code: function send () {
        sent = true;
        // next tick it to avoid express catching runtime error in the callback
        //   getting caught by express and triggering app's error handler
        process.nextTick(function () {
          res.emit('finish');
          cb(null, res, body);
        });
      }
docs: sent=true should be the last line if error w/in res.send (above code)