Create a Zip as a browser download attachment in IIS - icsharpcode/SharpZipLib GitHub Wiki

// the aspx page has just one line e.g. <%@ Page language="c#" Codebehind=...
// but if you must run this from within a page that has other output, start
// with a Response.Clear();

using ICSharpCode.SharpZipLib.Zip;

// This will accumulate each of the files named in the fileList into a zip file,
// and stream it to the browser.
// This approach writes directly to the Response OutputStream.
// The browser starts to receive data immediately which should avoid 
// timeout problems.
// This also avoids an intermediate memorystream, saving memory on large files.
private void DownloadZipToBrowser(List <string> zipFileList) {

    Response.ContentType = "application/zip";
    // If the browser is receiving a mangled zipfile, IIS Compression may cause
    // this problem. Some members have found that 
    //Response.ContentType = "application/octet-stream" 
    // has solved this. May be specific to Internet Explorer.

    Response.AppendHeader("Content-Disposition", 
        "attachment; filename=\"Download.zip\"");
    Response.CacheControl = "Private";

    Response.Cache.SetExpires(DateTime.Now.AddMinutes(3));
    // or put a timestamp in the filename in the content-disposition

    var buffer = new byte[4096];

    using(var zipOutputStream = new ZipOutputStream(Response.OutputStream)){

        // 0-9, 9 being the highest level of compression
        zipOutputStream.SetLevel(3);

        foreach (string fileName in zipFileList) {

            using(Stream fs = File.OpenRead(fileName)) {

                var entry = new ZipEntry(ZipEntry.CleanName(fileName));
                entry.Size = fs.Length;
                // Setting the Size provides WinXP built-in extractor 
                // compatibility, but if not available, you can instead set 
                //zipOutputStream.UseZip64 = UseZip64.Off

                zipOutputStream.PutNextEntry(entry);

                int count = fs.Read(buffer, 0, buffer.Length);
                while (count > 0) {
                    zipOutputStream.Write(buffer, 0, count);
                    count = fs.Read(buffer, 0, buffer.Length);
                    if (!Response.IsClientConnected) {
                        break;
                    }
                    Response.Flush();
                }
            }
        }
    }

    Response.Flush();
    Response.End();
}