CSHARP-2678: Raise an actionable error message when retryWrites fails due to using an unsupported storage engine

Author: vincentkam

src/MongoDB.Driver.Core/Core/WireProtocol/CommandUsingCommandMessageWireProtocol.cs

@@ -234,6 +234,16 @@ private Type0CommandMessageSection<BsonDocument> CreateType0Section(ConnectionDe
             return new Type0CommandMessageSection<BsonDocument>(_command, elementAppendingSerializer);
         }
 
+        private bool IsRetryableWriteExceptionAndDeploymentDoesNotSupportRetryableWrites(MongoCommandException exception)
+        {
+            return
+                exception.Result.TryGetValue("code", out var errorCode) &&
+                errorCode.ToInt32() == 20 &&
+                exception.Result.TryGetValue("errmsg", out var errmsg) &&
+                errmsg.AsString.StartsWith("Transaction numbers");
+        }
+
+
         private void MessageWasProbablySent(CommandRequestMessage message)
         {
             if (_session.Id != null)
@@ -319,7 +329,17 @@ private TCommandResult ProcessResponse(ConnectionId connectionId, CommandMessage
                         message = string.Format("Command {0} failed.", commandName);
                     }
 
-                    throw new MongoCommandException(connectionId, message, _command, materializedDocument);
+                    var exception = new MongoCommandException(connectionId, message, _command, materializedDocument);
+
+                    // https://jira.mongodb.org/browse/CSHARP-2678
+                    if (IsRetryableWriteExceptionAndDeploymentDoesNotSupportRetryableWrites(exception))
+                    {
+                        throw WrapNotSupportedRetryableWriteException(exception);
+                    }
+                    else
+                    {
+                        throw exception;
+                    }
                 }
 
                 if (rawDocument.Contains("writeConcernError"))
@@ -354,5 +374,18 @@ private bool ShouldAddTransientTransactionError(MongoException exception)
 
             return false;
         }
+
+        private MongoException WrapNotSupportedRetryableWriteException(MongoCommandException exception)
+        {
+            const string friendlyErrorMessage =
+                "This MongoDB deployment does not support retryable writes. " +
+                "Please add retryWrites=false to your connection string.";
+            return new MongoCommandException(
+                exception.ConnectionId,
+                friendlyErrorMessage,
+                exception.Command,
+                exception.Result,
+                innerException: exception);
+        }
     }
 }

src/MongoDB.Driver.Core/MongoCommandException.cs

@@ -75,7 +75,21 @@ public MongoCommandException(ConnectionId connectionId, string message, BsonDocu
         /// <param name="command">The command.</param>
         /// <param name="result">The command result.</param>
         public MongoCommandException(ConnectionId connectionId, string message, BsonDocument command, BsonDocument result)
-            : base(connectionId, message)
+            : this(connectionId, message, command, result, innerException: null)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="MongoCommandException"/> class.
+        /// </summary>
+        /// <param name="connectionId">The connection identifier.</param>
+        /// <param name="message">The message.</param>
+        /// <param name="command">The command.</param>
+        /// // <param name="result">The command result.</param>
+        /// <param name="innerException">The inner exception.</param>
+        ///
+        public MongoCommandException(ConnectionId connectionId, string message, BsonDocument command, BsonDocument result, Exception innerException)
+            : base(connectionId, message, innerException)
         {
             _command = command; // can be null
             _result = result; // can be null

tests/MongoDB.Driver.Tests/RetryableWritesTests.cs

@@ -43,6 +43,26 @@ public void Insert_with_RetryWrites_true_should_work_whether_retryable_writes_ar
             }
         }
 
+        [SkippableFact]
+        public void Retryable_write_operation_should_throw_custom_exception_on_servers_using_mmapv1()
+        {
+            RequireSupportForRetryableWrites();
+            RequireServer.Check().StorageEngine("mmapv1");
+
+            using (var client = GetClient())
+            using (var session = client.StartSession())
+            {
+                var database = client.GetDatabase(DriverTestConfiguration.DatabaseNamespace.DatabaseName);
+                var collection = database.GetCollection<BsonDocument>(DriverTestConfiguration.CollectionNamespace.CollectionName);
+                var document = new BsonDocument("x", 1);
+                var exception = Record.Exception(() => collection.InsertOne(document));
+
+                exception.Message.Should().Contain(
+                    "This MongoDB deployment does not support retryable writes. " +
+                    "Please add retryWrites=false to your connection string.");
+            }
+        }
+
         [SkippableFact]
         public void TxnNumber_should_be_included_with_FindOneAndDelete()
         {

tests/MongoDB.Driver.Tests/Specifications/retryable-writes/RetryableWriteTestRunner.cs

@@ -55,6 +55,11 @@ private void VerifyServerRequirements(BsonDocument definition)
         {
             RequireServer.Check().ClusterType(ClusterType.ReplicaSet);
 
+            if (CoreTestConfiguration.GetStorageEngine() == "mmapv1")
+            {
+                throw new SkipException("Test skipped because mmapv1 does not support retryable writes.");
+            }
+
             BsonValue minServerVersion;
             if (definition.TryGetValue("minServerVersion", out minServerVersion))
             {