CSharpFunctionalExtensions.HttpResults

Extensions for CSharpFunctionalExtensions to map Results to HttpResults in your Web-API

Overview

This library streamlines returning HttpResults from endpoints that leverage CSharpFunctionalExtensions by offering convenient extension methods to map you result to an HttpResult. With these, you can maintain a fluent, railway-oriented style by simply invoking the appropriate method at the end of your result chain. It also supports custom error types and ensures a clear separation between your domain logic and API by using specific mappers to translate domain details into API responses.

Installation

Available on NuGet.

dotnet add package CSharpFunctionalExtensions.HttpResults

or

PM> Install-Package CSharpFunctionalExtensions.HttpResults

Usage

This library provides you extension methods to map the following Result types to HttpResults:

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

These methods are available:

Method	Short Description
.ToStatusCodeHttpResult()	Returns StatusCodeHttpResult or ProblemHttpResult
.ToStatusCodeHttpResult<T>()	Returns StatusCodeHttpResult or ProblemHttpResult
.ToStatusCodeHttpResult<T,E>()	Returns StatusCodeHttpResult or custom error
.ToStatusCodeHttpResult<E>()	Returns StatusCodeHttpResult or custom error
.ToJsonHttpResult<T>()	Returns JsonHttpResult<T> or ProblemHttpResult
.ToJsonHttpResult<T,E>()	Returns JsonHttpResult<T> or custom error
.ToOkHttpResult<T>()	Returns Ok<T> or ProblemHttpResult
.ToOkHttpResult<T,E>()	Returns Ok<T> or custom error
.ToNoContentHttpResult()	Returns NoContent or ProblemHttpResult
.ToNoContentHttpResult<T>()	Discards value of Result<T> and returns NoContent or ProblemHttpResult
.ToNoContentHttpResult<T,E>()	Discards value of Result<T> and returns NoContent or custom error
.ToNoContentHttpResult<E>()	Returns NoContent or custom error
.ToCreatedHttpResult<T>()	Returns Created<T> or ProblemHttpResult
.ToCreatedHttpResult<T,E>()	Returns Created<T> or custom error
.ToCreatedAtRouteHttpResult<T>()	Returns CreatedAtRoute<T> or ProblemHttpResult
.ToCreatedAtRouteHttpResult<T,E>()	Returns CreatedAtRoute<T> or custom error
.ToAcceptedHttpResult<T>()	Returns Accepted<T> or ProblemHttpResult
.ToAcceptedHttpResult<T,E>()	Returns Accepted<T> or custom error
.ToAcceptedAtRouteHttpResult<T>()	Returns AcceptedAtRoute<T> or ProblemHttpResult
.ToAcceptedAtRouteHttpResult<T,E>()	Returns AcceptedAtRoute<T> or custom error
.ToFileHttpResult<byte[]>()	Returns FileContentHttpResult or ProblemHttpResult
.ToFileHttpResult<byte[],E>()	Returns FileContentHttpResult or custom error
.ToFileStreamHttpResult<Stream>()	Returns FileStreamHttpResult or ProblemHttpResult
.ToFileStreamHttpResult<Stream,E>()	Returns FileStreamHttpResult or custom error

For almost every method you can override the default status codes for Success/Failure case.

All methods are available in sync and async variants.

By default, failures get mapped to a ProblemHttpResult based on RFC9457. The status property contains the status code. 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 property of the Result.

If you want your own mapping logic read on.

Custom errors

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

1. First 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 that you want to return in your Web-API:

   public class UserNotFoundErrorMapper : IResultErrorMapper<UserNotFoundError, ProblemHttpResult>
   {
       public Func<UserNotFoundErrorMapper, ProblemHttpResult> Map => 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) => {
       return userRepository.Find(id)  //Result<User,UserNotFoundError>
           .ToOkHttpResult();          //Results<Ok<User>,ProblemHttpResult>
   });

Make sure that every custom error type has exactly one corresponding IResultMapper implementation. Otherwise, the build might fail with diagnostic error CFEHTTPR002.

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

Optionally, there is a helper method ProblemDetailsMap.Find() to find a suitable title and type for a status code based on RFC9110.

Examples

Examples for CRUD, FileStreams, custom errors, etc. in context of a Web-API are available in the CSharpFunctionalExtensions.HttpResults.Examples project.

Development

You're welcome to contribute. Please keep these few 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
3. Add methods for UnitResult<E> to CSharpFunctionalExtensions.HttpResults.Generators.UnitResultExtensions
4. Add tests for all new methods to CSharpFunctionalExtensions.HttpResults.Tests
5. Add methods to README