ASP.NET Core WebApi return error message to AngularJS $http promise

Question

I would like to return exception message to the AngularJS UI. As a back-end I use ASP.NET Core Web Api controller:

    [Route("api/cars/{carNumber}")]
    public string Get(string carNumber)
    {
        var jsonHttpResponse = _carInfoProvider.GetAllCarsByNumber(carNumber);
        if (jsonHttpResponse.HasError)
        {
            var message = new HttpResponseMessage(HttpStatusCode.InternalServerError)
            {
                Content = new StringContent(jsonHttpResponse.ErrorMessage)
            };

            throw new HttpResponseException(message);
        }

        return jsonHttpResponse.Content;
    }

But on Angular side, failure promise sees only status and statusText "Internal server error":

How can I pass the error message to the Angular $http failure promise from Core Web Api?

Answer 1

Unless you're doing some exception filtering, throw new HttpResponseException(message) is going to become an uncaught exception, which will be returned to your frontend as a generic 500 Internal Server Error.

What you should do instead is return a status code result, such as BadRequestResult. This means that instead of returning a string, your method needs to return IActionResult:

[Route("api/cars/{carNumber}")]
public IActionResult Get(string carNumber)
{
    var jsonHttpResponse = _carInfoProvider.GetAllCarsByNumber(carNumber);
    if (jsonHttpResponse.HasError)
    {
        return BadRequest(jsonHttpResponse.ErrorMessage);
    }

    return Ok(jsonHttpResponse.Content);
}

See also: my answer on how to return uncaught exceptions as JSON. (If you want all uncaught exceptions to be returned as JSON, instead.)