初读nodeClub源码 对app.use('/agent', proxyMiddleware.proxy)的作用不理解？

var urllib = require(‘url’); var request = require(‘request’); var logger = require(’…/common/logger’) var _ = require(‘lodash’)

var ALLOW_HOSTNAME = [ ‘avatars.githubusercontent.com’, ‘www.gravatar.com’, ‘gravatar.com’, ‘www.google-analytics.com’, ]; exports.proxy = function (req, res, next) { var url = decodeURIComponent(req.query.url); var hostname = urllib.parse(url).hostname;

if (ALLOW_HOSTNAME.indexOf(hostname) === -1) { return res.send(hostname + ’ is not allowed’); }

request.get({ url: url, headers: _.omit(req.headers, [‘cookie’, ‘refer’]), }) .on(‘response’, function (response) { res.set(response.headers); }) .on(‘error’, function (err) { logger.error(err); }) .pipe(res); };

然后再app.js中调用 app.use(’/agent’, proxyMiddleware.proxy)

我不太理解这段代码的意思，请帮忙解答。初学node.js所以找了nodeClud的源码进行学习