server.js

const express = require('express');
const { join } = require('path');
const { createServer } = require('http');
const { renderFile } = require('ejs');

const app = express();
const server = createServer(app);
const io = (require('socket.io'))(server);

app.use(express.static(join(__dirname, 'public')));
app.set('views', join(__dirname, 'public'));
app.engine('html', renderFile);
app.set('view engine', 'html');

app.use('/', (_, res) => res.render('index.html'));
app.use('/chat', (_, res) => res.render('index.html'));

const lastDate = {};
const rateLimiter = {};

const linkRegExp = new RegExp('(https?:\/\/(?:www\.|(?!www))[a-zA-Z0-9][a-zA-Z0-9-]+[a-zA-Z0-9]\.[^\s]{2,}|www\.[a-zA-Z0-9][a-zA-Z0-9-]+[a-zA-Z0-9]\.[^\s]{2,}|https?:\/\/(?:www\.|(?!www))[a-zA-Z0-9]+\.[^\s]{2,}|www\.[a-zA-Z0-9]+\.[^\s]{2,})')
const mentionRegExp = new RegExp('\@([a-zA-Z0-9]+)', 'gm')

const breakString = (s, a) => s.length > a ? s.slice(0, a) : s;
const getMentions = (s) => s.match(mentionRegExp) || [];

let connections = 0;

function escapeHTML(string) {
    return string
        .replace(/&/g, "&")
        .replace(/>/g, ">")
        .replace(/</g, "&lt;")
        .replace(/"/g, "&quot;")
}

io.on('connection', (socket) => {
    connections++;

    socket.broadcast.emit("userJoin", socket.id);

    socket.on('disconnect', () => {
        connections--;

        delete lastDate[socket.id];
        delete rateLimiter[socket.id];

        socket.broadcast.emit("userLeft", socket.id);
        socket.broadcast.emit("usersCountUpdated", connections);
    });

    socket.on('sendMessage', (data) => {
        // Remove additional information sended by client.
        const avatar = data.author.avatar_url
        data = {
            author: {
                name: escapeHTML(breakString(data.author.name, 10)),
                avatar_url: avatar ? encodeURI(avatar) : DEFAULT_USER_AVATAR,
            },
            content: escapeHTML(breakString(data.content, 250)),
        };

        data.mentions = getMentions(data.content)

        data.content = data.content.replace(linkRegExp, (item) => {
            item = encodeURI(item)
            return `<a href='${item}' class='link' target='_blank'>${item}</a>`
        });

        let lastMessageSendedDate = lastDate[socket.id];
        if (!lastMessageSendedDate) lastMessageSendedDate = Date.now();

        let rateLimit = rateLimiter[socket.id]
        if (!rateLimit) {
            rateLimiter[socket.id] = [];
            rateLimit = rateLimiter[socket.id];
        }

        if (rateLimit.length >= 5 && rateLimit.reduce((a, b) => a + b, 0) <= 800) {
            if (lastMessageSendedDate + 30 * 1000 <= Date.now()) rateLimiter[socket.id] = [];

            return socket.emit('messageNotSended', data);
        }

        if (lastMessageSendedDate <= Date.now()) {
            rateLimiter[socket.id].push(Date.now() - lastMessageSendedDate);
            lastDate[socket.id] = Date.now() + 1000;

            socket.broadcast.emit('receivedMessage', data);
            return socket.emit('messageSended', data);
        }
        
        return socket.emit('messageNotSended', data);
    });

    socket.emit("usersCountUpdated", connections);
    socket.broadcast.emit("usersCountUpdated", connections);
});

server.listen(process.env.PORT || 3000, () => console.log('Running!'));

var DEFAULT_USER_AVATAR = 'https://i.imgur.com/HXv93eV.jpg'; // quem mudar daqui, vai cair o pau quando for mijar