OutOfMemoryException when send big file 500MB using FileStream ASPNET

I've created download page which allows user to download up to 4gb (may be more) few months ago. Here is my working snippet:

  private void TransmitFile(string fullPath, string outFileName)
    {
        System.IO.Stream iStream = null;

        // Buffer to read 10K bytes in chunk:
        byte[] buffer = new Byte[10000];

        // Length of the file:
        int length;

        // Total bytes to read:
        long dataToRead;

        // Identify the file to download including its path.
        string filepath = fullPath;

        // Identify the file name.
        string filename = System.IO.Path.GetFileName(filepath);

        try
        {
            // Open the file.
            iStream = new System.IO.FileStream(filepath, System.IO.FileMode.Open,
                        System.IO.FileAccess.Read, System.IO.FileShare.Read);


            // Total bytes to read:
            dataToRead = iStream.Length;

            Response.Clear();
            Response.ContentType = "application/octet-stream";
            Response.AddHeader("Content-Disposition", "attachment; filename=" + outFileName);
            Response.AddHeader("Content-Length", iStream.Length.ToString());

            // Read the bytes.
            while (dataToRead > 0)
            {
                // Verify that the client is connected.
                if (Response.IsClientConnected)
                {
                    // Read the data in buffer.
                    length = iStream.Read(buffer, 0, 10000);

                    // Write the data to the current output stream.
                    Response.OutputStream.Write(buffer, 0, length);

                    // Flush the data to the output.
                    Response.Flush();

                    buffer = new Byte[10000];
                    dataToRead = dataToRead - length;
                }
                else
                {
                    //prevent infinite loop if user disconnects
                    dataToRead = -1;
                }
            }
        }
        catch (Exception ex)
        {
            throw new ApplicationException(ex.Message);
        }
        finally
        {
            if (iStream != null)
            {
                //Close the file.
                iStream.Close();
            }
            Response.Close();
        }
    }

You do not need to hold the whole file in memory just read it and write to the response stream in a loop.

I came across this question in my search to return a FileStreamResult from a controller, as I kept running into issues while working with large streams due to .Net trying to build the entire response all at once. Pavel Morshenyuk's answer was a huge help, but I figured I'd share the BufferedFileStreamResult that I ended up with.

/// <summary>Based upon https://stackoverflow.com/a/3363015/595473 </summary>
public class BufferedFileStreamResult : System.Web.Mvc.FileStreamResult
{
    public BufferedFileStreamResult(System.IO.Stream stream, string contentType, string fileDownloadName)
        : base(stream, contentType)
    {
        FileDownloadName = fileDownloadName;
    }

    public int BufferSize { get; set; } = 16 * 1024 * 1024;//--16MiB

    protected override void WriteFile(System.Web.HttpResponseBase response)
    {
        try
        {
            response.Clear();
            response.Headers.Set("Content-Disposition", $"attachment; filename={FileDownloadName}");
            response.Headers.Set("Content-Length", FileStream.Length.ToString());

            byte[] buffer;
            int bytesRead;

            while (response.IsClientConnected)//--Prevent infinite loop if user disconnects
            {
                buffer = new byte[BufferSize];

                //--Read the data in buffer
                if ((bytesRead = FileStream.Read(buffer, 0, BufferSize)) == 0)
                {
                    break;//--Stop writing if there's nothing left to write
                }

                //--Write the data to the current output stream
                response.OutputStream.Write(buffer, 0, bytesRead);

                //--Flush the data to the output
                response.Flush();
            }
        }
        finally
        {
            FileStream?.Close();
            response.Close();
        }
    }
}

Now, in my controller, I can just

return new BufferedFileStreamResult(stream, contentType, fileDownloadName);