Question

I’m working on a system where I have a Stream (which is seekable) that I am reading a ZIP file from, then am writing the modified ZIP file back to that stream. Doing so results in a corrupt file. This can be demonstrated using the following code:

using System;
using System.Collections.Generic;
using System.Text;
using Ionic.Zip;
using System.Windows.Forms;
using System.IO;
namespace ziptester
{
    class Program
    {
        [STAThread]
        static void Main(string[] args)
        {
            OpenFileDialog mdlg = new OpenFileDialog();
            mdlg.ShowDialog();
            Stream fstream = File.Open(mdlg.FileName,FileMode.Open,FileAccess.ReadWrite);
            ZipFile mfile = ZipFile.Read(fstream);
            mfile.UpdateEntry("test.txt", new byte[500]);
            fstream.Position = 0;
            mfile.SaveProgress += new EventHandler(mfile_SaveProgress);
            mfile.Save(fstream);


            Console.ReadKey();
        }

        static void mfile_SaveProgress(object sender, SaveProgressEventArgs e)
        {
            if (e.EventType == ZipProgressEventType.Saving_Completed)
            {
                Console.WriteLine("Save completed");
            }
        }
    }
}

Answer 1

Doing so results in a corrupt file.

So, don’t do that.

Zip archives are a complicated format, they don’t support read/write streams.

You will have to write to a new ‘file’ and when complete delete the old one and rename.