Goals

Your primary goal for this lab is to write a simple socket-based client to connect to a given server.

Getting started

First, download the networking.tar file to get the code for the lab. Make sure you are on mantis.

wget https://www.cs.carleton.edu/faculty/tamert/courses/cs208-s25/resources/samples/networking.tar

Copy it into a folder for today’s lab, and then un-tar the file:

tar xvf networking.tar

You should find the following files in a folder sockets_lab:

• client.c: The client code you’ll be modifying.
• common.h: Some useful #defines used by both the client and the server.
• server.c: The code for the server you’ll be connecting to.

Part 1: Read through what you’ve got to work with

Take a look through server.c, trying to get a feel for how it sets up its end of the socket(s) to accept connection(s).

Then, look at client.c. There are a bunch of // TODOs for you to fill in.

Think back on what we talked about today – how will the client and server interact? Can multiple users interact with the server at the same time?

Part 2: Implementing a socket-based client

Now you’ll actually implement your client. Again, make sure you’re on mantis, or this will be less execiting. Try compiling your code after each step below, and make sure to run it once you think it works.

1. Find the comment // 1) TODO in client.c. You need to add code to call socket() to create a UDP socket. Take a look at server.c for an example.

2. Find the comment // 2) TODO in client.c. Now, you need to use connect() to connect to the server using the servaddr info. Don’t forget to check for errors!

Note: I found this page really helpful in figuring out how to use connect(). Note that we aren’t using getaddrinfo here, but you can get away with casting a struct sockaddr_in * as struct sockadd *. You also might find it handy to compare to the bind() call in server.c.

3. Find the comment // 3) TODO in client.c. Add a call to send() the message. This should be analagous to the recv call in client.c, but you don’t need the loop. You should store the return value in a variable named sent_bytes.

4. Un-comment the line after // 4) TODO to print out the number of bytes sent.

Try running it – check the screen up front to see if the server receives your message!

Part 3: Next steps

Once you have all that, play around some more!

• Find the // 5) TODO comment and maybe prompt the user to type a message to send (read it with scanf() or fgets() (but NOT gets), or maybe take the message as a command-line argument.

• Maybe try setting up a loop to continually prompt the user to type new messages, sending each one.