superagent-cache

superagent-cache

Superagent with flexible built-in caching.

Upgrading from an older version? Please see the Breaking Change History section.

Basic Usage

Require and instantiate superagent-cache as follows to get the default configuration:

var superagent = require('superagent-cache')();

Now you're ready for the magic! All of your existing GET and HEAD requests will be cached with no extra bloat in your queries! Any matching DELETE or PUT requests will automatically invalidate the associated cache key and value.

superagent
  .get(uri)
  .end(function (err, response){
    // response is now cached!
    // subsequent calls to this superagent request will now fetch the cached response
  }
);

Enjoy!

Install

npm install superagent-cache --save

Run Tests

npm test

How Does it Work?

superagent-cache patches superagent so that it can evaluate HTTP calls you make. Whenever a GET or HEAD request is made, superagent-cache generates a cache key by stringifying four properties:

• your cache's nameSpace attribute (defaults to undefined if the property is not set)
• you request's URI
• your request's query params whether they're passed as an object or a string
• your request's headers

With the generated cache key, superagent-cache then checks its internal cache instance (which you have full power to configure). If the key exists, superagent-cache returns it without performing the HTTP request and if the key does not exist, it makes the request, caches the response object (mostly), and returns it.

What Exactly Gets Cached?

If you don't use the .prune() or .responseProp() chainables detailed in the API, then superagent-cache will cache a gutted version of the response object. There are two reasons it doesn't just cache the entire response object:

• The object is almost always circular and therefore not feasible to serialize
• The object is huge and would use way more space than necessary

superagent-cache takes all of the following properties from the response object and clones each of them into a new object which then gets cached:

• response.body
• response.text
• response.headers
• response.statusCode
• response.status
• response.ok

If you find yourself occasionally needing more than this, try out the .prune() or .responseProp() chainables. If your find yourself consistently needing more than this, make a pull request that adds the properties you need.

Where does superagent-cache store data?

By default, superagent-cache stores data in a bundled instance of cacheModule, but it can natively handle any cache that matches cache-service's API. See this list of supported caches to see what works best with your use case. Because cache-service and all of the supported caches have identical APIs, superagent-cache doesn't care which you use, so pick the one that's best for you or make a new one.

What Does the Default Configuration Give Me?

You get the 'default configuration' when you don't provide any params to the require('superagent-cache')() command. This will return a fresh instance of superagent and bundle an instance of cacheModule for storing data. cacheModule is a slim, in-memory cache.

How Do I Use a Custom Configuration?

To use a custom configuraiton, take advantage of the the two optional params you can hand to superagent-cache's require command as follows:

//Require superagent and the cache module I want
var superagent = require('superagent');
var redisModule = require('cache-service-redis');
var redisCache = new redisModule({redisEnv: 'REDISCLOUD_URL'});

//Patch my superagent instance and pass in my redis cache
require('superagent-cache')(superagent, redisCache);

This example allows you to provide your own instance of superagent to be patched as well as allowing you to pass in your own, pre-instantiated cache. Here's a list of supported caches.

For more information on require command params usage, see this section.

Supported Caches

cache-service

A tiered caching solution capable of wrapping any number of the below supported caches. Available on NPM.

cache-service-redis

A redis wrapper for cache-service or standalone use. Available on NPM.

cache-service-node-cache

An in-memory cache wrapper for cache-service or standalone use. Available on NPM.

cache-service-cache-module

A super-light in-memory cache for cache-service or standalone use. (This module is bundled with superagent-cache and provided in the default configuration if you do not provide a cache require param.) Available on NPM.

API

require('superagent-cache')([superagent, cache])

All params here are optional. If the superagent param is empty or falsy, then the require statement will return a brand new, patched instance of superagent.

Arguments

• (optional) superagent: an instance of superagent
• (optional) cache: a pre-instantiated cache module that matches the cache-service API

.get(uri), .head(uri)

Same as superagent except that superagent's response object will be cached.

.put(uri), .del(uri)

Same as superagent except that the generated cache key will be automatically invalidated when these HTTP verbs are used.

.end(callback ([err,] response [, key]))

Same as superagent except it optionally exposes the key superagent-cache generates as the third param in the callback's argument list. See the usage example for a more detailed explanation.

.responseProp(prop)

Caution: if you use this function, supergent-cache will not gut the response object for you. Be sure that the result of your .responseProp() call will never be circular and is not larger than it needs to be. Consider using .prune() if you need to dig several layers into the response object.

If you know you want a single, top-level property from superagent's response object, you can optimize what you cache by passing the property's name here. When used, it causes the .end() function's response to return superagent's response[prop].

Arguments

• prop: string

Example

//response will now be replaced with superagent's response.body
//but all other top-level response properties,such as response.ok and response.status, will be ommitted
superagent
  .get(uri)
  .responseProp('body')
  .end(function (error, response){
    // handle response
  }
);

.prune(callback (response))

Caution: if you use this function, supergent-cache will not gut the response object for you. Be sure that the result of your .prune() callback function will never be circular and is not larger than it needs to be.

If you need to dig several layers into superagent's response, you can do so by passing a function to .prune(). Your prune function will receive superagent's response and should return a truthy value or null. The benefit of using this function is that you can cache only what you need.

Arguments

• callback: a function that accepts superagent's response object and returns a truthy value or null

Example

var prune = funtion(r){
  return (r && r.ok && r.body && r.body.user) ? r.body.user : null;
}

//response will now be replaced with r.body.urer or null
//and only r.body.user will be cached rather than the entire superagent response
superagent
  .get(uri)
  .prune(prune)
  .end(function (error, response){
    // handle response
  }
);

.pruneParams(params)

In the event that you need certain query params to execute a query but cannot have those params as part of your cache key (useful when security or time-related params are sent), use .pruneParams() to remove those properties. Pass .pruneParams() an array containing the param keys you want omitted from the cache key.

Arguments

• params: array of strings

Example

//the superagent query will be executed with all params
//but the key used to store the superagent response will be generated without the passed param keys
superagent
  .get(uri)
  .query(query)
  .pruneParams(['token'])
  .end(function (error, response){
    // handle response
  }
);

.pruneOptions(options)

This function works just like the .pruneParams() funciton except that it modifies the arguments passed to the .set() chainable method rather than those passed to the .query() chainable method.

Arguments

• options: array of strings

Example

//the superagent query will be executed with all headers
//but the key used to store the superagent response will be generated without the passed header keys
superagent
  .get(uri)
  .set(options)
  .pruneOptions(['token'])
  .end(function (error, response){
    // handle response
  }
);

.expiration(seconds)

Use this function when you need to override your cache's defaultExpiration property for a particular cache entry.

Arguments

• seconds: integer

.cacheWhenEmpty(bool)

Tell superagent-cache whether to cache the response object when it's false, null, or {}.This is especially useful when using .responseProp() or .prune() which can cause response to be falsy. By default, cacheWhenEmpty is true.

Arguments

• bool: boolean, default: true

.doQuery(bool)

Tell superagent-cache whether to perform an ajax call if the generated cache key is not found. By default, cacheWhenEmpty is true.

Arguments

• bool: boolean, default: true

.backgroundRefresh(value)

See the Using Background Refresh section for more information.

Tell the underlying cache provided in the require command to enable background refresh for the generated key and value. If a function is provided, it will use the function, if a boolean is provided, it will use the boolean, if nothing is provided, it will default to true.

Arguments

• value: boolean || function || undefined, default: true

._end(callback (err, response))

This is a convenience method that allows you to skip all caching logic and use superagent as normal.

Arguments

• callback: a function that accepts superagent's error and response objects

.cache

This is the second constructor param you handed in when you instantiated superagent-cache. If you didn't provide one, then it's an instance of cacheModule.

Example

superagent.cache... //You can call any function existing on the cache you passed in

Using Background Refresh

With a typical cache setup, you're left to find the perfect compromise between having a long expiration so that users don't have to suffer through the worst case load time, and a short expiration so data doesn't get stale. superagent-cache eliminates the need to worry about users suffering through the longest wait time by automatically refreshing keys for you.

How do I turn it on?

By default, background refresh is off. It will turn itself on the first time you use the .backgroundRefresh) chainable.

Setup

superagent-cache relies on the background refresh feature of the cache param you pass into the require command. When you use the .backgroundRefresh() chainable, superagent-cache passes the provided value into cache. This means that if you're using cache-service, you almost certainly want cache-service's writeToVolatileCaches property set to true (it defaults to true) so that the data set by background refresh will propogate forward to earlier caches (cache-service ONLY background refreshses to the final cache passed to it)

Configure

If desired, configure the following properties within cache:

• backgroundRefreshInterval
• backgroundRefreshMinTtl
• backgroundRefreshIntervalCheck

Use

Background refresh is exposed via the .backgroundRefresh() chainable.

When true or no param is passed to .backgroundRefresh(), it will generate a superagent call identical to the one that triggered it and pass that to cache.

superagent
  .get(uri)
  .backgroundRefresh()
  .end(function (err, response){
    //Response will no be refreshed in the background
  }
);

When a function is passed, it will use that function. Read on for background refresh function requirements.

var refresh = function(key, cb){
  var response = goGetData();
  cb(null, response);
}

superagent
  .get(uri)
  .backgroundRefresh(refresh)
  .end(function (err, response){
    //Response will no be refreshed in the background
  }
);

When false is passed, it will do nothing.

The Refresh Param

refresh(key, cb(err, response))

• key: type: string: this is the key that is being refreshed
• cb: type: function: you must trigger this function to pass the data that should replace the current key's value

The refresh param MUST be a function that accepts key and a callback function that accepts err and response as follows:

var refresh = function(key, cb){
  var response = goGetData();
  cb(null, response);
}

More Usage Examples

.end() callback argument list options

As an optional parameter in the .end(cb) callback argument list, superagent-cache can give you the key it generated for each query as follows:

superagent
  .get(uri)
  .end(function (err, response, key){
    console.log('GENERATED KEY:', key);
  }
);

This can be useful if you need external access to a cache key and for testing purposes.

However, you can only get it when you pass 3 params to the callback's argument list. The following rules will apply when listing arguments in the .end(cb) callback argument list:

• 1 param: the param will always be response
• 2 params: the params will always be err and response
• 3 params: the params will always be err, response, and key

Various ways of requiring superagent-cache

When no params are passed

//...it will return a patched superagent instance and create a cache-service instance with the default configuration
var superagent = require('superagent-cache')();

When only superagent is passed

//...it will patch the provided superagent and create a cacheModule instance (see 'default configuration')
var superagent = require('superagent');
require('superagent-cache)(superagent)

When only cache is passed

//...it will return a patched superagent instance and consume cache as its data store
var redisModule = require('cache-service-redis');
var redisCache = new redisModule({redisEnv: 'REDISCLOUD_URL'});
var superagent = require('superagent-cache')(null, redisCache);

Breaking Change History

0.2.0

• superagent-cache is now more flexible, allowing usage of any cache that matches cache-service's API. To make it lighter, then, the hard dependency on cache-service was replaced with the much lighter cacheModule. As a result, superagent-cache can no longer construct a cache-service instance for you. If you wish to use cache-service, you must instantiate it externally and hand it in as cache--the second param in the require command.