Handle Errors in Middleware in ASP.NET Core

Create a new folder named CustomExceptionMiddleware and a class ExceptionMiddleware.cs inside it.

The first thing we need to do is to register our IloggerManager service and RequestDelegate through the dependency injection.

The _next parameter of RequestDeleagate type is a function delegate that can process our HTTP requests.

After the registration process, we need to create the InvokeAsync() method. RequestDelegate can’t process requests without it.

The _next delegate should process the request and the Get action from our controller should generate a successful response. But if a request is unsuccessful (and it is, because we are forcing exception),

our middleware will trigger the catch block and call the HandleExceptionAsync method.

public class ExceptionMiddleware{
   private readonly RequestDelegate _next;
   private readonly ILoggerManager _logger;
   public ExceptionMiddleware(RequestDelegate next, ILoggerManager logger){
      _logger = logger;
      _next = next;
   }
   public async Task InvokeAsync(HttpContext httpContext){
      try{
            await _next(httpContext);
      }
      catch (Exception ex){
         _logger.LogError($"Something went wrong: {ex}");
         await HandleExceptionAsync(httpContext, ex);
      }
   }
   private Task HandleExceptionAsync(HttpContext context, Exception exception){
      context.Response.ContentType = "application/json";
      context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;
      return context.Response.WriteAsync(new ErrorDetails(){
         StatusCode = context.Response.StatusCode,
         Message = "Internal Server Error from the custom middleware."
      }.ToString());
   }
}

Modify our ExceptionMiddlewareExtensions class with another static method −

public static void ConfigureCustomExceptionMiddleware(this IApplicationBuilder
app){
   app.UseMiddleware<ExceptionMiddleware>();
}

use this method in the Configure method in the Startup class −

app.ConfigureCustomExceptionMiddleware();