Simple Express/Connect middleware that dumps a stack trace to console when response-headers are written. Useful to debug "Can't set headers after they are sent" issues.

gistfile1.js

// include this middleware before any middleware/routes that is suspected of triggering the error
app.use(function(req, res, next) {
  res.on('header', function() {
    console.trace('HEADERS GOING TO BE WRITTEN');
  });
  next();
});