fix: Include the last data source error in provider error and stale events

src/LaunchDarkly.OpenFeature.ServerProvider/Provider.cs

@@ -153,10 +153,12 @@ public override Task InitializeAsync(EvaluationContext context, CancellationToke
                 _initCompletion.TrySetResult(true);
             }
 
-            if (_client.DataSourceStatusProvider.Status.State == DataSourceState.Off)
+            var dataSourceStatus = _client.DataSourceStatusProvider.Status;
+            if (dataSourceStatus.State == DataSourceState.Off)
             {
-                _statusProvider.SetStatus(ProviderStatus.Error, ProviderShutdownMessage);
-                _initCompletion.TrySetException(new LaunchDarklyProviderInitException(ProviderShutdownMessage));
+                var message = DescribeLastError(dataSourceStatus, ProviderShutdownMessage);
+                _statusProvider.SetStatus(ProviderStatus.Error, message);
+                _initCompletion.TrySetException(new LaunchDarklyProviderInitException(message));
             }
 
             return _initCompletion.Task;
@@ -210,18 +212,29 @@ private void StatusChangeHandler(object sender, DataSourceStatus status)
                     // The "ProviderStatus.Error" state says it is unable to evaluate flags. We can always evaluate
                     // flags.
                     _statusProvider.SetStatus(ProviderStatus.Stale,
-                        status.LastError?.Message ?? "encountered an unknown error");
+                        DescribeLastError(status, "encountered an unknown error"));
                     break;
                 case DataSourceState.Off:
                 default:
                     // The status is an error, and not fatal, because the LaunchDarkly client can continue to
                     // evaluate flags using the data it already has.
-                    _statusProvider.SetStatus(ProviderStatus.Error, ProviderShutdownMessage);
-                    _initCompletion.TrySetException(new LaunchDarklyProviderInitException(ProviderShutdownMessage));
+                    var message = DescribeLastError(status, ProviderShutdownMessage);
+                    _statusProvider.SetStatus(ProviderStatus.Error, message);
+                    _initCompletion.TrySetException(new LaunchDarklyProviderInitException(message));
                     break;
             }
         }
 
+        private static string DescribeLastError(DataSourceStatus status, string fallback)
+        {
+            if (status.LastError is DataSourceStatus.ErrorInfo lastError)
+            {
+                return lastError.Message ?? lastError.ToString();
+            }
+
+            return fallback;
+        }
+
         /// <inheritdoc />
         public override void Track(string trackingEventName, EvaluationContext evaluationContext = null, TrackingEventDetails trackingEventDetails = default)
         {

test/LaunchDarkly.OpenFeature.ServerProvider.Tests/ProviderTests.cs

@@ -6,6 +6,7 @@
 using LaunchDarkly.Sdk.Server;
 using LaunchDarkly.Sdk.Server.Interfaces;
 using Moq;
+using OpenFeature.Constant;
 using OpenFeature.Model;
 using Xunit;
 using LaunchDarkly.Sdk.Server.Integrations;
@@ -273,6 +274,78 @@ public async Task ItEmitsConfigurationChangedEvents()
             Assert.NotEqual(eventPayloadA?.FlagsChanged[0], eventPayloadB?.FlagsChanged[0]);
         }
 
+        private static async Task<ProviderEventPayload> EmitStatusAndReadEvent(DataSourceStatus status)
+        {
+            var mockClient = new Mock<ILdClient>();
+            mockClient.Setup(l => l.GetLogger())
+                .Returns(Components.NoLogging.Build(null).LogAdapter.Logger(null));
+            mockClient.Setup(l => l.Initialized).Returns(true);
+
+            var mockDataSourceStatus = new Mock<IDataSourceStatusProvider>();
+            mockDataSourceStatus.Setup(l => l.Status).Returns(new DataSourceStatus
+            {
+                State = DataSourceState.Valid
+            });
+            mockClient.Setup(l => l.DataSourceStatusProvider).Returns(mockDataSourceStatus.Object);
+
+            var mockFlagTracker = new Mock<IFlagTracker>();
+            mockClient.Setup(l => l.FlagTracker).Returns(mockFlagTracker.Object);
+
+            var provider = new Provider(mockClient.Object);
+            await provider.InitializeAsync(EvaluationContext.Empty);
+
+            mockDataSourceStatus.Raise(e => e.StatusChanged += null, mockDataSourceStatus.Object, status);
+
+            return await provider.GetEventChannel().Reader.ReadAsync() as ProviderEventPayload;
+        }
+
+        [Fact(Timeout = 5000)]
+        public async Task ItIncludesTheLastErrorMessageInErrorEvents()
+        {
+            var errorEvent = await EmitStatusAndReadEvent(new DataSourceStatus
+            {
+                State = DataSourceState.Off,
+                LastError = DataSourceStatus.ErrorInfo.FromException(new System.Exception("the key was invalid"))
+            });
+            Assert.Equal(ProviderEventTypes.ProviderError, errorEvent?.Type);
+            Assert.Equal("the key was invalid", errorEvent?.Message);
+        }
+
+        [Fact(Timeout = 5000)]
+        public async Task ItDescribesHttpErrorsWithoutAMessageInErrorEvents()
+        {
+            var lastError = DataSourceStatus.ErrorInfo.FromHttpError(401);
+            var errorEvent = await EmitStatusAndReadEvent(new DataSourceStatus
+            {
+                State = DataSourceState.Off,
+                LastError = lastError
+            });
+            Assert.Equal(ProviderEventTypes.ProviderError, errorEvent?.Type);
+            Assert.Equal(lastError.ToString(), errorEvent?.Message);
+            Assert.Contains("401", errorEvent?.Message);
+        }
+
+        [Fact(Timeout = 5000)]
+        public async Task ItUsesADefaultMessageInErrorEventsWithoutALastError()
+        {
+            var errorEvent = await EmitStatusAndReadEvent(new DataSourceStatus { State = DataSourceState.Off });
+            Assert.Equal(ProviderEventTypes.ProviderError, errorEvent?.Type);
+            Assert.Equal("the provider has encountered a permanent error or been shutdown", errorEvent?.Message);
+        }
+
+        [Fact(Timeout = 5000)]
+        public async Task ItDescribesHttpErrorsWithoutAMessageInStaleEvents()
+        {
+            var lastError = DataSourceStatus.ErrorInfo.FromHttpError(503);
+            var staleEvent = await EmitStatusAndReadEvent(new DataSourceStatus
+            {
+                State = DataSourceState.Interrupted,
+                LastError = lastError
+            });
+            Assert.Equal(ProviderEventTypes.ProviderStale, staleEvent?.Type);
+            Assert.Equal(lastError.ToString(), staleEvent?.Message);
+        }
+
         [Fact(Timeout = 5000)]
         public void ItTracksCustomEvents()
         {