The document outlines the process of building client/server applications that communicate using sockets, detailing both UDP (unreliable) and TCP (reliable) socket programming. It provides examples of how clients and servers interact using Python code, illustrating the creation of sockets, data transmission, and handling responses. Additionally, it touches on multithreading for handling multiple client connections in a TCP server environment.

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Basics of Socket Programming using python

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  goal: learn howto build client/server applications thatcommunicate using socketssocket: door between application process and end-end-transport protocolInternetcontrolledby OScontrolled byapp developertransportapplicationphysicallinknetworkprocesstransportapplicationphysicallinknetworkprocesssocketSocket Programming
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  Two socket typesfor two transport services:• UDP: unreliable datagram• TCP: reliable, byte stream-orientedApplication Example:1. Client reads a line of characters (data) from itskeyboard and sends the data to the server.2. The server receives the data and convertscharacters to uppercase.3. The server sends the modified data to the client.4. The client receives the modified data and displaysthe line on its screen.Socket Programming
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  UDP: no “connection”between client & server• no handshaking before sending data• sender explicitly attaches IP destination address andport # to each packet• rcvr extracts sender IP address and port# from receivedpacketUDP: transmitted data may be lost or receivedout-of-orderApplication viewpoint:• UDP provides unreliable transfer of groups of bytes(“datagrams”) between client and serverSocket Programming w/ UDP
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  closeclientSocketread datagram fromclientSocketcreatesocket:clientSocket =socket(AF_INET,SOCK_DGRAM)Create datagram with server IP andport=x; send datagram viaclientSocketcreate socket, port= x:serverSocket =socket(AF_INET,SOCK_DGRAM)read datagram fromserverSocketwrite reply toserverSocketspecifyingclient address,port numberserver (running on serverIP) clientSocket Programming w/ UDP
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  from socket import*serverName = ‘hostname’serverPort = 12000clientSocket = socket(socket.AF_INET,socket.SOCK_DGRAM)message = raw_input(’Input lowercase sentence:’)clientSocket.sendto(message,(serverName, serverPort))modifiedMessage, serverAddress =clientSocket.recvfrom(2048)print modifiedMessageclientSocket.close()Python UDPClientinclude Python’s socketlibrarycreate UDP socket forserverget user keyboardinputAttach server name, port tomessage; send into socketprint out received stringand close socketread reply characters fromsocket into stringSocket Programming w/ UDP
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  from socket import*serverPort = 12000serverSocket = 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 UDPServercreate UDP socketbind socket to local portnumber 12000loop foreverRead from UDP socket intomessage, getting client’saddress (client IP and port)send upper case stringback to this clientSocket Programming w/ UDP
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  client must contactserver• server process must first berunning• server must have createdsocket (door) that welcomesclient’s contactclient contacts server by:• Creating TCP socket, specifyingIP address, port number ofserver process• when client creates socket:client TCP establishesconnection to server TCP• when contacted by client, serverTCP creates new socket forserver process to communicatewith that particular client• allows server to talk withmultiple clients• source port numbers usedto distinguish clients (morein Chap 3)TCP provides reliable, in-orderbyte-stream transfer (“pipe”)between client and serverapplication viewpoint:Socket Programming w/ TCP
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  wait for incomingconnectionrequestconnectionSocket =serverSocket.accept()create socket,port=x, for incomingrequest:serverSocket = socket()create socket,connect to hostid, port=xclientSocket = socket()server (running on hostid) clientsend request usingclientSocketread request fromconnectionSocketwrite reply toconnectionSocketTCPconnection setupcloseconnectionSocketread reply fromclientSocketcloseclientSocketSocket Programming w/ TCP
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  from socket import*serverName = ’servername’serverPort = 12000clientSocket = 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:’, modifiedSentenceclientSocket.close()Python TCPClientcreate TCP socket forserver, remote port 12000No need to attach servername, portSocket Programming w/ TCP
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  from socket import*serverPort = 12000serverSocket = 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 TCPServercreate TCP welcomingsocketserver begins listening forincoming TCP requestsloop foreverserver waits on accept()for incoming requests, newsocket created on returnread bytes from socket (butnot address as in UDP)close connection to thisclient (but not welcomingsocket)Socket Programming w/ TCP
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  Multithreading in python
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  Thread Lifecycle
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  Multithreading in python
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  Multithreading in python
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  Multithreading in python
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  MultiClient TCP programmingin Python
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  Multithreaded TCP Serverin Python
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  Multithreaded TCP Clientin Python