feat(go-feature-flag): Support exporter metadata (#45)

## This PR
In this PR we support `exporterMetadata` that will allow to add static
information that will be added to your feature event sent to the GO
Feature Flag exporter.

In this PR we add those exporter metadata to the evaluation context in
order to pass them to GO Feature Flag relay-proxy.


### Related Issues
thomaspoignant/go-feature-flag#2983

---------

Signed-off-by: Thomas Poignant <[email protected]>

Author: thomaspoignant

providers/openfeature-go-feature-flag-provider/lib/openfeature/go-feature-flag/go_feature_flag_provider.rb

@@ -35,6 +35,10 @@ def evaluate(flag_key:, default_value:, allowed_classes:, evaluation_context: ni
         evaluation_context = OpenFeature::SDK::EvaluationContext.new if evaluation_context.nil?
         validate_parameters(flag_key, evaluation_context)
 
+        # enrich the evaluation context with the exporter_metadata
+        @options.exporter_metadata.merge!("openfeature" => true, "provider" => "ruby")
+        evaluation_context.fields["gofeatureflag"] = {"exporterMetadata" => @options.exporter_metadata}
+
         # do a http call to the go feature flag server
         parsed_response = @goff_api.evaluate_ofrep_api(flag_key: flag_key, evaluation_context: evaluation_context)
         parsed_response = OfrepApiResponse unless parsed_response.is_a?(OfrepApiResponse)

providers/openfeature-go-feature-flag-provider/lib/openfeature/go-feature-flag/options.rb

@@ -6,12 +6,13 @@ module OpenFeature
   module GoFeatureFlag
     # This class is the configuration class for the GoFeatureFlagProvider
     class Options
-      attr_accessor :endpoint, :custom_headers
+      attr_accessor :endpoint, :custom_headers, :exporter_metadata
 
-      def initialize(endpoint: nil, headers: {})
+      def initialize(endpoint: nil, headers: {}, exporter_metadata: {})
         validate_endpoint(endpoint: endpoint)
         @endpoint = endpoint
         @custom_headers = headers
+        @exporter_metadata = exporter_metadata
       end
 
       private

providers/openfeature-go-feature-flag-provider/spec/openfeature/gofeatureflag/provider_spec.rb

@@ -684,4 +684,41 @@
       expect(eval).to eql(want)
     end
   end
+
+  context "#exporter_metadata" do
+    it "should send exporter_metadata in the API if set in provider" do
+      test_name = RSpec.current_example.description
+      request_body = nil
+      stub_request(:post, "http://localhost:1031/ofrep/v1/evaluate/flags/boolean_flag")
+        .with { |req| request_body = req.body }
+        .to_return(status: 200, body:
+          {
+            key: "double_key",
+            metadata: {"website" => "https://gofeatureflag.org"},
+            value: true,
+            reason: "TARGETING_MATCH",
+            variant: "variantA"
+          }.to_json)
+
+      options = OpenFeature::GoFeatureFlag::Options.new(endpoint: "http://localhost:1031", exporter_metadata: {
+        "key1" => "value1",
+        "key2" => 123,
+        "key3" => 123.45
+      })
+      goff_test_provider = OpenFeature::GoFeatureFlag::Provider.new(options: options)
+
+      OpenFeature::SDK.configure do |config|
+        config.set_provider(goff_test_provider, domain: test_name)
+      end
+      client = OpenFeature::SDK.build_client(domain: test_name)
+      client.fetch_boolean_details(
+        flag_key: "boolean_flag",
+        default_value: false,
+        evaluation_context: OpenFeature::SDK::EvaluationContext.new(targeting_key: "9b9450f8-ab5c-4dcf-872f-feda3f6ccb16")
+      )
+      got = JSON.parse(request_body)
+      want = JSON.parse('{"context":{"gofeatureflag":{"exporterMetadata":{"key1":"value1","openfeature":true,"provider":"ruby", "key2": 123, "key3":123.45}},"targetingKey":"9b9450f8-ab5c-4dcf-872f-feda3f6ccb16"}}')
+      expect(got).to eql(want)
+    end
+  end
 end