How to Successfully Create an In-Memory ZIP Archive Using C# and Avoid the 'Invalid ZIP' Error?

Creating a ZIP Archive in Memory Using System.IO.Compression: Overcoming the Invalid ZIP Error

When attempting to create a ZIP archive in memory using a MemoryStream, you may encounter the issue where the archive is created but lacks its desired contents. This issue arises due to the need to write final bytes, such as checksums, to the archive to complete it.

To resolve this, you can use the following modified code:

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);
   }
}

The key difference here is the third parameter in the ZipArchive constructor, which is set to true. This parameter indicates that the ZipArchive can be disposed without closing the underlying stream. This allows you to reuse the MemoryStream after creating the archive.

By using the modified code, you can successfully create a ZIP archive in memory with the desired contents, even when using a MemoryStream. This flexibility allows you to manipulate archives in various scenarios without the need for intermediate file handling.

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