Kompressor/Kompressor/FileWriteAllBytesPatch.cs

using System.IO;
using System.IO.Compression;
using HarmonyLib;

namespace Kompressor
{
    [HarmonyPatch(typeof(File), "WriteAllBytes")]
    public class FileWriteAllBytesPatch
    {
        public static void Prefix(string path, ref byte[] bytes)
        {
            if (!path.EndsWith("GameSave.GC")) return; // not a save file; do nothing
            GamecraftModdingAPI.Utility.Logging.MetaLog($"Writing compressed save to {path}");
            MemoryStream data = new MemoryStream();
            // compress files
            GZipStream gzip = new GZipStream(data, CompressionLevel.Optimal, true);
            gzip.Write(bytes, 0, bytes.Length);
            //GamecraftModdingAPI.Utility.Logging.MetaLog($"bytes.Length: {bytes.Length}");
            gzip.Flush();
            gzip.Close();
            gzip.Dispose();
            byte[] compressedData = new byte[data.Length + MyPlugin.COMPRESSION_FRAME_START.Length];
            // copy frame into start of compressedData
            for (byte i = 0; i < MyPlugin.COMPRESSION_FRAME_START.Length; i++)
            {
                compressedData[i] = MyPlugin.COMPRESSION_FRAME_START[i];
            }
            //GamecraftModdingAPI.Utility.Logging.MetaLog($"compressedData.Length: {data.Length}");
            data.Seek(0, 0);
            data.Read(compressedData, MyPlugin.COMPRESSION_FRAME_START.Length, (int) data.Length);
            // update stuff to write
            bytes = compressedData;
        }
    }
}