How can I merge 2 zip files into 1?

Question

i have 2 zip files (zip1 and zip2), i need merge this files in one, how can i solve it? I understand that I can fix it decompressing ZIP1 to a temp folder and then add it to zip2, but i think it is inefficient, what is the faster method?

I'm using System.IO.Compression library...

I use this code to explore Zip2:

 using (ZipArchive archive = ZipFile.OpenRead(Zip2))
 {
    foreach (ZipArchiveEntry entry in archive.Entries)
    {
       /*...*/
    }
 }

PD/: The Zip1 and Zip2 files have FILES, FOLDERS AND SUBFOLDERS

Answer 1

I haven't really tested this, but you can give it a try:

    public ZipArchive Merge(List<ZipArchive> archives)
    {
        if (archives == null) throw new ArgumentNullException("archives");
        if (archives.Count == 1) return archives.Single();

        using (var memoryStream = new MemoryStream())
        {
            using (var archive = new ZipArchive(memoryStream, ZipArchiveMode.Create, true))
            {
                foreach (var zipArchive in archives)
                {
                    foreach (var zipArchiveEntry in zipArchive.Entries)
                    {
                        var file = archive.CreateEntry(zipArchiveEntry.FullName);

                        using (var entryStream = file.Open()) {
                            using (var streamWriter = new StreamWriter(entryStream)) { streamWriter.Write(zipArchiveEntry.Open()); }
                        }
                    }
                }

                return archive;
            }
        }
    }