Cache Headers

Create cache headers as application-level or route-level middleware. This has only been tested as middleware for an express app. The primary cache header set is the Cache-Control header value. All time values are set as seconds per the w3 spec.

This package is developed using ES6 and transpiled with babel. It is also using the 1stdibs eslint rules.

Installation

$ yarn add cache-headers
// with npm 
$ npm install --save cache-headers

Tests

$ yarn
$ yarn test
// with npm
$ npm install
$ npm test

Usage

App-level setup middleware

const express = require('express');
const app = express();
const cache = require('cache-headers');
const pathsConfig = {
    paths: {
        '/**/generic': {
            staleRevalidate: 'ONE_HOUR',
            staleError: 'ONE_HOUR'
        },
        '/default/values': {},
        '/user/route': false,
        '/**': 60
    }
};

// some other middleware

app.use(cache.setupInitialCacheHeaders(pathsConfig));

// rest of app setup

With the example above, the Cache-Control header is set as follows when a user hits these different site routes:

• /**/generic (any route ending in generic)
  • Cache-Control: no-cache, no-store, must-revalidate, stale-while-revalidate=3600, stale-if-error=3600
  • Surrogate-Control: maxAge=600
• /default/values
  • Cache-Control: no-cache, no-store, must-revalidate
  • Surrogate-Control: maxAge=600
• /user/route
  • Cache-Control: private, no-cache, no-store, must-revalidate
  • Surrogate-Control: maxAge=0
  • Last-Modified: (NOW)
• /** (any other route not listed)
  • Cache-Control: no-cache, no-store, must-revalidate
  • Surrogate-Control: maxAge=60

Router-level middleware

Taking the app-level setup above, you can additionally override the default pathsConfig initially set.

const express = require('express');
const router = express.Router();
const cache = require('cache-headers');
const overrideConfig = {
    "maxAge": 2000
};

// app.use(cache.setupInitialCacheHeaders(pathsConfig)) is loaded prior to this route, therefore running by default
// and any subsequent call to set the header is then overwritten

router.get('/endswith/generic', cache.overrideCacheHeaders(overrideConfig), (req, res, next) => {
    // do route-y stuff
    next();
});

Rather than set the original headers defined in the pathsConfig config in the app-level setup (for the /**/generic path), this will output the following:

Cache-Control: no-cache, no-store, must-revalidate
Surrogate-Control: maxAge=2000

API

cache.setupInitialCacheHeaders(pathsConfig)

{
    '/glob/**/path': object|string|boolean=false
}

The following are acceptable keys to use if an object is passed in

| key | type | description | default | | --- | ---- | ----------- | ------- | | lastModified | string | set Last-Modified Header | | | maxAge | string, number | number or string representing a number for Surrogate-Control: max-age (forced to 0 if setPrivate=true) | TEN_MINUTES (600 seconds) | | setPrivate | boolean | should add Cache-Control: private (if set to true forces Surrogate-Control: maxAge=0 and Last-Modified: (NOW)) | false | | staleError | string, number | number or string representing a number for Cache-Control: stale-if-error | | | staleRevalidate | string, number | number or string representing a number for Cache-Control: stale-while-revalidate | |

The following are acceptable values to use if a string is passed in for cache values:

• 'ONE_MINUTE'
• 'TEN_MINUTES'
• 'ONE_HOUR'
• 'ONE_DAY'
• 'ONE_WEEK'
• 'ONE_MONTH'
• 'ONE_YEAR'

The following are acceptable values to use if a boolean is passed in

• false - this is equivalent to passing { setPrivate: true, maxAge: 0 }

If no options are passed in, the default value set is

Cache-Control: no-cache, no-store, must-revalidate
Surrogate-Control: max-age=600

cache.overrideCacheHeaders(overrideConfig)

{
    lastModified: string,
    maxAge: number|string,
    setPrivate: boolean,
    staleError: number|string,
    staleRevalidate: number|string
}

| key | type | description | default | | --- | ---- | ----------- | ------- | | lastModified | string | set Last-Modified Header | | | maxAge | string, number | number or string representing a number for Surrogate-Control: max-age (forced to 0 if setPrivate=true) | TEN_MINUTES (600 seconds) | | setPrivate | boolean | should add Cache-Control: private (if set to true forces Surrogate-Control: maxAge=0 and Last-Modified: (NOW)) | false | | staleError | string, number | number or string representing a number for Cache-Control: stale-if-error | | | staleRevalidate | string, number | number or string representing a number for Cache-Control: stale-while-revalidate | |

Recipes

Private Pages

Options for pages that are intended for a single user and should not be cached.

{
    setPrivate: true    
}

Headers Output:

'Cache-Control': 'private, no-cache, no-store, must-revalidate'
'Surrogate-Control': 'maxAge=0'
'Pragma': 'no-cache'
'Expires': 0
'Last-Modified': (NOW)

Browser/Server Cached Pages

Options for pages that are intended for all users and should be cached in both the browser and the server.

{
    maxAge: 'ONE_WEEK',                             // cache on server
    staleError: 'ONE_MONTH',                        // cache on browser if server returns error
    staleRevalidate: 'TEN_MINUTES',                 // cache on browser for 10 min
    lastModified: 'Fri, 23 Jun 2017 14:35:44 GMT'   // some deployTime from a versionReport
}

Headers Output:

'Cache-Control': 'no-cache, no-store, must-revalidate, stale-while-revalidate=600, stale-if-error=2592000'
'Surrogate-Control': 'maxAge=604800'
'Pragma': 'no-cache'
'Expires': 0
'Last-Modified': 'Fri, 23 Jun 2017 14:35:44 GMT'

Additional notes on header use / specification

• Cache-Control
  • private - response intended for single user and should not be cached
  • no-cache, no-store, must-revalidate - turns off browser caching
  • stale-while-revalidate={seconds} - use stale version for up to {seconds} while re-fetching latest version background
  • stale-if-error={seconds} - use stale version if re-fetch fails within {seconds} of response becoming stale
• Surrogate-Control
  • takes priority over Cache-Control, but is stripped so browsers don't see it
  • max-age={seconds} - how long the response can be considered fresh

(For more information on Surrogate-Control/Cache-Control headers read Fastly Cache Control Tutorials and W3 Specification.)

Contributing

All code additions and bugfixes must be accompanied by unit tests. Tests are run with jest and written with the node assert module.

Acknowledgement

A portion of this code was taken from this cache-control package/repo.