real-time-tweet-stream | Get real-time tweets and display on webpage with socket.io | Socket library

After each of the places that you send a response, you need to return so your function doesn't continue executing and cause it to attempt to send another response. I see multiple places in the /api/rules route where you need to add the return after sending a response because if you don't, it executes the res.end(response) even though you've already send a response. That is what causes the error you see.