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index.js
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index.js
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/**
* @author Peter Marton, Gergely Nemeth, SciDock LLC
*/
const fetch = require('isomorphic-fetch');
const url = require('url');
const crawlerUserAgents = [
'googlebot',
'bingbot',
'baiduspider',
'facebookexternalhit',
'twitterbot',
'rogerbot',
'linkedinbot',
'embedly',
'quora link preview',
'showyoubot',
'outbrain',
'pinterest/0.',
'developers.google.com/+/web/snippet',
'slackbot',
'vkShare',
'W3C_Validator',
'redditbot',
'Applebot',
'WhatsApp',
'flipboard',
'tumblr',
'bitlybot',
'SkypeUriPreview',
'nuzzel',
'Discordbot',
'Google Page Speed',
'Qwantify',
'pinterestbot',
'Bitrix link preview',
'XING-contenttabreceiver',
].map(str => str.toLowerCase());
const extensionsToIgnore = [
'.js',
'.css',
'.xml',
'.less',
'.png',
'.jpg',
'.jpeg',
'.gif',
'.pdf',
'.doc',
'.txt',
'.ico',
'.rss',
'.zip',
'.mp3',
'.rar',
'.exe',
'.wmv',
'.doc',
'.avi',
'.ppt',
'.mpg',
'.mpeg',
'.tif',
'.wav',
'.mov',
'.psd',
'.ai',
'.xls',
'.mp4',
'.m4a',
'.swf',
'.dat',
'.dmg',
'.iso',
'.flv',
'.m4v',
'.torrent',
'.woff',
'.ttf',
'.svg',
];
/*
* @param {Object} options
* @return {boolean}
*/
function shouldPreRender(options) {
if (
options.method !== 'GET' && options.method !== 'HEAD' ||
!options.userAgent ||
extensionsToIgnore.some(extension => options.url.indexOf(extension) !== -1)
) {
return false;
}
const {query} = url.parse(options.url, true /* parseQueryString */);
if (
query && query['_escaped_fragment_'] != null ||
options.bufferAgent
) {
return true;
}
const userAgent = options.userAgent.toLowerCase();
return crawlerUserAgents.some(crawlerUserAgent => userAgent.indexOf(crawlerUserAgent) !== -1);
}
/*
* @param {Object} options
*/
function preRenderMiddleware(options) {
options = options || {};
options.prerender = options.prerender || 'http://service.prerender.io/';
/*
* @param {Object} ctx
* @param {Function} next
*/
return (ctx, next) => {
const protocol = options.protocol || ctx.protocol;
const host = options.host || ctx.host || ctx.get('X-Forwarded-Host');
const userAgent = ctx.get('User-Agent');
if (shouldPreRender({
bufferAgent: ctx.get('X-Bufferbot'),
method: ctx.method,
url: ctx.url,
userAgent,
})) {
ctx.set('X-Prerender', 'true');
const preRenderUrl = `${options.prerender}${protocol}://${host}${ctx.url}`;
const headers = {
'User-Agent': userAgent,
'X-Prerender-Token': options.prerenderToken || process.env.PRERENDER_TOKEN,
};
return fetch(preRenderUrl, {headers}).then((res) => {
ctx.res.writeHead(200, {'Content-Type': 'text/html'});
ctx.body = res.body;
});
}
ctx.set('X-Prerender', 'false');
return next();
};
};
module.exports = preRenderMiddleware;