[Functions] Legacy Event Hubs Checkpoint Fix (#53342)

* [Functions] Legacy Event Hubs Checkpoint Fix

The focus of these changes is to fix an issue where
a legacy ownership record without checkpoint data
was interpreted as a valid checkpoint and used to
initialize a partition when no current generation
checkpoint was present.

* Update sdk/eventhub/Azure.Messaging.EventHubs.Shared/tests/BlobCheckpointStore/BlobsCheckpointStoreInternalTests.cs

Co-authored-by: Copilot <[email protected]>

---------

Co-authored-by: Copilot <[email protected]>

Author: jsquire

sdk/eventhub/Azure.Messaging.EventHubs.Shared/src/BlobCheckpointStore/BlobCheckpointStoreInternal.cs

@@ -603,10 +603,6 @@ private async Task<EventProcessorCheckpoint> CreateLegacyCheckpoint(string fully
                 {
                     startingPosition ??= EventPosition.FromOffset(offset, false);
                 }
-                else if (sequenceNumber.HasValue && sequenceNumber.Value != long.MinValue)
-                {
-                    startingPosition = EventPosition.FromSequenceNumber(sequenceNumber.Value, false);
-                }
                 else
                 {
                     // Skip checkpoints without an offset without logging an error.

sdk/eventhub/Azure.Messaging.EventHubs.Shared/tests/BlobCheckpointStore/BlobsCheckpointStoreInternalTests.cs

@@ -589,13 +589,13 @@ public async Task GetCheckpointUsesOffsetAsTheStartingPositionWhenPresentInLegac
             containerClient.AddBlobClient($"{FullyQualifiedNamespace}/{EventHubName}/{ConsumerGroup}/0", client =>
             {
                 client.Content = Encoding.UTF8.GetBytes("{" +
-                                                            "\"PartitionId\":\"0\"," +
-                                                            "\"Owner\":\"681d365b-de1b-4288-9733-76294e17daf0\"," +
-                                                            "\"Token\":\"2d0c4276-827d-4ca4-a345-729caeca3b82\"," +
-                                                            "\"Epoch\":386," +
-                                                            "\"Offset\":\"13\"," +
-                                                            "\"SequenceNumber\":960180" +
-                                                            "}");
+                                                          "\"PartitionId\":\"0\"," +
+                                                          "\"Owner\":\"681d365b-de1b-4288-9733-76294e17daf0\"," +
+                                                          "\"Token\":\"2d0c4276-827d-4ca4-a345-729caeca3b82\"," +
+                                                          "\"Epoch\":386," +
+                                                          "\"Offset\":\"13\"," +
+                                                          "\"SequenceNumber\":960180" +
+                                                        "}");
             });
 
             var target = new BlobCheckpointStoreInternal(containerClient, initializeWithLegacyCheckpoints: true);
@@ -606,6 +606,44 @@ public async Task GetCheckpointUsesOffsetAsTheStartingPositionWhenPresentInLegac
             Assert.That(checkpoint.PartitionId, Is.EqualTo("0"));
         }
 
+        /// <summary>
+        ///   Verifies basic functionality of GetCheckpointAsync and ensures the starting position is set correctly.
+        /// </summary>
+        ///
+        [Test]
+        [TestCase(null)]
+        [TestCase("")]
+        public async Task GetCheckpointLegacyCheckpointWithoutOffset(string offsetValue)
+        {
+            var blobList = new List<BlobItem>
+            {
+                BlobsModelFactory.BlobItem($"{FullyQualifiedNamespace}/{EventHubName}/{ConsumerGroup}/0",
+                                           false,
+                                           BlobsModelFactory.BlobItemProperties(true, lastModified: DateTime.UtcNow, eTag: new ETag(MatchingEtag)),
+                                           "snapshot")
+            };
+
+            var offsetJsonValue = offsetValue is null ? "null" : $"\"{offsetValue}\"";
+            var containerClient = new MockBlobContainerClient() { Blobs = blobList };
+
+            containerClient.AddBlobClient($"{FullyQualifiedNamespace}/{EventHubName}/{ConsumerGroup}/0", client =>
+            {
+                client.Content = Encoding.UTF8.GetBytes("{" +
+                                                          "\"PartitionId\":\"0\"," +
+                                                          "\"Owner\":\"681d365b-de1b-4288-9733-76294e17daf0\"," +
+                                                          "\"Token\":\"2d0c4276-827d-4ca4-a345-729caeca3b82\"," +
+                                                          "\"Epoch\":386," +
+                                                          $"\"Offset\":{offsetJsonValue}," +
+                                                          "\"SequenceNumber\":960180" +
+                                                        "}");
+            });
+
+            var target = new BlobCheckpointStoreInternal(containerClient, initializeWithLegacyCheckpoints: true);
+            var checkpoint = await target.GetCheckpointAsync(FullyQualifiedNamespace, EventHubName, ConsumerGroup, "0", CancellationToken.None);
+
+            Assert.That(checkpoint, Is.Null, "A checkpoint should have not been returned.");
+        }
+
         /// <summary>
         ///   Verifies basic functionality of GetCheckpointAsync and ensures the appropriate events are emitted on failure.
         /// </summary>

sdk/eventhub/Azure.Messaging.EventHubs.sln

@@ -67,8 +67,6 @@ Global
 	EndGlobalSection
 	GlobalSection(NestedProjects) = preSolution
 		{327A0C67-D9B6-4831-A53F-BFE059934787} = {4C209B69-98C3-4B12-B777-111EFF0E6F66}
-		{AF73A238-61D1-4D1C-807F-57C19F193DC6} = {4C209B69-98C3-4B12-B777-111EFF0E6F66}
-		{5CFD80DB-98F3-4E59-9792-1C421786D3D0} = {4C209B69-98C3-4B12-B777-111EFF0E6F66}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {A9B7844C-B066-4B3D-A0E7-D5008C5EC232}

sdk/eventhub/Microsoft.Azure.WebJobs.Extensions.EventHubs/CHANGELOG.md

@@ -8,6 +8,8 @@
 
 ### Bugs Fixed
 
+- Fixed an issue where a legacy ownership record without checkpoint data was interpreted as a valid checkpoint and used to initialize a partition when no current generation checkpoint was present.
+
 ### Other Changes
 
 ## 6.5.2 (2025-06-16)