express-legacy-csp/lib/preprocessCaniuseData.js

Downgrade content-security-policy version and fidelity to support the requesting browser

const semver = require('semver');

function buildVersion(major, minor, patch) {
  return [major, minor, patch]
    .map(digit => (typeof digit === 'undefined' ? 0 : parseInt(digit, 10)))
    .join('.');
}

function addZeroesIfMinorOrPatchIsMissing(version) {
  version = String(version);
  version += '.0'.repeat(3 - version.split('.').length);
  return version;
}

module.exports = function preprocessCaniuseData(stats) {
  const isSupportedByCaniuseIdAndVersion = {};
  const checkSupportedRangeByCaniuseId = {};
  Object.keys(stats).forEach(caniuseId => {
    let highestVersionSeen;
    let highestVersionIsSupported;
    let lowestVersionSeen;

    function registerVersion(version, isSupported) {
      version = addZeroesIfMinorOrPatchIsMissing(version);
      if (!highestVersionSeen || semver.gt(version, highestVersionSeen)) {
        highestVersionSeen = version;
        highestVersionIsSupported = isSupported;
      }
      if (!lowestVersionSeen || semver.lt(version, lowestVersionSeen)) {
        lowestVersionSeen = version;
      }
    }

    isSupportedByCaniuseIdAndVersion[caniuseId] = {};
    Object.keys(stats[caniuseId]).forEach(version => {
      const isSupported = /^y/.test(stats[caniuseId][version]);
      if (version === 'all') {
        (checkSupportedRangeByCaniuseId[caniuseId] =
          checkSupportedRangeByCaniuseId[caniuseId] || []).push(
          () => isSupported
        );
      } else if (/^\d+(\.\d+){0,2}$/.test(version)) {
        // Exact major or major.minor or major.minor.patch version
        isSupportedByCaniuseIdAndVersion[caniuseId][version] = isSupported;
        registerVersion(version, isSupported);
      } else {
        const matchRange = version.match(
          /^(\d+(?:\.\d+){0,2})-(\d+(?:\.\d+){0,2})$/
        );
        if (matchRange) {
          registerVersion(matchRange[2], isSupported);
          const range = new semver.Range(`${matchRange[1]} - ${matchRange[2]}`);
          (checkSupportedRangeByCaniuseId[caniuseId] =
            checkSupportedRangeByCaniuseId[caniuseId] || []).push(
            (major, minor, patch) => {
              if (range.test(buildVersion(major, minor, patch))) {
                return isSupported;
              }
            }
          );
        } else {
          // Ignore unsupported version specifier such as "TP"
        }
      }
    });
    if (highestVersionSeen) {
      (checkSupportedRangeByCaniuseId[caniuseId] =
        checkSupportedRangeByCaniuseId[caniuseId] || []).push(
        (major, minor, patch) => {
          if (
            semver.gt(buildVersion(major, minor, patch), highestVersionSeen)
          ) {
            return highestVersionIsSupported;
          }
        }
      );
    }
    if (lowestVersionSeen) {
      (checkSupportedRangeByCaniuseId[caniuseId] =
        checkSupportedRangeByCaniuseId[caniuseId] || []).push(
        (major, minor, patch) => {
          if (
            semver.lt(buildVersion(major, minor, patch), highestVersionSeen)
          ) {
            return false;
          }
        }
      );
    }
  });

  return function checkSupported(caniuseId, major, minor, patch) {
    const isSupportedByVersion = isSupportedByCaniuseIdAndVersion[caniuseId];
    if (isSupportedByVersion) {
      if (typeof patch !== 'undefined') {
        const cspIsSupportedInPatchVersion =
          isSupportedByCaniuseIdAndVersion[caniuseId][
            `${major}.${minor}.${patch}`
          ];
        if (typeof cspIsSupportedInPatchVersion === 'boolean') {
          return cspIsSupportedInPatchVersion;
        }
      }

      const cspIsSupportedInMinorVersion =
        isSupportedByCaniuseIdAndVersion[caniuseId][`${major}.${minor}`];
      if (typeof cspIsSupportedInMinorVersion === 'boolean') {
        return cspIsSupportedInMinorVersion;
      }

      const cspIsSupportedInMajorVersion =
        isSupportedByCaniuseIdAndVersion[caniuseId][major];
      if (typeof cspIsSupportedInMajorVersion === 'boolean') {
        return cspIsSupportedInMajorVersion;
      }
    }
    const ranges = checkSupportedRangeByCaniuseId[caniuseId];
    if (ranges) {
      for (var i = 0; i < ranges.length; i += 1) {
        const isRangeSupported = ranges[i](major, minor, patch);
        if (typeof isRangeSupported === 'boolean') {
          return isRangeSupported;
        }
      }
    }
  };
};