Error Handling and Exception Management in C# REST APIs

If you want to ensure your C# REST APIs run smoothly and without errors this guide will show about error handling and exception management, allowing you to create powerful and dependable APIs.

Understanding Errors and Exceptions in C# REST APIs

Before we start on error handling and exception management with C# REST APIs, it is important to understand the difference between errors and exceptions.

Errors in programming are unanticipated events or conditions that occur during the execution of a program and can cause it to terminate or act abnormally.

Exceptions are events that occur during programme execution but may be addressed and recovered from. Understanding the distinction between mistakes and exceptions is important for controlling and handling them efficiently in your C# REST APIs.

Implementing Error Handling Strategies in C# REST APIs

Implementing appropriate error-handling solutions is important for ensuring that your C# REST APIs run smoothly. You can give users relevant error messages, log errors for troubleshooting purposes, and gracefully recover from exceptions by handling failures correctly.

You can handle issues in your APIs via various methods, including try-catch blocks, handling global exceptions, and returning proper HTTP status codes.

Handling Exceptions and Returning Appropriate Responses

Error handling must be done appropriately to return acceptable responses to the clients while working with C# REST APIs. This is quite important in many applications, as sometimes users are made aware of an error notification, which aids in troubleshooting and recovering exceptions. The most common practice for handling such errors could be using a try-catch block to capture and handle specific exceptions. You can catch exceptions for appropriate measures and custom error messages. Other methods include global exception handling, which enables you to centralize error-handling logic and provide consistent error answers throughout your API. Proper HTTP status codes are needed to represent whether API requests have succeeded or failed.

Structured Exception Handling

Use structured exception handling within your application to catch and process the exception further up your application, where appropriate. Therefore, handle exceptions softly and do not lead to application crashes.

try
{
    // Code that may throw exceptions
}
catch (Exception ex)
{
    // Handle the exception, log it, and provide a meaningful response
}

Global Exception Handling Middleware

Use global exception handling middleware to catch unhandled exceptions and offer consistent error answers. You can write your middleware to catch exceptions and return a structured error response.

Create a custom middleware class that handles exceptions:

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Http;
using Newtonsoft.Json;
using System;
using System.Net;
using System.Threading.Tasks;

public class GlobalExceptionHandlerMiddleware
{
    private readonly RequestDelegate next;

    public GlobalExceptionHandlerMiddleware(RequestDelegate next)
    {
        this.next = next;
    }

    public async Task InvokeAsync(HttpContext context)
    {
        try
        {
            await next(context);
        }
        catch (Exception ex)
        {
            await HandleExceptionAsync(context, ex);
        }
    }

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

        var errorResponse = new ErrorResponse
        {
            Message = "An error occurred while processing your request.",
            Detail = exception.Message
            // You can include more properties as needed
        };

        return context.Response.WriteAsync(JsonConvert.SerializeObject(errorResponse));
    }
}

Next, create a custom error response class:

public class ErrorResponse
{
    public string Message { get; set; }
    public string Detail { get; set; }
    // You can add more properties as needed
}

Register the GlobalExceptionHandlerMiddleware in your Startup.cs

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if (env.IsDevelopment())
    {
        // Add development-specific error handling, e.g., detailed error messages
    }
    else
    {
        // Use the global exception handler middleware for other environments
        app.UseMiddleware<GlobalExceptionHandlerMiddleware>();
    }

    // ...
}

Your controller actions should throw exceptions when an error occurs.

[ApiController]
[Route("api/[controller]")]
public class YourController : ControllerBase
{
    [HttpGet("{id}")]
    public IActionResult Get(int id)
    {
        // Simulate an error by throwing an exception
        if (id == 0)
        {
            throw new ApplicationException("Invalid ID");
        }

        // Your regular controller logic
        return Ok($"Received ID: {id}");
    }
}

When an exception is thrown within your controller actions or middleware, the 'GlobalExceptionHandlerMiddleware' will catch it. After that, the middleware serialises the error response as JSON and transmits it to the client with the appropriate HTTP status code.

Depending on your application's requirements, you can further customise the error handling logic, add extra error data, and log errors to other sources.

Logging and Monitoring Errors in C# REST APIs

Error logging and monitoring in your C# REST APIs is important for quickly uncovering and addressing issues. You can log all errors in your API using a logging system, including the specifics of the error, such as the request URL, the user who made the request, and any applicable data. This information can be useful for troubleshooting and debugging.

API Monitoring technologies can assist you in proactively identifying and addressing any potential issues before they affect your users. You may gain insights into the performance and reliability of your API and make necessary modifications by checking your logs and monitoring metrics regularly.

Using SeriLog to Log Exceptions

To use Serilog to log exceptions in a C# ASP.NET Core REST API, first install Serilog and configure it to capture and log exceptions.

dotnet add package Serilog
dotnet add package Serilog.Sinks.Console

Configure Serilog in the ConfigureServices method of your Startup.cs file. Serilog is often configured to log to various sinks, such as the console, file, or other destinations. The following is a basic configuration for logging exceptions to the console; you can also log in to the SQL database and more.

using Serilog;
using Serilog.Events;

public void ConfigureServices(IServiceCollection services)
{
    // Add Serilog to the built-in ASP.NET Core logger
    Log.Logger = new LoggerConfiguration()
        .MinimumLevel.Error()  // Log only errors and higher
        .WriteTo.Console()
        .CreateLogger();

    services.AddLogging(loggingBuilder =>
    {
        loggingBuilder.AddSerilog();
    });

    // Other service configurations...
}

This sets up Serilog to log only errors and higher-level events and send them to the console.

You should now add Serilog to your global exception-handling middleware to log exceptions. In your Startup.cs, configure the UseExceptionHandler middleware to log unhandled exceptions.

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    // ... other middleware ...

    // Global exception handling
    app.UseExceptionHandler(errorApp =>
    {
        errorApp.Run(async context =>
        {
            var exceptionHandlerPathFeature = context.Features.Get<IExceptionHandlerPathFeature>();
            var exception = exceptionHandlerPathFeature.Error;

            Log.Error(exception, "Unhandled exception occurred");

            context.Response.StatusCode = 500; // Internal Server Error
            context.Response.ContentType = "application/json";
            await context.Response.WriteAsync("An error occurred. Please try again later.");
        });
    });

    // ... other middleware ...
}

Unhandled exceptions are caught and logged using Serilog's 'Log.Error' method, and an appropriate response is returned to the client. Serilog can also log exceptions within your API endpoints and services. As an example:

try
{
    // Code that may throw exceptions
}
catch (Exception ex)
{
    Log.Error(ex, "An error occurred in the API endpoint");
}

Launch your ASP.NET Core REST API and trigger an exception to test if Serilog logs the exception details to the console and other configured sinks.

In your Serilog configuration, configure additional sinks such as log files, log levels, and log output types. On most production systems, exceptions are usually logged to a central logging system, such as Elasticsearch, Seq, or some log aggregation server. Serilog has several types of sinks and many options to customize your logging setup.

Best Practices for Exception Management in C# REST APIs

1. Structured exception handling is a best practice that allows you to catch and handle specified sorts of exceptions in a controlled manner. This helps to avoid unexpected crashes and allows you to handle problems in a manner appropriate for your application.
2. Give clients informative error messages that include specifics about the error and any applicable troubleshooting actions. This can assist users in better understanding and resolving difficulties. It would be best to use correct HTTP status codes to reflect errors or messages.
   • 200 (OK) for successful requests.
   • 201 (Created) for resource creation.
   • 204 (No Content) for successful requests without a response.
   • 400 (Bad Request) for client errors.
   • 401 (Unauthorised) for authentication failure.
   • 404 (Not Found) for resource not found.
   • 500 (Internal Server Error) for server errors.
3. Logging exceptions is necessary for troubleshooting and debugging. You can track and analyse failures, detect patterns, and make necessary API enhancements by recording exceptions. Implementing these recommended practices will assist you in creating dependable and user-friendly C# REST APIs.
4. When dealing with validation errors (e.g., input validation, model validation), return a 400 Bad Request status code with detailed error information in the response, such as validation errors for specific fields.
5. Consider using API versioning to ensure backward compatibility when making changes to your API. This helps in handling breaking changes and exceptions caused by version differences.
6. Unit tests should be written to confirm that your exception-handling logic works as planned. Experiment with scenarios such as successful requests, client failures, and server problems.
7. In your API documentation, include clear and descriptive error messages and potential fixes. This helps your API users understand what went wrong and how to manage issues.