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redirect-handler.js
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145 lines (128 loc) · 4.3 KB
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/*
* Copyright 2019 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.
*/
const yaml = require('js-yaml');
const fs = require('fs');
const escapeStringRegexp = require('escape-string-regexp');
const baseUrlPrefix = 'https://web.dev/';
/**
* Normalizes the passed path (not a whole URL) to ensure that it ends with a
* simple trailing slash. Removes "index.html" if found.
*
* @param {string} path to normalize
* @return {string}
*/
function ensureTrailingSlashOnly(path) {
if (path.endsWith('/index.html')) {
return path.slice(0, -'index.html'.length);
} else if (!path.endsWith('/')) {
return `${path}/`;
}
return path;
}
/**
* Builds a method which returns a URL to redirect to.
*
* @param {string} yamlSource to parse redirects from
* @param {string} baseUrlPrefix domain prefix to use, e.g. "https://web.dev/"
* @return {function(string): ?string}
*/
function prepareHandler(yamlSource, baseUrlPrefix) {
const doc = yaml.safeLoad(yamlSource);
baseUrlPrefix = ensureTrailingSlashOnly(baseUrlPrefix);
const groupRedirect = {};
const singleRedirect = {};
for (const {from, to} of doc.redirects) {
const hasExtra = from.indexOf('...') !== -1;
if (!hasExtra) {
singleRedirect[ensureTrailingSlashOnly(from)] = to;
continue;
}
// "Group" redirects' from must end with "/...", i.e., match the last
// whole path component.
if (!from.endsWith('/...')) {
throw new TypeError(`got redirect with invalid ...: ${from} => ${to}`);
}
groupRedirect[from.slice(0, -3)] = to;
}
// Build a single RegExp for group matches, for speed of matching.
const escaped = Object.keys(groupRedirect).map(escapeStringRegexp);
const groupMatcher = new RegExp(`^(${escaped.join('|')})`);
return (raw) => {
let target;
// Split the raw URL (expected to be "/foo?bar") into path and query parts.
const parts = raw.split('?');
const path = parts[0];
const query = parts[1] || '';
const url = ensureTrailingSlashOnly(path);
if (url in singleRedirect) {
target = new URL(singleRedirect[url], baseUrlPrefix);
} else {
const m = groupMatcher.exec(url);
if (!(m && m[1] in groupRedirect)) {
return null;
}
const base = groupRedirect[m[1]];
const rest = url.slice(m[1].length);
if (base.endsWith('/...')) {
target = new URL(base.slice(0, -3) + rest, baseUrlPrefix);
} else {
target = new URL(base, baseUrlPrefix);
}
}
// Merge the original request's params into the target. We don't use
// Express' req.query here as it expands the query too much, e.g.,
// 'foo[bar]=123' ends up like "{foo: {bar: 123}}".
const requestParams = new URLSearchParams(query);
for (const [key, value] of requestParams) {
target.searchParams.append(key, value);
}
// If the result URL starts with "https://web.dev/" (with trailing slash),
// then strip it and treat as local. This allows redirects to work in dev,
// where the domain is localhost or a staging URL.
let s = target.toString();
if (s.startsWith(baseUrlPrefix)) {
s = '/' + s.substr(baseUrlPrefix.length);
}
return s;
};
}
/**
* Builds HTTP middleware that serves redirects for web.dev's _redirects.yaml
* configuration file, originally from DevSite.
*
* @param {string} filename to load configuration from
* @param {number=} code to use (DevSite uses 301)
* @return {!Function}
*/
function build(filename, code = 301) {
const handler = prepareHandler(
fs.readFileSync(filename, 'utf8'),
baseUrlPrefix,
);
return (req, res, next) => {
const target = handler(req.url);
if (target !== null) {
return res.redirect(code, target);
}
return next();
};
}
module.exports = {
build,
prepareHandler,
baseUrlPrefix,
ensureTrailingSlashOnly,
};