Fix race condition with less than 1 seconds left (#84)

* Special case

* return

* test

* readme

changelog.md

@@ -4,6 +4,12 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 
 ## Unreleased
 
+## <a name="1.6.2"/> 1.6.2 - 2024-08-30
+
+### Fixed
+
+- [#84](https://github.com/Azure/Microsoft.Extensions.Caching.Cosmos/pull/84) Fix race condition with less than 1 seconds left on sliding expiration
+
 ## <a name="1.6.1"/> 1.6.1 - 2024-03-27
 
 ### Fixed

src/CosmosCache.cs

@@ -129,6 +129,13 @@ namespace Microsoft.Extensions.Caching.Cosmos
                         else
                         {
                             double pendingSeconds = (absoluteExpiration - DateTimeOffset.UtcNow).TotalSeconds;
+                            if (pendingSeconds == 0)
+                            {
+                                // Cosmos DB TTL works on seconds granularity and this item has less than a second to live.
+                                // Return the content because it does exist, but it will be cleaned up by the TTL shortly after.
+                                return cosmosCacheSessionResponse.Resource.Content;
+                            }
+
                             if (pendingSeconds < ttl)
                             {
                                 cosmosCacheSessionResponse.Resource.TimeToLive = (long)pendingSeconds;
@@ -224,6 +231,13 @@ namespace Microsoft.Extensions.Caching.Cosmos
                         else
                         {
                             double pendingSeconds = (absoluteExpiration - DateTimeOffset.UtcNow).TotalSeconds;
+                            if (pendingSeconds == 0)
+                            {
+                                // Cosmos DB TTL works on seconds granularity and this item has less than a second to live.
+                                // Treat it as a cache-miss.
+                                return;
+                            }
+
                             if (pendingSeconds < ttl)
                             {
                                 cosmosCacheSessionResponse.Resource.TimeToLive = (long)pendingSeconds;

src/CosmosDistributedCache.csproj

@@ -6,7 +6,7 @@
     <Copyright>© Microsoft Corporation. All rights reserved.</Copyright>
     <CurrentDate>$([System.DateTime]::Now.ToString(yyyyMMdd))</CurrentDate>
     <NeutralLanguage>en-US</NeutralLanguage>
-    <ClientVersion>1.6.1</ClientVersion>
+    <ClientVersion>1.6.2</ClientVersion>
     <VersionSuffix Condition=" '$(IsPreview)' == 'true' ">preview</VersionSuffix>
     <Version Condition=" '$(VersionSuffix)' == '' ">$(ClientVersion)</Version>
     <Version Condition=" '$(VersionSuffix)' != '' ">$(ClientVersion)-$(VersionSuffix)</Version>

tests/unit/CosmosCacheTests.cs

@@ -715,6 +715,46 @@ namespace Microsoft.Extensions.Caching.Cosmos.Tests
             mockedContainer.Verify(c => c.ReplaceItemAsync<CosmosCacheSession>(It.Is<CosmosCacheSession>(item => item.TimeToLive == ttlSliding), It.Is<string>(id => id == "key"), It.IsAny<PartitionKey?>(), It.IsAny<ItemRequestOptions>(), It.IsAny<CancellationToken>()), Times.Once);
         }
 
+        [Fact]
+        public async Task SlidingExpirationWithAbsoluteExpirationOnAlmostExpiredRead()
+        {
+            const int ttlSliding = 20;
+            const int ttlAbsolute = 500;
+            string etag = "etag";
+            CosmosCacheSession existingSession = new CosmosCacheSession();
+            existingSession.SessionKey = "key";
+            existingSession.Content = new byte[0];
+            existingSession.IsSlidingExpiration = true;
+            existingSession.TimeToLive = ttlSliding;
+            existingSession.AbsoluteSlidingExpiration = DateTimeOffset.UtcNow.AddMilliseconds(ttlAbsolute).ToUnixTimeSeconds();
+            Mock<ItemResponse<CosmosCacheSession>> mockedItemResponse = new Mock<ItemResponse<CosmosCacheSession>>();
+            Mock<CosmosClient> mockedClient = new Mock<CosmosClient>();
+            Mock<Container> mockedContainer = new Mock<Container>();
+            Mock<Database> mockedDatabase = new Mock<Database>();
+            Mock<ContainerResponse> mockedResponse = new Mock<ContainerResponse>();
+            mockedItemResponse.Setup(c => c.Resource).Returns(existingSession);
+            mockedItemResponse.Setup(c => c.ETag).Returns(etag);
+            mockedResponse.Setup(c => c.StatusCode).Returns(HttpStatusCode.OK);
+            mockedContainer.Setup(c => c.ReadContainerAsync(It.IsAny<ContainerRequestOptions>(), It.IsAny<CancellationToken>())).ReturnsAsync(mockedResponse.Object);
+            mockedContainer.Setup(c => c.ReadItemAsync<CosmosCacheSession>(It.Is<string>(id => id == "key"), It.IsAny<PartitionKey>(), It.IsAny<ItemRequestOptions>(), It.IsAny<CancellationToken>())).ReturnsAsync(mockedItemResponse.Object);
+            mockedClient.Setup(c => c.GetContainer(It.IsAny<string>(), It.IsAny<string>())).Returns(mockedContainer.Object);
+            mockedClient.Setup(c => c.GetDatabase(It.IsAny<string>())).Returns(mockedDatabase.Object);
+            mockedClient.Setup(x => x.Endpoint).Returns(new Uri("http://localhost"));
+            CosmosCache cache = new CosmosCache(Options.Create(new CosmosCacheOptions()
+            {
+                DatabaseName = "something",
+                ContainerName = "something",
+                CreateIfNotExists = true,
+                CosmosClient = mockedClient.Object
+            }));
+
+            Assert.NotNull(await cache.GetAsync("key"));
+            // Checks for Db existence due to CreateIfNotExists
+            mockedClient.Verify(c => c.CreateDatabaseIfNotExistsAsync(It.IsAny<string>(), It.IsAny<int?>(), It.IsAny<RequestOptions>(), It.IsAny<CancellationToken>()), Times.Once);
+            mockedContainer.Verify(c => c.ReadItemAsync<CosmosCacheSession>(It.Is<string>(id => id == "key"), It.IsAny<PartitionKey>(), It.IsAny<ItemRequestOptions>(), It.IsAny<CancellationToken>()), Times.Once);
+            mockedContainer.Verify(c => c.ReplaceItemAsync<CosmosCacheSession>(It.Is<CosmosCacheSession>(item => item.TimeToLive == ttlSliding), It.Is<string>(id => id == "key"), It.IsAny<PartitionKey?>(), It.IsAny<ItemRequestOptions>(), It.IsAny<CancellationToken>()), Times.Never);
+        }
+
         private class DiagnosticsSink 
         {
             private List<CosmosDiagnostics> capturedDiagnostics = new List<CosmosDiagnostics>();