Question

I was reading C# 4.0 in a Nutshell by Joseph and Ben Albahari and came across this code in Networking chapter which reads the mails using POP3. POP3 has a defined communication as we all know. When I use the code in the chapter it looks obvious that it should work but it doesn’t. This is the code:

private static string ReadLine(Stream stream)
        {
            List<byte> list = new List<byte>();
            while (true)
            {
                int b = stream.ReadByte();
                if (b == 10 || b < 0) break;

                if (b != 13) list.Add( (byte)b);
            }
            return Encoding.UTF8.GetString(list.ToArray());
        }

        private static void SendCommand(Stream stream, string line)
        {
            byte[] byteArr = Encoding.UTF8.GetBytes(line + "\r\n");
            stream.Write(byteArr, 0, byteArr.Length);
            string response = ReadLine(stream);
            if (!response.StartsWith("+OK"))
                throw new Exception("Pop exception: " + response);
        }

        static void Main(string[] args)
        {

            using (TcpClient client = new TcpClient("pop.gmail.com", 995))
            {

                using (NetworkStream stream = client.GetStream())
                {
                    ReadLine(stream);
                }
            }

The code is incomplete in the sense that it doesn’t download mails. I was just trying to see what is the 1st reponse that we get from Gmail. But unfortunately, the program just stucks at ReadByte in ReadLine method. I think I should get this line when I first connect to the gmail:

+OK Hello there.

But my program just hangs. As per this page:

http://mail.google.com/support/bin/answer.py?answer=13287

you have to connect on pop.gmail.com which is exactly what I have done. Can anybody tell me what is missing?

Note: Do not send me any 3rd party projects to do this sort of this. I know it is very easy using them. But I am just trying to see what happens under the hoods. It would be better for me if you find the bug present in my program itself.

Thanks.

Answer 1

Use SslStream instead of NetworkStream as gmail requires ssl

TcpClient objTcpClient = new TcpClient();
//Connecting to the pop3 server at the specified port 
objTcpClient.Connect(pop3Server, pop3PortNumber);

//ValidateCertificate is a delegate
SslStream netStream = new SslStream(objTcpClient.GetStream(), false, ValidateCertificate); //Authenticates the client on the server
netStream.AuthenticateAsClient(pop3Server);
//Stream Reader to read response stream 
StreamReader netStreamReader = new StreamReader(netStream, Encoding.UTF8, true);