>();

builder.Configuration
    .AddInMemoryCollection(new Dictionary<string, string> { { "MyKey", "MyValue" } });

var handler = builder.Build();

Builder ConfigureServices Example

Call the ConfigureServices method on the builder to register services with IServiceCollection. Call Configure before calling ConfigureServices.

var builder = RequestHandlerBuilder.New<string, string>();

builder.Services
    .AddSingleton<IMyService, MyService>()
    .AddSerilog();

var handler = builder.Build();

Void Response Example

For request handlers that don't return a response, use Void as the response type.

var handler = RequestHandlerBuilder.New<string, Void>() // TResponse of type Void
    .Build()
    .Prepare();