Example of using CsvHelper to write a CSV file (up to 10MB in size) to SharePoint Online

CsvHelperExample.cs

using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using OfficeDevPnP.Core;
using Microsoft.SharePoint.Client;
using System.IO;
using CsvHelper;
using File = Microsoft.SharePoint.Client.File;

using CsvHelper.Configuration.Attributes;

public class CsvRow
{
      [Index(0)]
      public DateTime TimeStamp { get; set; }
      [Index(1)]
      public string SiteUrl { get; set; }
      [Index(2)]
      public string Message { get; set; }
      [Index(3)]
      public string Level { get; set; }
      
      public CsvRow() {}
}

public class CsvHelperExample
{
   public ClientContext ClientContext { get; set; }
   
   public void WriteFile(string listName, string folderName, string fileName, List<CsvRow> csvRows)
   {
      // load list, get/create folder
      List list = ClientContext.Web.GetListByTitle(listName, li => li.RootFolder);
      Folder folder = list.RootFolder.EnsureFolder(folderName);

      using (MemoryStream stream = new MemoryStream())
      {
         using (TextWriter writer = new StreamWriter(stream))
         using (var csv = new CsvWriter(writer))
         {
            csv.WriteRecords(csvRows);

            writer.Flush();
            stream.Position = 0;

            // write stream to file and upload
            using (StreamReader reader = new StreamReader(stream))
            {
               folder.UploadFile($"{fileName}.csv", stream, true);
            }
         }
      }
   }
   
   public CsvHelperExample(ClientContext clientContext)
   {
      ClientContext = clientContext;   
   }
}