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Programming language: JavaScript
License: MIT License
Tags: Express     Proxy     Reverse     Middleware     Connect     Server-push     Http2    

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This is a reverse proxy that helps you to automatically make use of HTTP/2.0's server push mechanism for your static websites.


How it works

Usually, websites consist of multiple assets, like CSS and JS files as well as images like PNGs, JPGs and SVGs. Traditionally, a user's browser fetches the HTML first, parses it and then downloads all linked assets. However, this is slow, since the assets can't be loaded before the HTML is completely fetched and parsed. With server push, your webserver can actively sends those assets to the client browser even before it requested them. To prevent you from having to implement this functionality, http2-serverpush-proxy sits as a proxy between your actual webserver and the user. In contrast to some other approaches like http2-push-manifest, where the assets to be pushed are declared statically, this library dynamically parses the HTML files and extracts contained asset that should be pushed.

Without server push With server push



One way to use this is as a standalone proxy by installing it globally with npm install -g http2-serverpush-proxy

$ serverpush-proxy --extensions=css,js,svg --target=http://localhost:8080 --key=./certs/dev-key.pem --cert=./certs/dev-cert.pem --port 3000


  • --target [required]: The target URL to be proxied. E.g. if your website runs at http://localhost:8080, this would be your target URL.
  • --extensions: File extensions to be push candidates Defaults to: see this section
  • --key [required]: Path to your SSL key (HTTP/2 requires TLS (HTTPS) encryption) .
  • --cert [required]: Path to your SSL certificate.
  • --port: Port to make the proxy listen on. Defaults to 8080.

Embedded (connect middleware)

You can also use this library as connect middleware in your application. You need a webserver running with node-spdy (you need HTTP/2!). Please not that currently this middleware must be the last one in your stack, since it calls res.end().


const pushMiddleware = require('http2-serverpush-proxy')({ baseUrl: 'http://localhost:8080' })
    , app = require('express')()
    , http = require('spdy')
    , fs = require('fs');

app.use('/static', pushMiddleware.proxy);
app.use('/static', pushMiddleware.push);
app.get('/', (req, res) => {
    res.send('It works!');

const spdyOpts = {
    key: fs.readFileSync(__dirname + '/certs/dev-key.pem'),
    cert: fs.readFileSync(__dirname + '/certs/dev-cert.pem'),
    spdy: {
        protocols: ['h2', 'spdy/3.1', 'http/1.1'],
        plain: false,
        'x-forwarded-for': true,

http.createServer(spdyOpts, app).listen(8081);

This would spawn an Express webserver, where all requests to /static are proxied to http://localhost:8080 and all HTML (Content-Type: text/html) responses are parsed for assets to get server-pushed.


Instantiating the middleware happens through calling a function (see line 1) that receives a config object with following parameters.

  • baseUrl [required]: The target URL to be proxied. E.g. if your website runs at http://localhost:8080, this would be your target URL.
  • extensions [optional]: File extensions to be push candidates Defaults to: see this section

What is pushed?

Currently, <img src="...", <script src="..." and <link href="..." attributes are parsed when looking for assets. Supported file types to be pushed include css, js, png, jpg, gif and , svg.

Non-GET requests as well as requests, which don't Accept HTML are directly piped to and from the proxy. GET requests, which accept HTML (text/html, text/*, */*) are fetched by the proxy first. If Content-Type doesn't equal text/html, they're written to the response. Otherwise the HTML response body (the one from the proxied server) is parsed, assets are fetched and pushed and finally the HTML payload is also written to the response.


  • The proxied server mustn't use encryption (no HTTPS)
  • The proxied server mustn't use compression (no Content-Encoding). Accept-Encoding headers are removed from any request.
  • The proxied server musn't require authentication
  • The proxy only listens for HTTPS connections. If you want to support "upgrading" an http:// request to https://, you'd need another proxy (like nginx) to do that redirect.

What doesn't work / Todo

This library is not completely finished, yet. Consequently it still lacks of some useful features, which should be implemented some time.

  • Support for Websockets
  • Support for HTTP authentication
  • Also push dynamically included HTML (WebComponents, ng-include, ...)
  • Support for compression (gzip, deflate)
  • Avoid this from having to be the very last middleware step, but support further middleware after it


If you find bugs, feel free to do a pull request or open an issue. If you want to implement some of the above Todos, that'd be great of course ;-)


MIT @ Ferdinand MĂĽtsch

*Note that all licence references and agreements mentioned in the http2-serverpush-proxy README section above are relevant to that project's source code only.