LdapJS exop Request timeout - node.js

Question

I have an LdapJS server which implements standard operation and an extended operation to check health:
const server = ldap.createServer();
server.exop('healthcheck', (req, res, next) => {
res.end();
console.log('ended');
return next();
});
...
Then I wrote a simple client script to ping healthcheck service:
const { createClient } = require('ldapjs');
const client = createClient({
url: 'ldap://localhost:1389',
timeout: 2000,
connectTimeout: 2000
});
client.exop('healthcheck', (err, value, res) => {
if (err) {
console.log(`ERROR: ${err.message}`);
process.exit(1);
}
else {
console.log(`STATUS: ${res.status}`);
process.exit(0);
}
});
The problem is that the exop is correctly received by server (I can see the log inside its callback), but the client always logs: ERROR: request timeout (client interrupt).
Why the request is not correctly terminated?
EDIT
I wrote a mocha test for the exop and it works. Seems that the problem is related to the standalone call in healthcheck script.
describe('#healthcheck()', function () {
before(function () {
server = createServer();
server.listen(config.get('port'), config.get('host'), () => {});
});
after(function () {
server.close();
});
it('should return status 0', function (done) {
const { createClient } = require('ldapjs');
const client = createClient({
url: 'ldap://localhost:1389',
timeout: 2000,
connectTimeout: 2000
});
client.exop('healthcheck', (err, value, res) => {
should.not.exist(err);
res.status.should.be.equal(0);
client.destroy();
return done();
});
});
});