SOCKETS IN C

1
SOCKETS IN C

• Heading towards the Chat Program

2
Basic Introduction to Sockets

• What is a socket?
• A way to communicate with other programs using
  standard file descriptors
• Types of Sockets
• Datagram and Stream Sockets

3
Basic Client Side Algorithm

• Create a socket
• Get the IP address and port number of the server
  (create a data pipe)
• Send Data
• Receive acknowledgement/data
• Send Data

4
Basic Server Side Algorithm

• Create a Listening Socket
• Get IP Address and Port number of the Client that
  is communicating
• Receive Data sent
• Send Data/Acknowledge data
• Receive Data

5
Absolute Basics

• All socket services in System.Net.Sockets
  namespace
• System.Net provides services for DNS, IP
  Addresses, HTTP services etc

6
Creating a Socket

• Must specify address family, socket type and
  protocol type
• Address Family InterNetwork (Addr for IP Ver
  4).. InterNetworkV6 (ver 6)
• Socket Type Stream, Dgram, Raw etc
• Protocol Type Tcp, Udp
• Socket s new Socket(AddressFamily.InterNetwork,
  SocketType.Stream, ProtocolType.Tcp)

7
Next Step..Creating a data pipe

• What we need IP address and port number
  162.312.324.4008000
• What we have a more user friendly web address
• What we need is known in C as an Endpointthere
  is an Endpoint Class for each family, for IP
  addresses the class is known as IPEndPoint

8
Creating the EndPoint...

• Give user friendly address to Dns.Resolve
• Returns a list of addresses select one
• Use the address to create the EndPoint
• IPHostEntry iphost Dns.Resolve
  (http//ist.psu.edu)
• IPAddress ipiphost.AddressList0
• IPEndPoint EndPointnew IPEndPoint(ip,
  portnumber)
• s.Connect(EndPoint)
• (note that port number must be Int16..use
  System.Convert.ToInt16)

9
Sending Data

• The Send method can send data through a CONNECTED
  socket
• byte msg System.Text.Encoding.ASCII.GetBytes("
  This is a test")
• int bytesSent s.Send(msg)

10
Receiving Data

• We use the Receive method (similar to Send)
• byte bytes new byte1024
• s.Receive(bytes)
• //Displays to the screen.
• Console.WriteLine(Encoding.ASCII.GetString(bytes
  ))

11
Shutdown sockets

• The SocketShutdown enumeration defines constants
  that indicate whether the socket should be closed
  for sending, for receiving, or for both.
• Call the Close method to free all managed and
  unmanaged resources associated with the Socket
• s.Shutdown(SocketShutdown.Both)
• s.Close()