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Basics of Socket Programming using python
- 1. goal: learn howto build client/server applications that communicate using sockets socket: door between application process and end-end- transport protocol Internet controlled by OS controlled by app developer transport application physical link network process transport application physical link network process socket Socket Programming
- 2. Two socket typesfor two transport services: • UDP: unreliable datagram • TCP: reliable, byte stream-oriented Application Example: 1. Client reads a line of characters (data) from its keyboard and sends the data to the server. 2. The server receives the data and converts characters to uppercase. 3. The server sends the modified data to the client. 4. The client receives the modified data and displays the line on its screen. Socket Programming
- 3. UDP: no “connection”between client & server • no handshaking before sending data • sender explicitly attaches IP destination address and port # to each packet • rcvr extracts sender IP address and port# from received packet UDP: transmitted data may be lost or received out-of-order Application viewpoint: • UDP provides unreliable transfer of groups of bytes (“datagrams”) between client and server Socket Programming w/ UDP
- 4. close clientSocket read datagram from clientSocket createsocket: clientSocket = socket(AF_INET,SOCK_DGRAM) Create datagram with server IP and port=x; send datagram via clientSocket create socket, port= x: serverSocket = socket(AF_INET,SOCK_DGRAM) read datagram from serverSocket write reply to serverSocket specifying client address, port number server (running on serverIP) client Socket Programming w/ UDP
- 5. from socket import* serverName = ‘hostname’ serverPort = 12000 clientSocket = socket(socket.AF_INET, socket.SOCK_DGRAM) message = raw_input(’Input lowercase sentence:’) clientSocket.sendto(message,(serverName, serverPort)) modifiedMessage, serverAddress = clientSocket.recvfrom(2048) print modifiedMessage clientSocket.close() Python UDPClient include Python’s socket library create UDP socket for server get user keyboard input Attach server name, port to message; send into socket print out received string and close socket read reply characters from socket into string Socket Programming w/ UDP
- 6. from socket import* serverPort = 12000 serverSocket = socket(AF_INET, SOCK_DGRAM) serverSocket.bind(('', serverPort)) print “The server is ready to receive” while 1: message, clientAddress = serverSocket.recvfrom(2048) modifiedMessage = message.upper() serverSocket.sendto(modifiedMessage, clientAddress) Python UDPServer create UDP socket bind socket to local port number 12000 loop forever Read from UDP socket into message, getting client’s address (client IP and port) send upper case string back to this client Socket Programming w/ UDP
- 7. client must contactserver • server process must first be running • server must have created socket (door) that welcomes client’s contact client contacts server by: • Creating TCP socket, specifying IP address, port number of server process • when client creates socket: client TCP establishes connection to server TCP • when contacted by client, server TCP creates new socket for server process to communicate with that particular client • allows server to talk with multiple clients • source port numbers used to distinguish clients (more in Chap 3) TCP provides reliable, in-order byte-stream transfer (“pipe”) between client and server application viewpoint: Socket Programming w/ TCP
- 8. wait for incoming connectionrequest connectionSocket = serverSocket.accept() create socket, port=x, for incoming request: serverSocket = socket() create socket, connect to hostid, port=x clientSocket = socket() server (running on hostid) client send request using clientSocket read request from connectionSocket write reply to connectionSocket TCP connection setup close connectionSocket read reply from clientSocket close clientSocket Socket Programming w/ TCP
- 9. from socket import* serverName = ’servername’ serverPort = 12000 clientSocket = socket(AF_INET, SOCK_STREAM) clientSocket.connect((serverName,serverPort)) sentence = raw_input(‘Input lowercase sentence:’) clientSocket.send(sentence) modifiedSentence = clientSocket.recv(1024) print ‘From Server:’, modifiedSentence clientSocket.close() Python TCPClient create TCP socket for server, remote port 12000 No need to attach server name, port Socket Programming w/ TCP
- 10. from socket import* serverPort = 12000 serverSocket = socket(AF_INET,SOCK_STREAM) serverSocket.bind((‘’,serverPort)) serverSocket.listen(1) print ‘The server is ready to receive’ while 1: connectionSocket, addr = serverSocket.accept() sentence = connectionSocket.recv(1024) capitalizedSentence = sentence.upper() connectionSocket.send(capitalizedSentence) connectionSocket.close() Python TCPServer create TCP welcoming socket server begins listening for incoming TCP requests loop forever server waits on accept() for incoming requests, new socket created on return read bytes from socket (but not address as in UDP) close connection to this client (but not welcoming socket) Socket Programming w/ TCP
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- 16. MultiClient TCP programmingin Python
- 17. Multithreaded TCP Serverin Python
- 18. Multithreaded TCP Clientin Python