How to Dispose My Filestream When Implementing a File Download in ASP.NET

How do I dispose my filestream when implementing a file download in ASP.NET?

You don't need to dispose the stream. It will be disposed by the FileStreamResult.WriteFile method. Code excerpt from this class:

public FileStreamResult(Stream fileStream, string contentType) : base(contentType)
{
    if (fileStream == null)
    {
        throw new ArgumentNullException("fileStream");
    }
    this.FileStream = fileStream;
}

protected override void WriteFile(HttpResponseBase response)
{
    Stream outputStream = response.OutputStream;
    using (this.FileStream)
    {
        byte[] buffer = new byte[0x1000];
        while (true)
        {
            int count = this.FileStream.Read(buffer, 0, 0x1000);
            if (count == 0)
            {
                return;
            }
            outputStream.Write(buffer, 0, count);
        }
    }
}

Notice the using. When you call File(dg.GetDocumentStream(), "text/plain", filename) from your controller this invokes the constructor which stores the stream into a public property which is disposed during the rendering.

Conclusion: you don't need to worry about disposing the stream obtain with dg.GetDocumentStream().

Does a Stream get Disposed when returning a File from an Action?

According to source code here aspnet/AspNetWebStack/blob/master/src/System.Web.Mvc/FileStreamResult.cs

Yes

protected override void WriteFile(HttpResponseBase response)
{
    // grab chunks of data and write to the output stream
    Stream outputStream = response.OutputStream;
    using (FileStream)
    {
        byte[] buffer = new byte[BufferSize];

        while (true)
        {
            int bytesRead = FileStream.Read(buffer, 0, BufferSize);
            if (bytesRead == 0)
            {
                // no more data
                break;
            }

            outputStream.Write(buffer, 0, bytesRead);
        }
    }
}

Where FileStream would have been the stream passed when you called

return File(stream, "application/octet-stream", "forums.csv");

Update.

Your question was originally tagged as Asp.Net MVC but the code looks like the more recent core framework.

Found it there as well though written differently it does the same thing technically.

aspnet/AspNetCore/blob/master/src/Mvc/Mvc.Core/src/Infrastructure/FileResultExecutorBase.cs

protected static async Task WriteFileAsync(HttpContext context, Stream fileStream, RangeItemHeaderValue range, long rangeLength)
{
    var outputStream = context.Response.Body;
    using (fileStream)
    {
        try
        {
            if (range == null)
            {
                await StreamCopyOperation.CopyToAsync(fileStream, outputStream, count: null, bufferSize: BufferSize, cancel: context.RequestAborted);
            }
            else
            {
                fileStream.Seek(range.From.Value, SeekOrigin.Begin);
                await StreamCopyOperation.CopyToAsync(fileStream, outputStream, rangeLength, BufferSize, context.RequestAborted);
            }
        }
        catch (OperationCanceledException)
        {
            // Don't throw this exception, it's most likely caused by the client disconnecting.
            // However, if it was cancelled for any other reason we need to prevent empty responses.
            context.Abort();
        }
    }
}

SQL Server stream file output in ASP.NET MVC and disposing connection

David Browne's answer gave me the information. I needed to register the disposable components using HttpContext.Response.RegisterForDispose();. This ensures it gets disposed after the request is complete.

Below is the updated code

public async Task<IActionResult> DownloadFile(Guid FileId)
{
    var connection = new SqlConnection(DatabaseService.ConnectionString);
    HttpContext.Response.RegisterForDispose(connection);

    await connection.OpenAsync();
    var command = connection.CreateCommand();
    HttpContext.Response.RegisterForDispose(command);

    command.CommandText = "select FileName, FileContent from Files where FileId=@FileId";
    command.CommandType = System.Data.CommandType.Text;
    command.Parameters.AddWithValue("@FileId", FileId);

    var reader = await command.ExecuteReaderAsync(System.Data.CommandBehavior.SequentialAccess | System.Data.CommandBehavior.SingleRow);
    HttpContext.Response.RegisterForDispose(reader);

    if (!await reader.ReadAsync())
        return NotFound();
    var attachmentName = Convert.ToString(reader[0]);

    var stream = reader.GetStream(1);
    HttpContext.Response.RegisterForDispose(stream);

    var response = File(stream, "application/octet-stream", attachmentName);
    return response;
}

I added this answer for clarity if others have the same issue

FileStreamResult - The process cannot access the file, because it is being used by another process

It seems the source of the FileStreamResult class shows it has no support for cancellation.
You will need to implement your own, if required. E.g. (not-tested, just imagined)

using System.IO;

namespace System.Web.Mvc
{
    public class CancellableFileStreamResult : FileResult
    {
        // default buffer size as defined in BufferedStream type
        private const int BufferSize = 0x1000;

        private readonly CancellationToken _cancellationToken;

        public CancellableFileStreamResult(Stream fileStream, string contentType,
            CancellationToken cancellationToken)
            : base(contentType)
        {
            if (fileStream == null)
            {
                throw new ArgumentNullException("fileStream");
            }

            FileStream = fileStream;
            _cancellationToken = cancellationToken;
        }

        public Stream FileStream { get; private set; }

        protected override void WriteFile(HttpResponseBase response)
        {
            // grab chunks of data and write to the output stream
            Stream outputStream = response.OutputStream;
            using (FileStream)
            {
                byte[] buffer = new byte[BufferSize];

                while (!_cancellationToken.IsCancellationRequested)
                {
                    int bytesRead = FileStream.Read(buffer, 0, BufferSize);
                    if (bytesRead == 0)
                    {
                        // no more data
                        break;
                    }

                    outputStream.Write(buffer, 0, bytesRead);
                }
            }
        }
    }
}

You can then use it like

public IActionResult Download(string path, string fileName, CancellationToken cancellationToken)
{
    var fileStream = System.IO.File.OpenRead(path);
    var result = new CancellableFileStreamResult(
        fileStream, "application/force-download", cancellationToken);
    result.FileDownloadName = fileName;
    return result;
}

Again, I'm this is not tested, just imagined.
Maybe this doesn't work, as the action is already finished, thus cannot be cancelled anymore.

EDIT:
The above answer "Imagined" for ASP.net framework. ASP.net core has a quite different underlying framework: In .net core, the action is processed by and executor, as shown in the source. That will eventually call WriteFileAsync in the FileResultHelper. There you can see that StreamCopyOperation is called with the cancellationToken context.RequestAborted. I.e. cancellation is in place in .net Core.

The big question is: why isn't the request aborted in your case.

How to dispose file stream in api?

First of all, remember about concurrency and thread safety. (many request can pass to your controller at the same time. And in this case if you are writing som,ething to the file - the behaviour of app can be wrong).
If you are not writing to the file (only reading), then you can just specify the sharing mode for other threads like this:

using(var file = File.Open(path, FileMode.Open, FileAccess.Read, FileShare.ReadWrite)){
   //your code goes here
}

How to delete file after download with ASP.NET MVC?

You could create a custom actionfilter for the action with an OnActionExecuted Method that would then remove the file after the action was completed, something like

public class DeleteFileAttribute : ActionFilterAttribute 
{ 
    public override void OnActionExecuted(ActionExecutedContext filterContext) 
    { 
        // Delete file 
    } 
} 

then your action has

[DeleteFileAttribute]
public FileContentResult GetFile(int id)
{
   ...
}

Does FileStreamResult close Stream?

Yes. It uses a using block around the stream, and that ensures that the resource will dispose.

Here is the internal implementation of the FileStreamResult WriteFile method:

protected override void WriteFile(HttpResponseBase response)
{
    // grab chunks of data and write to the output stream
    Stream outputStream = response.OutputStream;
    using (FileStream)
    {
        byte[] buffer = new byte[BufferSize];

        while (true)
        {
            int bytesRead = FileStream.Read(buffer, 0, BufferSize);
            if (bytesRead == 0)
            {
                // no more data
                break;
            }

            outputStream.Write(buffer, 0, bytesRead);
        }
    }
}

How to copy or grab a file from stream and copy it to a folder in the server

fileStream.CopyTo(fileStream) seems to be attempting to copy a stream to itself.

Try replacing with fileStreamResult.FileStream.CopyTo(fileStream) ?

ASP.NET MVC FileStreamResult, fileDownloadName is not used

No, this is not possible with a PDF displayed inline. You could achieve this if you send the Content-Disposition header with as an attachment:

public ActionResult PDFGenerator(int id)
{
    Stream stream = GeneratePDF(id);
    return File(stream, "application/pdf", "myPDF.pdf");
}

Also notice how I removed the unnecessary MemoryStream you were using and loading the PDF in memory where you could have directly streamed it to the client which would have been far more efficient.

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