A Survey System

The goal of this exercise is to develop a client/server application for making surveys over the Internet. A survey will be composed of the following elements:

A question
One or more possible choices

Here is one possible example:

Question: "What is your favorite programming language?"
Choice 1: Java
Choice 2: C#
Choice 2: Python

The server will store a list of surveys that some administrative user (identified with a password) will have created. Clients will connect to the server and vote for the choices. The server will store, in addition to the question and the choices, the following information:

The number of votes that each choice has received so far.

The client and server applications will have a text (console) interface.

Client

The client will first connect to a server right after it starts. The IP address and port are given as commandline parameters. Here is what you would see on the terminal:

C:\Users\Telecom> Client.exe 10.20.30.40 1234

We are using the Windows console, we are inside the folder C:\Users\Telecom and we run the client, providing the IP address and port of the server.

If the client fails to connect to the server, it will show an error message and terminate. If it succeeds, it will show the following menu:

0. List all surveys and statistics
1. Vote in one survey
2. Create a survey (admin only)
3. Remove a survey (admin only)
4. Exit

Choose an option :

If the user chooses an option different from 0 to 4, the client will show an error message and display again the menu.

The last option terminates the client. The first 4 options allow the user to do the following:

List the surveys and statistics about the answers stored in the server.
Select a survey and vote for one of its choices.
An authorized administrator will be also to create and remove surveys.

Option 0 - List all surveys and statistics

When the user selects this option, the client will request to server for the list of surveys defined in the server, together with the number of votes that each choice received. The client will display the data using the following format:

Question 0: What is your favorite programming language?
- Choice 0 ( 5 votes,  25%): Java
- Choice 1 ( 5 votes,  25%): C#
- Choice 2 (10 votes,  50%): Python

Question 1: What grade you think you will get on the .NET course?
- Choice 0 ( 5 votes,  33%): Less than 12
- Choice 1 (10 votes,  66%): More than 12

Question 2: Do you know what is a critical section?
- Choice 0 ( 8 votes, 100%): Yesssss!
- Choice 1 ( 0 votes,   0%): No :(

Option 1 - Vote in one survey

The user has typed 1 and now the client shows the menu to vote. In the following example the user will select the question number 2 and will vote for the choice 0 to that question:

Ok, choose a question to vote for:

Question 0: What is your favorite programming language?
Question 1: What grade you think you will get on the .NET course?
Question 2: Do you know what is a critical section?

Choose a question: (the user enters 2)

Question 2: Do you know what is a critical section?
- Choice 0: Yesssss!
- Choice 1: No :(

Choose a choice: (the user enters 0)

Thank you, you voted 0 on question 2!
Sending the data to the server... Done!

After the client gets the choice from the user, it will send it to the server. Observe that, to implement this menu you will have to retrieve from the server the list of surveys and options currently defined in the server.

Option 2 - Create a survey

After the user selects this option, the client will ask for a password. The password will be sent to the server together with the data defining the survey. If the server accepts the password, the survey will be created and the client will indicate so to the user. If it is not accepted, the client will show an error message and come back to the main menu.

This is example execution, where the user creates a new survey with 3 choices:

Question : (the user types "How many planes orbit around the Sun?")
Choice 0 : (the user types "7 planets")
Choice 1 : (the user types "9 planets")
Choice 2 : (the user types "Not even NASA really knows...")
Choice 3 : (the user just types Enter)

Password: (the user types "admin")

Sending the data to the server... Done!

If the password is wrong, the server will send an error message to the client, and the client will show something different on the last line:

Sending the data to the server... ERROR, password not accepted :(

Option 3 - Remove a survey

Similarly to the previous option, the client requests for a password and sends it to the server. If its accepted it asks the user to provide the number of the question to remove. In the following example the user provides wrong data, and the client asks again:

Which question should I remove ?

Question 0: What is your favorite programming language?
Question 1: What grade you think you will get on the .NET course?
Question 2: Do you know what is a critical section?
Question 3: How many planes orbit around the Sun?

Choose a question: (the user enters 123)

Sorry, 123 is not a valid question id.
Which question should I remove ?

Question 0: What is your favorite programming language?
Question 1: What grade you think you will get on the .NET course?
Question 2: Do you know what is a critical section?
Question 3: How many planes orbit around the Sun?

Choose a question: (the user types 0)
Password: (the user types "admin")

Sending the data to the server... Done!

Server

The server will be a multithreaded application. Whenever a client connects to the server, the server will spawn one thread to handle the client. That thread will read and write the data socket used to communicate with the client. It will also read and write the list of surveys stored in the server. Observe that the list is shared among all the threads that handle the currently open connections to the server, so you will need to use appropriate synchronization primitives to avoid unexpected results when you update the shared data structures.

The server will be capable of replying to 4 different requests:

A request to produce the list of all surveys currently present in the server. The reply message will include the text of the question, the different choices and the number of votes for each choice.
A request to vote for some choice on some question. The request message will obviously contain the question number and the choice number. The server will replay with an OK or error message.
A request to remove a survey. It will include the number of the survey to remove as well as the password. The server will replay with an OK or error message.
A request to create a new survey, including a password, the text of the question and the choices. The server will replay with an OK or error message.

The server will operate as follows:

The server is started.
It displays on the console the IP address and port number on which it listens.
It then executes (in an infinite loop) the following actions:
- Accept a new client.
- Create a thread to deal with it

The thread will be responsible for one client. It will access data structures shared with other threads (who deal with other clients). The thread will operate as follows:

Wait for a client request. If the client closes the connection, then the thread will close the connexion and terminate.
Parse the request from the client.
Perform the necessary actions on the server's data structures (listing surveys currently open, votes within given survey, create/remove surveys)
Send a reply to the client.
Close the connexion.

Final remarks

Synchronization. The server is a multithreaded application. Access to data structures needs to be performed using the appropriate mutual exclusion in order to guarantee the absence of data races (as explained in the course). Section 2.8 will be of help here.
You must use TCP/IP connexions to transfer client requests and server replies through the net. You are free to design any protocol that you consider best for the task of encoding and decoding requests and replies. You might want ton consider the Bencode protocol.
Errors when parsing network packets (on the client or the server) should be reported to the user, and the connexion should be closed. This aspect of your proposed solution will be closely evaluated.
Your code should handle the most obvious exceptions and display error messages indicating what happened. Unhandled exceptions that originate in a thread could kill the entire server. This behaviour, for instance, should be avoided.
The quality of your code as well as the maturity in terms of testing will be evaluated. The code should be clear, well indented, and well tested. This aspect will also be closely evaluated.
If you have questions concerning the definition of the problem that this exercise is asking you to solve, please contact me. You are equally encouraged to take responsibility and make choices about the details of the problem statement that you consider missing in the above text. You will be asked to explain you decisions if they are not deemed adequate.