ASP.NET Core WebApp Self-Documented Problem Result Extension

© 2025 DotNet Brightener

Introduction

Have you ever wanted to have a consistent way of returning errors from your ASP.NET Core Web application? This package provides an abstraction for responding errors from your application to the client, base on the RFC 9457 specification.

When the application encounter an error, it should return a ProblemDetails object that contains information about the error.

This package

• Added a global exception handler to catch unhandled exceptions and return a ProblemDetails object. An ILogger is also added to log the exception automatically for the unhandled exceptions.

• Provides a based IProblembResult interface and its extension methods ToProblemDetails() or ToProblemResult(), to create consistent error responses. The error response format is based on the RFC 9457 specification.

When your application needs to response the error, you can either throw an exception derived from BaseProblemDetailsError class or simply create a class that implements IProblemResult interface. The error object will be converted to ProblemDetails object and returned to the client. Check Usage section for more information.

Installation

You can install the package from NuGet:

dotnet add package DotNetBrightener.AspNet.Extensions.SelfDocumentedProblemResult

Usage

1. Enable the global exception handler

Add the following code to your Startup.cs (if you use Startup.cs) or Program.cs (by default) file:

// this can be omitted if your application already added IHttpContextAccessor builder.Services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>(); // The default way of handling unhandled exceptions builder.Services.AddExceptionHandler<UnhandledExceptionResponseHandler>(); // Adds services required for creation of <see cref="ProblemDetails"/> for failed requests. builder.Services.AddProblemDetails(); // Add the following to your Configure method, // or after // var app = builder.Build(); if you use Program.cs app.UseExceptionHandler();

After the configuration above, if your application throws an exception, the response will be a ProblemDetails object.

2. Create a consistent error response

2.1. Using Exception approach

Traditionally we used to throw exceptions when there are errors. You can create an exception class that inherits BaseProblemDetailsError class. The <summary> and <remarks> XML comments will be used to generate the ProblemDetails object.

/// <summary> /// The error represents the requested object of type `User` could not be found /// </summary> /// <remarks> /// The error is thrown because the requested resource of type `User` could not be found /// </remarks> public class UserNotFoundException : BaseProblemDetailsError { public UserNotFoundException() : base("User Not Found", HttpStatusCode.BadRequest) { } public UserNotFoundException(long userId) : this() { Data.Add("userId", userId); } }

Somewhere in your application, where an error is expected, you can throw the exception as followed:

// UserService.cs public User GetUser(long userId) { var user = _userRepository.GetUser(userId); if (user == null) { throw new UserNotFoundException(userId); } return user; }

Without having to handle the exception, the error will be caught by the global exception handler and return a ProblemDetails object.

// UserController.cs [HttpGet("{userId}")] public IActionResult GetUserDetail(long userId) { var user = _userService.GetUser(userId); // Without handling the exception, the error will be caught by the global exception handler return Ok(user); }

2.2. Using ProblemResult approach

Create a class that inherits BaseProblemDetailsError. The <summary> and <remarks> XML comments will be used to generate the ProblemDetails object.

using AspNet.Extensions.SelfDocumentedProblemResult.ErrorResults; /// <summary> /// The error represents the requested object of type `User` could not be found /// </summary> /// <remarks> /// The error is thrown because the requested resource of type `User` could not be found /// </remarks> public class UserNotFoundError : BaseProblemDetailsError { public UserNotFoundError() : base(HttpStatusCode.NotFound) { } public UserNotFoundError(long userId) : this() { Data.Add("userId", userId); } } // UserService.cs public User GetUser(long userId) { var user = _userRepository.GetUser(userId); return user; }

Somewhere in your controller, where an error is expected, you can return the error like this:

// UserController.cs [HttpGet("{userId}")] public IActionResult GetUserDetail(long userId) { var user = _userService.GetUser(userId); if (user == null) { // Explicitly return the error var error = new UserNotFoundError(userId); return error.ToProblemResult(); } // Omited for brevity }

In the above snippet, where the user is not found, a response of status code 404 will be returned with the following body:

{ "type": "UserNotFoundError", "title": "User Not Found Error", "status": 404, "detail": "The error is thrown because the requested resource of type `User` could not be found", "instance": "/users/123", "data": { "userId": 123 } }

The XML comments for the class will be used to generate the detail information about the error. It can be useful if you use the UI package, as the error information can be obtain via the UI.