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DotNetZip: Adding files to archive faster in web app

Submitted by: @import:stackexchange-codereview·Mar 10, 2026·

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appaddingfasterfileswebdotnetziparchive

Problem

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 _files = new Dictionary();

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?

Solution

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.

Context

StackExchange Code Review Q#138247, answer score: 3

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