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INP112 Homework 02 - Network Chat Server

This project involves designing a chat server capable of handling multiple client connections using a single process. The server supports various user commands to register, log in, chat, and manage chat rooms.

Description

In this homework, you are asked to design a chat server. Your program should be a single process and use select or poll to handle multiple connections and receive user commands from the client socket. After receiving the command message, the server should send the corresponding message back.

:::danger The TAs use the diff tool to compare your output directly against our prepared sample test data. When comparing against the sample test data, continuous spaces and tabs in the output are consolidated into a single space character. :::

Your server should show a welcome message once a client is connected.

*********************************
** Welcome to the Chat server. **
*********************************

Basic commands

The server accepts commands sent from the users, processes the commands, and responds to the users. The details of valid commands are introduced as follows.

:::warning If a client sends an incomplete command, e.g., missing required parameters, the server should show the client the correct command format (usage). :::

  • register

    register <username> <password>

    1. If there is any missing or redundant parameter
      • Usage: register <username> <password>
    2. If <username> already exists
      • Username is already used.
    3. If a client successfully registers an account
      • Register successfully.

    :::info :bulb:The username and password only contain one word. Their respective length is less than 20 characters. :::

  • login

    login <username> <password>

    1. If there is any missing or redundant parameter
      • Usage: login <username> <password>
    2. If the client has already logged in with an account
      • Please logout first.
    3. If the username does not exist
      • Login failed.
    4. If the password is wrong
      • Login failed.
    5. If an account is already logged in by another client
      • Login failed.
    6. If a client successfully logs in
      • Welcome, <username>.

    :::info :bulb: If client A has already successfully logged in as user A, other clients (including client A) cannot log in as user A until client A logs out. :::

  • logout

    logout

    1. If there is any missing or redundant parameter
      • Usage: logout
    2. If the client has not logged in
      • Please login first.
    3. If the client successfully logs out
      • Bye, <username>.

  • exit

    exit

    1. If there is any missing or redundant parameter
      • Usage: exit
    2. If the client has not logged out, run the logout command first and then the exit command implicitly. The terminal would show:
      • Bye, <username>.
    3. If the exit command works successfully, the connection will be closed.

  • whoami

    whoami

    1. If there is any missing or redundant parameter:
      • Usage: whoami
    2. If the client has not logged in:
      • Please login first.
    3. Show the username:
      • <username>

  • set-status

    set-status : online, offline, busy

    1. If there is any missing or redundant parameter:
      • Usage: set-status <status>
    2. If the client has not logged in:
      • Please login first.
    3. The status should be online, offline, or busy. If there is any other status:
      • set-status failed
    4. The default status for all users is offline:
    5. If setting successfully:
      • <username> <status>

    :::info :bulb: The status of a user should be set to online after login. The status of a user should be set to offline after logging out or exiting. You do not need to show any set-status-related messages when invoking login, logout, and exit commands. :::

  • list-user

    list-user

    1. If there is any missing or redundant parameter:
      • Usage: list-user
    2. If the client has not logged in:
      • Please login first.
    3. List all users and the corresponding status in the server and sort by user names alphabetically.
      • <username 1> <status>
      • <username 2> <status>
      • ...

  • Enter a chat room

    enter-chat-room <number>

    1. If there is any missing or redundant parameter:
      • Usage: enter-chat-room <number>
    2. If <number> is not a valid room number(not between 1 to 100)
      • Number <number> is not valid.
    3. If the client has not logged in:
      • Please login first.
    4. If the chat room does not exist, create a new room and enter this room:
      • Welcome to the public chat room.
      • Room number: <number>
      • Owner: <creator>
    5. If one client successfully enters the chat room:
      • Show the message to all clients in the chat room.
        • <username> had enter the chat room.
      • Show the messages below to the new client.
        • Welcome to the public chat room.
        • Room number: <number>
        • Owner: <creator>
        • <chat_history>
      • Format of <chat_history>:
        • Chat history is composed of several Records.
          • Record 1 + Record 2 + ... + Record n
        • The format of a Record is
          • [<username>]: <message>\n
        • Only show the latest 10 Records.

    :::info :bulb: Every <message> in <chat_history> should also be filtered (see here). If there is a pin message, add a mark after Record n in the format Pin -> [<username>]: <message>\n.(see here) :::

  • list chat room

    list-chat-room

    1. If there is any missing or redundant parameter:
      • Usage: list-chat-room
    2. If the client has not logged in:
      • Please login first.
    3. List all existing chat rooms and the corresponding owners in the server and sort by the room number.
      • <owner username> <room number>
      • ...

  • close chat room

    close-chat-room

    1. If there is any missing or redundant parameter:
      • Usage: close-chat-room <number>
    2. If the client has not logged in:
      • Please login first.
    3. If the user is not the owner:
      • Only the owner can close this chat room.
    4. If the chat room does not exist:
      • Chat room <number> does not exist.
    5. After closing successfully:
      • Chat room <number> was closed.

    :::info :bulb: All users in a chat room must be kicked out when the room no longer exists. Once a chat room is closed, the server should show a message in the format Chat room <number> was closed. to all users in the chat room. :::

  • unknown command

    • Show the error message if the input command is not specified:
      • Error: Unknown command

Chat room commands

  • pin

    /pin

    1. Messages should be sent by TCP packets.
    2. The length of the message can be at most 150 characters.
    3. Send Pin -> [<username>]: <message>\n to all users in the chatroom.
    4. Set the pin message in the chat room.

    :::info :bulb: Only one message can be pinned in a chat room. The chat room only keeps the latest pinned message. :::

  • delete pin

    /delete-pin

    1. If there is no pin message in the chat room:
      • No pin message in chat room <number>
    2. Delete the pin message in the chat room.

  • exit chat room

    /exit-chat-room

    1. Switch to the chat server mode.
    2. Send the message <username> had left the chat room. to all clients in the chat room.

  • list user

    /list-user

    1. List all users in this chat room
      • <usename> <status>
      • <usename> <status>
      • ...

  • chat message

    1. The length of the message can be at most 150 characters.
    2. Send [<username>]: <message>\n to all users in the chatroom.

    :::info :bulb: In our test cases, <message> contains all printable ASCII characters except \0 and \n. :::

:::warning A client can use only chat room commands when entering a chat room. The client cannot use all basic commands in a chat room. Input without a leading / is considered a typical message. If a command is not specified in this document, the terminal will show Error: Unknown command .

:::

Chat History

When a client joins a (enter-chat-room) chat room, the server should immediately encapsulate all messages in chat history in the format of <chat_history> and send it to the client in the TCP connection. The format of <chat_history> is:

[<username>]: <message>\n[<username>]: <message>\n...

Content Filtering

To keep our chat room a joyful and peaceful space, some keywords should not be used. Below is the filtering list of those keywords. The server must mask each matched word in <message> sent by the clients by replacing the word with a sequence of * characters of the same length.

You must hard code the filtering list in your C/C++ program file.

filtering list

==
Superpie
hello
Starburst Stream
Domain Expansion

:::info :bulb: Keyword matching is case insensitive. :::

For more details about the implementation, please check the demonstration section for the sample input and the corresponding output.

Use ‘’% “ as the basic command line prompt. Notice that there is only one space after the prompt message. The server closes the connection for the client invoking the exit command. Nevertheless, the server keeps running in the background and accepts new incoming clients.

To run your server, you must provide the port number for your program. You can use nc or telnet command line tool to connect to your server.

server usage: ./hw2_chat_server [port number]

Demonstration

Example 1

register login logout whoami set-status list-user

  • ta1
    bash$ nc localhost 1234
    *********************************
    ** Welcome to the Chat server. **
    *********************************
1.  % register
    Usage: register <username> <password>
2.  % register ta1 420420
    Register successfully.
3.  % register ta1 420420
    Username is already used.
4.  % login
    Usage: login <username> <password>
5.  % login ta1
    Usage: login <username> <password>
6.  % login ta1 000000
    Login failed.
7.  % login Tom 420420
    Login failed.
8.  % login ta1 420420
    Welcome, ta1.
9.  % whoami
    ta1
10. % login ta1 420420
    Please logout first.
11. % logout
    Bye, ta1.
12. % logout
    Please login first.
13. % register ta2 777777
    Register successfully.
17. % exit
  • ta3 (login after ta2 has registered)
    bash$ nc localhost 1234
    *********************************
    ** Welcome to the Chat server. **
    *********************************
14. % register ta3 ta3
    Register successfully.
15. % login ta3 ta3
    Welcome, ta3.
16. % list-user
    ta1 offline
    ta2 offline
    ta3 online
18. % set-status happyhappy
    set-status failed
19. % set-status busy
    ta3 busy
20. % list-user
    ta1 offline
    ta2 offline
    ta3 busy
21. % exit
    Bye, ta3.

Example 2

enter-chat-room <number> list-chat-room close-chat-room <number> unknown command chat

  • ta1 (login as a registered user ta1)
    *********************************
    ** Welcome to the Chat server. **
    *********************************
1.  % login ta1 420420
    Welcome, ta1.
2.  % enter-chat-room
    Usage: enter-chat-room <number>
3.  % enter-chat-room 1010
    Number 1010 is not valid.
4.  % enter-chat-room 20
    Welcome to the public chat room.
    Room number: 20
    Owner: ta1
5.  /exit-chat-room
6.  % enter-chat-room 30
    Welcome to the public chat room.
    Room number: 30
    Owner: ta1
7.  hello, i am ta1.
    [ta1]: *****, i am ta1.
8.  i am waiting for everyone.
    [ta1]: i am waiting for everyone.
    ta2 had enter the chat room.
    [ta2]: merry christmas!
15. exit
    [ta1]: exit
17. /exit-chat-room
18. % list-chat-room
    ta1 20
    ta1 30
19. % close-chat-room 35
    Chat room 35 does not exist.
20. % close-chat-room 20
    Chat room 20 was closed.
21. % list-chat-room
    ta1 30
22. % close-chat-room 30
    Chat room 30 was closed.
23. % list-chat-room
24. % exit
    Bye, ta1.
  • ta2 (login as a registered user ta2)
    *********************************
    ** Welcome to the Chat server. **
    *********************************
9.  % login ta2 ta2
    Welcome, ta2.
10. % list-chat-room
    ta1 20
    ta1 30
11. % close-chat-room
    Usage: close-chat-room <number>
12. % close-chat-room 30
    Only the owner can close this chat room.
13. % enter-chat-room 30
    Welcome to the public chat room.
    Room number: 30
    Owner: ta1
    [ta1]: *****, i am ta1.
    [ta1]: i am waiting for everyone.
14. merry christmas!
    [ta2]: merry christmas!
    [ta1]: exit
16. /close-chat-room 30
    Error: Unknown command
    ta1 had left the chat room.
    Chat room 30 was closed.
25. % close-chat-room 30
    Chat room 30 does not exist.
26. % hello
    Error: Unknown command
27. % exit
    Bye, ta2.

Example 3

/pin <message> /delete-pin /exit-chat-room /list-user chat

  • Bob (The second enter-chat-room command is sent after Tom enters the chat room)
    *********************************
    ** Welcome to the Chat server. **
    *********************************
1.  % register Bob 55555
    Register successfully.
2.  % login Bob 55555
    Welcome, Bob. 
3.  % enter-chat-room 25
    Welcome to the public chat room.
    Room number: 25
    Owner: Bob
4.  I will win !!!
    [Bob]: I will win !!!
5.  /delete-pin
    No pin message in chat room 25
6.  /pin You are the challenger.
    Pin -> [Bob]: You are the challenger.
7.  /exit-chat-room   
11. % enter-chat-room 25
    Welcome to the public chat room.
    Room number: 25
    Owner: Bob
    [Bob]: I will win !!!
    Pin -> [Bob]: You are the challenger.
    [Tom]: *****
13. ?
    [Bob]: ?
14. domain expansion.
    [Bob]: ****************.
    [Tom]: What?
16. domain expansion!!!???
    [Bob]: ****************!!!???
    Pin -> [Tom]: You are an ordinary person.
18. /exit-chat-room
19. % set-status offline
    Bob offline
20. % enter-chat-room 25
    Welcome to the public chat room.
    Room number: 25
    Owner: Bob
    [Bob]: I will win !!!
    [Tom]: *****
    [Bob]: ?
    [Bob]: ****************.
    [Tom]: What?
    [Bob]: ****************!!!???
    Pin -> [Tom]: You are an ordinary person.
21. I'm sorry.
    [Bob]: I'm sorry.
22. I couldn't bring out the best in you.
    [Bob]: I couldn't bring out the best in you.
24. /delete-pin
    [Tom]: I won't forget you.
    [Tom]: You can't beat me.
    [Tom]: Cheer up !!!
28. /exit-chat-room
%
  • Tom (enter the chat room after the first exit-chat-room command of Bob)
    *********************************
    ** Welcome to the Chat server. **
    *********************************
8.  % register Tom 22222
    Register successfully.
9.  % login Tom 22222
    Welcome, Tom.
10. % enter-chat-room 25
    Welcome to the public chat room.
    Room number: 25
    Owner: Bob
    [Bob]: I will win !!!
    Pin -> [Bob]: You are the challenger.
    Bob had enter the chat room.
12. hello
    [Tom]: *****
    [Bob]: ?
    [Bob]: ****************.
15. What?
    [Tom]: What?
    [Bob]: ****************!!!???
17. /pin You are an ordinary person.
    Pin -> [Tom]: You are an ordinary person.
    Bob had left the chat room.
    Bob had enter the chat room.
    [Bob]: I'm sorry.
    [Bob]: I couldn't bring out the best in you.
23. /list-user
    Bob offline
    Tom online
25. I won't forget you.
    [Tom]: I won't forget you.
26. You can't beat me.
    [Tom]: You can't beat me.
27. Cheer up !!!
    [Tom]: Cheer up !!!
    Bob had left the chat room.
29. Bye Bye.
    [Tom]: Bye Bye.
30. Who else?
    [Tom]: Who else? 
    nobody had enter the chat room.
    nobody had left the chat room.
35. /exit-chat-room
%
  • nobody (enter the chat room after the third exit-chat-room command of Bob)
    *********************************
    ** Welcome to the Chat server. **
    *********************************
31. % register nobody 11111
    Register successfully.
32. % login nobody 11111
    Welcome, nobody.
33. % enter-chat-room 25
    Welcome to the public chat room.
    Room number: 25
    Owner: Bob
    [Bob]: ****************.
    [Tom]: What?
    [Bob]: ****************!!!???
    [Bob]: I'm sorry.
    [Bob]: I couldn't bring out the best in you.
    [Tom]: I won't forget you.
    [Tom]: You can't beat me.
    [Tom]: Cheer up !!!
    [Tom]: Bye Bye.
    [Tom]: Who else?
34. /exit-chat-room
%

Scoring

  1. [20pts] Your server passes Example 1.
  2. [20pts] Your server passes Example 2.
  3. [20pts] Your server passes Example 3.
  4. [40pts] Your server passes the hidden test cases announced by TAs on January 4th.

Homework Submission

We will compile your homework by simply typing make.

Please pack your C/C++ code into a zip archive. The directory structure must follow the below illustration.

Please note that you do not need to enclose your id with the braces.

You must put your files in a folder named {id}_hw2 before you compress the files. :::danger If the file structure is wrong after decompression, you will get 10 pts score penalty. If we cannot use ./hw2_chat_server [port number] command to run after typing make, you will get 10 pts score penalty. :::

{student_id}_hw2.zip
└── {student_id}_hw2/
    ├── hw2_chat_server.c/hw2_chat_server.cpp
    ├── Makefile
    └── (any other c/c++ files if needed)

Remarks

  • Please implement your homework in C or C++.
  • Using any non-standard libraries or any external binaries (e.g., via system() or other functions that invoke an external process) is not allowed. :::danger Please upload your homework to E3 before the deadline. We will check your uploaded time to make sure late submission. You will get 0 if you don't demo on 1/4 or upload to E3 after 1/4 13:00. :::

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A chat server implemented in C++

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