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language-redirect.js
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74 lines (64 loc) · 2.08 KB
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/*
* Copyright 2022 Google LLC
*
* 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
*
* https://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.
*/
// Included for types only.
// eslint-disable-next-line no-unused-vars
const express = require('express');
const path = require('path');
const Negotiator = require('negotiator');
const {doRedirect} = require('./env');
const {defaultLocale, locales} = require('../site/_data/site.json');
/**
* List of parent directories this handler simply skips in
* order to save time, as that's language unspecific content
*/
const ignoredPathPrefixes = [
'_static',
'fonts',
'images',
'js',
'css',
'feeds',
];
/**
* @type {express.RequestHandler}
*/
const languageRedirectHandler = (req, res, next) => {
const pathParts = req.path.substring(1).split('/');
const pathPrefix = pathParts[0];
// If the request path is a root level path, is one of the known locales
// or any directory that does not contain pages, let express.static take over
if (
pathParts.length === 1 ||
locales.includes(pathPrefix) ||
ignoredPathPrefixes.includes(pathPrefix)
) {
return next();
}
const negotiator = new Negotiator(req);
const preferredLanguage = negotiator.language();
// If the preferred language is the default language,
// none is set (meaning *) or the path prefix already
// matches the preferred language just go ahead
if (
preferredLanguage === defaultLocale ||
preferredLanguage === '*' ||
preferredLanguage === pathPrefix
) {
return next();
}
return doRedirect(res, path.join('/', preferredLanguage, ...pathParts));
};
module.exports = {languageRedirectHandler};