before sending html, check if response is still open

[bhurlow]

current with next if you try something like this:

export default class Foo extends React.Component {

  static getInitialProps ({ req, res }) {

   // manually override server side react rendering 
    if (req) {
        res.end('my hijacked response!');
        return {}
    }
    return {}
  }

  render() {
    return <h1> Hi </h1>
  }
}

next will attempt to write rendered html to the now closed http response which results in a "can't set headers after they've been sent" error.

This PR checks to see if the response is still open before sending html, allowing for more adhoc hijacking of the request in getInitialProps

[rauchg]

The best way to hijack will be #25, so that rendering the component is not attempted at all

[bhurlow]

cool! agreed, better to not render at all if req/res is intercepted