Programming Lab - Introduction to Sockets

Download and compile individually the following files:

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

Example:

• Compile with: gcc tcp_client.c -o tcp_client
  • Note the name after -o flag
• Run with: ./tcp_client

We use the following simple client/server applications do demonstrate UDP and TCP socket programming.

• The client reads a line from its standard input and sends it to the server via its socket.
• The server receives the line through its socket and processes it.
• The server converts the line to uppercase.
• The server sends the modified line back to the client through its socket.
• The client receives the modified line via its socket and prints it to the standard output.

To ensure proper execution of each exercise, please remember to stop and recompile both the server and client before running. This helps to clear any previous configurations and ensures a clean environment for accurate results.

Please respond to the following questions:

• Suppose you run tcp_client before you run tcp_server. Enter a value.
  • What happens?
  • Why?
• Suppose you run udp_client before you run udp_server. Enter a value.
  • What happens?
  • Why?
• What occurs if different port numbers are used for the UDP client and UDP server? Please ensure that both programs are running before providing your response.
• What occurs if different port numbers are used for the TCP client and TCP server? Please ensure that both programs are running before providing your response.
• UDP Test Instructions
  • Start the udp_server.
  • Launch the udp_client and send a message to the server.
  • While the udp_server is still running, rerun the udp_client again, but this time send a shorter message.
    • What happens?
    • Why?
    • Fix it. Make sure to include your code fix as part of your submission.
  • Modify the send_msg function in udp_client to allocate 5 bytes instead of 50.
  • Restart both the udp_server and the updated udp_client. Don’t forget to recompile the udp_client before restarting!
  • Use the udp_client to send a message that exceeds 5 bytes in length.
    • What happens?
    • Why?
  • Revert your changes in udp_client and modify the allocation size of recv_msg to 5. After making this adjustment, rerun the udp_client and send a message that exceeds 5 bytes in length.
    • What outcomes do you anticipate from this change?
    • What was the actual outcome?
    • Why?

Programming Section:

• Update tcp_client, udp_client, tcp_server and udp_server to accept the client and server port numbers as user input.
• Modify tcp_client and udp_client to accept the server IP Address as user input.
• Implement functionality that allows both clients to continuously send messages until a QUIT command is entered.

Extra Credit:

• Enhance the tcp_server to support multiple clients.
• Feel free to experiment with the code and surprise me! Don’t hesitate to explore and push boundaries—breaking things can lead to valuable learning experiences. Embrace the process!

References

• Linux socket interface
• Beej’s Guide to Network Programming
• Debugging with GDB

Testing

• Netcat is a command line tool that connects to an arbitrary TCP or UDP port and allows you to send and receive data.
• To see what TCP ports are in use: netstat -antop, for UDP: netstat -anoup
• To kill a process: kill PID or pkill PATTERN

Grading

Post your report including source in Marmoset by the scheduled due date in the syllabus.