Kawa.Core 0.2.1

Design Principles

Kawa is a contract-first .NET web framework that lays a thin waterway on top of ASP.NET Core.

Kawa keeps application flow centered on request/response contracts and use cases. ASP.NET Core stays as the host and transport layer; Kawa only provides the small boundary pieces needed to execute use cases and translate KawaResult<T> values into HTTP responses.

Packages

• Kawa.Abstractions: shared use case, result, and error contracts
• Kawa.Core: transport-independent use case execution
• Kawa.Web: ASP.NET Core Minimal API integration
• Kawa.FSharp: F# helpers

Installation

dotnet add package Kawa.Web

Kawa.Web brings in the core Kawa runtime pieces needed for ASP.NET Core Minimal API integration.

Quick Start

Define one use case under UseCases/, with its request and response contracts nested in the same source file:

// UseCases/CreateUser.cs
using Kawa.Abstractions;

[KawaUseCase(
    "users.create",
    Summary = "Create user",
    Description = "Creates a user account.",
    Version = "v1",
    Tags = new[] { "Users" })]
[KawaErrorResponse(KawaErrorKind.Validation, Description = "Name is required.")]
public sealed class CreateUser
    : IUseCase<CreateUser.Request, CreateUser.Response>
{
    public sealed record Request(string Name);

    public sealed record Response(string Message);

    public Task<KawaResult<Response>> ExecuteAsync(
        Request request,
        CancellationToken cancellationToken = default)
    {
        if (string.IsNullOrWhiteSpace(request.Name))
        {
            var error = new KawaError(KawaErrorKind.Validation, "Name is required.");
            return Task.FromResult(KawaResult<Response>.Failure(error));
        }

        var response = new Response($"Created user {request.Name}.");
        return Task.FromResult(KawaResult<Response>.Success(response));
    }
}

Register Kawa, scan for use cases, and map the endpoint from the use case type:

using Kawa.Web;

var builder = WebApplication.CreateBuilder(args);

builder.Services
    .AddKawa()
    .AddKawaUseCasesFromAssemblies(typeof(CreateUser).Assembly)
    .AddKawaWeb();

var app = builder.Build();

app.MapKawaPost<CreateUser>("/users");
app.MapKawaOpenApi();

if (app.Environment.IsDevelopment())
{
    app.MapKawaSwagger();
    app.MapKawaReDoc();
}

app.Run();

Kawa.Web exposes the same contracts through OpenAPI at /openapi/v1.json. Swagger UI is available at /swagger and ReDoc is available at /redoc when the corresponding Kawa UI middleware is mapped. The convention is that Kawa request/response contracts are the source of the OpenAPI schema.

The documentation UIs are middleware, so map them only where they should be public. The recommended default is development-only; exposing /swagger or /redoc in production should be an explicit application decision.

Use case metadata and error response attributes are transport-independent. Kawa.Web maps them to OpenAPI, and future RPC / CLI / Worker adapters can use the same API catalog.

Then call the endpoint:

curl -X POST http://localhost:5000/users \
  -H "Content-Type: application/json" \
  -d '{"name":"Louisa"}'

Result to HTTP Mapping

MapKawaPost<TUseCase> reads the matching IUseCase<TRequest,TResponse> contract from the use case type, resolves that contract from dependency injection, executes it through UseCaseExecutor, and converts the result to an ASP.NET Core IResult.

MapKawaPost<TRequest,TResponse> is also available when you want to map explicit request and response types.

Current failure mappings:

Samples

Run the C# sample:

dotnet run --project samples/Kawa.Sample.CSharp

Run the mixed C# host + F# use case sample:

dotnet run --project samples/Kawa.Sample.Mixed

Run the mixed C# host + VB.NET use case sample:

dotnet run --project samples/Kawa.Sample.VB

All samples expose POST /users.

Development

Restore, build, and test:

dotnet restore Kawa.sln
dotnet build Kawa.sln --no-restore
dotnet test Kawa.sln --no-restore --no-build

Run tests with coverage:

dotnet test Kawa.sln \
  --no-restore \
  --no-build \
  --collect:"XPlat Code Coverage" \
  --results-directory TestResults \
  -- \
  DataCollectionRunSettings.DataCollectors.DataCollector.Configuration.Format=cobertura

The CI pipeline audits NuGet packages during restore and uploads coverage to Codecov using the repository secret CODECOV_TOKEN. Project and patch coverage are configured to target 100%.

To create local NuGet packages:

bash eng/pack.sh

To publish the generated packages to NuGet.org:

NUGET_API_KEY=... bash eng/push-nuget.sh

NuGet packages and GitHub Releases are published by GitHub Actions when a tag in vX.Y.Z format is pushed, for example:

git tag v0.1.1
git push origin v0.1.1

The release workflow uses the repository secret NUGET_API_KEY.

See:

• Design Principles
• Rails-like Convention Proposal
• 設計思想メモ 日本語版
• Rails-like Convention Proposal 日本語版

License

Kawa is licensed under the MIT License.