Programming Lab - Introduction to Sockets

Download and Compile Individually

Download and compile the following files:

• tcp_client.c
• udp_client.c
• tcp_server.c
• udp_server.c

Example:
Compile:

gcc tcp_client.c -o tcp_client

Run with:

./tcp_client

Be sure to stop any running servers or clients and recompile after making changes.

Lab Overview

We will use simple client/server applications to explore TCP and UDP socket programming:

• The client reads a line from standard input.
• It sends the line to the server over a socket.
• The server converts the line to uppercase.
• The server sends the modified line back to the client.
• The client prints the result to standard output.

TCP vs UDP Quick Reference

Questions

Answer the following in your lab report:

1. Run tcp_client before starting tcp_server:
   • What happens?
   • Why?
2. Run udp_client before starting udp_server:
   • What happens?
   • Why?
3. UDP port mismatch:
   • Run both programs with different port numbers.
   • What happens?
   • Why?
4. TCP port mismatch:
   • Run both programs with different port numbers.
   • What happens?
   • Why?
5. UDP Buffer Test:
   • Start the udp_server.
   • Launch udp_client and send a message.
   • While the server is running, rerun udp_client and send a shorter message.
     • What happens?
     • Why?
     • Fix it. Include your code fix in your submission.
6. Send buffer limit (udp_client):
   • Modify send_msg in udp_client to allocate 5 bytes instead of 50.
   • Restart both client and server.
   • Send a message longer than 5 bytes.
     • What happens?
     • Why?
7. Receive buffer limit (udp_client):
   • Revert previous change and instead reduce recv_msg allocation to 5 bytes.
   • Send a message longer than 5 bytes.
     • What do you expect?
     • What actually happened?
     • Why?

Programming Tasks

1. Accept user input for IP and port

Update all programs to prompt the user for:

• Server IP address (in client programs)
• Server and client port numbers

Example:

Enter server IP: 127.0.0.1
Enter server port: 9000

2. Loop until QUIT

Update tcp_client and udp_client to:

• Continuously read input from the user
• Send the message to the server
• Exit the loop when the user types QUIT

Note: Use standard input methods like fgets() or scanf(). Match QUIT exactly (case-sensitive).

Extra Credit (Optional)

• Add multi-client support in tcp_server.
• Add logging features (client IP, timestamps, etc.)
• Add error recovery or retry logic in UDP.
• Feel free to experiment and go beyond the lab instructions! Surprise me!

Helpful References

• Linux socket interface (man 7 socket)
• Beej’s Guide to Network Programming
• Debugging with GDB

Testing & Debugging Tools

• Netcat – tool for sending and receiving data
• Check open ports:
  • TCP: netstat -antop
  • UDP: netstat -anoup
• Kill processes:
  • By PID: kill PID
  • By name: pkill PATTERN

Grading

Submit your lab report, including answers to all questions, modified source code files and screenshots, via Marmoset by the scheduled due date listed in the syllabus.