A CSV Writer that can be used to write directly to a response stream in ASP.NET

CsvWriter.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;

namespace DataUtils
{
    /// <summary>
    /// Derived from Richard Carr's (Black Wasp) CsvWriter class at http://blackwasp.co.uk/WriteCsv.aspx
    /// </summary>
    public class CsvWriter : StreamWriter
    {
        char _delimiter, _quote;
        string _singleQuote, _doubleQuote;
        List<char> _quotableCharacters;
        string _commentToken;

        public char Delimiter
        {
            get
            {
                return _delimiter;
            }
            set
            {
                _delimiter = value;
                ResetQuotableCharacters();
            }
        }

        public char Quote
        {
            get
            {
                return _quote;
            }
            set
            {
                _quote = value;
                _singleQuote = value.ToString();
                _doubleQuote = _singleQuote + _singleQuote;
                ResetQuotableCharacters();
            }
        }

        public string CommentToken
        {
            get
            {
                return _commentToken;
            }
            set
            {
                if (value == null) throw new ArgumentNullException("value");
                if (value.Length == 0) throw new ArgumentException("Value must not be empty");

                _commentToken = value;
            }
        }

        private void ResetQuotableCharacters()
        {
            _quotableCharacters = new List<char>();
            _quotableCharacters.AddRange(Environment.NewLine.ToCharArray());
            _quotableCharacters.Add(_delimiter);
            _quotableCharacters.Add(_quote);
        }

        public CsvWriter(Stream stream)
            : base(stream)
        {
            Delimiter = ',';
            Quote = '"';
            CommentToken = "## ";
        }

        public void WriteLine(string[] fields)
        {
            bool first = true;
            foreach (string field in fields)
            {
                WriteField(first, field);
                first = false;
            }
            WriteLine();
        }

        private void WriteField(bool first, string field)
        {
            if (!first)
            {
                Write(_delimiter);
            }
            WritePreparedField(field);
        }

        private void WritePreparedField(string field)
        {
            string prepared = PrepareField(field);
            Write(prepared);
        }

        private string PrepareField(string field)
        {
            string quotesDoubled = DoubleQuotes(field);
            string prepared = AddQuotesIfRequired(quotesDoubled);
            return prepared;
        }

        private string DoubleQuotes(string field)
        {
            return field.Replace(_singleQuote, _doubleQuote);
        }

        private string AddQuotesIfRequired(string field)
        {
            foreach (char quotable in _quotableCharacters)
            {
                if (field.StartsWith(_commentToken) || field.Contains(quotable))
                {
                    return string.Format("{0}{1}{0}", _quote, field);
                }
            }
            return field;
        }

        public void WriteComment(string comment)
        {
            Write(_commentToken);
            WriteLine(comment);
        }
    }
}

usage.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using DataUtils;

namespace WebApplication1
{
    public partial class Default : System.Web.UI.Page
    {
        protected void Unnamed1_Click(object sender, EventArgs e)
        {
            Response.Clear();
            Response.ContentType = "text/csv";
            Response.AddHeader("Content-Disposition", "attachment; filename=data-export.csv");

            var csvWriter = new CsvWriter(Response.OutputStream);

            // Output column list
            var columns = new List<string>();

            columns.Add("Column 1");
            columns.Add("Column 2");

            csvWriter.WriteLine(columns.ToArray());

            // Output data                                              
            // In your loop, write the columns                          
            //for (int i = 0; i < UPPER; i++)                           
            //{                                                         
            var data = new List<string>();

            data.Add("data 1");
            data.Add("data 2");

            csvWriter.WriteLine(data.ToArray());
            //}                                                                                                                           

            csvWriter.Flush();

            Response.End();
        }
    }
}

What is the option for "Response.OutputStream" in ASP.NET core