How create FileStream but not save?

Question

I have code function

public static void DecryptFile(string inFile, string outFile, string password)
{
    // create and open the file streams
    using (FileStream fin = File.OpenRead(inFile),
              fout = File.OpenWrite(outFile))
    {
        int size = (int)fin.Length; // the size of the file for progress notification
        byte[] bytes = new byte[BUFFER_SIZE]; // byte buffer
        int read = -1; // the amount of bytes read from the stream
        int value = 0;
        int outValue = 0; // the amount of bytes written out

        // read off the IV and Salt
        byte[] IV = new byte[16];
        fin.Read(IV, 0, 16);
        byte[] salt = new byte[16];
        fin.Read(salt, 0, 16);

        // create the crypting stream
        SymmetricAlgorithm sma = CryptoHelp.CreateRijndael(password, salt);
        sma.IV = IV;

        value = 32; // the value for the progress
        long lSize = -1; // the size stored in the input stream

        // create the hashing object, so that we can verify the file
        HashAlgorithm hasher = SHA256.Create();

        // create the cryptostreams that will process the file
        using (CryptoStream cin = new CryptoStream(fin, sma.CreateDecryptor(), CryptoStreamMode.Read),
                  chash = new CryptoStream(Stream.Null, hasher, CryptoStreamMode.Write))
        {
            // read size from file
            BinaryReader br = new BinaryReader(cin);
            lSize = br.ReadInt64();
            ulong tag = br.ReadUInt64();

            if (FC_TAG != tag)
                throw new CryptoHelpException("File Corrupted!");

            //determine number of reads to process on the file
            long numReads = lSize / BUFFER_SIZE;

            // determine what is left of the file, after numReads
            long slack = (long)lSize % BUFFER_SIZE;

            // read the buffer_sized chunks
            for (int i = 0; i < numReads; ++i)
            {
                read = cin.Read(bytes, 0, bytes.Length);
                fout.Write(bytes, 0, read);
                chash.Write(bytes, 0, read);
                value += read;
                outValue += read;
            }

            // now read the slack
            if (slack > 0)
            {
                read = cin.Read(bytes, 0, (int)slack);
                fout.Write(bytes, 0, read);
                chash.Write(bytes, 0, read);
                value += read;
                outValue += read;
            }
            // flush and close the hashing stream
            chash.Flush();
            chash.Close();

            // flush and close the output file
            fout.Flush();
            fout.Close();

            // read the current hash value
            byte[] curHash = hasher.Hash;

            // get and compare the current and old hash values
            byte[] oldHash = new byte[hasher.HashSize / 8];
            read = cin.Read(oldHash, 0, oldHash.Length);
            if ((oldHash.Length != read) || (!CheckByteArrays(oldHash, curHash)))
                throw new CryptoHelpException("File Corrupted!");
        }

        // make sure the written and stored size are equal
        if (outValue != lSize)
            throw new CryptoHelpException("File Sizes don't match!");
    }
}

I need return FileStream (fout) and fout not save to hard disk

UPDATE:

YES, MemoryStream is good. but then I will need to use the FileStream otherwise an error occurs:

not work:

using (ZipInputStream s = new ZipInputStream(fout))
{

  ZipEntry theEntry;
  while ((theEntry = s.GetNextEntry()) != null)//exception

is work:

using (ZipInputStream s = new ZipInputStream(File.OpenRead(zipFile)))
{

  ZipEntry theEntry;
  while ((theEntry = s.GetNextEntry()) != null)

I need to decrypt the file, unzip it and then still get the text without saving

Answer 1

Don't use a second FileStream. You can use a MemoryStream instead.

using (FileStream fin = File.OpenRead(inFile))
  using(Stream fout = new MemoryStream())
...