Avoids SET NAMES commands if not needed

for MariaDB since 15.1 (https://jira.mariadb.org/browse/MDEV-31609) followed session variables are sent in initial OK_Packet. This permits to avoids  initial query SET NAMES command, since charset is really know, defaulting to server corresponding default collation.

Signed-off-by: rusher <[email protected]>

Author: rusher

src/MySqlConnector/Core/ConcatenatedCommandPayloadCreator.cs

@@ -17,7 +17,7 @@ public bool WriteQueryCommand(ref CommandListPosition commandListPosition, IDict
 
 		// ConcatenatedCommandPayloadCreator is only used by MySqlBatch, and MySqlBatchCommand doesn't expose attributes,
 		// so just write an empty attribute set if the server needs it.
-		if (commandListPosition.CommandAt(commandListPosition.CommandIndex).Connection!.Session.SupportsQueryAttributes)
+		if (commandListPosition.CommandAt(commandListPosition.CommandIndex).Connection!.Session.Context.SupportsQueryAttributes)
 		{
 			// attribute count
 			writer.WriteLengthEncodedInteger(0);

src/MySqlConnector/Core/ConnectionPool.cs

@@ -65,7 +65,7 @@ public async ValueTask<ServerSession> GetSessionAsync(MySqlConnection connection
 				}
 				else
 				{
-					if (ConnectionSettings.ConnectionReset || session.DatabaseOverride is not null)
+					if (ConnectionSettings.ConnectionReset || !session.Context.IsInitialDatabase())
 					{
 						if (timeoutMilliseconds != 0)
 							session.SetTimeout(Math.Max(1, timeoutMilliseconds - Utility.GetElapsedMilliseconds(startingTimestamp)));

src/MySqlConnector/Core/Context.cs

@@ -0,0 +1,29 @@
+using MySqlConnector.Protocol;
+
+namespace MySqlConnector.Core;
+
+internal sealed class Context
+{
+	public Context(ProtocolCapabilities protocolCapabilities, string? database, int connectionId)
+	{
+		SupportsDeprecateEof = (protocolCapabilities & ProtocolCapabilities.DeprecateEof) != 0;
+		SupportsCachedPreparedMetadata = (protocolCapabilities & ProtocolCapabilities.MariaDbCacheMetadata) != 0;
+		SupportsQueryAttributes = (protocolCapabilities & ProtocolCapabilities.QueryAttributes) != 0;
+		SupportsSessionTrack = (protocolCapabilities & ProtocolCapabilities.SessionTrack) != 0;
+		ConnectionId = connectionId;
+		Database = database;
+		m_initialDatabase = database;
+	}
+
+	public bool SupportsDeprecateEof { get; }
+	public bool SupportsQueryAttributes { get; }
+	public bool SupportsSessionTrack { get; }
+	public bool SupportsCachedPreparedMetadata { get; }
+	public string? ClientCharset { get; set; }
+
+	public string? Database { get; set; }
+	private readonly string? m_initialDatabase;
+	public bool IsInitialDatabase() => string.Equals(m_initialDatabase, Database, StringComparison.Ordinal);
+
+	public int ConnectionId { get; set; }
+}

src/MySqlConnector/Core/ResultSet.cs

@@ -38,7 +38,7 @@ public async Task ReadResultSetHeaderAsync(IOBehavior ioBehavior)
 				var firstByte = payload.HeaderByte;
 				if (firstByte == OkPayload.Signature)
 				{
-					var ok = OkPayload.Create(payload.Span, Session.SupportsDeprecateEof, Session.SupportsSessionTrack);
+					var ok = OkPayload.Create(payload.Span, Session.Context);
 
 					// if we've read a result set header then this is a SELECT statement, so we shouldn't overwrite RecordsAffected
 					// (which should be -1 for SELECT) unless the server reports a non-zero count
@@ -48,8 +48,6 @@ public async Task ReadResultSetHeaderAsync(IOBehavior ioBehavior)
 					if (ok.LastInsertId != 0)
 						Command?.SetLastInsertedId((long) ok.LastInsertId);
 					WarningCount = ok.WarningCount;
-					if (ok.NewSchema is not null)
-						Connection.Session.DatabaseOverride = ok.NewSchema;
 					m_columnDefinitions = default;
 					State = (ok.ServerStatus & ServerStatus.MoreResultsExist) == 0
 						? ResultSetState.NoMoreData
@@ -109,7 +107,7 @@ public async Task ReadResultSetHeaderAsync(IOBehavior ioBehavior)
 				}
 				else
 				{
-					var columnCountPacket = ColumnCountPayload.Create(payload.Span, Session.SupportsCachedPreparedMetadata);
+					var columnCountPacket = ColumnCountPayload.Create(payload.Span, Session.Context.SupportsCachedPreparedMetadata);
 					var columnCount = columnCountPacket.ColumnCount;
 					if (!columnCountPacket.MetadataFollows)
 					{
@@ -132,7 +130,7 @@ public async Task ReadResultSetHeaderAsync(IOBehavior ioBehavior)
 						m_columnDefinitions = m_columnDefinitionPayloadCache.AsMemory(0, columnCount);
 
 						// if the server supports metadata caching but has re-sent it, something has changed since last prepare/execution and we need to update the columns
-						var preparedColumns = Session.SupportsCachedPreparedMetadata ? DataReader.LastUsedPreparedStatement?.Columns : null;
+						var preparedColumns = Session.Context.SupportsCachedPreparedMetadata ? DataReader.LastUsedPreparedStatement?.Columns : null;
 
 						for (var column = 0; column < columnCount; column++)
 						{
@@ -156,7 +154,7 @@ public async Task ReadResultSetHeaderAsync(IOBehavior ioBehavior)
 						}
 					}
 
-					if (!Session.SupportsDeprecateEof)
+					if (!Session.Context.SupportsDeprecateEof)
 					{
 						payload = await Session.ReceiveReplyAsync(ioBehavior, CancellationToken.None).ConfigureAwait(false);
 						_ = EofPayload.Create(payload.Span);
@@ -252,13 +250,13 @@ public async Task<bool> ReadAsync(IOBehavior ioBehavior, CancellationToken cance
 
 		if (payload.HeaderByte == EofPayload.Signature)
 		{
-			if (Session.SupportsDeprecateEof && OkPayload.IsOk(payload.Span, Session.SupportsDeprecateEof))
+			if (Session.Context.SupportsDeprecateEof && OkPayload.IsOk(payload.Span, Session.Context))
 			{
-				var ok = OkPayload.Create(payload.Span, Session.SupportsDeprecateEof, Session.SupportsSessionTrack);
+				var ok = OkPayload.Create(payload.Span, Session.Context);
 				BufferState = (ok.ServerStatus & ServerStatus.MoreResultsExist) == 0 ? ResultSetState.NoMoreData : ResultSetState.HasMoreData;
 				return null;
 			}
-			if (!Session.SupportsDeprecateEof && EofPayload.IsEof(payload))
+			if (!Session.Context.SupportsDeprecateEof && EofPayload.IsEof(payload))
 			{
 				var eof = EofPayload.Create(payload.Span);
 				BufferState = (eof.ServerStatus & ServerStatus.MoreResultsExist) == 0 ? ResultSetState.NoMoreData : ResultSetState.HasMoreData;