@mountainpass/axios-cache-interceptor

axios-cache-interceptor

A clean, minimal implementation of common HTTP caching mechanisms for axios (web).

Provides a wrapper around an axios instance to enable out of the box, cache strategies.

Almost all caching logic is handled by the browser's native caching and/or intermediary caches (i.e. web proxy).

Additionally, provides an indication of whether your response is fresh, stale or none (not cached. @see x-cache-status response header below).

stale responses

Knowing a Reponse is stale is extremely useful. If you receive a stale status, the browser will asychronously fetch a fresh request in the background, meaing the next response will instantly respond with fresh data.

You will only ever receive the same stale response once. Subsequent requests will wait for the background request to complete¹.

The stale-while-revalidate is not only a useful tool for providing a seamless user experience, but is also very useful for updating proxy caches. The client's asynchronous background refresh, will trigger off a refresh in shared proxy caches, meaning caches are refreshed with fresh data in the background, providing benefit to all subsequent users of the endpoint. (Ideally these proxy caches also implement stale-while-revalidate logic!)

¹ Tested in Chrome

Implementation

The wrapper stores all successful AxiosResponse objects for the purpose of:

1. returning a cached response, if the server returns a 304 Not Modified
2. determining if a response is fresh or stale when re-requesting an endpoint

Supports response headers:

• Etag
• Last-Modified
• Cache-Control max-age
• Cache-Control stale-while-revalidate
• Date

Supports response status:

• 304 Not Modified

Automatically adds request headers (if relevant):

• If-None-Match
• If-Modified-Since

Cache

The default cache is an InMemoryCache - it provides a bare minimum implementation.

• It uses an inmemory map to store all successful GET responses.
• There is no cache eviction.
• There is no persistence (data is transient).
• It uses "${request.method}#${request.url}" as a key, for storing cached data (Note: no query params or headers).

These options can all be overridden, by providing a custom implementation of the CacheInterface interface.

const axiosInstance = wrapAxios(axiosInstance, myCustomCache)

Install

npm i @mountainpass/axios-cache-interceptor

Usage (Web Client)

import { wrapAxios } from "@mountainpass/axios-cache-interceptor";

// setup
const axiosInstance = wrapAxios(axiosInstance)

// use
const result = await axiosInstance.get('http://www.localhost:3000/test')

// check browser cache status
console.log(result.headers['x-cache-status']) // 'fresh' | 'stale' | 'none'

Server Side Example

Here is an example response, which utilises both Etag and stale-while-revalidate cache controls.

const app = express();

app.set('etag', true) // (redundant, default is on)

app.get("/test/", (req: Request, res: Response) => {
  res.setHeader("Cache-Control", "public, max-age=60, stale-while-revalidate=3600")
  res.json({ your: 'response' })
});

For an example of the api / ui integration, please check the example folder.

x-cache-status response header

The cache status is a derived value, based on the HTTP headers Date, Cache-Control: max-age, Cache-Control: stale-while-revalidate and the current date timestamp (i.e. Date.now()).

• fresh - If Date.now() is between Date and Date + max-age.
• stale - If Date.now() is between Date + max-age and Date + max-age + stale-while-revalidate.
• none - If Date.now() is greater than Date + max-age + stale-while-revalidate.

Request strategy

We rely heavily on the browser's inbuilt caching mechanisms. Here is the request interceptor logic:

1. if local cache is fresh, return result from browser cache (should be instant)
2. if local cache is stale, return result from browser cache (should be instant, and browser handles the asynchronous refetch in the background).
3. otherwise, add the following Request headers:
   1. if etag exists, send If-None-Match
   2. else, if last-modified exists, send If-Modified-Since
   3. else, if date exists, send If-Modified-Since

Alternatives

I was inspired by https://github.com/arthurfiorette/axios-cache-interceptor , however:

• It is very complex
• It is very large (1.2.0 = 463kB)
• It does not support stale-while-revalidate - https://github.com/arthurfiorette/axios-cache-interceptor/issues/512