Lab 2 CS Majors

UDP Programming in C++

Lab Objective:

• To gain experience using Unix/Linux UDP socket programming. You will be writting a UDP peer-to-peer chat program. This program will NOT have a server, it will make connections directly between two clients. Upon running the program, it will "search" for partners, and list them for the user. If no partners are available, it will continue to search until one (or more) is found. Once a partner is selected, the program will then allow the two clients to type messages to each other. There are enhancemens beyond this which you may choose.

• Sockets Tutorial
• Linux Network Programming, Part 1
• Programming Linux sockets, Part 2: Using UDP
• Five pitfalls of Linux sockets programming
• Practical C++ Sockets - Information on Broadcast/Multicast operations
• Threads in C++
• C++ Multithreading
• Linux functions for converting networking numbers

You will create programs using UDP to perform general chat sessions. You can use the code in /home/class/CSC4093/UDBChat/ and /home/class/CSC4093/BroadcastUDP/ as a starting point, but do not simply hack the code to achieve functionality. I will expect you to create a set of useful, reusable, network functions using sockets, and then to create well designed, structured code to achieve the required functionality.

Below first is the simple code from the first lab. This project is client/server oriented. You program will be peer-to-peer, that is you will only write ONE program, and run multiple instances that program to talk to each other.

The user will NOT enter IP addresses or port numbers - this aspect is hidden from the user. Rather each program will start up and broadcast packets announcing it's presence on a single port you choose (something above 5000). It will also listen on the same port, and build a list of partners it discovers. The user can than select a partner, or accept a request from another partner, and enter into a two way chat with that partner. If one partner terminates the chat by typing $exit, both sides will resume search for chat partners.

A tricky aspect of this project is that once you start waiting for a packet on a port, the program waits until it gets a packet, blocked. There is a solution - threads. The idea of threads is that the program is running multiple routine at the same time. The idea is that you can have a thread broadcasting beacons, another listening for beacon, one waiting for packets from a chat partner(s), and one waiting for user input. You can start all these threads, and than have them communicate through shared data structures in the program. Be careful, however, of race conditions.

Sample code for UDP Programming on Linux: (in "/home/class/csc4093/UDPChat")

• Makefile
• client.cpp
• server.cpp

• Makefile
• BroadcastReceiver.cpp
• BroadcastSender.cpp
• DieWithError.cpp

• Makefile
• ThreadExample.cpp

• Makefile
• ThreadBroadcast.cpp

The threads library provides three synchronization mechanisms:

• mutexes - Mutual exclusion lock: Block access to variables by other threads. This enforces exclusive access by a thread to a variable or set of variables.
• joins - Make a thread wait till others are complete (terminated).
• condition variables - data type pthread_cond_t

• Makefile
• ThreadBroadcastSync.cpp

Lab tasks:

The lab is worth 100 points total. Below I give you a set of requirements and options. You may do as many or few – this is a chance to get extra credit. However, no matter what you do, you will not get higher then a 100 if you do not have good clean code. Your score is dependent on the highest level of CS course you have taken.

In general, if you want to do more than one thing at a time, threads are required, this is asynchronous interaction. The more simple approach is synchronous, where only one thig happens at a time, and one side must wait for the other.

Feature	Required	CS II	Soft Dev	Op Sys
Well commented code	yes	5	5	5
On startup ask user for name to broadcast	yes	5	5	5
Well Designed/Written Code	yes	20	20	20
Transmit at least one beacon on startup (synchronous)	yes	20	15	10
Wait for a partner beacon - Show name and allow user to connect and chat, or wait for next beacon (synchronous)	yes	20	15	10
Display "Typing" if other user typing	not with next	20	15	15
Character at a time transmission/reception (see characters as typed	not with prev	20	15	15
Synchronous two-way chat function (take turns typing)	Must do this or next	30	25	15
Display new possible partners as they appear (asynchronous)		30	20	15
N-way chat. Allow used to bring in multiple partners in a group chat		35	30	25
Asynchronous two-way chat function (Either side can type any time, asynchronous, requires threads)	Must do this or previous	50	40	30
MAXIMUM SCORE		185	160	135

Turn in

1. A document listing the features you support
2. Screen captures clearly (with headings) demonstrating each feature support above.
3. All source code (including makefile)