CSHARP-3516: Use hello command when API Version is declared. (#536)

Author: JamesKovacs

src/MongoDB.Driver.Core/Core/Authentication/DefaultAuthenticator.cs

@@ -87,7 +87,7 @@ public void Authenticate(IConnection connection, ConnectionDescription descripti
             if (!description.IsMasterResult.HasSaslSupportedMechs
                 && Feature.ScramSha256Authentication.IsSupported(description.ServerVersion))
             {
-                var command = CustomizeInitialIsMasterCommand(HelloHelper.CreateCommand());
+                var command = CustomizeInitialIsMasterCommand(HelloHelper.CreateCommand(_serverApi));
                 var helloProtocol = HelloHelper.CreateProtocol(command, _serverApi);
                 var helloResult = HelloHelper.GetResult(connection, helloProtocol, cancellationToken);
                 var mergedHelloResult = new IsMasterResult(description.IsMasterResult.Wrapped.Merge(helloResult.Wrapped));
@@ -113,7 +113,7 @@ public async Task AuthenticateAsync(IConnection connection, ConnectionDescriptio
             if (!description.IsMasterResult.HasSaslSupportedMechs
                 && Feature.ScramSha256Authentication.IsSupported(description.ServerVersion))
             {
-                var command = CustomizeInitialIsMasterCommand(HelloHelper.CreateCommand());
+                var command = CustomizeInitialIsMasterCommand(HelloHelper.CreateCommand(_serverApi));
                 var helloProtocol = HelloHelper.CreateProtocol(command, _serverApi);
                 var helloResult = await HelloHelper.GetResultAsync(connection, helloProtocol, cancellationToken).ConfigureAwait(false);
                 var mergedHelloResult = new IsMasterResult(description.IsMasterResult.Wrapped.Merge(helloResult.Wrapped));

src/MongoDB.Driver.Core/Core/Connections/CommandEventHelper.cs

@@ -23,6 +23,7 @@
 using MongoDB.Bson.IO;
 using MongoDB.Bson.Serialization.Serializers;
 using MongoDB.Driver.Core.Events;
+using MongoDB.Driver.Core.Misc;
 using MongoDB.Driver.Core.WireProtocol.Messages;
 using MongoDB.Driver.Core.WireProtocol.Messages.Encoders;
 using MongoDB.Driver.Core.WireProtocol.Messages.Encoders.BinaryEncoders;
@@ -1109,7 +1110,8 @@ private static bool ShouldRedactCommand(BsonDocument command)
                 case "copydb":
                     return true;
 
-                case "ismaster":
+                case "hello":
+                case OppressiveLanguageConstants.LegacyHelloCommandNameLowerCase:
                     return command.Names.Any(n => n.ToLowerInvariant() == "speculativeauthenticate");
 
                 default:

src/MongoDB.Driver.Core/Core/Connections/ConnectionInitializer.cs

@@ -160,7 +160,7 @@ private CommandWireProtocol<BsonDocument> CreateGetLastErrorProtocol(ServerApi s
 
         private BsonDocument CreateInitialHelloCommand(IReadOnlyList<IAuthenticator> authenticators)
         {
-            var command = HelloHelper.CreateCommand();
+            var command = HelloHelper.CreateCommand(_serverApi);
             HelloHelper.AddClientDocumentToCommand(command, _clientDocument);
             HelloHelper.AddCompressorsToCommand(command, _compressors);
             return HelloHelper.CustomizeCommand(command, authenticators);

src/MongoDB.Driver.Core/Core/Connections/HelloHelper.cs

@@ -43,16 +43,17 @@ internal static BsonDocument AddCompressorsToCommand(BsonDocument command, IEnum
             return command.Add("compression", compressorsArray);
         }
 
-        internal static BsonDocument CreateCommand(TopologyVersion topologyVersion = null, TimeSpan? maxAwaitTime = null)
+        internal static BsonDocument CreateCommand(ServerApi serverApi, TopologyVersion topologyVersion = null, TimeSpan? maxAwaitTime = null)
         {
             Ensure.That(
                 (topologyVersion == null && !maxAwaitTime.HasValue) ||
                 (topologyVersion != null && maxAwaitTime.HasValue),
                 $"Both {nameof(topologyVersion)} and {nameof(maxAwaitTime)} must be filled or null.");
 
+            var helloCommandName = serverApi != null ? "hello" : OppressiveLanguageConstants.LegacyHelloCommandName;
             return new BsonDocument
             {
-                { "isMaster", 1 },
+                { helloCommandName, 1 },
                 { "topologyVersion", () => topologyVersion.ToBsonDocument(), topologyVersion != null },
                 { "maxAwaitTimeMS", () => (long)maxAwaitTime.Value.TotalMilliseconds, maxAwaitTime.HasValue }
             };

src/MongoDB.Driver.Core/Core/Connections/IsMasterResult.cs

@@ -293,7 +293,8 @@ public ServerType ServerType
 
                 if (_wrapped.Contains("setName"))
                 {
-                    if (_wrapped.GetValue("ismaster", false).ToBoolean())
+                    if (_wrapped.GetValue("isWritablePrimary", false).ToBoolean() ||
+                        _wrapped.GetValue(OppressiveLanguageConstants.LegacyHelloResponseIsWritablePrimaryFieldName, false).ToBoolean())
                     {
                         return ServerType.ReplicaSetPrimary;
                     }

src/MongoDB.Driver.Core/Core/Misc/OppressiveLanguageConstants.cs

@@ -0,0 +1,26 @@
+/* Copyright 2021-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.
+*/
+
+namespace MongoDB.Driver.Core.Misc
+{
+    internal static class OppressiveLanguageConstants
+    {
+        public const string LegacyHelloCommandName = "isMaster";
+        public const string LegacyHelloCommandNameLowerCase = "ismaster";
+        // The isMaster command response contains a boolean field ismaster (all lowercase)
+        // to indicate whether the current node is the primary.
+        public const string LegacyHelloResponseIsWritablePrimaryFieldName = "ismaster";
+    }
+}

src/MongoDB.Driver.Core/Core/Servers/RoundTripTimeMonitor.cs

@@ -97,7 +97,7 @@ public async Task RunAsync()
                     }
                     else
                     {
-                        var helloCommand = HelloHelper.CreateCommand();
+                        var helloCommand = HelloHelper.CreateCommand(_serverApi);
                         var helloProtocol = HelloHelper.CreateProtocol(helloCommand, _serverApi);
 
                         var stopwatch = Stopwatch.StartNew();

src/MongoDB.Driver.Core/Core/Servers/ServerMonitor.cs

@@ -178,11 +178,11 @@ private CommandWireProtocol<BsonDocument> InitializeHelloProtocol(IConnection co
 
                 var veryLargeHeartbeatInterval = TimeSpan.FromDays(1); // the server doesn't support Infinite value, so we set just a big enough value
                 var maxAwaitTime = _serverMonitorSettings.HeartbeatInterval == Timeout.InfiniteTimeSpan ? veryLargeHeartbeatInterval : _serverMonitorSettings.HeartbeatInterval;
-                helloCommand = HelloHelper.CreateCommand(connection.Description.IsMasterResult.TopologyVersion, maxAwaitTime);
+                helloCommand = HelloHelper.CreateCommand(_serverApi, connection.Description.IsMasterResult.TopologyVersion, maxAwaitTime);
             }
             else
             {
-                helloCommand = HelloHelper.CreateCommand();
+                helloCommand = HelloHelper.CreateCommand(_serverApi);
             }
 
             return HelloHelper.CreateProtocol(helloCommand, _serverApi, commandResponseHandling);

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

@@ -147,7 +147,7 @@ public TCommandResult Execute(IConnection connection, CancellationToken cancella
             }
             catch (Exception exception)
             {
-                AddErrorLabelIfRequired(exception, connection.Description.ServerVersion);
+                AddErrorLabelIfRequired(exception, connection.Description?.ServerVersion);
 
                 TransactionHelper.UnpinServerIfNeededOnCommandException(_session, exception);
                 throw;
@@ -201,7 +201,7 @@ public async Task<TCommandResult> ExecuteAsync(IConnection connection, Cancellat
             }
             catch (Exception exception)
             {
-                AddErrorLabelIfRequired(exception, connection.Description.ServerVersion);
+                AddErrorLabelIfRequired(exception, connection.Description?.ServerVersion);
 
                 TransactionHelper.UnpinServerIfNeededOnCommandException(_session, exception);
                 throw;
@@ -324,7 +324,7 @@ private Type0CommandMessageSection<BsonDocument> CreateType0Section(ConnectionDe
 
             AddIfNotAlreadyAdded("$db", _databaseNamespace.DatabaseName);
 
-            if (connectionDescription.IsMasterResult.ServerType != ServerType.Standalone
+            if (connectionDescription?.IsMasterResult.ServerType != ServerType.Standalone
                 && _readPreference != null
                 && _readPreference != ReadPreference.Primary)
             {

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

@@ -188,7 +188,14 @@ private IWireProtocol<TCommandResult> CreateSupportedWireProtocol(IConnection co
             {
                 _cachedConnectionId = connection.ConnectionId;
                 var serverVersion = connection.Description?.ServerVersion;
-                if (serverVersion != null && Feature.CommandMessage.IsSupported(serverVersion))
+                // If server API versioning has been requested, then we SHOULD send the initial hello command
+                // using OP_MSG. Since this is the first message and buildInfo hasn't been sent yet,
+                // connection.Description will be null and we can't rely on the semver check to determine if
+                // the server supports OP_MSG.
+                // As well since server API versioning is supported on MongoDB 5.0+, we also know that
+                // OP_MSG will be supported regardless and can skip the semver checks for other messages.
+                if (_serverApi != null ||
+                    (serverVersion != null && Feature.CommandMessage.IsSupported(serverVersion)))
                 {
                     return _cachedWireProtocol = CreateCommandUsingCommandMessageWireProtocol();
                 }