Overview

This library provides convenient extension methods to seamlessly map Results from CSharpFunctionalExtensions to HttpResults. With this, it streamlines your Web API resulting in cleaner, more fluent code.

Key Benefits

• ⚙️ Zero Configuration: Get started immediately — the mapping works out of the box without any configuration.
• 🛠️ Customizable Mappings: Tailor default mappings or define custom mappings for specific use cases.
• 🔗 Fluent API: Maintain a smooth, railway-oriented flow by chaining HttpResult mappings at the end of your Result chain.
• 🧱 Separation of Domain and HTTP Errors: Keeps domain errors distinct from HTTP errors, improving maintainability and clarity between business logic and web API concerns.
• ⚡ Minimal APIs & Controllers Support: Works with both Minimal APIs and traditional controllers in ASP.NET.
• 📦 Full Support for ASP.NET Results: Supports all built-in HTTP response types in ASP.NET, including Ok, Created, NoContent, Accepted, FileStream, and more.
• 🦺 Typed Results: Utilizes TypedResults for consistent, type-safe API responses.
• 📑 OpenAPI Ready: Ensures accurate OpenAPI generation for clear and reliable API documentation.
• 🛡️ RFC Compliance: Default mappings adhere to the RFC 9457 standard (ProblemDetails), ensuring your API errors are standardized and interoperable.
• 🧑‍💻 Developer-Friendly: Includes built-in analyzers and source generators to speed up development and reduce errors.

Installation

Available on NuGet.

or

[!NOTE] This library references an older version of CSharpFunctionalExtensions for wider compatibility. It's recommended to additionally install the latest version of CSharpFunctionalExtensions in your project to get the latest features and fixes.

Usage

This library provides you extension methods to map the following Result types to HttpResults at the end of our result chain:

• Result
• Result<T>
• Result<T,E>
• UnitResult<E>

Example:

Available methods

All methods are available in sync and async variants.

Default mapping

By default, Result and Result<T> failures are mapped to a ProblemHttpResult based on RFC9457.

• The status property contains the status code of the HTTP response. Note: For almost every method you can override the default status codes for Success/Failure case.
• The type property contains a URI to the corresponding RFC9110 entry based on the status code.
• The title property contains a generic short messages based on the status code.
• The detail property contains the error string of the Result.

This default mapping behaviour is configured inside the ProblemDetailsMappingProvider.

Override default mapping

You can override this behavior by providing your own dictionary that maps status codes to their corresponding title and type of the resulting ProblemDetails object.

You don't have to provide the whole dictionary; you can also override or add mappings for specific status codes like this:

It's recommended to override the mappings during startup e.g. in Program.cs.

Override mapping for single use case

If you need to override the mapping for a specific use case in a single location, you can provide an Action<ProblemDetails> to fully customize the ProblemDetails. This is particularly useful when you want to add extensions or tailor the ProblemDetails specifically for that use case.

Custom error mapping

When using Result<T,E> or UnitResult<E>, this library uses a Source Generator to generate extension methods for your own custom error types.

1. Create a custom error type public record UserNotFoundError(string UserId);
2. Create a mapper that implements IResultErrorMapper which maps this custom error type to an HttpResult / Microsoft.AspNetCore.Http.IResult that you want to return in your Web API: public class UserNotFoundErrorMapper : IResultErrorMapper<UserNotFoundError, ProblemHttpResult> { public ProblemHttpResult Map(UserNotFoundError error) { var problemDetails = new ProblemDetails { Status = 404, Title = "User not found", Type = "https://tools.ietf.org/html/rfc9110#section-15.5.5", Detail = $"The user with ID {error.UserId} couldn't be found. }; return TypedResults.Problem(problemDetails); }; }
3. Use the auto-generated extension method: app.MapGet("/users/{id}", (string id, UserRepository repo) => repo.Find(id) //Result<User,UserNotFoundError> .ToOkHttpResult() //Results<Ok<User>,ProblemHttpResult> );

[!IMPORTANT]
Make sure that each custom error type has exactly one corresponding IResultMapper implementation.

[!TIP] You can use the ProblemDetailsMappingProvider.FindMapping() method to find a suitable title and type for a status code based on RFC9110.

[!NOTE] If extension methods for custom errors are missing, rebuild the project to trigger Source Generation.

Analyzers

This library includes analyzers to help you use it correctly.

For example, they will notify you if you have multiple mappers for the same custom error type or if your mapper class doesn't have a parameterless constructor.

You can find a complete list of all analyzers here.

Examples

The CSharpFunctionalExtensions.HttpResults.Examples project contains various examples demonstrating how to use this library in different scenarios, including:

• Basic CRUD operations – Handling GET, POST, PUT, and DELETE requests
• File handling – Returning files from your Web API
• Custom error mapping – Defining and mapping custom error types to meaningful HTTP responses
• Multiple errors in chain – Using different kind of custom errors in the same result chain
• Customizing default mapping – Overriding default mappings for localization or specific use cases

Check out the example project for hands-on implementation details!

Development

Contributions are welcome! Please keep the following rules in mind:

• add documentation in the form of summary comments
• add tests for your additions
• add sync and async variants where possible
• refer to existing code files and the folder structure when adding something

This project uses CSharpier for code formatting. You can format your code with dotnet csharpier ..

Add new extension methods

To add new methods follow these steps:

1. Add methods for Result and Result<T> to CSharpFunctionalExtensions.HttpResults.ResultExtensions
2. Add methods for Result<T,E> to CSharpFunctionalExtensions.HttpResults.Generators.ResultExtensions and add the class to ResultExtensionsClassBuilder
3. Add methods for UnitResult<E> to CSharpFunctionalExtensions.HttpResults.Generators.UnitResultExtensions and add the class to UnitResultExtensionsClassBuilder
4. Add tests for all new methods to CSharpFunctionalExtensions.HttpResults.Tests
5. Add methods to README