Exception Handler not catching whole exception in custom middleware (.NET Core 2.0)

Question

I try to use middleware to exception handling. I wrote some code, but it is not working. Some thing wrong. In normaly, if I use try catch scope, I can catch the exception. But I couldn't catch in middleware. What is wrong?

I looking result entity in try scope. Result entity have an exception so I try to use if condition. I solve this problem but I think it is not acceptable:)

I throw some exception in my business layer (onion architecture) for example: throw new Exception("have a problem");

And my middleware class in webapi layer. I want to send response some data if I catch error.

My middleware code in below

public class ExceptionHandlingMiddleware
{
    private readonly RequestDelegate _next;

    public ExceptionHandlingMiddleware(RequestDelegate next)
    {
        _next = next;
    }

    public Task Invoke(HttpContext httpContext)
    {
        try
        {
            var result = _next(httpContext);
            if (result.Exception != null)
                throw result.Exception;
            return result;
        }
        catch (Exception ex)
        {
            return HandleExceptionAsync(httpContext, ex);
        }
    }

    private Task HandleExceptionAsync(HttpContext context, Exception exception)
    {
        var code = ResponseCode.Alliswell;

        switch (exception)
        {
            case ServiceException _:
                code = ResponseCode.ServiceError;
                break;
            case BusinessException _:
                code = ResponseCode.BusinessError;
                break;
            case DataLayerException _:
                code = ResponseCode.DataLayerError;
                break;
            case EsriServiceException _:
                code = ResponseCode.EsriServiceError;
                break;
        }

        //var result = JsonConvert.SerializeObject(new { error = ex.Message });

        context.Response.ContentType = "application/json";
        context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;
        var responseEntity = new Response<object>
        {
            Data = null,
            Code = code,
            ErrorMessage = exception.Message,
            State = ResponseState.Error
        };
        var result = context.Response.WriteAsync(JsonConvert.SerializeObject(responseEntity));
        return result;
    }
}

Nkosi · Accepted Answer · 2018-08-17 10:30:14Z

Use async await syntax within the middleware so that any exceptions thrown can be caught

public class ExceptionHandlingMiddleware {
    private readonly RequestDelegate _next;

    public ExceptionHandlingMiddleware(RequestDelegate next) {
        _next = next;
    }

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

    private async Task HandleExceptionAsync(HttpContext context, Exception exception) {
        var code = ResponseCode.Alliswell;

        switch (exception) {
            case ServiceException _:
                code = ResponseCode.ServiceError;
                break;
            case BusinessException _:
                code = ResponseCode.BusinessError;
                break;
            case DataLayerException _:
                code = ResponseCode.DataLayerError;
                break;
            case EsriServiceException _:
                code = ResponseCode.EsriServiceError;
                break;
        }

        //var result = JsonConvert.SerializeObject(new { error = ex.Message });

        context.Response.ContentType = "application/json";
        context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;
        var responseEntity = new Response<object> {
            Data = null,
            Code = code,
            ErrorMessage = exception.Message,
            State = ResponseState.Error
        };
        await context.Response.WriteAsync(JsonConvert.SerializeObject(responseEntity));
    }
}

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