How to create and fill a ZIP file using ASP.NET?

You don't have to use an external library anymore. System.IO.Packaging has classes that can be used to drop content into a zip file. Its not simple, however. Here's a blog post with an example (its at the end; dig for it).

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The link isn't stable, so here's the example Jon provided in the post.

using System;
using System.IO;
using System.IO.Packaging;

namespace ZipSample
{
    class Program
    {
        static void Main(string[] args)
        {
            AddFileToZip("Output.zip", @"C:\Windows\Notepad.exe");
            AddFileToZip("Output.zip", @"C:\Windows\System32\Calc.exe");
        }

        private const long BUFFER_SIZE = 4096;

        private static void AddFileToZip(string zipFilename, string fileToAdd)
        {
            using (Package zip = System.IO.Packaging.Package.Open(zipFilename, FileMode.OpenOrCreate))
            {
                string destFilename = ".\\" + Path.GetFileName(fileToAdd);
                Uri uri = PackUriHelper.CreatePartUri(new Uri(destFilename, UriKind.Relative));
                if (zip.PartExists(uri))
                {
                    zip.DeletePart(uri);
                }
                PackagePart part = zip.CreatePart(uri, "",CompressionOption.Normal);
                using (FileStream fileStream = new FileStream(fileToAdd, FileMode.Open, FileAccess.Read))
                {
                    using (Stream dest = part.GetStream())
                    {
                        CopyStream(fileStream, dest);
                    }
                }
            }
        }

        private static void CopyStream(System.IO.FileStream inputStream, System.IO.Stream outputStream)
        {
            long bufferSize = inputStream.Length < BUFFER_SIZE ? inputStream.Length : BUFFER_SIZE;
            byte[] buffer = new byte[bufferSize];
            int bytesRead = 0;
            long bytesWritten = 0;
            while ((bytesRead = inputStream.Read(buffer, 0, buffer.Length)) != 0)
            {
                outputStream.Write(buffer, 0, bytesRead);
                bytesWritten += bytesRead;
            }
        }
    }
}

DotNetZip is nice for this.

You can write the zip directly to the Response.OutputStream. The code looks like this:

    Response.Clear();
    Response.BufferOutput = false; // for large files...
    System.Web.HttpContext c= System.Web.HttpContext.Current;
    String ReadmeText= "Hello!\n\nThis is a README..." + DateTime.Now.ToString("G"); 
    string archiveName= String.Format("archive-{0}.zip", 
                                      DateTime.Now.ToString("yyyy-MMM-dd-HHmmss")); 
    Response.ContentType = "application/zip";
    Response.AddHeader("content-disposition", "filename=" + archiveName);

    using (ZipFile zip = new ZipFile())
    {
        // filesToInclude is an IEnumerable<String>, like String[] or List<String>
        zip.AddFiles(filesToInclude, "files");            

        // Add a file from a string
        zip.AddEntry("Readme.txt", "", ReadmeText);
        zip.Save(Response.OutputStream);
    }
    // Response.End();  // no! See http://stackoverflow.com/questions/1087777
    Response.Close();

DotNetZip is free.