Martyn Loughran

You want to use the Twitter API but you don’t want to die? I have the solution to API caching:

APICache.get("http://twitter.com/statuses/public_timeline.rss")

You get the following functionality for free:

• New data every 10 minutes
• If the twitter API dies then keep using the last data received for a day. Then assume it’s invalid and announce that Twitter has FAILED (optional).
• Don’t hit the rate limit (70 requests per 60 minutes)

So what exactly does APICache do? Given cached data less than 10 minutes old, it returns that. Otherwise, assuming it didn’t try to request the URL within the last minute (to avoid the rate limit), it makes a get request to the Twitter API. If the Twitter API timeouts or doesn’t return a 2xx code (very likely) we’re still fine: it just returns the last data fetched (as long as it’s less than a day old). In the exceptional case that all is lost and no data can be returned, it raises an APICache::NotAvailableError exception. You’re responsible for catching this exception and complaining bitterly to the internet.

All very simple. What if you need to do something more complicated? Say you need authentication or the silly API you’re using doesn’t follow a nice convention of returning 2xx for success. Then you need a block:

APICache.get('twitter_replies', :cache => 3600) do
  Net::HTTP.start('twitter.com') do |http|
    req = Net::HTTP::Get.new('/statuses/replies.xml')
    req.basic_auth 'username', 'password'
    response = http.request(req)
    case response
    when Net::HTTPSuccess
      # 2xx response code
      response.body
    else
      raise APICache::Invalid
    end
  end
end

All the caching is still handled for you. If you supply a block then the first argument to APICache.get is assumed to be a unique key rather than a URL. Throwing APICache::Invalid signals to APICache that the request was not successful.

You can send any of the following options to APICache.get(url, options = {}, &block). These are the default values (times are all in seconds):

{
  :cache => 600,    # 10 minutes  After this time fetch new data
  :valid => 86400,  # 1 day       Maximum time to use old data
                    #             :forever is a valid option
  :period => 60,    # 1 minute    Maximum frequency to call API
  :timeout => 5     # 5 seconds   API response timeout
}

Before using the APICache you need to initialize the caches. In merb, for example, put this in your init.rb:

APICache.start

Currently there are two stores available: MemcacheStore and MemoryStore. MemcacheStore is the default but if you’d like to use MemoryStore, or another store - see AbstractStore, just supply it to the start method:

APICache.start(APICache::MemoryStore)

I suppose you’ll want to get your hands on this magic. For now just grab the source from http://github.com/mloughran/api_cache/tree/master and rake install. I’ll get a gem sorted soon.

This is the irb quickstart so that you don’t have to re-parse the above:

require 'rubygems'
require 'api_cache'
APICache.start(APICache::MemoryStore)
APICache.get("http://twitter.com/statuses/public_timeline.rss")

Please send feedback if you think of any other functionality that would be handy.

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