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.)

Can I write directly into the HttpResponse stream? In that case, which IView object should the controller action should return? Can I return 'null'?

Answer 1

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

/// <summary> /// MVC action result that generates the file content using a delegate that writes the content directly to the output stream. /// </summary> public class FileGeneratingResult : FileResult {     /// <summary>     /// The delegate that will generate the file content.     /// </summary>     private readonly Action<System.IO.Stream> content;      private readonly bool bufferOutput;      /// <summary>     /// Initializes a new instance of the <see cref="FileGeneratingResult" /> class.     /// </summary>     /// <param name="fileName">Name of the file.</param>     /// <param name="contentType">Type of the content.</param>     /// <param name="content">Delegate with Stream parameter. This is the stream to which content should be written.</param>     /// <param name="bufferOutput">use output buffering. Set to false for large files to prevent OutOfMemoryException.</param>     public FileGeneratingResult(string fileName, string contentType, Action<System.IO.Stream> content,bool bufferOutput=true)         : base(contentType)     {         if (content == null)             throw new ArgumentNullException("content");          this.content = content;         this.bufferOutput = bufferOutput;         FileDownloadName = fileName;     }      /// <summary>     /// Writes the file to the response.     /// </summary>     /// <param name="response">The response object.</param>     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

Answer 2

Yes, you can write directly to the Response. After you're done, you can call CompleteRequest() and you shouldn't need to return anything.

For example:

// GET: /Test/Edit/5
public ActionResult Edit(int id)
{

    Response.Write("hi");
    HttpContext.ApplicationInstance.CompleteRequest();

    return View();     // does not execute!
}