From b249b70679dee081ea3723a5cc90766a440c7ccf Mon Sep 17 00:00:00 2001
From: Ryan Lamb <4955475+kinyoklion@users.noreply.github.com>
Date: Fri, 25 Sep 2026 15:49:55 -0700
Subject: [PATCH] feat: Add flag overrides to the contract test service

The test service advertises the flag-overrides capability and accepts the
overrides block of the SDK configuration: filePaths, duplicateKeysHandling,
changeDetection, and pollIntervalMs map to the options of
LaunchDarkly::Integrations::FileData.override_source on the FDv2 data
system builder. Overrides without a data system configuration are an
error. The listen gem joins the contract test bundle so that the watching
change detection mode can run. The service port can be set with the PORT
environment variable and still defaults to 9000.
---
 contract-tests/Gemfile          |  3 +++
 contract-tests/client_entity.rb | 22 ++++++++++++++++++++++
 contract-tests/service.rb       |  3 ++-
 3 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/contract-tests/Gemfile b/contract-tests/Gemfile
index 2cf6ac62..af66f0bc 100644
--- a/contract-tests/Gemfile
+++ b/contract-tests/Gemfile
@@ -8,6 +8,9 @@ gem "puma", "~> 8.0"
 gem "rackup", "~> 2.2"
 gem 'sinatra', '>= 4.1'
 
+# The file-based override source uses the listen gem for its watching change detection mode.
+gem 'listen', '~> 3.3'
+
 gem 'rubocop', '~> 1.37', group: 'development'
 gem 'rubocop-performance', '~> 1.15', group: 'development'
 
diff --git a/contract-tests/client_entity.rb b/contract-tests/client_entity.rb
index 5df1f56a..8fe1ce60 100644
--- a/contract-tests/client_entity.rb
+++ b/contract-tests/client_entity.rb
@@ -56,7 +56,12 @@ def initialize(log, config)
         opts[:payload_filter_key] = data_system_config[:payloadFilter]
       end
 
+      # Flag overrides are an option of the FDv2 data system configuration.
+      data_system.overrides(build_override_source(config[:overrides])) if config[:overrides]
+
       opts[:data_system_config] = data_system.build
+    elsif config[:overrides]
+      raise ArgumentError, "flag overrides require the data system to be configured"
     elsif config[:streaming]
       streaming = config[:streaming]
       opts[:stream_uri] = streaming[:baseUri] unless streaming[:baseUri].nil?
@@ -365,6 +370,23 @@ def close
     builder
   end
 
+  #
+  # Builds the file-based override source from the `overrides` block of the contract test
+  # configuration.
+  #
+  # @param overrides_config [Hash] the overrides configuration
+  # @return [Object] a builder for LaunchDarkly::DataSystem::ConfigBuilder#overrides
+  #
+  private def build_override_source(overrides_config)
+    options = { paths: overrides_config[:filePaths] }
+    if overrides_config[:duplicateKeysHandling]
+      options[:duplicate_keys_handling] = overrides_config[:duplicateKeysHandling].to_sym
+    end
+    options[:change_detection] = overrides_config[:changeDetection].to_sym if overrides_config[:changeDetection]
+    set_optional_time_prop(overrides_config, :pollIntervalMs, options, :poll_interval)
+    LaunchDarkly::Integrations::FileData.override_source(options)
+  end
+
   #
   # Builds a persistent data store from the contract test configuration.
   #
diff --git a/contract-tests/service.rb b/contract-tests/service.rb
index 779ed37d..246220a6 100644
--- a/contract-tests/service.rb
+++ b/contract-tests/service.rb
@@ -17,7 +17,7 @@
 }
 
 set :bind, '0.0.0.0'
-set :port, 9000
+set :port, (ENV['PORT'] || 9000).to_i
 set :logging, false
 
 clients = {}
@@ -55,6 +55,7 @@
       'flag-change-listeners',
       'flag-value-change-listeners',
       'fdv1-fallback',
+      'flag-overrides',
     ],
   }.to_json
 end