API cache extracted from mloughran.com.

Some major limitations right now:

* Only the :cache and :timeout options are implemented
* There is only one cache store and it's an in memory hash

.gitignore

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+pkg

LICENSE

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+Copyright (c) 2008 Martyn Loughran
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

README

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+api_cache
+=========
+

Rakefile

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+require 'rubygems'
+require 'rake/gempackagetask'
+require 'rubygems/specification'
+require 'date'
+
+PLUGIN = "api_cache"
+NAME = "api_cache"
+GEM_VERSION = "0.0.1"
+AUTHOR = "Martyn Loughran"
+EMAIL = "me@mloughran.com"
+HOMEPAGE = "http://merb-plugins.rubyforge.org/api_cache/"
+SUMMARY = "Library to handle caching external API calls"
+
+spec = Gem::Specification.new do |s|
+  s.name = NAME
+  s.version = GEM_VERSION
+  s.platform = Gem::Platform::RUBY
+  s.has_rdoc = true
+  s.extra_rdoc_files = ["README", "LICENSE", 'TODO']
+  s.summary = SUMMARY
+  s.description = s.summary
+  s.author = AUTHOR
+  s.email = EMAIL
+  s.homepage = HOMEPAGE
+  s.require_path = 'lib'
+  s.autorequire = PLUGIN
+  s.files = %w(LICENSE README Rakefile TODO) + Dir.glob("{lib,spec}/**/*")
+end
+
+Rake::GemPackageTask.new(spec) do |pkg|
+  pkg.gem_spec = spec
+end
+
+desc "install the plugin locally"
+task :install => [:package] do
+  sh %{sudo gem install pkg/#{NAME}-#{GEM_VERSION} --no-update-sources}
+end
+
+desc "create a gemspec file"
+task :make_spec do
+  File.open("#{GEM}.gemspec", "w") do |file|
+    file.puts spec.to_ruby
+  end
+end

lib/api_cache.rb

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+class APICache
+  class Error < RuntimeError; end
+  class Invalid <  RuntimeError; end
+
+  class << self
+    attr_accessor :cache
+  end
+
+  # Initializes the cache
+  def self.start
+    APICache.cache = APICache::MemoryStore.new
+  end
+
+  # Raises an APICache::Error if it can't get a value. You should rescue this.
+  # 
+  # Optionally call with a block. The value of the block is then used to 
+  # set the cache rather than calling the url. Use it for example if you need
+  # to make another type of request, catch custom error codes etc. To signal
+  # that the call failed just throw :invalid - the value will then not be
+  # cached and the api will not be called again for options[:timeout] seconds.
+  # 
+  # For example:
+  # [Add example here]
+  def self.get(url, options = {}, &block)
+    options = {
+      :cache => 600,    # 10 minutes  After this time fetch new value
+      :valid => 86400,  # 1 day       Expire even if not fetched new data
+      :period => 60,    # 1 minute    Don't call API more frequently than this
+      :timeout => 5     # 5 seconds   Timeout to wait for response
+    }.merge(options)
+
+    if cache.exists?(url) && !cache.expired?(url, options[:cache])
+      # Cache is populated and not expired
+      cache.get(url)
+    else
+      # Cache is not populated or is expired
+      begin
+        r = Timeout::timeout(options[:timeout]) do
+          if block_given?
+            # This should raise APICache::Invalid if it is not correct
+            yield
+          else
+            r = Net::HTTP.get_response(URI.parse(url)).body
+            # TODO: Check that it's a 200 response
+          end
+        end
+        cache.set(url, r)
+      rescue Timeout::Error, APICache::Invalid
+        if cache.exists?(url)
+          cache.get(url)
+        else
+          raise APICache::Error
+        end
+      end
+    end 
+  end
+end
+
+require 'api_cache/memory_store'

lib/api_cache/memory_store.rb

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+class APICache::MemoryStore
+  def initialize
+    puts "Init cache"
+    @cache = {}
+  end
+
+  def expired?(name, timeout)
+    Time.now - created(name) > timeout
+  end
+
+  def set(name, value)
+    puts "Setting the cache"
+    @cache[name] = [Time.now, value]
+    value
+  end
+
+  def get(name)
+    puts "Serving from cache"
+    @cache[name][1]
+  end
+
+  def exists?(name)
+    !@cache[name].nil?
+  end
+
+  private
+
+  def created(name)
+    @cache[name][0]
+  end
+end

spec/api_cache_spec.rb

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+require File.dirname(__FILE__) + '/spec_helper'
+
+describe "api_cache" do
+  it "should do nothing" do
+    true.should == true
+  end
+end

spec/spec_helper.rb

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+$TESTING=true
+$:.push File.join(File.dirname(__FILE__), '..', 'lib')