1. COMP2322 Lab 4 Socket Programming
Yuvraj Sahni
March 8, 2017

2. Requirement Experience in Python Programming Python for Programmers
Learn Python Online

3. 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)
Hong Kong Polytechnic University&sensor=false&region=Hong Kong

5. Client/Server Model

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

7. Make a Raw HTTP Connection

8. 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

9. Make a Request By Socket

10. 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 ( ), 80 - HTTP (web), 110 – POP3 ( ), 443 – HTTPS (secure web)

11. 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

12. “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 ???)

13. “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

14. A Simple TCP Client and Server

15. A Simple TCP Client and Server

17. 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

18. Modified TCP Client and Server

19. Modified TCP Client and Server

21. 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 d, name the client file as client_ d.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

22. 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.

23. 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.”

26. 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

28. 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

30. Submission 6. Submission (5 marks)
Submit two python program for each exercise (3,4, and 5) to 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!

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