Problem when trying to stream encrypted movies.

[Roomie]

My application used to run fine until I encrypted the movie (flv) files my application uses. Now for some users it sometimes crashes and leaves them with this error message:

System.IO.IOException: An I/O-error occurred,
at System.Windows.Forms.Control.MarshaledInvoke(Control caller, Delegate method, Object[] args, Boolean synchronous)
at System.Windows.Forms.Control.Invoke(Delegate method, Object[] args)
at f_in_box__lib.StreamBasedOnIStream.Write(Byte[] buffer, Int32 offset, Int32 count)
at System.Security.Cryptography.CryptoStream.Write(Byte[] buffer, Int32 offset, Int32 count)
at Pausit.FromStreamToStreamWriter.Main()

My guess is that the requested file has not been decrypted enough when my original stream tries to read more, but that’s just my guess.

My question is if there’s any way I can make sure that the crypto stream has buffered up enough before it gets read by the original stream. Or even better if it can decrypt the whole movie before it gets read.

Any help appreciated since I’m a bit stuck on this.
I’m still not all that comfortable when working with streams so please give me descriptive suggestions if you can.

Patrik

My code looks like this:

Code: Select all

private void OnLoadExternalResourceByFullPath(object sender, String URL, System.IO.Stream Stream, ref bool Handled)
{
    string tempString = Application.StartupPath + "\\VideoData\" + URL.Substring(11);

    System.IO.FileStream FLVStream = System.IO.File.OpenRead(tempString);

    FromStreamToStreamWriter writer = new FromStreamToStreamWriter(FLVStream, Stream);

    Handled = true;
}

Code: Select all

class FromStreamToStreamWriter
    {
        internal System.IO.FileStream FromStream;
        internal System.IO.Stream ToStream;
        internal System.Threading.Thread Thread;

        public FromStreamToStreamWriter(System.IO.FileStream FromStream, System.IO.Stream ToStream)
        {
            this.FromStream = FromStream;
            this.ToStream = ToStream;

            Thread = new System.Threading.Thread(new System.Threading.ThreadStart(Main));

            Thread.Start();
        }

        private void Main()
        {

           
            PasswordDeriveBytes pdb = new PasswordDeriveBytes("Password", new byte[] { 0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76 });
           
            Rijndael alg = Rijndael.Create();
                       
            alg.Key = pdb.GetBytes(32);
            alg.IV = pdb.GetBytes(16);

            CryptoStream cs = new CryptoStream(ToStream, alg.CreateDecryptor(), CryptoStreamMode.Write);

            const int size = 64 * 1024;
            byte[] buffer = new byte[size];
            int ReadBytes;

            while ((ReadBytes = FromStream.Read(buffer, 0, size)) > 0)
            {
                try
                {
                    cs.Write(buffer, 0, ReadBytes);
                }
                catch (System.IO.IOException e)
                {
                    MessageBox.Show(e.ToString());
                    break;
                }
            }

            cs.Close();
            FromStream.Close();
        }
    }

[Softanics]

Thank you for your question.

ToStream.Write can throw IOException when Flash stops loading for some reason, for example, when new movie / resource should be loaded.

Does is it really crash? You handle IOException in your code, right?

Thank you.

[Roomie]

Thank you for helping out.

Well first of, I can't get this error on my own computer (or any computer I’ve tried the application on) so it’s kind of hard to bug test. But evidently the error occurs on my users machines. Secondly I never had anyone report this error before I encrypted the movies.

How would you suggest I handle such an exception? Could you give me some code sample or some descriptions on what I want do, as I said in my original post I’m still not so comfortable when it comes to handling streams.

Thanks again
Patrik

[Roomie]

Or if my previous question was unclear, what exactly could I do to distinguish such an exception from other IOExceptions.

I’ve read something about InnerException. Is that something I could use here or is it not valid?

Thanks again
Patrik

[Softanics]

Your code seems to be correct.

When this exception throws, the block:

Code: Select all

   catch (System.IO.IOException e)
                {
                    MessageBox.Show(e.ToString());
                    break;
                }


executes. This is correct.

[danielgianni]

Get your all Exception to details error:

Code: Select all

catch (Exception ex)
{
    MessageBox.Show(ex.ToString());
    break;
}


This code shows all the details of any exception. This code display all details from any exception. Easy to debug!

Your code seems to be correct.

When this exception throws, the block:

Code: Select all

   catch (System.IO.IOException e)
                {
                    MessageBox.Show(e.ToString());
                    break;
                }


executes. This is correct.

Code: Select all

[Softanics]

You should handle IOException separately. Just ignore it. It means that the loading has stopped.

Thank you.