Streaming In Memory Word Document using OpenXML SDK w/ASP.NET results in "corrupt" document

Question

I am unable to stream a word document that I create on the fly down to the browser. I am constantly getting a message from Microsoft Word that the document is corrupt.

When I run the code via a Console Application and take ASP.NET out of the picture, the document is generated correctly with no problems. I believe everything centers around writing the file down.

Here is my code:

using (MemoryStream mem = new MemoryStream())
{
    // Create Document
    using (WordprocessingDocument wordDocument = WordprocessingDocument.Create(mem, WordprocessingDocumentType.Document, true))
    {
        // Add a main document part. 
        MainDocumentPart mainPart = wordDocument.AddMainDocumentPart();

        new Document(new Body()).Save(mainPart);

        Body body = mainPart.Document.Body;
        body.Append(new Paragraph(new Run(new Text("Hello World!"))));

        mainPart.Document.Save();
        // Stream it down to the browser

        // THIS IS PROBABLY THE CRUX OF THE MATTER <---
        Response.AppendHeader("Content-Disposition", "attachment;filename=HelloWorld.docx");
        Response.ContentType = "application/vnd.ms-word.document";
        mem.WriteTo(Response.OutputStream);
        Response.End();
    }
}

I have looked at a lot of links – but nothing quite works. I lot of people use MemoryStream.WriteTo and some use BinaryWrite – at this point I'm not sure what the correct way is. Also I've tried the longer content type, i.e. application/vnd.openxmlformats-officedocument.wordprocessingml.document but no luck.

Some screenshots – even if you try to recover you get the same "parts are missing or invalid"

Solution for those who stumble on this question:

Within the using directive of the WordProcessingDocument, you must call:

wordDocument.Save();

Also to correctly stream the MemoryStream, use this in the outer using block:

Response.ContentType = "application/vnd.openxmlformats-officedocument.wordprocessingml.document";
Response.AppendHeader("Content-Disposition", "attachment;filename=HelloWorld.docx");
mem.Position = 0;
mem.CopyTo(Response.OutputStream);
Response.Flush();
Response.End();

Answer 1

Use CopyTo instead, there is a bug in WriteTo which makes it fail to write the entire content of the buffer when the target stream does not support writing everything in one go.

Answer 2

As variant for .NET Framework 3.5 and lower. This version of framework haven't method CopyTo in class Stream. Therefore, method WriteTo is replaced by next code:

byte[] arr = documentStream.ToArray();
fileStream.Write(arr, 0, arr.Length);

Example was found by http://blogs.msdn.com/b/mcsuksoldev/archive/2010/04/09/creating-a-new-microsoft-word-document-from-a-template-using-openxml.aspx