ASP.NET ExceptionMiddleware not continuing block of code

Question

I have a controller in ASP.NET that will be making a handful of api calls.

public async Task<IActionResult> PostRequest([FromBody] RequestModel request)
{    
    var firstApiCall = await _service.MakeFirstApiCall( ... );
    var secondApiCall = await _service.MakeSecondApiCall( ... );

    return new OkObjectResult(new { });
}

I need middleware to handle exceptions globally (shown below).

After firstApiCall throws an error, the exceptionMiddleware catches it, but then continues to return new OkObjectResult(new { }); instead of the next line, secondApiCall

The middleware is shown below. This is the complete vanilla version, I just want to see it continue to the next line rather then go to the return statement.

public class ExceptionMiddleware
    {
        private readonly RequestDelegate _next;
        private readonly ILogger<ExceptionMiddleware> _logger;

        public ExceptionMiddleware(RequestDelegate next, ILoggerFactory loggerFactory)
        {
            _next = next ?? throw new ArgumentNullException(nameof(next));
            _logger = loggerFactory?.CreateLogger<ApiExceptionMiddleware>() ?? throw new ArgumentNullException(nameof(loggerFactory));
        }

        public async Task Invoke(HttpContext context)
        {
            try
            {
                await _next(context);
            }
            catch (Exception ex)
            {
            }
        }
    }

If I wrap a try/catch around firstApiCall, it continues to the next line fine. Unsure why the behaviour isn't the same through the middleware.

Because When firstApiCall throw an exceptions, the execution of the action will be ended. Actions just behave like other methods. Middlewares can do some job only before or after of an Action. — Ali Zeinali
– Ali Zeinali, Commented Aug 11, 2019 at 14:00
Its working as expected. but I doubt return new OkObjectResult(new { }); of your action is ever called on exception, thats not how exceptions work. Its probably our middleware which returns it? Also don't abuse exceptions for flow control. Last but not least, you can start both task without awaiting them directly but wait for both: await Task.WhenAll(task1, task2) this way your second call can be called w/o awaiting the response of the first one (assuming it doesnt depend on a value returned from the first one) — Tseng
– Tseng, Commented Aug 11, 2019 at 20:08

grinay · Accepted Answer · 2019-08-11 14:05:09Z

0

Your middleware wrap action. Exception throws within this action and start propagate up to call stack until it reach place where it would be handled. In your case in your middleware. To order achieve your expected behavior you need to catch your exception within action .

answered Aug 11, 2019 at 14:05

grinay

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