Handling with temporary file stream

Question

Say I want to define a TempFileStream class that creates a temporary file using Path.GetTempFileName() method. A temporary file must be deleted when TempFileStream\'s object

Answer 1

I know this is an older thread, but here's an alternate solution. I started to implement the TempFileStream, but I wanted more concurrency. My use-case involves exporting [potentially MBs of] database results to a CSV file via MVC. I want to begin downloading to the client as soon as data are available from the database query rather than wait for a potentially large temp file to be written before I start downloading.

In this solution, I launch the query in a separate thread which fills an AnonymousPipeStream. The main thread can then slurp the data from the other end of the pipe as its available. It uses .Net 4 Tasks.

Hope someone else finds this useful.

-Rob

Controller method:

public FileResult ResultExport ( ReportOptions options )
{
    ResultExport rpt = new ResultExport( options );
    HttpContext.Response.BufferOutput = false;
    return File( rpt.Export(), "text/csv", "results.csv" );
}

Model:

public ResultExport
{
    private AnonymousPipeServerStream WriteStream = null;

    public Stream Export()
    {
        //
        // We'll fire off the database query in a background
        // thread.  It will write data to one end of the pipe.  We'll return the reader
        // end of that pipe to our caller.
        //
        WriteStream = new AnonymousPipeServerStream( PipeDirection.Out );
        AnonymousPipeClientStream reader = new AnonymousPipeClientStream( PipeDirection.In, WriteStream.ClientSafePipeHandle );

        //
        // Call Execute() in a background thread.
        //
        Task.Factory.StartNew( () => Execute() );

        //
        // While Execute() is filling the pipe with data,
        // return the reader end of the pipe to our caller.
        //
        return reader;
    }

    private void Execute ()
    {
        //
        // WriteStream should only by populated by Export()
        //
        if( WriteStream != null )
        {
            using ( StreamWriter sw = new StreamWriter( WriteStream, Encoding.UTF8, 4096 ) )
            {
                //
                // Shove data into the StreamWriter as we get it from the database
                //
                foreach ( string line in ExportCore() )
                {
                    // Each line is a comma-delimited set of values
                    sw.WriteLine( line );
                }
            }
        }
    }
}