using System;

using System.IO;

using System.IO.Compression;

using System.Text;

public class Program

{

    public static void Main()

    {

        string json="{foo:bar}";

        byte[] compressedBytes;

        using (var uncompressedStream = new MemoryStream(Encoding.UTF8.GetBytes(json)))

        {

            using (var compressedStream = new MemoryStream())

            { 

                using (var compressorStream = new DeflateStream(compressedStream, CompressionLevel.Fastest, true))

                {

                    uncompressedStream.CopyTo(compressorStream);

                }

​

                // call compressedStream.ToArray() after the enclosing DeflateStream has closed and flushed its buffer to compressedStream

                compressedBytes = compressedStream.ToArray();

            }

        }

        //base64 encode compressed data

        Console.WriteLine(Convert.ToBase64String(compressedBytes));

    }

}