nodejs / express / oboe.js & pug: Get node() events to update the dom

First time working with node and template engines (yes i know, terrible place to "start" but whatever). I'm building some content from a json stream, and at the end I would like to spit this content out to a div in my html page, as follows in this (updated) expressjs snippet:

app.get('/foo', function (req, res) {

  //... get my stream called 'mystream'

  //... get ready to append content for items found in json stream
  var htmlbuf = "";

  //now process the json stream:
  oboe(mystream)
  .node('{bar}', function(aBar){
    //eventually, I'd like to actually append individual new DOM elements,
    //but for now I'll settle for just spitting out raw html:
    var buffer = '<p>Found a bar with name'+ aBar.name + '</p>';
    res.render('index', {itemsfound: htmlbuf});
    });
});

index.pug:

doctype html
html
    head
        link(type='text/css', rel='stylesheet', href='./css/main.css')
        title Hello
    body
        h1 Hello world!
        div#results.listing
            items= itemsfound

I get the error 'Error: Can't set headers after they are sent'. So I believe the issue is that the oboe.node() is firing at any time and I am not sending the response content at the right time? What is the code/framework needed to wire the oboe.node() events so that they can target or create dom elements in my pug template and send the response correctly? Thanks.

You'll need to do something like this:

app.get('/foo', function (req, res, next) {

  //... get my stream called 'mystream'

  //... get ready to append content for items found in json stream
  var htmlbuf = "";

  //now process the json stream:
  oboe(mystream)
  .node('{bar}', function(aBar){
    //eventually, I'd like to actually append individual new DOM elements,
    //but for now I'll settle for just spitting out raw html:
    htmlbuf += '<p>Found a bar with name' + aBar.name + '</p>';
  })
  .on('fail', function (err) {
    res.statusCode = err.statusCode
    next(err.thrown)
  })
  .on('done', function () {
    res.render('index', {itemsfound: htmlbuf});
  });
});