feat: Support the flag-overrides capability in the contract test service

pkgs/sdk/server/contract-tests/Representations.cs

@@ -35,6 +35,15 @@ public class SdkConfigParams
         public SdkTagParams Tags { get; set; }
         public SdkHookParams Hooks { get; set; }
         public SdkConfigDataSystemParams DataSystem { get; set; }
+        public SdkConfigOverridesParams Overrides { get; set; }
+    }
+
+    public class SdkConfigOverridesParams
+    {
+        public string[] FilePaths { get; set; }
+        public string DuplicateKeysHandling { get; set; }
+        public string ChangeDetection { get; set; }
+        public long? PollIntervalMs { get; set; }
     }
 
     public class SdkTagParams

pkgs/sdk/server/contract-tests/SdkClientEntity.cs

@@ -11,6 +11,7 @@
 using LaunchDarkly.Sdk.Server.Interfaces;
 using LaunchDarkly.Sdk.Server.Migrations;
 using LaunchDarkly.Sdk.Server.Subsystems;
+using YamlDotNet.Serialization;
 
 namespace TestService
 {
@@ -663,12 +664,61 @@ private static Configuration BuildSdkConfig(SdkConfigParams sdkParams, ILogAdapt
                     dataSystemBuilder.FDv1FallbackSynchronizer(fdv1FallbackBuilder);
                 }
 
+                // The override source is an option of the FDv2 data system.
+                if (sdkParams.Overrides != null)
+                {
+                    dataSystemBuilder.Overrides(BuildOverrideSource(sdkParams.Overrides));
+                }
+
                 builder.DataSystem(dataSystemBuilder);
             }
+            else if (sdkParams.Overrides != null)
+            {
+                throw new ArgumentException("the overrides configuration requires a dataSystem configuration");
+            }
 
             return builder.Build();
         }
 
+        private static FileOverrideSourceBuilder BuildOverrideSource(SdkConfigOverridesParams p)
+        {
+            var yaml = new DeserializerBuilder().WithAttemptingUnquotedStringTypeDeserialization().Build();
+            var source = FileOverrides.Source()
+                .FilePaths(p.FilePaths ?? new string[0])
+                .Parser(s => yaml.Deserialize<object>(s));
+            switch (p.DuplicateKeysHandling)
+            {
+                case null:
+                    break;
+                case "fail":
+                    source.DuplicateKeysHandling(FileOverrideTypes.DuplicateKeysHandling.Fail);
+                    break;
+                case "ignore":
+                    source.DuplicateKeysHandling(FileOverrideTypes.DuplicateKeysHandling.Ignore);
+                    break;
+                default:
+                    throw new ArgumentException("unrecognized duplicateKeysHandling: " + p.DuplicateKeysHandling);
+            }
+            switch (p.ChangeDetection)
+            {
+                case null:
+                    break;
+                case "polling":
+                    source.ChangeDetection(FileOverrideTypes.ChangeDetection.Polling);
+                    break;
+                case "watching":
+                    source.ChangeDetection(FileOverrideTypes.ChangeDetection.Watching);
+                    break;
+                default:
+                    throw new ArgumentException("unrecognized changeDetection: " + p.ChangeDetection);
+            }
+            if (p.PollIntervalMs.HasValue)
+            {
+                source.PollInterval(TimeSpan.FromMilliseconds(p.PollIntervalMs.Value));
+            }
+            return source;
+        }
+
         private static IComponentConfigurer<IDataSource> CreateSynchronizer(
             SdkConfigDataSynchronizerParams synchronizer,
             string payloadFilter)

pkgs/sdk/server/contract-tests/TestService.cs

@@ -12,9 +12,11 @@ public class Program
     {
         public static void Main(string[] args)
         {
+            // An optional first argument selects the port, so that several test services can run at once.
+            var port = args.Length > 0 ? int.Parse(args[0]) : 8000;
             var quitSignal = new EventWaitHandle(false, EventResetMode.AutoReset);
             var app = new Webapp(quitSignal);
-            var server = HttpServer.Start(8000, app.Handler);
+            var server = HttpServer.Start(port, app.Handler);
             server.Recorder.Enabled = false;
             quitSignal.WaitOne();
             server.Dispose();
@@ -49,7 +51,8 @@ public class Webapp
             "fdv1-fallback",
             "instance-id",
             "retry-conformance-fdv1-streaming",
-            "retry-conformance-fdv1-polling"
+            "retry-conformance-fdv1-polling",
+            "flag-overrides"
         };
 
         public readonly Handler Handler;

pkgs/sdk/server/contract-tests/TestService.csproj

@@ -17,6 +17,7 @@
 
   <ItemGroup>
     <PackageReference Include="LaunchDarkly.TestHelpers" Version="2.0.0" />
+    <PackageReference Include="YamlDotNet" Version="12.0.0" />
   </ItemGroup>
 
   <ItemGroup>