Work around server query attributes bug. Fixes #1106

MySQL Server versions 8.0.23-8.0.25 contain bugs that prevent them from parsing attributes in the COM_STMT_EXECUTE packet. The new PARAMETER_COUNT_AVAILABLE flag is added in 8.0.26 to enable attributes to be sent. If we detect an older server (that advertises support for query attributes), we send an empty string parameter name, but omit the attributes.

Author: bgrainger

src/MySqlConnector/Core/SingleCommandPayloadCreator.cs

@@ -82,25 +82,29 @@ private static void WritePreparedStatement(IMySqlCommand command, PreparedStatem
 
 		var attributes = command.RawAttributes;
 		var supportsQueryAttributes = command.Connection!.Session.SupportsQueryAttributes;
-
 		writer.Write(preparedStatement.StatementId);
 
 		// NOTE: documentation is not updated yet, but due to bugs in MySQL Server 8.0.23-8.0.25, the PARAMETER_COUNT_AVAILABLE (0x08)
-		// flag has to be set in the 'flags' block in order for query attributes to be sent with a prepared statement; we do not version-sniff the
-		// server but assume that it must support this flag
-		writer.Write((byte) (supportsQueryAttributes ? 8 : 0));
+		// flag has to be set in the 'flags' block in order for query attributes to be sent with a prepared statement.
+		var sendQueryAttributes = supportsQueryAttributes && command.Connection.Session.ServerVersion.Version is not { Major: 8, Minor: 0, Build: >= 23 and <= 25 };
+		writer.Write((byte) (sendQueryAttributes ? 8 : 0));
 		writer.Write(1);
 
 		var commandParameterCount = preparedStatement.Statement.ParameterNames?.Count ?? 0;
 		var attributeCount = attributes?.Count ?? 0;
-		if (supportsQueryAttributes)
+		if (sendQueryAttributes)
 		{
 			writer.WriteLengthEncodedInteger((uint) (commandParameterCount + attributeCount));
 		}
-		else if (attributeCount > 0)
+		else
 		{
-			Log.Warn("Session{0} has attributes for CommandId {1} but the server does not support them", command.Connection!.Session.Id, preparedStatement.StatementId);
-			attributeCount = 0;
+			if (supportsQueryAttributes && commandParameterCount > 0)
+				writer.WriteLengthEncodedInteger((uint) commandParameterCount);
+			if (attributeCount > 0)
+			{
+				Log.Warn("Session{0} has attributes for CommandId {1} but the server does not support them", command.Connection!.Session.Id, preparedStatement.StatementId);
+				attributeCount = 0;
+			}
 		}
 
 		if (commandParameterCount > 0 || attributeCount > 0)

tests/README.md

@@ -7,7 +7,7 @@ with Connector/NET and that [known bugs have been fixed](https://mysqlconnector.
 
 The tests require a MySQL server. The simplest way to run one is with [Docker](https://www.docker.com/community-edition):
 
-    docker run -d --rm --name mysqlconnector -e MYSQL_ROOT_PASSWORD=pass -p 3306:3306 mysql:8.0.23 --max-allowed-packet=96M --character-set-server=utf8mb4 --log-bin-trust-function-creators=1 --local-infile=1 --max-connections=250
+    docker run -d --rm --name mysqlconnector -e MYSQL_ROOT_PASSWORD=pass -p 3306:3306 mysql:8.0.27 --max-allowed-packet=96M --character-set-server=utf8mb4 --log-bin-trust-function-creators=1 --local-infile=1 --max-connections=250
 
 Copy the file `SideBySide/config.json.example` to `SideBySide/config.json`, then edit
 the `config.json` file in order to connect to your server. If you are using the Docker