NullReferenceException: Object reference not set to an instance of an object in ASP .NET MVC

Aspose.ZIP Product Family
1

I have a standard ASP .NET Core MVC application. I’m using dropzone JS plugin to upload files and send them to controller’s action that works in a way, that every time a file is uploaded - an action is called. So for example, if 5 files are uploaded - the HttpPost action will be called 5 times. The file is passed to action as a parameter using [FromForm] IFormFile file.

Now, my task is to write a service for my controller, that will add every uploaded file to ZIP archive and in the end, when user is done and clicked the button - ZIP archive will start downloading on user’s computer. I tried some ideas with Aspose package, but I get the error in the title, here’s how my service looks like:

using Aspose.Zip;

namespace EncryptionUtility.Services;

public class ArchiveHelperService
{
private Archive _archive = new();
private MemoryStream _memoryStream;

public void AddFileToZip(string fileName, MemoryStream fileStream)
{
    _archive.CreateEntry(fileName, fileStream);
}

public MemoryStream DownloadArchive()
{
    _archive.Save(_memoryStream);
    _archive.Dispose();
    return _memoryStream;
}

}

And these are controller’s actions:

[HttpPost(“upload”)]
public async Task Upload([FromForm] IFormFile file)
{
var fileName = file.Name;
var stream = new MemoryStream();
await file.CopyToAsync(stream);
stream.Position = 0;
_service.AddFileToZip(fileName, stream);
}

[Route("download")]
public IActionResult Download()
{
    var archiveStream = _service.DownloadArchive();
    return File(archiveStream, "application/zip", "archive.zip");
}

Is this approach too naive? What could be the issue?

2

Hello @maksusoniosu, it seems that source of the entry does not exist at the time of saving.
_archive.CreateEntry(fileName, fileStream) does not compress and does not keep the content of fileStream, it keeps only reference to data stream.
Compression performs in _archive.Save method. So, all references to fileStream you passed for each entry must exist when you call DownloadArchive method.