Retrieves RuntimeVersion from v0.js

runtimeVersionV0.js

/**
 * Copyright 2017 The AMP HTML Authors. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS-IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
'use strict';

const {OneBehindFetch} = require('amp-toolbox-core');

const V0_URL = 'https://cdn.ampproject.org/v0.js';
const CONFIG_REGEX = /self.AMP_CONFIG=({.+?})/;

/**
 * Queries cdn.ampproject.org for the lastest AMP runtime version. Uses a
 * stale-while-revalidate caching strategy to avoid refreshing the version.
 */
class RuntimeVersionV0 {

  constructor(request = OneBehindFetch.create()) {
    this.request_ = request;
  }

  /**
   * Returns the version of the current AMP runtime release.
   *
   * @returns {Promise<string>} a promise containing the current version
   */
  async currentVersion() {
    const data = await this.request_.get(V0_URL);
    const result = CONFIG_REGEX.exec(data);
    if (!result) {
      throw new Error('Unable to fidn self.AMP_CONFIG section.');
    }
    const ampConfig = JSON.parse(result[1]);
    return ampConfig.v;
  }
}

module.exports = RuntimeVersionV0;