error handling

content/posts/error-handling-dotnet.md

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+---
+title: "Error Handling Dotnet"
+date: 2024-06-20T20:00:06-03:00
+draft: false
+summary: "Because returning stack traces isn't secure."
+---
+
+The main idea behind having centralized error handling is that we can process any unhandled exception to:
+* Return formatted responses without revealing any internal functionality
+* Process issues so that they are properly logged on logs or other monitoring systems (like Sentry)
+* Make sure all errors have the same external behavior
+
+For that, we will use a new middleware class:
+```csharp
+public class ErrorResponse
+{
+    public string Message { get; set; }
+}
+
+
+public class ErrorHandlerMiddleware {
+    private readonly RequestDelegate _next;
+    private readonly ILogger<ErrorHandlerMiddleware> _logger;
+    private readonly IHostEnvironment _env;
+
+    public ErrorHandlerMiddleware(RequestDelegate next, ILogger<ErrorHandlerMiddleware> logger, IHostEnvironment env){
+        _next = next;
+        _logger = logger;
+        _env = env;
+    }
+
+    public async Task Invoke(HttpContext httpContext)
+    {
+        // Attempts to execute the next action on the http chain
+        // If it fails, we log the exception and trigger the HandleErrorAsync method
+        try
+        {
+            await _next(httpContext);
+        }
+        catch(Exception ex)
+        {
+            _logger.LogError(ex, "An unhandled exception has occurred: {Message}", ex.Message);
+            await HandleErrorAsync(httpContext, ex);
+        }
+    }
+
+    private async Task HandleErrorAsync(HttpContext context, Exception exception)
+    {
+        context.Response.ContentType = "application/json";
+        context.Response.StatusCode = (int) HttpStatusCode.InternalServerError;
+
+        ErrorResponse errorResponse;
+
+        if (_env.IsDevelopment())
+        {
+            // In development, we want to see the full details for easier debugging.
+            errorResponse = new ErrorResponse
+            {
+                Message = exception.ToString()
+            };
+        }
+        else
+        {
+            // In production, we return a generic message to avoid leaking details.
+            errorResponse = new ErrorResponse
+            {
+                Message = "An internal server error occurred. Please try again later."
+            };
+        }
+
+        // We use the modern System.Text.Json for serialization via WriteAsJsonAsync
+        await context.Response.WriteAsJsonAsync(errorResponse);
+    }
+}
+```
+
+We will also define a new Extension class to register this middleware:
+```csharp
+public static class ErrorHandlerExtensions
+{
+    public static IApplicationBuilder UseErrorHandler(this IApplicationBuilder appBuilder)
+    {
+        return appBuilder.UseMiddleware<ErrorHandler>();
+    }
+}
+```
+
+And then we just configure it on the `Configure()` method at the startup:
+```csharp
+public void Configure(IApplicationBuilder app)
+{
+    app.UseErrorHandler();
+}
+```
+
+Now, when there's an issue on the API execution, the API will return something like this:
+```json
+{
+    "Message": "Internal Server Error"
+}
+```
+
+Sources:
+* [https://learn.microsoft.com/en-us/aspnet/core/fundamentals/middleware/write?view=aspnetcore-8.0](https://learn.microsoft.com/en-us/aspnet/core/fundamentals/middleware/write?view=aspnetcore-8.0)