bla.js

// An express router

app.get('/view/{file}', function(req, res, o) {
  var d = domain(function() {
    var renderer = new MyTemplateRenderer(o.file);
    renderer.on('data', function(buf) {
      // is this allowed?
      res.write(buf, function() {
        // In which domain does this run?
      }); 
    });
  });
  
  d.on('error', function(e) {
    if (res.writable) {
      res.write(e);
    }
  });
});