Task on network

Οἱ ἄγγελοι (The messengers) #

The year is 480 B.C.
The Persian king Xerxes (Old Persian: 𐎧𐏁𐎹𐎠𐎾𐏁𐎠, Khshayārsha) has just invaded the Greek city-states.
This unfortunate event has caused many messengers traveling throughout Greece to begin acting as scouts.
They visit a variety of cities. Some settlements are controlled by the Greeks, while others have been taken by the Persians.

To gain an informational advantage, the citizens of Sparta (Doric Greek: Σπάρτα) decide to establish a library connected to the latest telecommunications network for messengers.

Each messenger receives a TCP client application that can connect to the library server.
The library contains a list of city-states and information about whether they are controlled by the Greeks or the Persians.
Each messenger maintains a similar list locally, updating it when new information is received from the central library.
There are 20 city-states. Each one is identified by a number in the range [1, 20].
Your task is to implement a library server compatible with the provided client.

The client program is delivered as a compiled executable. You can run it using:

./client <SERVER_ADDRESS> <PORT_NUMBER>

A compiled executable of a sample server implementation is also provided.

Stages #

  1. Implement handling of a single client connecting to a TCP server.
    The server accepts the port number as a command-line argument.
    Example server execution:

    ./server 8888

    After starting, the server listens for incoming client connections.
    Once connected to the first client, it waits to receive 4 bytes of data, prints them to stdout, closes the connection, and then exits.

  2. Implement handling of multiple clients and receiving data.

    • When a new client connects, they are added to the current list of clients.
    • The maximum number of clients is 4.
    • If the maximum number of clients is reached, new connections should be rejected.
    • Whenever the server receives a 4-byte message from any client, it prints it to the terminal. Use the epoll function to implement this step
      (alternatively, you may use pselect or ppoll).

    ⚠️ Note: In this step, you do not need to correctly handle client disconnections.

  3. Add to the server an array that stores information about which side each city belongs to.

    • Initially, all cities belong to the Greeks.
    • Each time the server receives a message in the format:
      pXX\n
      or
      gXX\n
      where XX is a two-digit number representing a city identifier, it indicates that city XX now belongs to the Persians or the Greeks, respectively.
    • If a city’s ownership hasn’t changed, take no action.
    • If the city’s owner has changed:
      • update the city ownership array,
      • broadcast the received message to all other connected clients.

    Assumptions:

    • You still do not need to handle client disconnections at this stage.
    • All incoming messages can be assumed to be in the correct format.

  4. Upon receiving a SIGINT signal, the server should:

    • close all connections,
    • print out which side each city belongs to,
    • free resources and terminate.

    Add proper handling for client disconnections in the following cases:

    • Reading from a client descriptor returns a message of length 0.
    • Writing to a client descriptor raises an EPIPE error.
    • The message received from the client is not in the correct format or the city number is outside the [1, 20] range.
    • The server receives a Control-C (C-c).

    ⚠️ Note: Disconnected clients free up space for new incoming clients.

Client and server executables #