C# – Creating a ZIP archive in memory using System.IO.Compression

ccompressionnetzipziparchive

I'm trying to create a ZIP archive with a simple demo text file using a MemoryStream as follows:

using (var memoryStream = new MemoryStream())
using (var archive = new ZipArchive(memoryStream , ZipArchiveMode.Create))
{
    var demoFile = archive.CreateEntry("foo.txt");

    using (var entryStream = demoFile.Open())
    using (var streamWriter = new StreamWriter(entryStream))
    {
        streamWriter.Write("Bar!");
    }

    using (var fileStream = new FileStream(@"C:\Temp\test.zip", FileMode.Create))
    {
        stream.CopyTo(fileStream);
    }
}

If I run this code, the archive file itself is created but foo.txt isn't.

However, if I replace the MemoryStream directly with the file stream, the archive is created correctly:

using (var fileStream = new FileStream(@"C:\Temp\test.zip", FileMode.Create))
using (var archive = new ZipArchive(fileStream, FileMode.Create))
{
    // ...
}

Is it possible to use a MemoryStream to create the ZIP archive without the FileStream?

Best Answer

Thanks to ZipArchive creates invalid ZIP file, I got:

using (var memoryStream = new MemoryStream())
{
   using (var archive = new ZipArchive(memoryStream, ZipArchiveMode.Create, true))
   {
      var demoFile = archive.CreateEntry("foo.txt");

      using (var entryStream = demoFile.Open())
      using (var streamWriter = new StreamWriter(entryStream))
      {
         streamWriter.Write("Bar!");
      }
   }

   using (var fileStream = new FileStream(@"C:\Temp\test.zip", FileMode.Create))
   {
      memoryStream.Seek(0, SeekOrigin.Begin);
      memoryStream.CopyTo(fileStream);
   }
}

That indicated we need to call Dispose on ZipArchive before we can use it, which as Amir suggests is likely because it writes final bytes like checksum to the archive that makes it complete. But in order not close the stream so we can re-use it after you need to pass true as the third parameter to ZipArchive.

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