DotNetZip: Adding files to archive faster in web app

Question

I'm looking for ways to speed up the process of adding entries to a zip-archive, in a web app, using DotNetZip.

The problem currently is that the response times out before all files has been added to the archive. There can potentially be between 200 - 500 entries in each archive, each entry between 1 - 4 meg in size. I've tried a sample of 100 files which is too slow.

Compression is not necessary since all files are .mp3-files.

I currently have this code:

private readonly IDictionary<string, Stream> _files = new Dictionary<string, Stream>();

public bool CreateZip(ref MemoryStream result, bool compress = true)
{
    using (ZipFile zip = new ZipFile())
    {
        zip.UseZip64WhenSaving = Zip64Option.AsNecessary;

        if (!compress)
            zip.CompressionLevel = CompressionLevel.None;

        if (_files.Any())
        {
            foreach (var file in _files)
            {
                ZipEntry entry = zip.AddEntry(file.Key, file.Value);
                entry.Comment = file.Key;
            }
        }

        zip.Save(result);
        result.Seek(0, SeekOrigin.Begin);
        result.Flush();
    }
    return true;
}

The files are first added to a dictionary (as streams from a RavenFS/RavenFileStorage) and then added to the archive. The zip itself is also saved to a stream.

I thought about threading but it seems that is not supported by the lib when adding entries to the archive.

Am I using the lib correctly or is any method faster?

Answer 1

• Don't use ref parameters. It's very rarely needed and it's of no use in your CreateZip method.
• Save the ZipFile directly to the Response.OutputStream instead of a temporary MemoryStream. This will allow you to start streaming the file while you're creating it.