Reprise 3.3.0

𝄇 Reprise

reprise /rɪˈpriːz/ noun [French] A repeated part of something, especially a piece of music

Reprise is a micro-framework that brings the REPR (Request-Endpoint-Response) pattern and vertical slice architecture into the ASP.NET Core 6/7 Minimal APIs. It aims to be unopioniated towards API behavior and to provide a thin layer of abstractions that encourages the creation of convention-based and modular implementations.

Getting started

1. Create a new ASP.NET Core 6/7 empty project.

2. Install the Reprise NuGet package.

3. Add Reprise as a global using.

4. Modify your Program.cs to use Reprise.

var builder = WebApplication.CreateBuilder();
builder.ConfigureServices();
var app = builder.Build();
app.UseExceptionHandling();
app.MapEndpoints();
app.Run();

5. Create an endpoint Endpoints/GetHelloEndpoint.cs.

[Endpoint]
public class GetHelloEndpoint
{
    [Get("/")]
    public static string Handle() => "Hello, world!";
}

6. Run the application.

Endpoints

An endpoint is a public class that is decorated with the EndpointAttribute. It should contain a public static Handle method which should be decorated with one of the HTTP method and route attributes. These are:

• GetAttribute
• PostAttribute
• PutAttribute
• PatchAttribute
• DeleteAttribute
• MapAttribute - for other/multiple HTTP methods

The Handle method can be synchronous as well as asynchronous and can have any signature and any return type.

[Endpoint]
public class UpdateUserEndpoint
{
    [Put("/users/{id}")]
    public static IResult Handle(int id, UserDto userDto, DataContext context)
    {
        // ...
    }
}

In the example id comes from the route, userDto - from the body, and context - from the DI container. Check the documentation for more information about parameter binding.

Services

Any class (including an endpoint) that has a public parameterless constructor and implements IServiceConfgurator can configure services.

[Endpoint]
public class GetWeatherEndpoint : IServiceConfigurator
{
    public void ConfigureServices(WebApplicationBuilder builder)
    {
        builder.Services.AddWeatherService();
    }

    [Get("/weather")]
    public static async Task<WeatherForecast[]> Handle(IWeatherService weatherService)
    {
        return await weatherService.GetForecast();
    }
}

Configuration

You can bind a strongly typed hierarchical configuration using the ConfigurationAttribute. A simple example would look like this:

[Endpoint]
public class GetGreetingsEndpoint
{
    [Get("/greetings")]
    public static IEnumerable<string> Handle(GreetingConfiguration configuration)
    {
        return configuration.Names.Select(name => string.Format(configuration.Message, name));
    }
}

[Configuration("Greeting")]
public class GreetingConfiguration
{
    public string Message { get; set; } = null!;

    public List<string> Names { get; set; } = null!;
}

The GreetingConfiguration is added to the DI container with a singleton lifetime and is bound to the following section in appsettings.json:

{
    "Greeting": {
        "Message": "Hello, {0}!",
        "Names": [ "Alice", "John", "Skylar" ]
    }
}

Deeper nested sub-sections could as well be bound using a key like "Foo:Bar". Check the documentation for more information about configuration.

Filters (.NET 7 only)

Reprise supports global and endpoint-specific filters that implement IEndpointFilter.

The filter execution order is determined by an order value that is set implicitly or explicitly. A higher value means the filter will be executed after the ones with a lower value. Filters having equal order values are run in an arbitrary order.

Global filters are implicitly assigned an incrementing order value starting from 0 according to the registration order.

app.MapEndpoints(options => 
{
    options.AddEndpointFilter<FilterA>(); // implicit order 0
    options.AddEndpointFilter<FilterB>(); // implicit order 1
    options.AddEndpointFilter<FilterC>(); // implicit order 2
    options.AddEndpointFilter<FilterD>(100); // explicit order 100
});

Endpoint-specific filters are implicitly assigned an order value of int.MaxValue.

[Endpoint]
public class DeleteUserEndpoint
{
    [Delete("/users/{id}")]
    [Filter(typeof(FilterE))] // implicit order int.MaxValue
    [Filter(typeof(FilterF))] // implicit order int.MaxValue
    [Filter(typeof(FilterG), -1)] // explicit order -1
    public static IResult Handle(int id, DataContext context)
    {
        // ...
    }
}

Check the documentation for more information about filters.

Validation

Reprise relies on FluentValidation. On application startup, all IValidator<T> implementations are added with a singleton lifetime. You can then inject the validator in your Handle method.

[Endpoint]
public class CreateUserEndpoint
{
    [Post("/users")]
    public static IResult Handle(UserDto userDto, IValidator<UserDto> validator, DataContext context)
    {
        validator.ValidateAndThrow(userDto);
        // ...
    }
}

public class UserDtoValidator : AbstractValidator<UserDto>
{
    public UserDtoValidator()
    {
        RuleFor(u => u.FirstName).NotEmpty();
        RuleFor(u => u.LastName).NotEmpty();
    }
}

Check the documentation for more information about FluentValidation.

Validation filter (.NET 7 only)

It's also possible to add a global validation filter. This way, you don't need to manually inject validators and validate.

app.MapEndpoints(options => options.AddValidationFilter());

The filter is registered using an endpoint filter factory, so it will be invoked only on endpoints having one or more parameters that are validatable.

Exception handling

By default, the exception handler returns no body and:

• On BadHttpRequestException (e.g. thrown when the request body couldn't be deserialized) logs an error and returns status code 400.
• On ValidationException returns status code 400.
• On all other exceptions logs an error and returns status code 500.

To customize exception logging, you can implement IExceptionLogger. Similarly, you can customize the response body by implementing IErrorResponseFactory.

Authorization

There are two ways to secure your API. You can require authorization only for specific endpoints by decorating the Handle method with the AuthorizeAttribute from Microsoft.AspNetCore.Authorization. Alternatively, you can require authorization for all endpoints and opt-out for specific ones using the AllowAnonymousAttribute.

app.MapEndpoints(options => options.RequireAuthorization());

Check the documentation for more information about authentication and authorization.

CORS

The CORS middleware and attributes work with Reprise exactly the same way as when using pure Minimal APIs.

Check the documentation for more information about CORS.

OpenAPI

You can enhance the OpenAPI description of your endpoints by decorating the Handle method with attributes.

• TagsAttribute assigns custom tags that are typically used to group operations in the Swagger UI. If no attribute is found, Reprise extracts a tag from the route of every endpoint. The first segment that is not "api" (case insensitive) or a parameter is capitalized and set as a tag. "/" is used when no match is found.

• NameAttribute assigns a name that is used for link generation and is also treated as the operation ID in the OpenAPI description.

• ProducesAttribute describes a response returned from an API endpoint. NB: Make sure you are using the Reprise' attribute and not the one from Microsoft.AspNetCore.Mvc.

• ExcludeFromDescriptionAttribute marks an endpoint that is excluded from the OpenAPI description.

Check the documentation for more information about OpenAPI.

Events

Events provide an elegant way to do some work using the publish-subscribe pattern. An event is handled by one or more handlers in parallel. All event handlers are added to the DI container with a scoped lifetime.

public record Greeting(string Message) : IEvent;

public class GreetingHandler : IEventHandler<Greeting>
{
    private readonly ILogger<GreetingHandler> _Logger;

    public GreetingHandler(ILogger<GreetingHandler> logger)
    {
        _Logger = logger;
    }

    public async Task Handle(Greeting payload, CancellationToken cancellationToken)
    {
        await Task.Delay(1_000, cancellationToken);
        _Logger.LogInformation("Received greeting with message: {Message}", payload.Message);
    }
}

You can publish events via the IEventBus. It has two methods:

• Publish does not wait for the handlers to finish execution. All matching handlers are resolved in a new IServiceScope. IHostApplicationLifetime.ApplicationStopping is passed to the handlers as a cancellation token. If a handler throws, the exception is logged.

• PublishAndWait waits for all handlers to finish execution. All matching handlers are resolved in the current IServiceScope. If one or more handlers throw, all exceptions are packed into an AggregateException.

Self-checks

Reprise tries to make sure the API will behave exactly the way you would expect. For this reason, it performs various self-checks on application startup and throws an InvalidOperationException when a problem is encountered. The problems covered by those checks include:

• Programming errors (e.g., an endpoint has no public static Handle method)
• Misconfigurations (e.g., a configuration model could not be bound)
• Code duplications (e.g., a model is validated by multiple validators)
• Ambiguities (e.g., an HTTP method and route combination is handled by more than one endpoint).

Performance

Besides the assembly scan at application startup when configuring the DI container and discovering endpoints, Reprise doesn't add any performance overhead when handling requests.

Startup

Request

Further reading

• API reference

• Sample app

Support

If you spot any problems and/or have improvement ideas, please share them via the issue tracker.