Dust js does not stream (show html) when using helmet

I want to use dust stream (or adaro stream) for async html template, so I tried using stream.
What I found was that if I added helmet to my express app, then the html is not rendered and is shown as text insted of the html on screen.
I tried dust.stream, and hoffman, and adaro, all the same result:
https://stackoverflow.com/questions/56507447/dust-js-and-helmet-not-rendering-html
Dust.stream:

var fs = require('fs'),
    path = require('path'),
    express = require('express'),
    request = require('request'),
    helmet = require('helmet'),
    dust = require('dustjs-linkedin');

dust.config.whitespace = true;
dust.config.cache = false;

// Define a custom `onLoad` function to tell Dust how to load templates
dust.onLoad = function(tmpl, cb) {
  fs.readFile(path.join('./views', path.relative('/', path.resolve('/', tmpl + '.dust'))),
              { encoding: 'utf8' }, cb);
};

var app = express();
app.use(helmet());

app.get('/streaming', function(req, res) {
  dust.stream('hello', {
    "async": request('http://www.dustjs.com/')
  }).pipe(res)
    .on('end', function() {
      console.log('Done streaming!');
    });
});

app.get('/rendering', function(req, res) {
  dust.render('hello', {
    "async": request('http://www.dustjs.com/')
  }, function(err, out) {
    res.send(out);
    console.log('Done rendering!');
  });
});


const port = process.env.PORT | 3002;
app.listen(port, function () {
  console.log(`Visit http://localhost:${port} to see streaming!`);
});

Hoffman:

hoffman = require('hoffman'),
    express = require('express'),
    helmet = require('helmet'),
    request = require('request');

var app = express();

app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'dust');
app.engine('dust', hoffman.__express());

app.use(helmet());
// This is the important part-- it adds res.stream()
app.use(hoffman.stream);

app.get('/', function (req, res) {
  res.stream("hello", {
    "async": function(chunk, context, bodies, params) {
      return chunk.map(function(chunk) {
        // Introducting an artificial delay to make streaming more apparent
        setTimeout(function() {
          request('http://www.dustjs.com/')
          .on('data', chunk.write.bind(chunk))
          .on('end', chunk.end.bind(chunk));
        }, 3000);
      });
    }
  });
});
const port = process.env.PORT | 3007;

app.listen(port, function () {
  console.log(`Visit http://localhost:${port} to see streaming!`);
});

Can you help me find a solution

The payload names no repository files or tests; begin with the supplied Dust.stream and Hoffman reproductions, focusing on app.use(helmet()) and the streaming response path. Compare behavior with and without helmet, then verify that the resulting response renders streamed HTML rather than showing it as text.