How to make ASP.NET Core Web API action execute asynchronously?

I had this code for processing large files (this was for a large CSV file upload):

    public async Task<IActionResult> UploadAsync(IFormFile file)
    {
        // Ensure the file has contents before processing.
        if (file == null || file.Length == 0)
            throw new ApiException("Csv file should not be null", HttpStatusCode.BadRequest)
                .AddApiExceptionResponseDetails(ErrorTypeCode.ValidationError, ErrorCode.BelowMinimumLength, SOURCE); 

        // Ensure the file is not over the allowed limit.
        if (file.Length > (_settings.MaxCsvFileSize * 1024))
            throw new ApiException("Max file size exceeded, limit of " + _settings.MaxCsvFileSize + "mb", HttpStatusCode.BadRequest)
                .AddApiExceptionResponseDetails(ErrorTypeCode.ValidationError, ErrorCode.ExceedsMaximumLength, SOURCE); 

        // Ensure the file type is csv and content type is correct for the file.
        if (Path.GetExtension(file.FileName) != ".csv" || 
            !Constants.CsvAcceptedContentType.Contains(file.ContentType.ToLower(CultureInfo.InvariantCulture)))
                throw new ApiException("Csv content only accepted").AddApiExceptionResponseDetails(ErrorTypeCode.ValidationError, ErrorCode.Invalid, SOURCE);

        // Read csv content.
        var content = await file.ReadCsvAsync<OrderCsvResponseDto>() as CsvProcessedResponseDto<OrderCsvResponseDto>;

        await ProcessBulkUpload(content);

        // Return information about the csv file.
        return Ok(content);
    }

    internal async Task ProcessBulkUpload(CsvProcessedResponseDto<OrderCsvResponseDto> content)
    {
         // do some processing...
    }

There are web.config settings to increase the allowed time for file upload, this might help: How to increase the max upload file size in ASP.NET?

If your request exceeds the max timeout allowed data wont be returned to your caller as expected!

If you want to execute "fire-and-forget" code from C#, you can do this:

public static void FireAndForget(this Task task)
{
    Task.Run(async() => await task).ConfigureAwait(false);
}

Javascript:

xhr.onreadystatechange = function() { xhr.abort(); }

AngularJS:

var defer = $q.defer();
$http.get('/example', { timeout: defer.promise }).success(callback);
// [...]
defer.resolve();

Some async/await tips for Js: http://2ality.com/2016/10/async-function-tips.html