C# Cannot access a closed stream while copying GZipStream to MemoryStream

Question

I've been trying to convert a GZipStream into a MemoryStream and then convert it to a byte array without having to write any files to the hard drive. I've been trying to copy it to a MemoryStream but I've been getting this error: Unhandled Exception: System.ObjectDisposedException: Cannot access a closed Stream.

I've looked at some of the other solutions, but I haven't been able to successfully implement them into what I'm trying to accomplish.

GZipStream decompressedStream = Decompress(new FileInfo(args[0]));
        using (var finalStream = new MemoryStream())
        {
            decompressedStream.CopyTo(finalStream);
            byte[] decompressedBytes = new byte[finalStream.Length];
        }

EDIT: Somebody wanted me to add the code for Decompress() so here it is

public static GZipStream Decompress(FileInfo fileToDecompress)
    {
        using (FileStream originalFileStream = fileToDecompress.OpenRead())
        {
            string currentFileName = fileToDecompress.FullName;
            string newFileName = currentFileName.Remove(currentFileName.Length - fileToDecompress.Extension.Length) + " (decompressed)";
            using (FileStream decompressedFileStream = File.Create(newFileName))
            {
                using (GZipStream decompressionStream = new GZipStream(originalFileStream, CompressionMode.Decompress))
                {
                    return decompressionStream;
                }
            }
        }
    }

Answer 1

The issue is here:

using (GZipStream decompressionStream = new GZipStream(originalFileStream, CompressionMode.Decompress))
{
     return decompressionStream;
}

using statement (see this article) disposes the stream and you can't use it outside of the block. Move your MemoryStream handling inside this block and return byte[] from the method.

Something like this should work:

public static byte[] Decompress(FileInfo fileToDecompress)
{
    using (FileStream originalFileStream = fileToDecompress.OpenRead())
    {
        string currentFileName = fileToDecompress.FullName;
        string newFileName = currentFileName.Remove(currentFileName.Length - fileToDecompress.Extension.Length) + " (decompressed)";
        using (FileStream decompressedFileStream = File.Create(newFileName))
        {
            using (GZipStream decompressionStream = new GZipStream(originalFileStream, CompressionMode.Decompress))
            using (var finalStream = new MemoryStream())
            {
                decompressionStream.CopyTo(finalStream);
                return finalStream.ToArray();
            }
        }
    }
}