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https://github.com/halvards/spdy-referrer-push

ExpressJS middleware for SPDY server push based on referrer headers
https://github.com/halvards/spdy-referrer-push

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ExpressJS middleware for SPDY server push based on referrer headers

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# Referrer-based SPDY server push for ExpressJS  [![Build Status](https://travis-ci.org/halvards/spdy-referrer-push.png)](https://travis-ci.org/halvards/spdy-referrer-push)



ExpressJS middleware for SPDY server push based on referrer headers.



## Usage



Install the module:



    $ npm install spdy-referrer-push



Import the module:



    var spdyPush = require('spdy-referrer-push');



Add as middleware to your already SPDY-enabled Express server:



    app.use(spdyPush.referrer());



If using the `express.static` or other resource serving middleware, the `spdy-referrer-push` middleware must appear

_before_ those other middleware in the stack.



That's it!



## Examples



Minimal server with SSL/TLS support:



    $ npm install spdy-referrer-push spdy express



```js

var spdyPush = require('spdy-referrer-push')

  , spdy = require('spdy')

  , express = require('express')

  , path = require('path')

  , fs = require('fs');



var app = express();

app.use(spdyPush.referrer());

var options = {

  key: fs.readFileSync(path.join(__dirname, '../test/keys/spdy-key.pem')),

  cert: fs.readFileSync(path.join(__dirname, '../test/keys/spdy-cert.pem')),

};

var port = 8443;

spdy.createServer(options, app).listen(port);

```



Minimal SPDY server without SSL/TLS support (keep in mind that most browsers don't support SPDY without SSL/TLS by default):



```js

var spdyPush = require('spdy-referrer-push')

  , spdy = require('spdy')

  , express = require('express')

  , fs = require('fs');



var app = express();

app.use(spdyPush.referrer());

var options = {

  plain: true,

  ssl: false

};

var port = 8080;

spdy.createServer(options, app).listen(port);

```



## Motivation



Server push is one of the most interesting features of

[SPDY](http://www.chromium.org/spdy/spdy-protocol/spdy-protocol-draft3-1#TOC-3.3-Server-Push-Transactions) and the

upcoming [HTTP 2.0](http://http2.github.io/http2-spec/index.html#PushResources).



Briefly, it allows a server to send additional resources in response to a client (web browser) request unsolicited

(e.g. CSS, JavaScript, and images). This makes techniques such as inlining and spriting redundant while allowing for

fine-grained control of resource caching.



The excellent [node-spdy](https://github.com/indutny/node-spdy) module provides the plumbing necessary for SPDY support

in NodeJS (and [Connect](https://github.com/senchalabs/connect)/[Express](https://github.com/visionmedia/express),

including server push. However, hardcoding which resources to push in the server implementation isn't ideal as this

must be kept in sync with references in HTML and CSS files.



The [Jetty](http://www.eclipse.org/jetty/) servlet container for Java has a good solution for this problem, called the

[ReferrerPushStrategy](http://www.eclipse.org/jetty/documentation/current/spdy-implementing-push.html), where the

HTTP [Referer](http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14%2E36) request header is used to track what

resource requests (say `/index.html`) trigger subsequent requests for additional resources. This is recorded and used

to determine what additional resources to push the next time someone requests the same main resource (say `/index.html`

again).



This module is a re-implementation of that algorithm in JavaScript as Express middleware.



## Implementation Notes



The middleware retrieves resources to be pushed by creating an "internal" request/response pair and calling Connect's

[`app.handle`](https://github.com/senchalabs/connect/blob/2.12.0/lib/proto.js#L101) function. This function kicks off

request handling using the server's middleware stack.



This approach avoids the overhead of a new socket connection and a TLS handshake (for resources served via https) while

still supporting dynamic behaviour in the handling of resource requests. For instance, if your CSS resources are

transpiled from LESS files on the fly, these CSS resources can still be pushed correctly to the client.



The "internal" request and response objects support the full Express request and response APIs but don't yet support

all the optional arguments of the NodeJS [Stream API](http://nodejs.org/api/stream.html). This is work in progress

(see the To Do section).



## When To Use



This module provides a simple way to test the impact that SPDY with server push can have on improving latency on your

site. Combine it with `tc` (on Unix systems) or Apple's [Network Link Conditioner](https://developer.apple.com/library/ios/documentation/NetworkingInternetWeb/Conceptual/NetworkingOverview/WhyNetworkingIsHard/WhyNetworkingIsHard.html#%2F%2Fapple_ref%2Fdoc%2Fuid%2FTP40010220-CH13-SW12),

to test your site under various latency and bandwidth constraints. You will see the biggest benefit in high latency

situations



For serious large scale use I would recommend serving static resources from a web server like

[Apache httpd](http://httpd.apache.org/) or [nginx](http://nginx.org/en/) instead of serving them from your NodeJS

server. [mod_spdy](https://developers.google.com/speed/spdy/mod_spdy/) is available for Apache httpd 2.2 or later and

[supports server push](https://code.google.com/p/mod-spdy/wiki/OptimizingForSpdy#Using_SPDY_server_push) when running

as a reverse proxy in front of the NodeJS application via the `X-Associated-Content` response header. That will take

you back to the problem of keeping the list of resources in sync between the NodeJS server and your HTML/CSS though.



## To Do



* ~~Setup Travis CI build.~~

* The "internal" request and response objects should support the full [Stream API](http://nodejs.org/api/stream.html),

  including all optional arguments.

* Compare referrer header based on scheme + hostname + port rather than just hostname + port.

* Support for the `trust proxy` Express [application setting](http://expressjs.com/api.html#app-settings).

* Improved configurability to match the [Jetty API](http://download.eclipse.org/jetty/stable-9/apidocs/org/eclipse/jetty/spdy/server/http/ReferrerPushStrategy.html).

* General code cleanup

* Allow for use with plain Connect (without Express).



## Contributors



* [Halvard Skogsrud](https://github.com/halvards)

* [Michael Leaney](https://github.com/leahciMic)