coach-core/lib/har/performance/connectionKeepAlive.js

Core package for the Coach.

import * as util from '../util.js';

export default {
  id: 'connectionKeepAlive',
  title: "Don't close a connection that is used multiple times",
  description:
    "Use keep-alive headers and don't close the connection when we have multiple requests to the same domain. There has been some hacks in the past that suggested closing the connection as fast as possible in order to create new ones, but that shouldn't be applicable anymore.",
  weight: 5,
  severity: 'info',
  tags: ['performance', 'server'],
  processPage: function (page) {
    let score = 100;
    let offending = [];
    let avoid = 'doc';

    let closedPerDomain = {};
    for (const asset of page.assets) {
      const headers = asset.headers.response;
      const connectionHeader = headers.connection ? headers.connection[0] : '';
      if (asset.type !== avoid && connectionHeader.includes('close')) {
        const hostname = util.getHostname(asset.url);
        if (closedPerDomain[hostname]) {
          closedPerDomain[hostname] += 1;
          offending.push(asset.url);
          score -= 10;
        } else {
          closedPerDomain[hostname] = 1;
          // TODO these assets should be reported too
        }
      }
    }
    return {
      score: Math.max(0, score),
      offending: offending,
      advice:
        score < 100
          ? 'The page has ' +
            util.plural(offending.length, 'request') +
            " to a domain where the connection had already been closed. Don't close the connection. Attempt to reuse it by using keep-alive!"
          : ''
    };
  }
};