I’m using SharpCompress and trying to read files which are archived in a 7z archive.
Now I got stuck at a point where my 7z archive contains another zip or 7z, which contains the file I want to read. Is there a way how the read the content of a file, which is archived multiple times without extracting the archives on disk?

Just for test purpose, I have my simple method which should write me all the entries from the archive.

namespace TestArchiv
{
    public partial class MainWindow : Window
    {
        
        public MainWindow()
        {
            InitializeComponent();
            frmReference = this;
            try
            {
                processArchive(@"C:temptemp.zip");
            }
            catch (Exception ex)
            {
                WriteToBox(ex.ToString());
            }
        }

        public void processArchive(string archivePath)
        {
            using (var archive = SevenZipArchive.Open(archivePath))
            {
                foreach (var entry in archive.Entries)
                {

                    if (entry.ToString().Contains("7z"))
                    {
                        using (SevenZipArchive inner2 = SevenZipArchive.Open(entry.OpenEntryStream()))
                        {

                            foreach (var entry2 in inner2.Entries)
                            {
                                WriteToBox(entry2.ToString());
                            }
                        }
                    }
                    WriteToBox(entry.ToString());
                    
                }
            }
        }

        public void WriteToBox(string text)
        {

            //frmReference.TextBox1.Clear();
            frmReference.TextBox1.AppendText("rn" + text);

        }
}
}

When I try to run this, I’m getting

System.NotSupportedException: Specified method is not supported.
   at SharpCompress.IO.ReadOnlySubStream.get_Length()
   at SharpCompress.IO.SourceStream.Seek(Int64 offset, SeekOrigin origin)
   at SharpCompress.IO.SourceStream.set_Position(Int64 value)
   at SharpCompress.IO.NonDisposingStream.set_Position(Int64 value)
   at SharpCompress.Archives.SevenZip.SevenZipArchive.LoadFactory(Stream stream)
   at SharpCompress.Archives.SevenZip.SevenZipArchive.LoadEntries(IEnumerable`1 volumes)
   at SharpCompress.Archives.AbstractArchive`2..ctor(ArchiveType type, SourceStream sourceStream)
   at SharpCompress.Archives.SevenZip.SevenZipArchive..ctor(SourceStream sourceStream)
   at SharpCompress.Archives.SevenZip.SevenZipArchive.Open(Stream stream, ReaderOptions readerOptions)
   at TestArchiv.MainWindow.processArchive(String archivePath) in C:Usersmartin.tomansourcereposTestArchivTestArchivMainWindow.xaml.cs:line 56
   at TestArchiv.MainWindow..ctor() in C:Usersmartin.tomansourcereposTestArchivTestArchivMainWindow.xaml.cs:line 38

Just to clarify, I’m processing C:tempCaCCdm30_2.7z which contains another CaCCdm30.7z

I was able to solve this problem for Zip files using the ZipFile class from C#, but I need to make it work for other archive types, so I went for SharpCompress.
This worked for zip files:

public void processArchive(ZipArchive archive)
 {
     foreach (ZipArchiveEntry entry in archive.Entries)
     {
         string fileName = entry.ToString();
         //WriteToBox(fileName);
         if (fileName.ToLower().Contains(".zip"))

         {
             ZipArchive innerArchive = new ZipArchive(entry.Open());
             processArchive(innerArchive);
         }
         else 
         .....
      }
}

EDIT: I added the complete code