feat: Add MetaProvider gem and basic implementation (#17)

Signed-off-by: Max VelDink <mveldink@justworks.com>
Signed-off-by: Alexandre Chakroun <alexandre.chakroun@doctolib.com>
Co-authored-by: Alexandre Chakroun <11556013+alxckn@users.noreply.github.com>

.github/workflows/ruby.yml

@@ -24,9 +24,12 @@ jobs:
         working-directory: ./providers/openfeature-flagd-provider
     strategy:
       matrix:
-        ruby-version: ['3.1']
+        ruby-version:
+          - "3.3"
+          - "3.2"
+          - "3.1"
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Set up Ruby
       uses: ruby/setup-ruby@v1
       with:
@@ -38,3 +41,24 @@ jobs:
       working-directory: ./providers/openfeature-flagd-provider/docker
     - name: Run tests
       run: bundle exec rspec
+  test_meta_provider:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: ./providers/openfeature-sdk-meta_provider
+    strategy:
+      matrix:
+        ruby-version:
+          - "3.3"
+          - "3.2"
+          - "3.1"
+    steps:
+    - uses: actions/checkout@v4
+    - name: Set up Ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby-version }}
+        bundler-cache: true # runs 'bundle install' and caches installed gems automatically
+        working-directory: ./providers/openfeature-sdk-meta_provider
+    - name: Lint and test
+      run: bin/rake

providers/openfeature-sdk-meta_provider/.gitignore

@@ -0,0 +1,12 @@
+/.bundle/
+/.yardoc
+/_yardoc/
+/coverage/
+/doc/
+/pkg/
+/spec/reports/
+/tmp/
+
+# rspec failure tracking
+.rspec_status
+spec/examples.txt

providers/openfeature-sdk-meta_provider/.rspec

@@ -0,0 +1,4 @@
+-I lib
+--format documentation
+--color
+--require spec_helper

providers/openfeature-sdk-meta_provider/.ruby-version

@@ -0,0 +1 @@
+3.3.0

providers/openfeature-sdk-meta_provider/.standard.yml

@@ -0,0 +1,3 @@
+parallel: true
+format: progress
+ruby_version: 3.1

providers/openfeature-sdk-meta_provider/.tool-versions

@@ -0,0 +1 @@
+ruby 3.3.0

providers/openfeature-sdk-meta_provider/Gemfile

@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+source "https://rubygems.org"
+
+# Specify your gem's dependencies in openfeature-sdk-meta_provider.gemspec
+gemspec

providers/openfeature-sdk-meta_provider/Gemfile.lock

@@ -0,0 +1,95 @@
+PATH
+  remote: .
+  specs:
+    openfeature-sdk-meta_provider (0.1.0)
+      openfeature-sdk (~> 0.3.0)
+
+GEM
+  remote: https://rubygems.org/
+  specs:
+    ast (2.4.2)
+    debug (1.9.2)
+      irb (~> 1.10)
+      reline (>= 0.3.8)
+    diff-lcs (1.5.1)
+    io-console (0.7.2)
+    irb (1.12.0)
+      rdoc
+      reline (>= 0.4.2)
+    json (2.7.2)
+    language_server-protocol (3.17.0.3)
+    lint_roller (1.1.0)
+    openfeature-sdk (0.3.0)
+    parallel (1.24.0)
+    parser (3.3.0.5)
+      ast (~> 2.4.1)
+      racc
+    psych (5.1.2)
+      stringio
+    racc (1.7.3)
+    rainbow (3.1.1)
+    rake (13.2.1)
+    rdoc (6.6.3.1)
+      psych (>= 4.0.0)
+    regexp_parser (2.9.0)
+    reline (0.5.0)
+      io-console (~> 0.5)
+    rexml (3.2.6)
+    rspec (3.13.0)
+      rspec-core (~> 3.13.0)
+      rspec-expectations (~> 3.13.0)
+      rspec-mocks (~> 3.13.0)
+    rspec-core (3.13.0)
+      rspec-support (~> 3.13.0)
+    rspec-expectations (3.13.0)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.13.0)
+    rspec-mocks (3.13.0)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.13.0)
+    rspec-support (3.13.1)
+    rubocop (1.62.1)
+      json (~> 2.3)
+      language_server-protocol (>= 3.17.0)
+      parallel (~> 1.10)
+      parser (>= 3.3.0.2)
+      rainbow (>= 2.2.2, < 4.0)
+      regexp_parser (>= 1.8, < 3.0)
+      rexml (>= 3.2.5, < 4.0)
+      rubocop-ast (>= 1.31.1, < 2.0)
+      ruby-progressbar (~> 1.7)
+      unicode-display_width (>= 2.4.0, < 3.0)
+    rubocop-ast (1.31.2)
+      parser (>= 3.3.0.4)
+    rubocop-performance (1.20.2)
+      rubocop (>= 1.48.1, < 2.0)
+      rubocop-ast (>= 1.30.0, < 2.0)
+    ruby-progressbar (1.13.0)
+    standard (1.35.1)
+      language_server-protocol (~> 3.17.0.2)
+      lint_roller (~> 1.0)
+      rubocop (~> 1.62.0)
+      standard-custom (~> 1.0.0)
+      standard-performance (~> 1.3)
+    standard-custom (1.0.2)
+      lint_roller (~> 1.0)
+      rubocop (~> 1.50)
+    standard-performance (1.3.1)
+      lint_roller (~> 1.1)
+      rubocop-performance (~> 1.20.2)
+    stringio (3.1.0)
+    unicode-display_width (2.5.0)
+
+PLATFORMS
+  arm64-darwin-23
+  ruby
+
+DEPENDENCIES
+  debug (~> 1.9.2)
+  openfeature-sdk-meta_provider!
+  rake (~> 13.0)
+  rspec (~> 3.12)
+  standard (~> 1.34)
+
+BUNDLED WITH
+   2.5.6

providers/openfeature-sdk-meta_provider/README.md

@@ -0,0 +1,38 @@
+# OpenFeature::SDK::Provider::MetaProvider for Ruby
+
+The `OpenFeature::SDK::Provider::MetaProvider` is a utility provider implementation that takes multiple [providers](https://docs.openfeature.dev/docs/specification/sections/providers) for use during flag resolution. This can be helpful when an organization is migrating or consolidating feature flag providers as they transition to OpenFeature. There are usually a combination of internal and vendor providers that are combined together to handle flag resolution. If your organization has different providers for different teams, consider looking at using [domains](https://openfeature.dev/specification/glossary#domain).
+
+## Installation
+
+Coming soon!
+
+## Usage
+
+The `MetaProvider` is initialized with a collection of `Provider`s and a strategy for fetching flags from them.
+
+```ruby
+# Create a MetaProvider
+meta_provider = OpenFeature::SDK::Provider::MetaProvider.new(
+  providers: [
+    OpenFeature::SDK::ProviderInMemoryProvider.new,
+    MyCustomProvider.new
+  ],
+  strategy: :first_match
+)
+
+# Use it as the default provider
+OpenFeature.configure do |c|
+  c.set_provider(meta_provider)
+end
+```
+
+### Strategies
+
+#### :first_match
+
+When `:first_match` is given as the strategy, each provider will be evaluated, in the order they were passed in, for the requested `flag_key`. The first provider where the `flag_key` is found will be returned, short-circuiting flag evaluation with the remaining providers. In the case of a provider error, or no matching flags, returns the default value.
+
+
+## Contributing
+
+https://github.com/open-feature/ruby-sdk-contrib

providers/openfeature-sdk-meta_provider/Rakefile

@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+require "bundler/gem_tasks"
+require "rspec/core/rake_task"
+
+RSpec::Core::RakeTask.new(:spec)
+
+require "standard/rake"
+
+task default: %i[standard spec]

providers/openfeature-sdk-meta_provider/bin/console

@@ -0,0 +1,15 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+require "bundler/setup"
+require "open_feature/sdk/provider/meta_provider"
+
+# You can add fixtures and/or initialization code here to make experimenting
+# with your gem easier. You can also use a different console, if you like.
+
+# (If you use this, don't forget to add pry to your Gemfile!)
+# require "pry"
+# Pry.start
+
+require "irb"
+IRB.start(__FILE__)

providers/openfeature-sdk-meta_provider/bin/rake

@@ -0,0 +1,27 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+#
+# This file was generated by Bundler.
+#
+# The application 'rake' is installed as part of a gem, and
+# this file is here to facilitate running it.
+#
+
+ENV["BUNDLE_GEMFILE"] ||= File.expand_path("../Gemfile", __dir__)
+
+bundle_binstub = File.expand_path("bundle", __dir__)
+
+if File.file?(bundle_binstub)
+  if File.read(bundle_binstub, 300).include?("This file was generated by Bundler")
+    load(bundle_binstub)
+  else
+    abort("Your `bin/bundle` was not generated by Bundler, so this binstub cannot run.
+Replace `bin/bundle` by running `bundle binstubs bundler --force`, then run this command again.")
+  end
+end
+
+require "rubygems"
+require "bundler/setup"
+
+load Gem.bin_path("rake", "rake")

providers/openfeature-sdk-meta_provider/bin/setup

@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+set -euo pipefail
+IFS=$'\n\t'
+set -vx
+
+bundle install
+
+# Do any other automated setup that you need to do here

providers/openfeature-sdk-meta_provider/lib/open_feature/sdk/provider/meta_provider.rb

@@ -0,0 +1,79 @@
+# frozen_string_literal: true
+
+module OpenFeature
+  module SDK
+    module Provider
+      # Used to pull from multiple providers.
+      class MetaProvider
+        # @param providers [Array<Provider>]
+        # @param strategy [Symbol] When `:first_match`, returns first matched resolution. Providers will be searched
+        #                          in the order they were given. Defaults to `:first_match`.
+        def initialize(providers:, strategy: :first_match)
+          @providers = providers
+          @strategy = strategy
+        end
+
+        def metadata
+          ProviderMetadata.new(name: "MetaProvider: #{providers.map { |provider| provider.metadata.name }.join(", ")}")
+        end
+
+        def init
+          providers.each { |provider| provider.init }
+        end
+
+        def shutdown
+          providers.each(&:shutdown)
+        end
+
+        def fetch_boolean_value(flag_key:, default_value:, evaluation_context: nil)
+          fetch_from_sources(default_value:) do |provider|
+            provider.fetch_boolean_value(flag_key:, default_value:, evaluation_context:)
+          end
+        end
+
+        def fetch_number_value(flag_key:, default_value:, evaluation_context: nil)
+          fetch_from_sources(default_value:) do |provider|
+            provider.fetch_number_value(flag_key:, default_value:, evaluation_context:)
+          end
+        end
+
+        def fetch_object_value(flag_key:, default_value:, evaluation_context: nil)
+          fetch_from_sources(default_value:) do |provider|
+            provider.fetch_object_value(flag_key:, default_value:, evaluation_context:)
+          end
+        end
+
+        def fetch_string_value(flag_key:, default_value:, evaluation_context: nil)
+          fetch_from_sources(default_value:) do |provider|
+            provider.fetch_string_value(flag_key:, default_value:, evaluation_context:)
+          end
+        end
+
+        private
+
+        attr_reader :providers, :strategy
+
+        def fetch_from_sources(default_value:, &blk)
+          case strategy
+          when :first_match
+            successful_details = providers.each do |provider|
+              details = yield(provider)
+
+              break details if details.error_code.nil?
+            rescue
+              next
+            end
+
+            if successful_details.is_a?(ResolutionDetails)
+              successful_details
+            else
+              ResolutionDetails.new(value: default_value, error_code: ErrorCode::GENERAL, reason: Reason::ERROR)
+            end
+          else
+            ResolutionDetails.new(value: default_value, error_code: ErrorCode::GENERAL, reason: "Unknown strategy for MetaProvider")
+          end
+        end
+      end
+    end
+  end
+end

providers/openfeature-sdk-meta_provider/openfeature-sdk-meta_provider.gemspec

@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+Gem::Specification.new do |spec|
+  spec.name = "openfeature-sdk-meta_provider"
+  spec.version = "0.1.0"
+  spec.authors = ["OpenFeature Authors"]
+  spec.email = ["cncf-openfeature-contributors@lists.cncf.io"]
+
+  spec.summary = "Meta provider for the OpenFeature Ruby SDK"
+  spec.description = "The MetaProvider wraps multiple other providers and uses a given strategy to resolve flags using all of them."
+  spec.homepage = "https://github.com/open-feature/ruby-sdk-contrib/providers/openfeature-sdk-meta_provider"
+  spec.license = "Apache-2.0"
+  spec.required_ruby_version = ">= 3.1"
+
+  spec.metadata["homepage_uri"] = spec.homepage
+  spec.metadata["source_code_uri"] = "https://github.com/open-feature/ruby-sdk-contrib/providers/openfeature-sdk-meta_provider"
+  spec.metadata["changelog_uri"] = "https://github.com/open-feature/ruby-sdk-contrib/blob/main/CHANGELOG.md"
+  spec.metadata["bug_tracker_uri"] = "https://github.com/open-feature/ruby-sdk-contrib/issues"
+  spec.metadata["documentation_uri"] = "https://github.com/open-feature/ruby-sdk-contrib/README.md"
+
+  # Specify which files should be added to the gem when it is released.
+  # The `git ls-files -z` loads the files in the RubyGem that have been added into git.
+  spec.files = Dir.chdir(File.expand_path(__dir__)) do
+    `git ls-files -z`.split("\x0").reject { |f| f.match(%r{^(test|spec|features)/}) }
+  end
+  spec.bindir = "exe"
+  spec.executables = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
+  spec.require_paths = ["lib"]
+
+  spec.add_dependency "openfeature-sdk", "~> 0.3.0"
+
+  spec.add_development_dependency "rake", "~> 13.0"
+  spec.add_development_dependency "rspec", "~> 3.12"
+  spec.add_development_dependency "standard", "~> 1.34"
+  spec.add_development_dependency "debug", "~> 1.9.2"
+end