COMP2322 Lab 4 Socket Programming Yuvraj Sahni March 8, 2017

Requirement Experience in Python Programming Python for Programmers https://wiki.python.org/moin/BeginnersGuide/Programmers Learn Python Online https://www.codecademy.com/learn/python http://www.learnpython.org/

Simple Example Suppose I am interested in knowing the latitude and longitude of The Hong Kong Polytechnic University I can enter the following URL in the browser to obtain the information (in JSON format) http://maps.google.com/maps/api/geocode/json?address=The Hong Kong Polytechnic University&sensor=false&region=Hong Kong

Client/Server Model

Client/Server Model Examples of Client Examples of Server Google Chrome, Firefox Examples of Server Apache, IIS

Make a Raw HTTP Connection

socket in Python Instead of making an HTTP request through httplib package We can make the request by using socket socket – support basic network communications on an IP network Low-level approach Raw network communication A matter of sending and receiving strings

Make a Request By Socket

Network Sockets Used to identify particular processes (programs) on particular machines Network Socket is composed of 2 numbers: IP address – machine identifier Port number – process identifier Well-known ports: 25 – SMTP (email), 80 - HTTP (web), 110 – POP3 (email), 443 – HTTPS (secure web)

Network Sockets Socket() used in previous example is NOT the lowest protocol level The layers below the socket() are: Transmission Control Protocol (TCP) One alternative to TCP is UDP (we focus on TCP in this lab) Internet Protocol (IP) Link layer

“Passive” Listening Socket VS Active “Connected” Socket Server The server is a machine that is ready to receive connections It holds the address and the port number Passive Listening Socket It DOES NOT represent any actual network conversation <= no data can be received / sent by this kind of port! (Q: HOW it works then ???)

“Passive” Listening Socket vs Active “Connected” Socket When the server get the request from the passive listening socket Server checks with the OS willingness to receive incoming connections If NO, drop the request If YES, an active connected socket is then created Bind this socket to one remote conversation partner Example: A busy web server, a thousand active sockets bind to its public IP address at port 80

A Simple TCP Client and Server

A Simple TCP Client and Server

Limitations At the moment, the message must be fixed to 16 characters (octets)! Solution: Client side, before sending the message Determine the length of the message L [Assume max. number of length is 255] Add L at the beginning of the message Send the new message to server Server side, after receiving the message Extract the length of the message (first 3 characters) Read the rest of the message with the proper length

Modified TCP Client and Server

Modified TCP Client and Server

Lab Exercise (Total mark: 55) [1 / 2] 1. Create 2 Python files (10 marks) Client file - client_studentID.py Server file - server_studentID.py E.g. if my student ID is 12345678d, name the client file as client_12345678d.py 2. Provide your full name and student ID (5 marks) At the beginning of each Python program, by using program comment, provide the following information Your full name Your student ID

Lab Exercise (Total mark: 50) [2 / 2] 3. Create a simple instant messaging system (25 marks) The messaging system should let the client and server send the message in one by one approach (20 marks) (more detail description is shown in next page) Coding - easy to read (5 marks) if there is any syntax error in your programs (i.e. cannot run), ZERO mark will be given in this section.

Message in one by one approach Message in one by one approach IS NOT the same as common messaging platform!! It works like this: Server is waiting for connection Client is connected to Server Client sends a message Server receives the message Server sends a message Client receives the message Go back to (3) until Client/Server sends message “BYEBYE.”

Remote case conversion 4. Create an application that will convert lowercase letters into upper case. (5 marks) Client should send your name in lower case letters and it should receive your name back from the server converted in uppercase letters. Create a different client and server file

Remote calculation 5. Create a simple calculator using socket programming (5 marks) It should implement four operations: Add, Subtract, Multiply, and Divide Client should send two numbers and type of operation to a server, and the server should reply with the result of the operation. If the client wants to exit, it should send "BYEBYE" to the server. Create a different client and server file

Submission 6. Submission (5 marks) Submit two python program for each exercise (3,4, and 5) to LEARN@POLYU before the submission deadline (20 March 2017, at 5:00pm) Name the file as: client1_studentID.py and server1_studentID.py for exercise 3 client2_studentID.py and server2_studentID.py for exercise 4 client3_studentID.py and server3_studentID.py for exercise 5 It is not required to zip the files!

Reference J. Goerzen and B. Rhodes, Foundations of Python Network Programming: The comprehensive guide to building network applications with Python, Second Edition, Apress, 2010.