CSC5930/9010: Security and Privacy in 
          Cyber-physical Systems
         Socket Programming using Python
   Socket Programming
     • Sockets
           – A means of sending data over a network from one application to another.
           – A door between application process and end-end-transport protocol
     • One socket node listens on a particular port and IP, while other socket 
         reaches out to the other to form a connection.
                                            application             socket                 application          controlled by
                                            process                                         process             app developer
                                            transport                                       transport
                                             network                                        network              controlled
                                               link                  Internet                  link              by OS
                                             physical                                       physical
                                                                                                                                                  Slide 2
  Client/server socket interaction: UDP
              server (runningon serverIP)         client
               create socket, port= x:            create socket:
               serverSocket =                     clientSocket =
               socket(AF_INET,SOCK_DGRAM)         socket(AF_INET,SOCK_DGRAM)
                                                  Create datagram with server IP and
                                                  port=x; send datagram via
                  read datagram from              clientSocket
                  serverSocket
                   write reply to
                   serverSocket                    read datagram from
                   specifying                      clientSocket
                   client address,
                   port number                     close
                                                   clientSocket
                                                                                       Slide 3
   Example app: UDP Client
                                                              Python UDPClient
                               include Python’s socket        from socket import *
                               library
                                                              serverName = ‘hostname’
                                                              serverPort = 12000
                               create UDP socket for          clientSocket = socket(AF_INET, 
                               server                                               SOCK_DGRAM)
                               get user keyboard              message = input(’Input lowercase sentence:’)
                               input                          clientSocket.sendto(str.encode(message),
                              Attach server name, port to                                 (serverName, serverPort))
                              message; send into socket
                                                              modifiedMessage, serverAddress = 
                               read reply characters from                           clientSocket.recvfrom(2048)
                               socket into string             print (bytes.decode(modifiedMessage))
                                                              clientSocket.close()
                               print out received string 
                               and close socket
                                                                                                                                     2-4     Slide 4