Exception handling in Dotnet Core


Exception handling in Dotnet Core 


This code defines a custom exception handling middleware in an ASP.NET Core application. The ExceptionMiddleware class is designed to catch, log, and handle exceptions globally, ensuring that detailed error information is captured and appropriate responses are returned to the client.

Key Features:

  1. Logging: The middleware logs key details when an exception occurs, including request method, URL, client IP address, and timestamp, which helps with debugging and monitoring.
  2. Custom Error Responses: Depending on the type of exception, it returns a specific HTTP status code and a structured error message to the client. It handles various exceptions like unauthorized access, bad requests, not found resources, validation issues, and rate-limiting errors.
  3. Environment-Sensitive Detail: In a development environment, the middleware includes more detailed exception information for easier debugging, while in production, it provides a more user-friendly error message to protect sensitive details.
  4. Custom Exception Types: It defines two custom exception types, ValidationException and RateLimitExceededException, for more specific handling of validation and rate-limiting errors.

Usage:

  • This middleware should be registered in the ASP.NET Core pipeline to handle any unhandled exceptions across the application.
  • It ensures that all exceptions are logged and a consistent, structured error response is returned to the client.

Overall, the middleware improves error handling, logging, and response consistency, while offering the flexibility to handle different types of errors in a meaningful way.

 


using System;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Hosting;  // Add this namespace for IHostEnvironment
using System.Text.Json;
using ECommerceWebAPI.Models;

namespace ECommerceWebAPI.Globals
{
    public class ExceptionMiddleware
    {
        private readonly RequestDelegate _next;
        private readonly ILogger<ExceptionMiddleware> _logger;
        private readonly IHostEnvironment _environment;  // Declare IHostEnvironment

        // Inject IHostEnvironment in the constructor
        public ExceptionMiddleware(RequestDelegate next, ILogger<ExceptionMiddleware> logger, IHostEnvironment environment)
        {
            _next = next;
            _logger = logger;
            _environment = environment;  // Assign it to the class field
        }

        public async Task InvokeAsync(HttpContext httpContext)
        {
            try
            {
                await _next(httpContext);
            }
            catch (Exception ex)
            {
                // Log the exception with details including request information
                LogException(httpContext, ex);
               
                // Handle the exception and return a custom response
                await HandleExceptionAsync(httpContext, ex);
            }
        }

        private void LogException(HttpContext context, Exception exception)
        {
            // Log details like the exception message, stack trace, request method, URL, and other useful info
            _logger.LogError(
                exception,
                "Exception occurred while processing request {Method} {Url} from {IpAddress} at {Time}. User: {User}.",
                context.Request.Method,
                context.Request.Path,
                context.Connection.RemoteIpAddress?.ToString(),
                DateTime.UtcNow,
                context.User.Identity?.Name);
        }

        private Task HandleExceptionAsync(HttpContext context, Exception exception)
        {
            context.Response.ContentType = "application/json";

            // Prepare a base error response structure
            var errorResponse = new ErrorResponse
            {
                StatusCode = context.Response.StatusCode,
                ErrorCode = "UNKNOWN_ERROR", // Default error code
                Message = "An unexpected error occurred.",
                UserMessage = "Something went wrong. Please try again later.",
                Timestamp = DateTime.UtcNow
            };

            // Handle specific exceptions and customize responses accordingly
            switch (exception)
            {
                case UnauthorizedAccessException _:
                    context.Response.StatusCode = StatusCodes.Status401Unauthorized;
                    errorResponse.ErrorCode = "UNAUTHORIZED";
                    errorResponse.Message = "You are not authorized to perform this action.";
                    errorResponse.UserMessage = "Access denied. Please check your credentials.";
                    break;

                case KeyNotFoundException _:
                case ArgumentException _:
                    context.Response.StatusCode = StatusCodes.Status400BadRequest;
                    errorResponse.ErrorCode = "BAD_REQUEST";
                    errorResponse.Message = "The request is invalid or contains bad data.";
                    errorResponse.UserMessage = "Please check your input and try again.";
                    break;

                case NotFoundException _:
                    context.Response.StatusCode = StatusCodes.Status404NotFound;
                    errorResponse.ErrorCode = "NOT_FOUND";
                    errorResponse.Message = "The resource you are looking for was not found.";
                    errorResponse.UserMessage = "We couldn't find the requested resource.";
                    break;

                case InvalidOperationException _:
                    context.Response.StatusCode = StatusCodes.Status409Conflict;
                    errorResponse.ErrorCode = "CONFLICT";
                    errorResponse.Message = "There was a conflict with the request.";
                    errorResponse.UserMessage = "There was an issue processing your request. Please try again.";
                    break;

                case ValidationException _:
                    context.Response.StatusCode = StatusCodes.Status422UnprocessableEntity;
                    errorResponse.ErrorCode = "VALIDATION_ERROR";
                    errorResponse.Message = "The request body is invalid.";
                    errorResponse.UserMessage = "Check the input data and try again.";
                    break;

                case RateLimitExceededException _:
                    context.Response.StatusCode = StatusCodes.Status429TooManyRequests;
                    errorResponse.ErrorCode = "RATE_LIMIT_EXCEEDED";
                    errorResponse.Message = "You have exceeded the maximum number of requests.";
                    errorResponse.UserMessage = "Please try again later.";
                    break;

                default:
                    context.Response.StatusCode = StatusCodes.Status500InternalServerError;
                    errorResponse.ErrorCode = "INTERNAL_SERVER_ERROR";
                    errorResponse.Message = exception.Message;
                    errorResponse.UserMessage = "An internal error occurred. Please try again later.";
                    break;
            }

            // In development, include more detailed information for debugging purposes.
            if (_environment.IsDevelopment())  // Use the injected IHostEnvironment here
            {
                errorResponse.Message = exception.ToString(); // Include full exception details in dev.
            }

            var responseJson = JsonSerializer.Serialize(errorResponse);
            return context.Response.WriteAsync(responseJson);
        }
    }

    // Custom exceptions
    public class ValidationException : Exception { }
    public class RateLimitExceededException : Exception { }
}




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