terminate http stream

.js

var request = require("request");

exports.foo = function(req, res) {
  request.get("foo.com")
  .on('response', function(){
    if (response.statusCode === 404) {
      // terminate and return {"error": "not found"}
      // How do i do this?
    }
  })
  .pipe(res);
  
  
}