GCP metadata server long polling

metadata.js

// https://cloud.google.com/compute/docs/storing-retrieving-metadata#waitforchange

// curl "http://metadata.google.internal/computeMetadata/v1/project/attributes/hoge?wait_for_change=true" -H "Metadata-Flavor: Google"

const http = require('http');

function longPollMetadataServer(path) {
  return new Promise((resolve, reject) => {
    http.get({
      hostname: "metadata.google.internal",
      path: path + "?wait_for_change=true",
      headers: {
        "Metadata-Flavor": "Google",
      },
    }, (res) => {
      let body = '';
      res.on('data', (data) => { body += data; });
      res.on('end', () => {
        try {
          resolve(JSON.parse(body));
        } catch(e) {
          reject(e);
        }
      });
    });
  });
}

function longPollProjectMetadata(key) {
  return longPollMetadataServer("/computeMetadata/v1/project/attributes/" + key);
}

function longPollAndProcessMetadata(key) {
  return longPollProjectMetadata(key).then((data) => {
    console.log(data); // XXX
  }).catch((e) => {
    console.error("err: ", e);
  });
};

function forever(generator, args) {
  return generator.apply(this, args).then(() => {
    return forever(generator, args);
  });
}

forever(() => { return longPollAndProcessMetadata('hoge'); });