Question

I am attempting to create a Save/Load class that has the option for saving & load files compressed files. Below is what I have so far. Stepping through it seems to work just fine, except that I get a “The magic number in GZip header is not correct” exception. I don’t understand how this can be as I am checking to make sure that the number is there before I pass it over, and I have verified via an external program that it is a GZip file.

Any assistance in finding out where I went wrong would be appreciated. Constructive criticism of my code is always welcome – Thanks!

public static class SaveLoad
{
    public static void Save(string fileName, object savefrom, bool compress)
    {
        FileStream stream = new FileStream(fileName, FileMode.Create);

        BinaryFormatter formatter = new BinaryFormatter();
        if (compress)
        {
            GZipStream compressor = new GZipStream(stream, CompressionMode.Compress);
            formatter.Serialize(compressor, savefrom);
            compressor.Close();
        }
        else { formatter.Serialize(stream, savefrom); }

        stream.Close();
    }

    public static object Load(string fileName)
    {
        object loadedObject = null;

        try
        {
            FileStream stream = new FileStream(fileName, FileMode.Open);

            BinaryFormatter formatter = new BinaryFormatter();

            if (stream.Length > 4)
            {
                byte[] data = new byte[4];
                stream.Read(data, 0, 4);

                if (BitConverter.ToUInt16(data, 0) == 0x8b1f) //GZIP_LEAD_BYTES == 0x8b1f
                {
                    GZipStream decompressor = new GZipStream(stream, CompressionMode.Decompress);
                    loadedObject = formatter.Deserialize(decompressor); //Exception
                    decompressor.Close();
                }
                else { loadedObject = formatter.Deserialize(stream); }
            }
            stream.Close();
        }
        catch (Exception e)
        {
            Logger.StaticLog.AddEvent(new Logger.lEvent(null, Logger.lEvent.EventTypes.Warning, "Failed to load file: " + fileName, e)
            {
                SendingObject = "SaveLoad"
            });
            Logger.StaticLog.WriteLog();
            throw;
        }

        return loadedObject;
    }
}

Answer 1

It seems that you read the magic number before passing the stream to decompressor (which won’t read the magic number then, because you’ve already read it).

Use stream.Seek(0,SeekOrigin.Begin) before you decompress.