Writing to Output Stream from Action

Question

For some strange reasons, I want to write HTML directly to the Response stream from a controller action. (I understand MVC separation, but this is a special case.)

C

Answer 1

I used a class derived from FileResult to achieve this using normal MVC pattern:

/// 

/// MVC action result that generates the file content using a delegate that writes the content directly to the output stream.
/// 
public class FileGeneratingResult : FileResult
{
    /// 

    /// The delegate that will generate the file content.
    /// 
    private readonly Action content;

    private readonly bool bufferOutput;

    /// 

    /// Initializes a new instance of the  class.
    /// 
    /// Name of the file.
    /// Type of the content.
    /// Delegate with Stream parameter. This is the stream to which content should be written.
    /// use output buffering. Set to false for large files to prevent OutOfMemoryException.
    public FileGeneratingResult(string fileName, string contentType, Action content,bool bufferOutput=true)
        : base(contentType)
    {
        if (content == null)
            throw new ArgumentNullException("content");

        this.content = content;
        this.bufferOutput = bufferOutput;
        FileDownloadName = fileName;
    }

    /// 

    /// Writes the file to the response.
    /// 
    /// The response object.
    protected override void WriteFile(System.Web.HttpResponseBase response)
    {
        response.Buffer = bufferOutput;
        content(response.OutputStream);
    }
}

The controller method would now be like this:

public ActionResult Export(int id)
{
    return new FileGeneratingResult(id + ".csv", "text/csv",
        stream => this.GenerateExportFile(id, stream));
}

public void GenerateExportFile(int id, Stream stream)
{
    stream.Write(/**/);
}

Note that if buffering is turned off,

stream.Write(/**/);

becomes extremely slow. The solution is to use a BufferedStream. Doing so improved performance by approximately 100x in one case. See

Unbuffered Output Very Slow