From 6dbac720e6d1c061f5808a003e2f36efc1b60e16 Mon Sep 17 00:00:00 2001
From: Sean McCullough <44180881+seanmcc-msft@users.noreply.github.com>
Date: Thu, 8 Jul 2021 15:33:15 -0500
Subject: [PATCH] Fixed bug where 'Segment doesn't have any more events
 exception' was throw when attempting to resume from a cusor pointed at a
 segment that had no more events, and newer segments exist in the Change Feed.
 (#22546)

---
 .../CHANGELOG.md                              |  4 +-
 .../src/Segment.cs                            |  2 +-
 .../tests/SegmentTests.cs                     | 88 +++++++++++++++++++
 3 files changed, 90 insertions(+), 4 deletions(-)

diff --git a/sdk/storage/Azure.Storage.Blobs.ChangeFeed/CHANGELOG.md b/sdk/storage/Azure.Storage.Blobs.ChangeFeed/CHANGELOG.md
index 36161c06b9554..54bfccb91be29 100644
--- a/sdk/storage/Azure.Storage.Blobs.ChangeFeed/CHANGELOG.md
+++ b/sdk/storage/Azure.Storage.Blobs.ChangeFeed/CHANGELOG.md
@@ -1,11 +1,9 @@
 # Release History
 
 ## 12.0.0-preview.14 (Unreleased)
-
 - TenantId can now be discovered through the service challenge response, when using a TokenCredential for authorization.
     - A new property is now available on the ClientOptions called `EnableTenantDiscovery`. If set to true, the client will attempt an initial unauthorized request to the service to prompt a challenge containing the tenantId hint.
-
-- This release contains bug fixes to improve quality.
+- Fixed bug where "Segment doesn't have any more events" exception was throw when attempting to resume from a cusor pointed at a segment that had no more events, and newer segments exist in the Change Feed.
 
 ## 12.0.0-preview.13 (2021-06-08)
 - This release contains bug fixes to improve quality.
diff --git a/sdk/storage/Azure.Storage.Blobs.ChangeFeed/src/Segment.cs b/sdk/storage/Azure.Storage.Blobs.ChangeFeed/src/Segment.cs
index 05be18cbc845d..272e632e42035 100644
--- a/sdk/storage/Azure.Storage.Blobs.ChangeFeed/src/Segment.cs
+++ b/sdk/storage/Azure.Storage.Blobs.ChangeFeed/src/Segment.cs
@@ -75,7 +75,7 @@ public virtual async Task<List<BlobChangeFeedEvent>> GetPage(
 
             if (!HasNext())
             {
-                throw new InvalidOperationException("Segment doesn't have any more events");
+                return new List<BlobChangeFeedEvent>(capacity: 0);
             }
 
             int i = 0;
diff --git a/sdk/storage/Azure.Storage.Blobs.ChangeFeed/tests/SegmentTests.cs b/sdk/storage/Azure.Storage.Blobs.ChangeFeed/tests/SegmentTests.cs
index 29e567a627723..602e29dd3495c 100644
--- a/sdk/storage/Azure.Storage.Blobs.ChangeFeed/tests/SegmentTests.cs
+++ b/sdk/storage/Azure.Storage.Blobs.ChangeFeed/tests/SegmentTests.cs
@@ -272,5 +272,93 @@ public async Task GetPage()
             shards[1].Verify(r => r.Next(IsAsync, default));
             shards[1].Verify(r => r.HasNext());
         }
+
+        [RecordedTest]
+        public async Task GetPage_NoMoreEvents()
+        {
+            // Arrange
+            string manifestPath = "idx/segments/2020/03/25/0200/meta.json";
+            int shardCount = 3;
+
+            Mock<BlobContainerClient> containerClient = new Mock<BlobContainerClient>(MockBehavior.Strict);
+            Mock<BlobClient> blobClient = new Mock<BlobClient>(MockBehavior.Strict);
+            Mock<ShardFactory> shardFactory = new Mock<ShardFactory>(MockBehavior.Strict);
+
+            List<Mock<Shard>> shards = new List<Mock<Shard>>();
+
+            for (int i = 0; i < shardCount; i++)
+            {
+                shards.Add(new Mock<Shard>(MockBehavior.Strict));
+            }
+
+            containerClient.Setup(r => r.GetBlobClient(It.IsAny<string>())).Returns(blobClient.Object);
+
+            using FileStream stream = File.OpenRead(
+                $"{Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location)}{Path.DirectorySeparatorChar}Resources{Path.DirectorySeparatorChar}{"SegmentManifest.json"}");
+            BlobDownloadStreamingResult blobDownloadStreamingResult = BlobsModelFactory.BlobDownloadStreamingResult(content: stream);
+            Response<BlobDownloadStreamingResult> downloadResponse = Response.FromValue(blobDownloadStreamingResult, new MockResponse(200));
+
+            if (IsAsync)
+            {
+                blobClient.Setup(r => r.DownloadStreamingAsync(default, default, default, default)).ReturnsAsync(downloadResponse);
+            }
+            else
+            {
+                blobClient.Setup(r => r.DownloadStreaming(default, default, default, default)).Returns(downloadResponse);
+            }
+
+            shardFactory.SetupSequence(r => r.BuildShard(
+                It.IsAny<bool>(),
+                It.IsAny<string>(),
+                It.IsAny<ShardCursor>()))
+                .ReturnsAsync(shards[0].Object)
+                .ReturnsAsync(shards[1].Object)
+                .ReturnsAsync(shards[2].Object);
+
+            // Set up Shards
+            shards[0].SetupSequence(r => r.HasNext())
+                .Returns(false);
+
+            shards[1].SetupSequence(r => r.HasNext())
+                .Returns(false);
+
+            shards[2].SetupSequence(r => r.HasNext())
+                .Returns(false);
+
+            SegmentFactory segmentFactory = new SegmentFactory(
+                containerClient.Object,
+                shardFactory.Object);
+            Segment segment = await segmentFactory.BuildSegment(
+                IsAsync,
+                manifestPath);
+
+            // Act
+            List<BlobChangeFeedEvent> events = await segment.GetPage(IsAsync, 25);
+
+            // Assert
+            Assert.AreEqual(0, events.Count);
+
+            containerClient.Verify(r => r.GetBlobClient(manifestPath));
+            if (IsAsync)
+            {
+                blobClient.Verify(r => r.DownloadStreamingAsync(default, default, default, default));
+            }
+            else
+            {
+                blobClient.Verify(r => r.DownloadStreaming(default, default, default, default));
+            }
+
+            for (int i = 0; i < shards.Count; i++)
+            {
+                shardFactory.Verify(r => r.BuildShard(
+                    IsAsync,
+                    $"log/0{i}/2020/03/25/0200/",
+                    default));
+            }
+
+            shards[0].Verify(r => r.HasNext());
+            shards[1].Verify(r => r.HasNext());
+            shards[2].Verify(r => r.HasNext());
+        }
     }
 }