io.on("connection", (socket) => {
    // Server is not reachable
    if (!bServerIsReachable)
        socket.disconnect();
    // Server is reachable
    else {
        // Store the connecting client
        stackSockets[socket.id] = [];
        stackSockets[socket.id].chrono     = Date.now();
        stackSockets[socket.id].registered = false;
        stackSockets[socket.id].country    = 'XX';
        stackSockets[socket.id].name       = 'Anonymous';
        
        // Send the welcome message to the client (this will show the registration form)
        SendToClient(socket, 'LAUNCH', welcomeMess);
    
        // Register callback
        socket.on("REGISTER", (usrnm) => {
        if (!stackSockets[socket.id].registered) {
            if (!IsOffensive(usrnm)) { // Checks if the username includes any forbidden word
            stackSockets[socket.id].registered = true;
            stackSockets[socket.id].name       = usrnm;
    
            // Push the current socket to the registered room
            socket.join('registered');
    
            // Define user's country
            GeoIp.open('./GeoLite2-Country.mmdb').then(reader => {
                // Get user's country
                var strCountry = reader.country(socket.handshake.address).country.isoCode;  
    
                // Store the user's country
                stackSockets[socket.id]['country'] = (strCountry || 'XX');
    
                // Add 1 to the number of online users coming from this country
                listCountry[strCountry] = (listCountry[strCountry] || 0) + 1;  
    
                // Send the users' country list to users currently playing
                BroadcastToRegisteredClients('ONLINE', JSON.stringify(listCountry));
            }).catch((error) => {
                // Can't get user's country, set the uknown country flag
                stackSockets[socket.id].country = 'XX';  
    
                // Add 1 to the number of online users from unknown locations
                listCountry['XX'] = (listCountry['XX'] || 0) + 1;
    
                // Send the users' country list to users currently playing
                BroadcastToRegisteredClients('ONLINE', JSON.stringify(listCountry));
            });
    
            // Store time point (used for the 10 sec cooldown between each submission, also used at start to mitigate cheat)
            stackSockets[socket.id].chrono = Date.now();
    
            // Send the trigger to show the game at the client, and current time point for comparison
            SendToClient(socket, 'REGISTER', JSON.stringify({ nsr: true, clk: Date.now() }));
            // Send progression informations (time elapsed, names of people who solved)
            SendToClient(socket, 'PROGRESS', JSON.stringify({0: PuzzleCurrTime, 1: iPuzzleIdCur, 2: arrProgress}));
    
            // Depending on the progression: send the current puzzle or the ending message
            if (iPuzzleIdCur < iPuzzleIdMax) {
                SendToClient(socket, 'HELPER_RES', JSON.stringify(Helpers[iPuzzleIdCur]));
                SendToClient(socket, 'HELPER_PCH', JSON.stringify({0: true, 1: iPuzzleIdMax, 2: Pitchs.slice(0, iPuzzleIdCur + 1)}));
            }
            else {
                SendToClient(socket, 'HELPER_RES', JSON.stringify({ type: 'txt', nchr: 0, rsrc: endingMess }));
                SendToClient(socket, 'HELPER_PCH', JSON.stringify({0: true, 1: iPuzzleIdMax, 2: Pitchs.slice(0, iPuzzleIdCur )}));
            }
            }
            // Send trigger to show an error message in the client form
            else
            SendToClient(socket, 'REGISTER', JSON.stringify({ nsr: false, clk: 0 }));
        }
        else
            socket.disconnect();
        });
    
        // Disconnection callback
        socket.on("disconnect", () => {
        // Remove the user country of the online users list
        --listCountry[stackSockets[socket.id].country];
        if (listCountry[stackSockets[socket.id].country] <= 0)
            delete listCountry[stackSockets[socket.id].country];
    
        // Remove the socket of the online user stack
        delete stackSockets[socket.id];
    
        // Send the users' country list to users currently playing
        BroadcastToRegisteredClients('ONLINE', JSON.stringify(listCountry));
        });
    
    ...
    
    }
});
            

    class Client extends Component {

        ...
        
        componentDidMount() {
        
            ...
        
            // Puzzle file reception
            this.socket.on('HELPER_RES', data => {
            // Parse data to jSon
            const jSon = JSON.parse(data);
        
            // Store the character length of the new puzzle keyword 
            this.setState({ keyLen: jSon.nchr });
        
            // Push the puzzle file to the div depending on its type
            if (jSon.type === 'txt') // Encodé en UTF-8
                this.refHelperRes.current.innerHTML = `<div style="text-align:left">${jSon.rsrc}</div>`;
            else if (jSon.type === 'img') // Encodée en PNG
                this.refHelperRes.current.innerHTML = `<img src=${jSon.rsrc} />`;
            else if (jSon.type === 'snd') // Encodé en MP3
                this.refHelperRes.current.innerHTML = `<audio controls="controls" autoPlay><source src=${jSon.rsrc} /></audio>`;
            else if (jSon.type === 'vid') // Encodée en WebM
                this.refHelperRes.current.innerHTML = `<video controls autoPlay loop><source type="video/webm" src=${jSon.rsrc}></video>`;
            });
        
            ...
        
        }
        
        ...
        
    }