Asp net core File result with Encoding

Question

From my ASP.Net Core 3.1 Web API I am trying to export simple CSV file. For that I am using CsvHelper package where I generate MemoryStream with following method:

public async Task<MemoryStream> ExportAsync(IEnumerable records)
{
    byte[] content = null;
    using (var mem = new MemoryStream())
    using (var writer = new StreamWriter(mem, Encoding.GetEncoding("windows-1250")))
    {
        using (var csvWriter = new CsvWriter(writer, CultureInfo.InvariantCulture))
        {
            csvWriter.Configuration.TypeConverterOptionsCache.GetOptions<DateTime>().Formats = new[] { "yyyy-MM-dd HH:mm:ss" };
            csvWriter.Configuration.Delimiter = "|";
            csvWriter.WriteField("sep=|", false);
            csvWriter.NextRecord();
            await csvWriter.WriteRecordsAsync(records).ConfigureAwait(false);
            await csvWriter.FlushAsync().ConfigureAwait(false);
            await writer.FlushAsync().ConfigureAwait(false);
            content = mem.ToArray();
        }
    }

    var output = new MemoryStream(content);
    return output;
}

This is called from my Controller in the following method:

[HttpGet("GetCountriesAsCSV")]
[SwaggerResponse(400, typeof(string))]
[SwaggerResponse(typeof(File))]
public async Task<IActionResult> GetCountriesAsCSV()
{
    try
    {
        var allCountries = await countryManager.GetAllAsync();
        var transformedCountries = mapper.Map<IEnumerable<CountryCsv>>(allCountries);
        var stream = await csvExportService.ExportAsync(transformedCountries).ConfigureAwait(false);

        return File(stream, "text/csv", $"AllCountries{DateTime.Now.Ticks}.csv");
    }
    catch (Exception ex)
    {
        return StatusCode((int)HttpStatusCode.BadRequest, ex.Message);
    }
}

The problem is, that when I open exported CSV file from Excel, special characters are not displayed correctly (due to encoding). This is what output looks like:

I have tried to use exactly the same method to generate CSV file, but instead of pushing it back as MemoryStream, I saved file directly in current folder as following:

private async Task WriteAll(IEnumerable records)
{
    using (var writer = new StreamWriter("RobertFile.csv", true, Encoding.GetEncoding("windows-1250")))
    {
        using (var csvWriter = new CsvWriter(writer, CultureInfo.InvariantCulture))
        {
            csvWriter.Configuration.TypeConverterOptionsCache.GetOptions<DateTime>().Formats = new[] { "yyyy-MM-dd HH:mm:ss" };
            csvWriter.Configuration.Delimiter = "|";
            csvWriter.WriteField("sep=|", false);
            csvWriter.NextRecord();
            await csvWriter.WriteRecordsAsync(records).ConfigureAwait(false);
            await csvWriter.FlushAsync().ConfigureAwait(false);
            await writer.FlushAsync().ConfigureAwait(false);
        }
    }
}

As you can see, the only difference between ExportAsync and this WriteAll method are StreamWriter parameters (yet, with the exact same encoding specifications).

Once I open this file, it looks perfectly fine as visible below:

I don't quite understand, why encoding is lost when converted to MemoryStream and then exported as a File object result.

Any help in respect to this matter would be highly appreciated.

Robert J. · Accepted Answer · 2021-02-21 11:24:03Z

4

So as soon as I changed Content Type from text/csv to application/octet-stream as following:

return File(stream, "application/octet-stream", "AllCountries.csv");

It suddenly worked like a charm.

answered Feb 21, 2021 at 11:24

Robert J.

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