jac

#jac

Really when you push something out live to the world, you never want to change it without changing the name because there are so many misconfigured proxies out there. About 1% to 10% of your users will never get an update unless you change the name.

You can make it cachable for 10 years, you're never going to push a change without changing the name of the file.

- Steve Souders. HTML5DevConf (Jan 10, 2013). Cache is king availalable from http://mrkn.co/3wzua

jac provides methods to reference asset urls using permanently cachable urls.

It achieves this by using urls unique to each version of a given asset, and provides middleware to serve the asset with long cache durations.

#Usage jac middleware will handle asset file serving and asset url resolution

Install it using

npm install jac

Example

The following example shows how to wire up jac with an express 3.x app

• App code sets up the jac middleware
• A JSON file stores the configuration for the jac middleware
• A script updates the configuration file

App

var express = require('express')
  , jac     = require('jac')
  , app     = express()
  , config  = require('./config');

// Add middleware for all requests
app.use(jac.middleware(config));

// Add view that resolves an image url
app.get('/someview', function (req, res) {
  var jac = res.locals.jac        // returns jac view helper
    , key = '/images/happy.png'     // matches config key
    , url = jac.resolve(key);       // returns url with digest, handled by middleware

  res.send(url);
});

Config

The configuration file is updated using jac's digester and read by the app. Here's a sample config json file loaded by the app.

{
  // required - files served by jac
  assets: [{
    fullPath: require('path').resolve(__dirname, './public/images/happy.png'),  // local file path
    key:      '/images/happy.png',                                              // key used in views: jac.resolve('/images/happy.png')
    route:    '/images/b64Digest/happy.png',                                    // route for middleware
    url:      '//cdn.host.net/images/b64Digest/happy.png'                       // url output to response and css
  }],

  // optional - cache control max age in seconds (default 2 weeks)
  maxAge: 5443200
}

Update script

The update script runs the digester against the files specified in configuration and updates the files key in the configuration file. This script can be run from package.json's scripts section after install.

jac --config ./config.json

Alternatively, the digester can be wired up manually

var path   = './config'
  , config = require(path)
  , digest = require('jac').digest;

function save (err, assets) {
  if (err) throw err;

  config.assets = assets;
  fs.writeFile(path, JSON.stringify(config, null, 2));
}

digest(config, save);

Replacing references in CSS

jac can be configured to process CSS files as part of the update process. It will ignore image references from external sites (eg urls with an authority) and data-uris, and will attempt to resolve all other urls.

If it fails to resolve a url, it will throw an error, allowing you to find the problematic reference. Most likely, this will easily be corrected by adjusting the path to the image to make it root relative.

Here's an example that will result in jac replacing the image reference

src/stylesheets/main.css

body {background: url(/images/happy.png);}

config.json

{
  // required - files served by jac
  assets: [{
    fullPath: require('path').resolve(__dirname, './public/images/happy.png'),  // local file path
    key:      '/images/happy.png',                                              // key used in views: jac.resolve('/images/happy.png')
    route:    '/images/b64Digest/happy.png',                                    // route for middleware
    url:      '//cdn.host.net/images/b64Digest/happy.png'                       // url output to response and css
  }],

  css: {
    'public/stylesheets/main.css': 'src/stylesheets/main.css'                   // format <output>: <input>
  }
}

To run the CSS replacement, update the jac config file to include the css property and use the following command

css --config ./config.json

The file at public/stylesheets/main.css will now contain the following

body {background: url(//cdn.host.net/images/b64Digest/happy.png);}

Compatibility

This version of jac is compatible with express 3.x. It depends on res.locals to get and set the view local jac via middleware.

Production

To support production usage with the best performance, it is required that a pre-processing step be executed to generate the image file digests stored in configuration.

jac --config ./config.json

It is recommended that the config file already exist, and the config file used by the app always be updated before deploying to production. This can be automated using package.json's scripts section after install.

{
  "name": "myproject",
  "dependencies": {
    "jac": "latest"
  },
  "scripts": {
    "postinstall": "./node_modules/jac/bin/jac"
  }
}

By default, jac will load the config from the jac.json file at the project root.

Running Tests

To run the test suite first invoke the following command within the repo, installing the development dependencies:

npm install

then run the tests:

npm test

License

(The MIT License)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Changelog

v0.1.0

• Update for express 3 compatibility.