CSharpFunctionalExtensions.HttpResults 0.8.0

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:

All methods are available in sync and async variants.

Default mapping

By default, Result and Result<T> failures get 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 behaviour by providing your own dictionary which maps status code to title and type of the resulting ProblemDetails object.

<details> <summary>Example for changing the default mapping for german localization</summary>

ProblemDetailsMappingProvider.DefaultMappings = new Dictionary<int, (string? Title, string? Type)>
{
  { 400, ("Ungültige Anfrage", "https://tools.ietf.org/html/rfc9110#section-15.5.1") },
  { 401, ("Nicht autorisiert", "https://tools.ietf.org/html/rfc9110#section-15.5.2") },
  { 403, ("Verboten", "https://tools.ietf.org/html/rfc9110#section-15.5.4") },
  { 404, ("Nicht gefunden", "https://tools.ietf.org/html/rfc9110#section-15.5.5") },
  { 405, ("Methode nicht erlaubt", "https://tools.ietf.org/html/rfc9110#section-15.5.6") },
  { 406, ("Nicht akzeptabel", "https://tools.ietf.org/html/rfc9110#section-15.5.7") },
  { 408, ("Zeitüberschreitung der Anfrage", "https://tools.ietf.org/html/rfc9110#section-15.5.9") },
  { 409, ("Konflikt", "https://tools.ietf.org/html/rfc9110#section-15.5.10") },
  { 412, ("Vorbedingung fehlgeschlagen", "https://tools.ietf.org/html/rfc9110#section-15.5.13") },
  { 415, ("Nicht unterstützter Medientyp", "https://tools.ietf.org/html/rfc9110#section-15.5.16") },
  { 422, ("Nicht verarbeitbare Entität", "https://tools.ietf.org/html/rfc4918#section-11.2") },
  { 426, ("Upgrade erforderlich", "https://tools.ietf.org/html/rfc9110#section-15.5.22") },
  { 500, ("Ein Fehler ist bei der Verarbeitung Ihrer Anfrage aufgetreten.", "https://tools.ietf.org/html/rfc9110#section-15.6.1") },
  { 502, ("Schlechtes Gateway", "https://tools.ietf.org/html/rfc9110#section-15.6.3") },
  { 503, ("Dienst nicht verfügbar", "https://tools.ietf.org/html/rfc9110#section-15.6.4") },
  { 504, ("Gateway-Zeitüberschreitung", "https://tools.ietf.org/html/rfc9110#section-15.6.5") },
};

Example from here

</details>

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

ProblemDetailsMappingProvider.AddOrUpdateMapping(420, "Enhance Your Calm", "https://http-status-code.de/420/");

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.

Result.Failure<string>(error)
  .ToOkHttpResult(customizeProblemDetails: problemDetails =>
  {
    problemDetails.Title = "Custom Title";
    problemDetails.Extensions.Add("custom", "value");
  });

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 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>
   });
   

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

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

[!TIP] 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 can notify you if you have multiple mappers for the same custom error type or if you forgot to implement the Map function in your custom error mapper.

You can find a complete list of all analyzers here.

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 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