phantomas/modules/caching/caching.js

Headless Chromium-based web performance metrics collector and monitoring tool

/**
 * Analyzes HTTP caching headers
 */
"use strict";

module.exports = function (phantomas) {
  var cacheControlRegExp = /max-age=(\d+)/;

  // @see https://developers.google.com/speed/docs/best-practices/caching
  function getCachingTime(url, headers) {
    // false means "no caching"
    var ttl = false,
      headerName,
      now = new Date(),
      headerDate;

    for (headerName in headers) {
      var value = headers[headerName];

      switch (headerName.toLowerCase()) {
        // parse max-age=...
        //
        // max-age=2592000
        // public, max-age=300, must-revalidate
        case "cache-control":
          var matches = value.match(cacheControlRegExp);

          if (matches) {
            ttl = parseInt(matches[1], 10);
          }
          break;

        case "expires": // catch Expires and Pragma headers
        case "pragma":
        case "x-pass-expires": // and Varnish specific headers
        case "x-pass-cache-control":
          phantomas.incrMetric("oldCachingHeaders"); // @desc number of responses with old, HTTP 1.0 caching headers (Expires and Pragma)
          phantomas.addOffender("oldCachingHeaders", {
            url,
            headerName,
            value,
          });
          if (ttl === false) {
            headerDate = Date.parse(value);
            if (headerDate) ttl = Math.round((headerDate - now) / 1000);
          }
          break;
      }
    }

    //console.log(JSON.stringify(headers)); console.log("TTL: " + ttl + ' s');

    return ttl;
  }

  phantomas.setMetric("cachingNotSpecified"); // @desc number of responses with no caching header sent (no Cache-Control header)
  phantomas.setMetric("cachingTooShort"); // @desc number of responses with too short (less than a week) caching time
  phantomas.setMetric("cachingDisabled"); // @desc number of responses with caching disabled (max-age=0)

  phantomas.setMetric("oldCachingHeaders");
  phantomas.setMetric("cachingUseImmutable"); // @desc number of responses with a long TTL that can benefit from Cache-Control: immutable

  phantomas.on("recv", (entry) => {
    var ttl = getCachingTime(entry.url, entry.headers),
      headerName;

    // static assets
    if (entry.isImage || entry.isJS || entry.isCSS) {
      if (ttl === false) {
        phantomas.incrMetric("cachingNotSpecified");
        phantomas.addOffender("cachingNotSpecified", entry.url);
      } else if (ttl <= 0) {
        phantomas.incrMetric("cachingDisabled");
        phantomas.addOffender("cachingDisabled", entry.url);
      } else if (ttl < 7 * 86400) {
        phantomas.incrMetric("cachingTooShort");
        phantomas.addOffender("cachingTooShort", { url: entry.url, ttl });
      } else {
        // long TTL, suggest the use of Cache-Control: immutable (issue #683)
        for (headerName in entry.headers) {
          var value = entry.headers[headerName];

          if (headerName.toLowerCase() === "cache-control") {
            if (/,\s?immutable/.test(value) === false) {
              phantomas.incrMetric("cachingUseImmutable");
              phantomas.addOffender("cachingUseImmutable", {
                url: entry.url,
                ttl,
              });
            } else {
              phantomas.log(
                "caching: Cache-Control: immutable used for <%s>",
                entry.url
              );
            }
          }
        }
      }
    }
  });
};