ASP.NET Core 3.1 MVC download file not found until IIS app pool recycle or run website from localhost

I am making an ASP.NET Core 3.1 MVC with Entity Framework website on a Microsoft server running IIS 10 with basic user file upload and download functions. I can upload files to the _webHostEnvironment.WebRootPath from the web but when I try to download them it cannot find them. However, if I recycle the app pool I can download the file (I can also download it from the web after accessing the website on localhost on the server).

Here is the code for when I upload the file:

string uniqueFileName = null;
if (model.Data != null)
{
    string uploadsFolder = Path.Combine(_webHostEnvironment.WebRootPath, "images");
    uniqueFileName = Guid.NewGuid().ToString() + "_" + model.Data.FileName;
    string filePath = Path.Combine(uploadsFolder, uniqueFileName);
    model.Data.CopyTo(new FileStream(filePath, FileMode.Create));
}

Here is the code for when I download it:

public FileResult DownloadData(string fileName, string tempAddCode, string patientName)
{
    byte[] fileBytes = System.IO.File.ReadAllBytes(Path.Combine(_webHostEnvironment.WebRootPath, "images") + "\" + fileName);
    var dataStream = new MemoryStream(fileBytes);
    return new FileStreamResult(dataStream, new MediaTypeHeaderValue("application/pdf"))
    {
        FileDownloadName = patientName.ToLower().Replace(" ", "_") + ".pdf"
    };
}

What is going on? Why would recycling the app pool fix this? Am I saving these user-uploaded files to the wrong location and ASP.NET is doing some sort of caching thing? I’d love any help finding a solution! Thanks.

Answers:

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Method 1

With this line you open file stream and never close it.

model.Data.CopyTo(new FileStream(filePath, FileMode.Create));

Make sure you always dispose your streams, so files don’t stay locked. Use code below to properly copy stream to file

using (var fs = new FileStream(filePath, FileMode.Create))
{
    model.Data.CopyTo(fs);
}

Method 2

What happens if you put a breakpoint in the DownloadData function, and step through? Does it successfully read the file into fileBytes, or do you get an exception – what exception do you get? Also check IIS logs to get the error code and post it, please.

Also, make sure the user that you’re running under, has Write access to the folder. By Default, it will not.

To add, right-click on the folder, security, and add (from computer)
IIS AppPool [whatever the appPool name is].

IIS AppPoolMyAppPool

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0