session.checkip(req.ip, function(result) {
        console.log(result);
    });
exports.checkip = function(ip, callback) {
  var r = false;
  let connection = mysql.createConnection({
    host: 'localhost',
    user: 'root',
    password: 'Escola171995',
    database: 'website_personal_trainer'
  });

  connection.connect(function(err) {
      if (err) {
        return console.error('error: ' + err.message);
      }

      console.log('Connected to the MySQL server. checkip');
    });

  connection.query('select * from session', function(err, result, fields){
    for (var i in result)
        if (result[i].ip == ip) {
            r = true;
            break;
        }
    connection.end(function(err) {
      if (err) {
        return console.log('error:' + err.message);
      }
      console.log('Close the database connection.');
      callback(r);
    });
  });