[POC] Expose SnapshotTime

src/MongoDB.Driver/ClientSessionHandle.cs

@@ -89,6 +89,8 @@ public IServerSession ServerSession
  }
  }
 
+ public BsonTimestamp SnapshotTime => _coreSession.SnapshotTime;
+
  /// <inheritdoc />
  public ICoreSessionHandle WrappedCoreSession => _coreSession;
 

src/MongoDB.Driver/ClientSessionOptions.cs

@@ -14,6 +14,7 @@
 */
 
 using System;
+using MongoDB.Bson;
 using MongoDB.Driver.Core.Bindings;
 
 namespace MongoDB.Driver
@@ -46,6 +47,12 @@ public class ClientSessionOptions
  /// </value>
  public bool Snapshot { get; set;}
 
+ /// <summary>
+ /// Gets or sets the snapshot time. If set, Snapshot must be true.
+ /// <value> The snapshot time </value>
+ /// </summary>
+ public BsonTimestamp SnapshotTime { get; set; }
+
  // internal methods
  internal CoreSessionOptions ToCore(bool isImplicit = false)
  {
@@ -55,7 +62,8 @@ internal CoreSessionOptions ToCore(bool isImplicit = false)
  isCausallyConsistent: isCausallyConsistent,
  isImplicit: isImplicit,
  isSnapshot: Snapshot,
- defaultTransactionOptions: DefaultTransactionOptions);
+ defaultTransactionOptions: DefaultTransactionOptions,
+ snapshotTime: SnapshotTime);
  }
  }
 }

src/MongoDB.Driver/Core/Bindings/CoreSession.cs

@@ -71,6 +71,7 @@ private CoreSession(
  {
  _cluster = Ensure.IsNotNull(cluster, nameof(cluster));
  _options = Ensure.IsNotNull(options, nameof(options));
+ _snapshotTime = options.SnapshotTime;
  }
 
  // public properties

src/MongoDB.Driver/Core/Bindings/CoreSessionOptions.cs

@@ -13,6 +13,8 @@
 * limitations under the License.
 */
 
+using MongoDB.Bson;
+
 namespace MongoDB.Driver.Core.Bindings
 {
  /// <summary>
@@ -25,6 +27,7 @@ public class CoreSessionOptions
  private readonly bool _isCausallyConsistent;
  private readonly bool _isImplicit;
  private readonly bool _isSnapshot;
+ private readonly BsonTimestamp _snapshotTime;
 
  // constructors
  /// <summary>
@@ -34,16 +37,35 @@ public class CoreSessionOptions
  /// <param name="isImplicit">if set to <c>true</c> this session is an implicit session.</param>
  /// <param name="isSnapshot">if set to <c>true</c> this session is a snapshot session.</param>
  /// <param name="defaultTransactionOptions">The default transaction options.</param>
+ /// <param name="snapshotTime">The snapshot time. If this is set, isSnapshot must be true.</param>
  public CoreSessionOptions(
  bool isCausallyConsistent = false,
  bool isImplicit = false,
  TransactionOptions defaultTransactionOptions = null,
- bool isSnapshot = false)
+ bool isSnapshot = false,
+ BsonTimestamp snapshotTime = null)
  {
  _isCausallyConsistent = isCausallyConsistent;
  _isImplicit = isImplicit;
  _isSnapshot = isSnapshot;
  _defaultTransactionOptions = defaultTransactionOptions;
+ _snapshotTime = snapshotTime;
+ }
+
+ /// <summary>
+ /// Initializes a new instance of the <see cref="CoreSessionOptions" /> class.
+ /// </summary>
+ /// <param name="isCausallyConsistent">if set to <c>true</c> this session is causally consistent]</param>
+ /// <param name="isImplicit">if set to <c>true</c> this session is an implicit session.</param>
+ /// <param name="isSnapshot">if set to <c>true</c> this session is a snapshot session.</param>
+ /// <param name="defaultTransactionOptions">The default transaction options.</param>
+ public CoreSessionOptions(
+ bool isCausallyConsistent,
+ bool isImplicit,
+ TransactionOptions defaultTransactionOptions,
+ bool isSnapshot)
+ : this(isCausallyConsistent, isImplicit, defaultTransactionOptions, isSnapshot, null)
+ {
  }
 
  // public properties
@@ -78,5 +100,10 @@ public CoreSessionOptions(
  /// <c>true</c> if this session is a snapshot session; otherwise, <c>false</c>.
  /// </value>
  public bool IsSnapshot => _isSnapshot;
+
+ /// <summary>
+ /// //TODO
+ /// </summary>
+ public BsonTimestamp SnapshotTime => _snapshotTime;
  }
 }

src/MongoDB.Driver/IClientSession.cs

@@ -21,6 +21,23 @@
 
 namespace MongoDB.Driver
 {
+ /// <summary>
+ /// //TODO
+ /// </summary>
+ public static class ClientSessionExtensions
+ {
+ //TODO This will need to be moved somewhere else
+ /// <summary>
+ /// //TODO
+ /// </summary>
+ /// <param name="session"></param>
+ /// <returns></returns>
+ public static BsonTimestamp GetSnapshotTime(this IClientSessionHandle session)
+ {
+ return ((ClientSessionHandle)session).SnapshotTime;
+ }
+ }
+
  /// <summary>
  /// The interface for a client session.
  /// </summary>

src/MongoDB.Driver/MongoClient.cs

@@ -622,9 +622,17 @@ private RenderArgs<BsonDocument> GetRenderArgs()
 
  private IClientSessionHandle StartSession(ClientSessionOptions options)
  {
- if (options != null && options.Snapshot && options.CausalConsistency == true)
+ if (options != null)
  {
- throw new NotSupportedException("Combining both causal consistency and snapshot options is not supported.");
+ if (options.SnapshotTime != null && !options.Snapshot)
+ {
+ throw new NotSupportedException("Specifying a snapshot time requires snapshot to be true.");
+ }
+
+ if (options.Snapshot && options.CausalConsistency == true)
+ {
+ throw new NotSupportedException("Combining both causal consistency and snapshot options is not supported.");
+ }
  }
 
  options ??= new ClientSessionOptions();

tests/MongoDB.Driver.Tests/AtClusterTimeTests.cs

@@ -0,0 +1,208 @@
+/* Copyright 2010-present MongoDB Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+using System.Collections.Generic;
+using MongoDB.Bson;
+using MongoDB.Bson.Serialization.Attributes;
+using MongoDB.Driver.Core.Clusters;
+using MongoDB.Driver.Core.Misc;
+using MongoDB.Driver.TestHelpers;
+using Xunit;
+
+namespace MongoDB.Driver.Tests;
+//TODO This file will need to be deleted, but it's useful for testing at the moment
+public class AtClusterTimeTests : IntegrationTest<AtClusterTimeTests.ClassFixture>
+{
+ public AtClusterTimeTests(ClassFixture fixture)
+ : base(fixture, server => server.Supports(Feature.SnapshotReads).ClusterType(ClusterType.ReplicaSet))
+ {
+ }
+
+ [Fact]
+ public void MainTest()
+ {
+ var client = Fixture.Client;
+ var collection = Fixture.Collection;
+
+ BsonTimestamp clusterTime1;
+
+ var sessionOptions1 = new ClientSessionOptions
+ {
+ Snapshot = true
+ };
+
+ using (var session1 = client.StartSession(sessionOptions1))
+ {
+ var results = GetTestObjects(collection, session1);
+ AssertOneObj(results);
+
+ clusterTime1 = session1.GetSnapshotTime();
+ Assert.NotEqual(null, clusterTime1);
+ }
+
+ var obj2 = new TestObject { Name = "obj2" };
+ collection.InsertOne(obj2);
+
+ var sessionOptions2 = new ClientSessionOptions
+ {
+ Snapshot = true,
+ SnapshotTime = clusterTime1
+ };
+
+ //Snapshot read session at clusterTime1 should not see obj2
+ using (var session2 = client.StartSession(sessionOptions2))
+ {
+ var results = GetTestObjects(collection, session2);
+ AssertOneObj(results);
+
+ var clusterTime2 = session2.GetSnapshotTime();
+ Assert.Equal(clusterTime2, clusterTime1);
+ }
+
+ var sessionOptions3 = new ClientSessionOptions
+ {
+ Snapshot = true,
+ };
+
+ //Snapshot read session without cluster time should see obj2
+ using (var session3 = client.StartSession(sessionOptions3))
+ {
+ var results = GetTestObjects(collection, session3);
+ AssertTwoObjs(results);
+
+ var clusterTime3 = session3.GetSnapshotTime();
+ Assert.NotEqual(clusterTime3, clusterTime1);
+ }
+ }
+
+ [Fact]
+ public void IncreasedTimestamp()
+ {
+ var client = Fixture.Client;
+ var collection = Fixture.Collection;
+
+ BsonTimestamp clusterTime1;
+
+ var sessionOptions1 = new ClientSessionOptions
+ {
+ Snapshot = true
+ };
+
+ using (var session1 = client.StartSession(sessionOptions1))
+ {
+ var results = GetTestObjects(collection, session1);
+ AssertOneObj(results);
+
+ clusterTime1 = session1.GetSnapshotTime();
+ Assert.NotEqual(null, clusterTime1);
+ }
+
+ var obj2 = new TestObject { Name = "obj2" };
+ collection.InsertOne(obj2);
+
+ var modifiedClusterTime = new BsonTimestamp(clusterTime1.Value + 1);
+ var sessionOptions2 = new ClientSessionOptions
+ {
+ Snapshot = true,
+ SnapshotTime = modifiedClusterTime
+ };
+
+ //Snapshot read session at clusterTime1+1 should see obj2
+ using (var session2 = client.StartSession(sessionOptions2))
+ {
+ var results = GetTestObjects(collection, session2);
+ AssertTwoObjs(results);
+
+ var clusterTime2 = session2.GetSnapshotTime();
+ Assert.Equal(modifiedClusterTime, clusterTime2);
+ }
+ }
+
+ [Fact]
+ public void DecreasedTimestamp()
+ {
+ var client = Fixture.Client;
+ var collection = Fixture.Collection;
+
+ BsonTimestamp clusterTime1;
+
+ var sessionOptions1 = new ClientSessionOptions
+ {
+ Snapshot = true
+ };
+
+ using (var session1 = client.StartSession(sessionOptions1))
+ {
+ var results = GetTestObjects(collection, session1);
+ AssertOneObj(results);
+
+ clusterTime1 = session1.GetSnapshotTime();
+ Assert.NotEqual(null, clusterTime1);
+ }
+
+ var obj2 = new TestObject { Name = "obj2" };
+ collection.InsertOne(obj2);
+
+ var modifiedClusterTime = new BsonTimestamp(clusterTime1.Value - 1);
+ var sessionOptions2 = new ClientSessionOptions
+ {
+ Snapshot = true,
+ SnapshotTime = modifiedClusterTime
+ };
+
+ //Snapshot read session at clusterTime1-1 should not see obj2
+ using (var session2 = client.StartSession(sessionOptions2))
+ {
+ var results = GetTestObjects(collection, session2);
+ Assert.Equal(0, results.Count);
+
+ var clusterTime2 = session2.GetSnapshotTime();
+ Assert.Equal(modifiedClusterTime, clusterTime2);
+ }
+ }
+
+ List<TestObject> GetTestObjects(IMongoCollection<TestObject> collection, IClientSessionHandle session)
+ {
+ var filterDefinition = Builders<TestObject>.Filter.Empty;
+ var sortDefinition = Builders<TestObject>.Sort.Ascending(o => o.Name);
+ return collection.Find(session, filterDefinition).Sort(sortDefinition).ToList();
+ }
+
+ void AssertOneObj(List<TestObject> objs)
+ {
+ Assert.Equal(1, objs.Count);
+ Assert.Equal("obj1", objs[0].Name);
+ }
+
+ void AssertTwoObjs(List<TestObject> objs)
+ {
+ Assert.Equal(2, objs.Count);
+ Assert.Equal("obj1", objs[0].Name);
+ Assert.Equal("obj2", objs[1].Name);
+ }
+
+ public class ClassFixture : MongoCollectionFixture<TestObject>
+ {
+ public override bool InitializeDataBeforeEachTestCase => true;
+ protected override IEnumerable<TestObject> InitialData => [new() { Name = "obj1" }] ;
+ }
+
+ public class TestObject
+ {
+ [BsonId]
+ public ObjectId Id { get; set; }
+ public string Name { get; set; }
+ }
+}

tests/MongoDB.Driver.Tests/Specifications/sessions/SessionsProseTests.cs

@@ -357,6 +357,24 @@ public void Ensure_cluster_times_are_not_gossiped_on_SDAM_commands()
  commandStartedEvents[0].Command["$clusterTime"].Should().Be(clusterTime);
  }
 
+ [Fact]
+ public void If_SnapshotTime_is_set_Snapshot_must_be_true()
+ {
+ RequireServer.Check();
+
+ var sessionOptions = new ClientSessionOptions
+ {
+ Snapshot = false,
+ SnapshotTime = new BsonTimestamp(1, 1)
+ };
+
+ var mongoClient = DriverTestConfiguration.Client;
+
+ var exception = Record.Exception(() => mongoClient.StartSession(sessionOptions));
+ exception.Should().BeOfType<NotSupportedException>();
+ }
+
+
  private sealed class MongocryptdContext : IDisposable
  {
  public IMongoClient MongoClient { get; }