I’m using Kestrel on Ubuntu 20.04 as an internet facing edge web server, using ASP.NET 5 with Razor Pages.

Update - am using nginx as a reverse proxy now so can handle: redirect to apex, ssl cert, no iptables direct to port 5000. Detailed blog here

I need to be able to handle large file uploads, which initially are zip files up to a few GB

https://github.com/djhmateer/tus-test is a sample project

https://github.com/osr4rightstools/osr4rights-tools bigger project


https://tus.io/ Open Protocol for Resumable File Uploads.


Give user feedback on upload progress

alt text

and then can resume even after the browser has been closed.

alt text

https://github.com/transloadit/uppy is build by the team at https://transloadit.com/ who wrote Tus.


https://github.com/tusdotnet/tusdotnet .NET server implementation of the Tus protocol for resumable file uploads.


https://github.com/tus/tus-js-client A pure JavaScript client for the tus resumable upload protocol

There is a nice html sample included in the project:

git clone https://github.com/tus/tus-js-client.git

# gets all the node_modules
npm install

# creates dist folder (essentially tus.js)
npm run build

# run the demos\browser\index.html file

alt text

Resume works fine with the sample server implementation

alt text

I had some issues with the server side implementation and resuming.

alt text

It uses local storage to remember previous uploads

Razor Pages Source for this demo is https://github.com/djhmateer/tus-test

Remember to run npm.

Test files

To test the validity of the files, we need something to verify:

https://github.com/NVlabs/ffhq-dataset/ - Flickr-Faces-HQ Dataset. Has 70k images on Google Drive totally 2.56TB.

I ended up making sample image zips up to

  • 100MB was a limit (imposed by cloudflare)
  • 2GB was a limit (imposed by some filesystems)
  • 4GB
  • 6GB

Manually Create large test files


dd if=/dev/zero of=1GB.test bs=1G count=1

Can be useful, but I prefer to have files I can sanity check.

A Simple Upload form

The simplest possible thing is always a great place to start, but having no user feedback is not a good experience.

<form method="post" enctype="multipart/form-data">
    <input type="file" asp-for="Upload" />
    <input type="submit" />

then on the code behind

public IFormFile? Upload { get; set; }

public async Task<IActionResult> OnPostAsync(CancellationToken cancellationToken)
    var connectionString = AppConfiguration.LoadFromEnvironment().ConnectionString;

    // check that Upload is something
    if (Upload is { } && Upload.Length > 0)
        Log.Information($"Uploaded file {Upload.FileName}");
        // eg C:\Users\djhma\AppData\Local\Temp on Windows
        var path = Path.GetTempPath();

        // get next jobId from Db
        var jobId = await Db.InsertJobWithOrigFileNameAndReturnJobId(connectionString, Upload.FileName);

        var fileName = Path.Combine(path, $"job-{jobId}.tmp");

        // copy uploaded file to tempPath location as job-{jobId}.tmp
        using (var fileStream = new FileStream(fileName, FileMode.Create, FileAccess.Write))
            await Upload.CopyToAsync(fileStream, cancellationToken);

        // The Result page will kick off the job
        return Redirect($"Results/{jobId}");

    return RedirectToPage("UploadFailed");


// to allow large form uploads
services.Configure<KestrelServerOptions>(options =>
    options.Limits.MaxRequestBodySize = int.MaxValue; // if don't set default value is: 30 MB

// to allow large form uploads
services.Configure<FormOptions>(x =>
    x.ValueLengthLimit = int.MaxValue;
    x.MultipartBodyLengthLimit = int.MaxValue; // if don't set default value is: 128 MB
    x.MultipartHeadersLengthLimit = int.MaxValue;

Cloudflare and Tus

After switching on cloudflare for my project to do:

  • SSL Certificates automatically
  • 301 Redirects to Apex domain from www

I noticed that my large file uploads were failing (on a simple pre Tus upload)

https://gridpane.com/kb/cloudflares-cdn-and-upload-limitations/ explained why - 100mb file upload limit

Uploading a 92Mb file worked fine, and 121Mb gave (sometimes)

413 Request Entity too large cloudflare

A 200Mb actually gave a blank screen in chrome and


Interestingly I found that chunking which Tus supports gave strange errors through Cloudflare. So I turned off Cloudflare.

Tus Bugs

When a successful file upload, why does it prompt if I upload that file again? I found that it was the file permissions on the tusstore on my production server. OSR4Rights-Tools has it implemented properly with the permissions set on VM build stage.

don’t have javascript popup as Chrome wont work if that window isn’t in focus


Below are some other file upload strategies



Can do processing on the client to give thumbnails Drag and drop

alt text

https://stackoverflow.com/questions/56905302/solved-blueimp-jquery-file-upload-doesnt-work-with-asp-net-core-razor-pages Razor Pages



Great example https://github.com/jayarjo/plupload-demos/blob/master/README.md the UI Widget here on jsfiddle

Not much seems to have been done over the last 5 years.

Tried examples but couldn’t get easily to work.


Firefox 4+ and Chrome 11+

From the guys https://github.com/23/resumable.js at 23.



https://www.syncfusion.com/sales/speciallicensingprograms - possible open source license