@adobe/helix-pipeline/src/utils/timing.js

This project provides helper functions and default implementations for creating Hypermedia Processing Pipelines.

/*
 * Copyright 2019 Adobe. All rights reserved.
 * This file is licensed to you 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 REPRESENTATIONS
 * OF ANY KIND, either express or implied. See the License for the specific language
 * governing permissions and limitations under the License.
 */

/**
 * Computes the time delta in seconds from HR timestamps
 * @param {int[]} t0 first HR timestamp
 * @param {int[]} t1 second HR timestamp
 * @returns {number} delta in seconds
 */
function delta(t0, t1) {
  const ds = t0[0] - t1[0]; // seconds
  const dn = t0[1] - t1[1]; // nanoseconds
  return ds * 1000 + dn / 1000000;
}

/**
 * Creates a timing object that records the timestamps using process.hrtime() and can set the
 * 'Server-Timing' response header accordingly.
 */
function create() {
  const startTime = process.hrtime();
  const times = [];

  /**
   * Update the timestamps. The 'taps' are executed before the pipeline step functions. Just record
   * the name and the timestamps for now.
   */
  function update(context, action, idx, name) {
    times.push({
      name: name ? name.split(':').pop() : 'undef',
      time: process.hrtime(),
    });
  }

  /**
   * Create the timing report and set the 'Server-Timing' header
   */
  function report(context, { logger }) {
    update();
    const total = delta(process.hrtime(), startTime);
    logger.debug(`total processing time: ${total}ms`);

    // calculate the deltas between 2 the timestamps of 2 steps and generate the metric string.
    const metrics = [];
    for (let i = 0; i < times.length - 1; i += 1) {
      const d = delta(times[i + 1].time, times[i].time);
      metrics.push(`p${String(i).padStart(2, '0')};dur=${d};desc=${times[i].name}`);
    }
    const timing = metrics.join(' ,');
    logger.debug(`timing: ${timing}`);

    context.response.headers['Server-Timing'] = [
      timing,
      `total;dur=${total}`,
    ].join(',');
  }

  return {
    update,
    report,
  };
}

module.exports = create;