Zip/Unzip a compressed folder in memory

memzip.cs

using System;
using System.IO.Compression;
using System.Text;

public class InMemoryZipCompresser
{
  public byte[] Compress (string fileContents)
  {
    using (var ms = new MemoryStream())
    {
      using (var archive = new ZipArchive(ms, ZipArchiveMode.Create, leaveOpen:true))
      {
        var jsonFile = archive.CreateEntry("contents.json");
        using (var entryStream = jsonFile.Open())
        {
          using (var streamWriter = new StreamWriter(entryStream))
          {
            streamWriter.Write(Encoding.UTF8.GetString(Encoding.Default.GetBytes(fileContents)));
          }
        }
      }
      return ms.ToArray();
    }
  }
  public string Decompress(byte[] zipped)
  {
    using (var zippedStream = new MemoryStream(zipped))
    {
      using (var archive = new ZipArchive(zippedStream))
      {
        var file = archive.GetEntry("contents.json");
        if (file == null) return null;
        using (var unzippedEntryStream = file.Open())
        {
          using (var ms = new MemoryStream())
          {
            unzippedEntryStream.CopyTo(ms);
            return Encoding.UTF8.GetString(ms.ToArray());
          }
        }
      }
    }
  }
}