Upload a Folder with Sub-folders and Files Recursively with Pure CSOM?

Question

Can someone please, share a CSOM (C# only) recursive method for uploading a folder with subfolders and files to a SharePoint Online Library?

I know about WebDav and FileExplorer, but it's not a solution in my case.

Answer 1

Here is a helper method I've written:

public class FileHelper
{
    public static void UploadDocument(ClientContext clientContext, string sourceFilePath, string serverRelativeDestinationPath)
    {
        using (var fs = new FileStream(sourceFilePath, FileMode.Open))
        {
            var fi = new FileInfo(sourceFilePath);
            Microsoft.SharePoint.Client.File.SaveBinaryDirect(clientContext, serverRelativeDestinationPath , fs, true);
        }
    }

    public static void UploadFolder(ClientContext clientContext, System.IO.DirectoryInfo folderInfo, Folder folder)
    {
        System.IO.FileInfo[] files = null;
        System.IO.DirectoryInfo[] subDirs = null;

        try
        {
            files = folderInfo.GetFiles("*.*");
        }
        catch (UnauthorizedAccessException e)
        {
            Console.WriteLine(e.Message);
        }

        catch (System.IO.DirectoryNotFoundException e)
        {
            Console.WriteLine(e.Message);
        }

        if (files != null)
        {
            foreach (System.IO.FileInfo fi in files)
            {
                Console.WriteLine(fi.FullName);
                clientContext.Load(folder);
                clientContext.ExecuteQuery();
                UploadDocument(clientContext, fi.FullName, folder.ServerRelativeUrl + "/" + fi.Name);
            }

            subDirs = folderInfo.GetDirectories();

            foreach (System.IO.DirectoryInfo dirInfo in subDirs)
            {
                Folder subFolder = folder.Folders.Add(dirInfo.Name);
                clientContext.ExecuteQuery();
                UploadFolder(clientContext, dirInfo, subFolder);
            }
        }
    }

    public static void UploadFoldersRecursively(ClientContext clientContext, string sourceFolder, string destinationLigraryTitle)
    {
        Web web = clientContext.Web;
        var query = clientContext.LoadQuery(web.Lists.Where(p => p.Title == destinationLigraryTitle));
        clientContext.ExecuteQuery();
        List documentsLibrary = query.FirstOrDefault();
        var folder = documentsLibrary.RootFolder;
        System.IO.DirectoryInfo di = new System.IO.DirectoryInfo(sourceFolder);

        clientContext.Load(documentsLibrary.RootFolder);
        clientContext.ExecuteQuery();

        folder = documentsLibrary.RootFolder.Folders.Add(di.Name);
        clientContext.ExecuteQuery();

        FileHelper.UploadFolder(clientContext, di, folder);
    }
}

Example of use:

FileHelper.UploadFoldersRecursively(clientContext, @"C:\BigFolder", "Documents");

Not sure if it's efficient enough, but at least it does the job