Monday, December 5, 2022

ASP.NET Core Web API: Exception Handling

In this post, let's see how we can provide a common approach for handling exceptions in ASP.NET Core Web APIs in the Development environment as well as in Production environments.

It's quite easy, basically, we can introduce UseExceptionHandler Middleware to handle exceptions.

Consider the following code.
WebApplicationBuilder builder = WebApplication.CreateBuilder(args);
// Add services to the container.
WebApplication app = builder.Build();
// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
Here I have added UseExceptionHandler passing in different routes based on the environment. Now we need to define controller actions to respond to /error-development and /error routes.
using Microsoft.AspNetCore.Diagnostics;
using Microsoft.AspNetCore.Mvc;
using System.Net;
namespace WebApplication1.Controllers;
[ApiExplorerSettings(IgnoreApi = true)]
public class ErrorController : ControllerBase
    private readonly IHostEnvironment _hostEnvironment;
    public ErrorController(IHostEnvironment hostEnvironment)
        _hostEnvironment = hostEnvironment;
    public IActionResult HandleErrorDevelopment()
        if (!_hostEnvironment.IsDevelopment())
            return NotFound();
        IExceptionHandlerFeature exceptionHandlerFeature = HttpContext.Features.Get<IExceptionHandlerFeature>()!;
        if (exceptionHandlerFeature == null)
            return Problem(
                title: $"'{nameof(IExceptionHandlerFeature)}' not found.");
        return exceptionHandlerFeature.Error switch
            NotImplementedException notImplementedException => Problem(
                title: notImplementedException.Message,
                detail: notImplementedException.StackTrace,
statusCode: (int)HttpStatusCode.NotImplemented), _ => Problem( title: exceptionHandlerFeature.Error.Message, detail: exceptionHandlerFeature.Error.StackTrace) }; } [Route("/error")] public IActionResult HandleError() => Problem(); }
Note: The actions aren't attributed with HttpVerbs and the controller is attributed with [ApiExplorerSettings(IgnoreApi = true)] to exclude from OpenAPI specification (if there's any).

For the Development environment, based on the type of the exception, I am returning different statusCodes and I am including the StackTrace to troubleshoot the issue easily. 

For an example, consider the following action.
[HttpGet(Name = "GetWeatherForecast")]
public IEnumerable<WeatherForecast> Get()
    throw new NotImplementedException("Not implemented.");
If we call the above action when running on a Development environment, I will be getting a response like below. It's the standard RFC 7807-compliant Problem Detail.
Development: StatusCode: 501
And now if I change the endpoint to throw a different exception,
[HttpGet(Name = "GetWeatherForecast")]
public IEnumerable<WeatherForecast> Get()
    throw new Exception("Something happened.");
I am getting the default Internal Server Error status code with the StackTrace.
Development: StatusCode: 500
And when in a production environment, we just get the response hiding internal details.
Production: StatusCode: 500

Hope this helps.

Happy Coding.


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