express-expeditious

An express middleware that simplifies caching responses for HTTP requests of any type. It also handles many unique cases such as piping data, using sessions, and ETags. This middleware is implemented at the socket level, so it is entirely transparent to the response methods such as res.json, res.end, etc. and stays out of your way as a result. TypeScript support is also included.

How Does it Work?

Using the default settings it works by:

1. Generating a cache key for all incoming GET requests
2. Checking if that key already exists in a storage engine
3. Responding with the cached data if found, otherwise process the request using the defined router logic and place the response in the cache if the status code was a HTTP 200 (success).

Features

• Support for TypeScript.
• Seamlessly caches responses without the need to modify route handler code.
• Caches all response functions and data types, e.g res.json, res.sendFile, res.pipe, etc.
• Cache storage engines can be swapped easily. You're not limited to node.js memory or redis (but there are adapters prebuilt for those two).
• Is express-session (req.session) aware. This ensures user data is not accidentally shared when two users request the same URL.
• Retains ETag (HTTP 304) support from express 4.12.X and for all response types including those piped or of file format.
• Support for custom cache key generation.
• Can override caching behaviours using a custom function.
• Cache times can be configured on a per status code basis.
• Cache inspection and invalidation using the underlying expeditious instance
• Support for timestring format for setting cache timeouts. For example you can pass '1 hour' instead of 60 * 60 * 1000.
• Responses contain an x-expeditious-cache header that states either hit or miss so clients can determine if the data is a cached copy.

Install

npm install express-expeditious --save

You can also install one of these to customise the cache storage location:

• expeditious-engine-redis
• expeditious-engine-memory (this is the default)

If you'd like to write an engine of your own for another storage system then take a look at the source code for those modules - it's pretty easy and there's more information here.

Usage

These examples will cache any successful request - this is a request that you send a 200 status code to the client.

Using the Default In-Memory Cache

const getExpeditiousCache = require('express-expeditious');
const express = require('express');

const cache = getExpeditiousCache({
  // Namespace used to prevent cache conflicts, must be alphanumeric
  namespace: 'expresscache',

  // Store cache entries for 1 minute (can also pass milliseconds e.g 60000)
  defaultTtl: '1 minute'
});

const app = express();

// the initial call to this will take 2 seconds, but any subsequent calls
// will receive a response instantly from cache for the next hour
app.get('/ping', cache.withTtl('1 hour'), (req, res) => {
  setTimeout(() => {
    res.end('pong');
  }, 2000);
});

// Cache everything below this line for 1 minute (defaultTtl)
app.use(cache);

Using the Default In-Memory Cache with TypeScript

Similar to the regular JavaScript example:

import * as expeditious from 'express-expeditious';
import * as express from 'express';

const cacheoptions: expeditious.ExpeditiousOptions = {
  namespace: 'expresscache',
  defaultTtl: '1 minute'
};

const cache = expeditious(cacheoptions);

const app = express();

// the initial call to this will take 2 seconds, but any subsequent calls
// will receive a response instantly from cache for the next hour
app.get('/ping', cache.withTtl('1 hour'), (req, res) => {
  setTimeout(() => {
    res.end('pong');
  }, 2000);
});

There's also a TypeScript sample folder in this repo at /example-ts.

Using Redis

Just like before, except we pass a redis engine:

const getExpeditiousCache = require('express-expeditious');
const express = require('express');

const cache = getExpeditiousCache({
  namespace: 'expresscache',
  defaultTtl: '1 minute',
  engine: require('expeditious-engine-redis')({
    // options for the redis driver
    host: 'redis.acme.com',
    port: 6379
  })
});

const app = express();

app.use(cache);

app.get('/ping', (req, res) => {
  setTimeout(() => {
    res.end('pong');
  }, 2000);
});

Cache Storage Format

Currently cached data is stored in the following format:

{
  headers: String
  data: {
    type: 'Buffer',
    data: Uint8Array
  }
}

For example, here's a cache entry that would be stored by the module:

{
  "headers": "HTTP/1.1 200 OK\r\nX-Powered-By: Express\r\nx-expeditious-cache: hit\r\nDate: Thu, 14 Jun 2018 16:16:33 GMT\r\nConnection: close\r\nTransfer-Encoding: chunked",
  "data": {
    "type": "Buffer",
    "data": [
      13,
      10,
      13,
      10,
      49,
      13,
      10,
      111,
      13,
      10,
      49,
      13,
      10,
      107,
      13,
      10,
      48,
      13,
      10,
      13,
      10
    ]
  }
}

This format could be changed to improve the ability to query for specific headers or data. The use of Buffers is to ensure binary/compressed data can be cached, but PRs and ideas surrounding this are welcome. For example, we could store non-binary data as strings to simplify the ability to query it.

Using Modifers

You can modify cache behaviour for specific endpoint or routers easily like so:

const app = require('express')();
const isEmpty = require('lodash.isempty');
const products = require('lib/products');
const cache = require('express-expeditious')({
  namespace: 'expresscache',
  defaultTtl: '1 minute'
});


/**
 * Exposes a /products endpoint that can be queried for a list of products.
 *
 * If the client provides a querystring then the request will NOT be cached.
 *
 * The endpoint is also session independent meaning the data returned is the
 * same regardless of the user that calls, so we set sessionAware to false since
 * it will reduce resource usage.
 */
app.get(
  '/products',

  cache
    .withSessionAwareness(false)
    .withCondition((req) => { return isEmpty(req.query) }),

  (req, res, next) => {
    products.list(req.query)
      .then((listOfProducts) => res.json(listOfProducts))
      .catch(next)
  }
);


/**
 * Expose a /orders endpoint that caches all HTTP 200 responses for 5 minutes.
 * It overrides the default behaviour and also caches 404 responses for a given
 * request for 1 minute - by default only 200 responses are cached
 */
app.use(
  '/orders',

  cache
    .withTtl('5 minutes')
    .withTtlForStatus('1 minute', 404),

  require('lib/routes/orders')
);

Debugging

If you need to enable logging for this module, simply run your application in a session with a DEBUG environment variable set to "express-expeditious" like so:

export DEBUG=express-expeditious
$ node your-app.js

This will have express-expeditious to enable the debug logger module it uses.

Benchmarks

Here's the performance increase seen in simple benchmarks using Apache Bench. All of these tests use expeditious-engine-memory for storage meaning the node.js process memory is used.

You can run the same tests using the following commands:

# after cloning the repo
cd express-expeditious/
npm install
npm run benchmark-server

You need to run MongoDB locally on its default port of 27017 also. These tests were performed with MongoDB running inside docker using the following command:

docker run --name mongodb -p 27017:27017 -p 28017:28017 -d mongo

Now, to start the tests run the command below in another terminal:

ab -n 1000 -c 100 http://localhost:8080/$ENDPOINT_TO_TEST

Here are the requests per second averaged from 4 runs:

And here is the average time taken for each request averaged over 4 runs:

It's clear that with caching applied using express-expeditious latency is reduced so your application will feel more responsive and the amount of requests per second that can be served increases significantly.

Full Example

See the example folder here.

You can hit HTTP endpoints on the example server using the following URLs:

• http://localhost:8080/ - Uses res.render to render a homepage
• http://localhost:8080/ping - Uses res.end
• http://localhost:8080/sendfile - Uses res.sendFile
• http://localhost:8080/pipe - Uses res.pipe
• http://localhost:8080/write - Uses res.write

All of these URLs respond after 2 seconds on the first call, but subsequent calls will use express-expeditious to respond instantly using the cache.

API

This module is a factory function (similar to express) that returns a middleware function. A number of options are supported and are explained in the following sections.

module(opts)

Create a middleware instance using opts. Supported options are:

• [Optional] expeditious - The expeditious instance that will be used for caching response data for requests.
• [Optional] shouldCache - Function that will be called to determine if the response for a request should be cached.
• [Optional] genCacheKey - Function that will be called to generate a custom key for reading and writing a response
• [Optional] sessionAware - Determines if the default cache key generation will include the session token in the key. Defaults to true since this is the safest option to prevent data leaks between users. If genCacheKey is also supplied then this option is ignored. from the cache. By default req.originalUrl is used as the key.
• [Optional] statusCodeExpires - Useful if you want different status code responses to be cached for different durations.
• [Optional] cacheStatusHeader - Default responses use x-expeditious-cache as the header key. Set a new string value to customize the header or false if you prefer not to write the expeditious response header.
• [Required/Optional] defaultTtl - This is required if the expeditious option is not passed. Represents time entries will remain in the cache. Can be set to any value the timestring module accepts.
• [Required/Optional] namespace - This is required if the expeditious option is not passed. It's used as a namespace to prevent cache conflicts.
• [Required/Optional] engine - This is required if the expeditious option is not passed. It is the storage engine for caching.

These options are covered in greater detail in the behaviours section below.

instance.withTtl(number)

Returns a new cache middleware that has a defaultTtl setting of number, but inherits other values of the parent instance.

const cache = require('express-expeditious')({
  namespace: 'mycache',
  defaultTtl: '30 minutes'
});

const userRoutes = require('./routes/users');

// Set cache time (defaultTtl) for /users to 15 minutes
app.use('/users', cache.withTtl('15 minutes'), userRoutes);

instance.withNamespace(string)

Creates a new cache instance with the given namespace. All other settings are inherited from the parent instance.

instance.withTtlForStatus(ttl, statusCode)

Creates a new cache instance with the given ttl for a specific status code. All other settings are inherited from the parent instance. Previously supplied values for statusCodeExpires will be used, but the values you pass to this function will override if a conflict in values is found.

instance.withCondition(function)

Returns a new cache middleware that has a shouldCache setting of its parent overwritten by the passed function. Passing nothing will create an instance without a shouldCache entry. Other settings are inherited.

instance.withCacheKey(function)

Returns a new cache middleware that has a genCacheKey setting of its parent overwritten by the passed function. Passing nothing will create an instance without a genCacheKey entry. Other settings are inherited.

instance.withSessionAwareness([boolean])

Returns a new cache instance that either respects or ignores sessions. Pass true to create a clone of the original instance, but ignore sessions. Passing false will create an instance that will include session IDs in generated cache keys. Passing no arguments is treated the same as passing true.

NOTE: If you supply a genCacheKey or withCacheKey option then this option will not apply since you have chosen to generate cache keys manually.

instance.flush([string, ]callback)

Deletes all cache entries associated with this middleware namespace and fires the callback once complete. If you supply a string for the first parameter this will be passed to the flush function to target specific keys.

Behaviours

When to use the Cache (shouldCache or withCondition)

Default

By default only HTTP GET requests with 200 responses are cached using the URL a