code: function fetch(url, id) {
    var req = http.request(url, function (res) {
      res.pipe(terminus.concat(function (contents) {
        tx.end(id, {type: "fetch", url: url, code: res.statusCode})
      }))
    })
    req.end()
  }
docs: passing the id here not because that's a good practice but intead to show that the transaction tracer is idempotent accross requires by different files. it would probably make more sense to simply have all the tracing logic in one of the two places used here for a real application.