1. Windows Programming Using C# Internet Programming

2. 2 Contents Basic Internet classes Internet protocols Client TCP/IP sockets Server TCP/IP sockets UDP sockets

3. 3 DNS Class The DNS class provides a simple interface to the domain name system This allows you to translate names to IP addresses and vice versa Remember that a computer with one name might have several IP addresses if it has several network cards

4. 4 DNS Class Methods  IPHostEntry GetHostEntry(string host) Returns an IPHostEntry for the host The host string can be a host name or a dotted address If an empty string is passed as the host, information is returned about the local machine

5. 5 IPHostEntry Class This holds all the information on a particular host Properties  IPAddress[] AddressList Returns an array of IP addresses for the host If the host cannot be resolved, this list has zero length  string[] Aliases Returns a list of aliases for the host  string HostName Returns the primary name for the host

6. 6 IPAddress Class This represents an IP address with support for IPV6 Methods  byte[] GetAddressBytes() Returns an array of bytes in the address  string ToString() Returns the address in the usual dotted notation

7. 7 IPAddress Class Many useful, pre-defined fields are provided  Any Matches any IP address Used for listening to accept any host  Broadcast An address which sends to all hosts on the local area network

8. 8 IPAddress Class  Loopback The loopback address for the local host  None An address which does not match any real address

9. 9 Communication Modes An internet connection is one of two types  Connection-oriented Similar to a phone connection A virtual path is set up between two hosts and the communication parameters are negotiated Guarantees that the packets are delivered and in the correct order

10. 10 Communication Modes  Connectionless This is like sending a letter There is no permanent connection between sender and recipient This saves  Setup time  Additional information in the packets to ensure they are received and in order Connectionless protocols do not guarantee delivery or delivery in the right order

11. 11 Protocols TCP  Transmission control protocol  Connection-oriented protocol with guaranteed delivery  Used for most communication with servers UDP  User datagram protocol  A connectionless protocol without guaranteed delivery  More efficient than TCP  Used for streaming media

12. 12 Sockets The software connection to the internet is called a socket A socket combines  The IP address of a machine  A port number Each program which opens a socket to communicate on the internet uses one of 65,535 sockets on the machine Data from the network is delivered to a particular socket and then to a particular program listening on that socket This allows one computer to have many network connections active at once.

13. 13 Sockets A socket can be of different types  TCP/IP Acts as a data stream between two computers which can be read from and written to The socket is set up to establish a virtual circuit to a single host  UDP Send discrete messages between computers Each message can be sent to a different computer There is no permanent connection between computers

14. 14 IPEndPoint Class Represents one end of a socket connection Includes  The IP address of a computer  A socket number

15. 15 AddressFamily An enumeration of the types of addressing that can be used by a socket Common values include  AppleTalk  InterNetwork// IPV4  InterNetworkV6// IPV6

16. 16 SocketType An enumeration of the types of sockets that can be created Common values  Dgram Connectionless UDP  Raw Access to underlying protocol Used for ICMP  Stream Connection-oriented TCP/IP

17. 17 ProtocolFamily The protocol used by a socket  Raw Raw protocol  Tcp Transmission control protocol  Udp User datagram protocol

18. 18 Socket Class This creates a real socket The namespace is System.Net.Sockets To create a socket  Socket s = new Socket( AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);

19. 19 Socket Class To connect a socket IPHostEntry hostEntry = Dns.GetHostEntry(hostName); IPAddress[] addresses = hostEntry.AddressList; IPEndPoint endPoint = new IPEndPoint(addresses[0], port); s.Connect(endPoint);

20. 20 Socket Class To check to see if the socket is connected  If(s.Connected) { … } To write data to the socket  s.Send(byte[], length, offset); To read from a socket  nread = s.Receive(byte[], length, offset); *see my_curl

21. 21 Servers A server  Creates a TcpListener  This listens on a particular port for connections  When a connection is received, a socket for the connection is returned  Data is exchanged over the socket  The socket is closed  The listener listens for the next connection

22. 22 TcpListener To create a server int port = 2001; IPAddress localAddr = IPAddress.Parse("127.0.0.1"); TcpListener listener = new TcpListener(localAddr, port); listener.Start();

23. 23 TcpListener To wait for a connection  Socket sock = listener.AcceptSocket(); To communicate on a socket  Use the Send and Receive methods  Close the socket when finished

24. 24 To Connect to a Server There are two ways  Use a TcpClient Create a client and connect  TcpClient client = new TcpClient(server, port); Get a stream to read and write to the server  NetworkStream stream = client.GetStream(); Read/write the stream  stream.Write(data, 0, data.Length);  Int32 bytes = stream.Read(data, 0, data.Length);

25. 25 To Connect to a Server  Use a Socket Create a normal Socket and connect to the host and port Use Send and Receive to communicate Close the socket when done  *see hello_client and hello_server

26. 26 UDP This sends discrete messages rather than a stream of bytes Each message can be sent to a different computer UDP is much more efficient than TCP/IP UDP is used for sending audio and video

27. 27 UdpClient While you can use a socket for UDP communication, it is easier to use a UdpClient To create a client and listen on a port  UdpClient client = new UdpClient(port); To send bytes to a computer  byte[] sendBytes = Encoding.ASCII.GetBytes(msg);  client.Send(sendBytes, sendBytes.Length, host, remotePort);

28. 28 UdpClient To receive bytes from any computer IPEndPoint remoteIpEndPoint = new IPEndPoint( IPAddress.Any, 0); Byte[] receiveBytes = client.Receive(ref remoteIpEndPoint); string returnData = Encoding.ASCII.GetString(receiveBytes); The IPEndPoint passed to Receive is filled in with the address of the sender of the message To find the message sender  remoteIpEndPoint.Address  remoteIpEndPoint.Port

29. 29 Socket Timeouts The Receive call blocks until it receives a message This can be a problem if nobody wants to talk to you You can only wait for the phone so long… You need to set a timeout which will interrupt the receive operation

30. 30 Socket Timeouts The time is expressed in milliseconds  client.Client.SetSocketOption( SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout, 5000); When the timeout fires, an exception is thrown, which must be caught * see UdpChat

31. 31 Broadcast Ever feel like just calling anybody? Then broadcast it! A broadcast message will be picked up by any listener on the local area network Broadcast messages will not pass through routers

32. 32 Broadcast To send a broadcast message use IPAddress.Broadcast IPEndPoint remoteIpEnd = new IPEndPoint( IPAddress.Broadcast, remotePort); Send(sendBytes, sendBytes.Length, remoteIpEnd);

33. 33 Finding Servers Normally, servers operate on well-known ports These are ports which are less that 1024 and are assigned for specific purposes Eg. Web servers are on port 80 This tells us what port the server is on What if we don’t know which machine is hosting the server?

34. 34 Finding Servers In this case, we can broadcast for a server  Send out a broadcast message to all machines on the LAN  Wait for a reply  Use that machine as a server You can broadcast with UDP on one port to locate the servers You can then stay with UDP to talk to the servers on another port or switch to TCP/IP on another port