Introduce Flipper::Adapters::FallbackToCached

lib/flipper/adapters/fallback_to_cached.rb

@@ -0,0 +1,86 @@
+require 'flipper/adapters/memoizable'
+
+module Flipper
+ module Adapters
+ # Public: Adapter that wraps another adapter and caches the result of all
+ # adapter get calls in memory. If the primary adapter raises an error, the
+ # cached value will be used instead.
+ class FallbackToCached < Memoizable
+ def initialize(adapter, cache = nil)
+ super
+ @memoize = true
+ end
+
+ def memoize=(value)
+ # raise "memoize cannot be disabled on FallbackToCached adapter"
+ end
+
+ # Public: The set of known features.
+ #
+ # Returns a set of features.
+ def features
+ response = @adapter.features
+ cache[@features_key] = response
+ response
+ rescue => e
+ cache[@features_key] || raise(e)
+ end
+
+ # Public: Gets the value for a feature from the primary adapter. If the
+ # primary adapter raises an error, the cached value will be returned
+ # instead.
+ #
+ # feature - The feature to get the value for.
+ #
+ # Returns the value for the feature.
+ def get(feature)
+ cache[key_for(feature.key)] = @adapter.get(feature)
+ rescue => e
+ cache[key_for(feature.key)] || raise(e)
+ end
+
+ # Public: Gets the values for multiple features from the primary adapter.
+ # If the primary adapter raises an error, the cached values will be
+ # returned instead.
+ #
+ # features - The features to get the values for.
+ #
+ # Returns a hash of feature keys to values.
+ def get_multi(features)
+ response = @adapter.get_multi(features)
+ cache.clear
+ features.each do |feature|
+ cache[key_for(feature.key)] = response[feature.key]
+ end
+ response
+ rescue => e
+ result = {}
+ features.each do |feature|
+ result[feature.key] = cache[key_for(feature.key)] || raise(e)
+ end
+ result
+ end
+
+ # Public: Gets all the values from the primary adapter. If the primary
+ # adapter raises an error, the cached values will be returned instead.
+ #
+ # Returns a hash of feature keys to values.
+ def get_all
+ response = @adapter.get_all
+ cache.clear
+ response.each do |key, value|
+ cache[key_for(key)] = value
+ end
+ cache[@features_key] = response.keys.to_set
+ response
+ rescue => e
+ raise e if cache[@features_key].empty?
+ response = {}
+ cache[@features_key].each do |key|
+ response[key] = cache[key_for(key)]
+ end
+ response
+ end
+ end
+ end
+end

spec/flipper/adapters/fallback_to_cached_spec.rb

@@ -0,0 +1,88 @@
+require 'flipper/adapters/fallback_to_cached'
+
+RSpec.describe Flipper::Adapters::FallbackToCached do
+ let(:adapter) { Flipper::Adapters::Memory.new }
+ let(:flipper) { Flipper.new(subject, memoize: false) }
+ let(:feature_a) { flipper[:malware_rule] }
+ let(:feature_b) { flipper[:spam_rule] }
+
+ subject { described_class.new(adapter) }
+
+ before do
+ feature_a.enable
+ feature_b.disable
+ end
+
+ describe "#features" do
+ it "uses primary adapter by default and caches value" do
+ expect(adapter).to receive(:features).and_call_original
+ expect(subject.features).to_not be_empty
+ end
+
+ it "falls back to cached value if primary adapter raises an error" do
+ subject.features
+ expect(adapter).to receive(:features).and_raise(StandardError)
+ expect(subject.features).to_not be_empty
+ end
+
+ it "raises an error if primary adapter fails and cache is empty" do
+ expect(adapter).to receive(:features).and_raise(StandardError)
+ expect { subject.features }.to raise_error StandardError
+ end
+ end
+
+ describe "#get" do
+ it "uses primary adapter by default and caches value" do
+ expect(adapter).to receive(:get).with(feature_a).and_call_original
+ expect(subject.get(feature_a)).to_not be_nil
+ end
+
+ it "falls back to cached value if primary adapter raises an error" do
+ subject.get(feature_a)
+ expect(adapter).to receive(:get).with(feature_a).and_raise(StandardError)
+ expect(subject.get(feature_a)).to_not be_nil
+ end
+
+ it "raises an error if primary adapter fails and cache is empty" do
+ expect(adapter).to receive(:get).with(feature_a).and_raise(StandardError)
+ expect { subject.get(feature_a) }.to raise_error StandardError
+ end
+ end
+
+ describe "#get_multi" do
+ it "uses primary adapter by default and caches value" do
+ expect(adapter).to receive(:get_multi).with([feature_a, feature_b]).and_call_original
+ expect(subject.get_multi([feature_a, feature_b])).to_not be_empty
+ end
+
+ it "falls back to cached value if primary adapter raises an error" do
+ subject.get_multi([feature_a, feature_b])
+ expect(adapter).to receive(:get_multi).with([feature_a, feature_b]).and_raise(StandardError)
+ expect(subject.get_multi([feature_a, feature_b])).to_not be_empty
+ end
+
+ it "raises an error if primary adapter fails and cache is empty" do
+ expect(adapter).to receive(:get_multi).with([feature_a, feature_b]).and_raise(StandardError)
+ expect { subject.get_multi([feature_a, feature_b]) }.to raise_error StandardError
+ end
+ end
+
+ describe "#get_all" do
+ it "uses primary adapter by default and caches value" do
+ expect(adapter).to receive(:get_all).and_call_original
+ expect(subject.get_all).to_not be_empty
+ end
+
+ it "falls back to cached value if primary adapter raises an error" do
+ subject.get_all
+ expect(adapter).to receive(:get_all).and_raise(StandardError)
+ expect(subject.get_all).to_not be_empty
+ end
+
+ it "raises an error if primary adapter fails and cache is empty" do
+ subject.cache.clear
+ expect(adapter).to receive(:get_all).and_raise(StandardError)
+ expect { subject.get_all }.to raise_error StandardError
+ end
+ end
+end