Replace server UUID/ID verification with hostname-based verification

Co-authored-by: bgrainger <[email protected]>

Author: Copilot

src/MySqlConnector/Core/ServerSession.cs

@@ -47,8 +47,7 @@ public ServerSession(ILogger logger, IConnectionPoolMetadata pool)
 	public int ActiveCommandId { get; private set; }
 	public int CancellationTimeout { get; private set; }
 	public int ConnectionId { get; set; }
-	public string? ServerUuid { get; set; }
-	public long? ServerId { get; set; }
+	public string? ServerHostname { get; set; }
 	public byte[]? AuthPluginData { get; set; }
 	public long CreatedTimestamp { get; }
 	public ConnectionPool? Pool { get; }
@@ -121,11 +120,21 @@ public void DoCancel(ICancellableCommand commandToCancel, MySqlCommand killComma
 
 			// Verify server identity before executing KILL QUERY to prevent cancelling on the wrong server
 			var killSession = killCommand.Connection!.Session;
-			if (!VerifyServerIdentity(killSession))
+			if (!string.IsNullOrEmpty(ServerHostname) && !string.IsNullOrEmpty(killSession.ServerHostname))
 			{
-				Log.IgnoringCancellationForDifferentServer(m_logger, Id, killSession.Id, ServerUuid, killSession.ServerUuid, ServerId, killSession.ServerId);
+				if (!string.Equals(ServerHostname, killSession.ServerHostname, StringComparison.Ordinal))
+				{
+					Log.IgnoringCancellationForDifferentServer(m_logger, Id, killSession.Id, ServerHostname, killSession.ServerHostname);
+					return;
+				}
+			}
+			else if (!string.IsNullOrEmpty(ServerHostname) || !string.IsNullOrEmpty(killSession.ServerHostname))
+			{
+				// One session has hostname, the other doesn't - this is a potential mismatch
+				Log.IgnoringCancellationForDifferentServer(m_logger, Id, killSession.Id, ServerHostname, killSession.ServerHostname);
 				return;
 			}
+			// If both sessions have no hostname, allow the operation for backward compatibility
 
 			// NOTE: This command is executed while holding the lock to prevent race conditions during asynchronous cancellation.
 			// For example, if the lock weren't held, the current command could finish and the other thread could set ActiveCommandId
@@ -147,26 +156,6 @@ public void AbortCancel(ICancellableCommand command)
 		}
 	}
 
-	private bool VerifyServerIdentity(ServerSession otherSession)
-	{
-		// If server UUID is available, use it as the primary identifier (most unique)
-		if (!string.IsNullOrEmpty(ServerUuid) && !string.IsNullOrEmpty(otherSession.ServerUuid))
-		{
-			return string.Equals(ServerUuid, otherSession.ServerUuid, StringComparison.Ordinal);
-		}
-
-		// Fall back to server ID if UUID is not available
-		if (ServerId.HasValue && otherSession.ServerId.HasValue)
-		{
-			return ServerId.Value == otherSession.ServerId.Value;
-		}
-
-		// If no server identification is available, allow the operation to proceed
-		// This maintains backward compatibility with older MySQL versions
-		Log.NoServerIdentificationForVerification(m_logger, Id, otherSession.Id);
-		return true;
-	}
-
 	public bool IsCancelingQuery => m_state == State.CancelingQuery;
 
 	public async Task PrepareAsync(IMySqlCommand command, IOBehavior ioBehavior, CancellationToken cancellationToken)
@@ -665,8 +654,8 @@ public async Task DisposeAsync(IOBehavior ioBehavior, CancellationToken cancella
 				ConnectionId = newConnectionId;
 			}
 
-			// Get server identification for KILL QUERY verification
-			await GetServerIdentificationAsync(ioBehavior, CancellationToken.None).ConfigureAwait(false);
+			// Get server hostname for KILL QUERY verification
+			await GetServerHostnameAsync(ioBehavior, CancellationToken.None).ConfigureAwait(false);
 
 			m_payloadHandler.ByteHandler.RemainingTimeout = Constants.InfiniteTimeout;
 			return redirectionUrl;
@@ -1984,76 +1973,36 @@ private async Task GetRealServerDetailsAsync(IOBehavior ioBehavior, Cancellation
 		}
 	}
 
-	private async Task GetServerIdentificationAsync(IOBehavior ioBehavior, CancellationToken cancellationToken)
+	private async Task GetServerHostnameAsync(IOBehavior ioBehavior, CancellationToken cancellationToken)
 	{
-		Log.GettingServerIdentification(m_logger, Id);
+		Log.GettingServerHostname(m_logger, Id);
 		try
 		{
-			PayloadData payload;
-			
-			// Try to get both server_uuid and server_id if server supports server_uuid (MySQL 5.6+)
-			if (!ServerVersion.IsMariaDb && ServerVersion.Version >= ServerVersions.SupportsServerUuid)
-			{
-				payload = SupportsQueryAttributes ? s_selectServerIdWithAttributesPayload : s_selectServerIdNoAttributesPayload;
-				await SendAsync(payload, ioBehavior, cancellationToken).ConfigureAwait(false);
-
-				// column count: 2
-				_ = await ReceiveReplyAsync(ioBehavior, cancellationToken).ConfigureAwait(false);
+			var payload = SupportsQueryAttributes ? s_selectHostnameWithAttributesPayload : s_selectHostnameNoAttributesPayload;
+			await SendAsync(payload, ioBehavior, cancellationToken).ConfigureAwait(false);
 
-				// @@server_uuid and @@server_id columns
-				_ = await ReceiveReplyAsync(ioBehavior, CancellationToken.None).ConfigureAwait(false);
-				_ = await ReceiveReplyAsync(ioBehavior, CancellationToken.None).ConfigureAwait(false);
+			// column count: 1
+			_ = await ReceiveReplyAsync(ioBehavior, cancellationToken).ConfigureAwait(false);
 
-				if (!SupportsDeprecateEof)
-				{
-					payload = await ReceiveReplyAsync(ioBehavior, CancellationToken.None).ConfigureAwait(false);
-					_ = EofPayload.Create(payload.Span);
-				}
+			// @@hostname column
+			_ = await ReceiveReplyAsync(ioBehavior, CancellationToken.None).ConfigureAwait(false);
 
-				// first (and only) row
+			if (!SupportsDeprecateEof)
+			{
 				payload = await ReceiveReplyAsync(ioBehavior, CancellationToken.None).ConfigureAwait(false);
-
-				var reader = new ByteArrayReader(payload.Span);
-				var length = reader.ReadLengthEncodedIntegerOrNull();
-				var serverUuid = length > 0 ? Encoding.UTF8.GetString(reader.ReadByteString(length)) : null;
-				length = reader.ReadLengthEncodedIntegerOrNull();
-				var serverId = (length > 0 && Utf8Parser.TryParse(reader.ReadByteString(length), out long id, out _)) ? id : default(long?);
-
-				ServerUuid = serverUuid;
-				ServerId = serverId;
-
-				Log.RetrievedServerIdentification(m_logger, Id, serverUuid, serverId);
+				_ = EofPayload.Create(payload.Span);
 			}
-			else
-			{
-				// Fall back to just server_id for older versions or MariaDB
-				payload = SupportsQueryAttributes ? s_selectServerIdOnlyWithAttributesPayload : s_selectServerIdOnlyNoAttributesPayload;
-				await SendAsync(payload, ioBehavior, cancellationToken).ConfigureAwait(false);
-
-				// column count: 1
-				_ = await ReceiveReplyAsync(ioBehavior, cancellationToken).ConfigureAwait(false);
-
-				// @@server_id column
-				_ = await ReceiveReplyAsync(ioBehavior, CancellationToken.None).ConfigureAwait(false);
 
-				if (!SupportsDeprecateEof)
-				{
-					payload = await ReceiveReplyAsync(ioBehavior, CancellationToken.None).ConfigureAwait(false);
-					_ = EofPayload.Create(payload.Span);
-				}
-
-				// first (and only) row
-				payload = await ReceiveReplyAsync(ioBehavior, CancellationToken.None).ConfigureAwait(false);
+			// first (and only) row
+			payload = await ReceiveReplyAsync(ioBehavior, CancellationToken.None).ConfigureAwait(false);
 
-				var reader = new ByteArrayReader(payload.Span);
-				var length = reader.ReadLengthEncodedIntegerOrNull();
-				var serverId = (length > 0 && Utf8Parser.TryParse(reader.ReadByteString(length), out long id, out _)) ? id : default(long?);
+			var reader = new ByteArrayReader(payload.Span);
+			var length = reader.ReadLengthEncodedIntegerOrNull();
+			var hostname = length > 0 ? Encoding.UTF8.GetString(reader.ReadByteString(length)) : null;
 
-				ServerUuid = null;
-				ServerId = serverId;
+			ServerHostname = hostname;
 
-				Log.RetrievedServerIdentification(m_logger, Id, null, serverId);
-			}
+			Log.RetrievedServerHostname(m_logger, Id, hostname);
 
 			// OK/EOF payload
 			payload = await ReceiveReplyAsync(ioBehavior, CancellationToken.None).ConfigureAwait(false);
@@ -2064,10 +2013,9 @@ private async Task GetServerIdentificationAsync(IOBehavior ioBehavior, Cancellat
 		}
 		catch (MySqlException ex)
 		{
-			Log.FailedToGetServerIdentification(m_logger, ex, Id);
-			// Set fallback values to ensure operation can continue
-			ServerUuid = null;
-			ServerId = null;
+			Log.FailedToGetServerHostname(m_logger, ex, Id);
+			// Set fallback value to ensure operation can continue
+			ServerHostname = null;
 		}
 	}
 
@@ -2302,10 +2250,8 @@ protected override void OnStatementBegin(int index)
 	private static readonly PayloadData s_sleepWithAttributesPayload = QueryPayload.Create(true, "SELECT SLEEP(0) INTO @__MySqlConnector__Sleep;"u8);
 	private static readonly PayloadData s_selectConnectionIdVersionNoAttributesPayload = QueryPayload.Create(false, "SELECT CONNECTION_ID(), VERSION();"u8);
 	private static readonly PayloadData s_selectConnectionIdVersionWithAttributesPayload = QueryPayload.Create(true, "SELECT CONNECTION_ID(), VERSION();"u8);
-	private static readonly PayloadData s_selectServerIdNoAttributesPayload = QueryPayload.Create(false, "SELECT @@server_uuid, @@server_id;"u8);
-	private static readonly PayloadData s_selectServerIdWithAttributesPayload = QueryPayload.Create(true, "SELECT @@server_uuid, @@server_id;"u8);
-	private static readonly PayloadData s_selectServerIdOnlyNoAttributesPayload = QueryPayload.Create(false, "SELECT @@server_id;"u8);
-	private static readonly PayloadData s_selectServerIdOnlyWithAttributesPayload = QueryPayload.Create(true, "SELECT @@server_id;"u8);
+	private static readonly PayloadData s_selectHostnameNoAttributesPayload = QueryPayload.Create(false, "SELECT @@hostname;"u8);
+	private static readonly PayloadData s_selectHostnameWithAttributesPayload = QueryPayload.Create(true, "SELECT @@hostname;"u8);
 
 	private readonly ILogger m_logger;
 #if NET9_0_OR_GREATER

src/MySqlConnector/Core/ServerVersions.cs

@@ -19,7 +19,4 @@ internal static class ServerVersions
 
 	// https://mariadb.com/kb/en/set-statement/
 	public static readonly Version MariaDbSupportsPerQueryVariables = new(10, 1, 2);
-
-	// https://dev.mysql.com/doc/refman/5.6/en/replication-options.html#sysvar_server_uuid
-	public static readonly Version SupportsServerUuid = new(5, 6, 0);
 }

src/MySqlConnector/Logging/EventIds.cs

@@ -86,9 +86,9 @@ internal static class EventIds
 	public const int CertificateErrorUnixSocket = 2158;
 	public const int CertificateErrorNoPassword = 2159;
 	public const int CertificateErrorValidThumbprint = 2160;
-	public const int GettingServerIdentification = 2161;
-	public const int RetrievedServerIdentification = 2162;
-	public const int FailedToGetServerIdentification = 2163;
+	public const int GettingServerHostname = 2161;
+	public const int RetrievedServerHostname = 2162;
+	public const int FailedToGetServerHostname = 2163;
 
 	// Command execution events, 2200-2299
 	public const int CannotExecuteNewCommandInState = 2200;
@@ -112,7 +112,6 @@ internal static class EventIds
 	public const int CancelingCommand = 2307;
 	public const int SendingSleepToClearPendingCancellation = 2308;
 	public const int IgnoringCancellationForDifferentServer = 2309;
-	public const int NoServerIdentificationForVerification = 2310;
 
 	// Cached procedure events, 2400-2499
 	public const int GettingCachedProcedure = 2400;

src/MySqlConnector/Logging/Log.cs

@@ -189,20 +189,17 @@ internal static partial class Log
 	[LoggerMessage(EventIds.FailedToGetConnectionId, LogLevel.Information, "Session {SessionId} failed to get CONNECTION_ID(), VERSION()")]
 	public static partial void FailedToGetConnectionId(ILogger logger, Exception exception, string sessionId);
 
-	[LoggerMessage(EventIds.GettingServerIdentification, LogLevel.Debug, "Session {SessionId} getting server identification")]
-	public static partial void GettingServerIdentification(ILogger logger, string sessionId);
+	[LoggerMessage(EventIds.GettingServerHostname, LogLevel.Debug, "Session {SessionId} getting server hostname")]
+	public static partial void GettingServerHostname(ILogger logger, string sessionId);
 
-	[LoggerMessage(EventIds.RetrievedServerIdentification, LogLevel.Debug, "Session {SessionId} retrieved server identification: UUID={ServerUuid}, ID={ServerId}")]
-	public static partial void RetrievedServerIdentification(ILogger logger, string sessionId, string? serverUuid, long? serverId);
+	[LoggerMessage(EventIds.RetrievedServerHostname, LogLevel.Debug, "Session {SessionId} retrieved server hostname: {ServerHostname}")]
+	public static partial void RetrievedServerHostname(ILogger logger, string sessionId, string? serverHostname);
 
-	[LoggerMessage(EventIds.FailedToGetServerIdentification, LogLevel.Information, "Session {SessionId} failed to get server identification")]
-	public static partial void FailedToGetServerIdentification(ILogger logger, Exception exception, string sessionId);
+	[LoggerMessage(EventIds.FailedToGetServerHostname, LogLevel.Information, "Session {SessionId} failed to get server hostname")]
+	public static partial void FailedToGetServerHostname(ILogger logger, Exception exception, string sessionId);
 
-	[LoggerMessage(EventIds.IgnoringCancellationForDifferentServer, LogLevel.Warning, "Session {SessionId} ignoring cancellation from session {KillSessionId}: server identity mismatch (this UUID={ServerUuid}, kill UUID={KillServerUuid}, this ID={ServerId}, kill ID={KillServerId})")]
-	public static partial void IgnoringCancellationForDifferentServer(ILogger logger, string sessionId, string killSessionId, string? serverUuid, string? killServerUuid, long? serverId, long? killServerId);
-
-	[LoggerMessage(EventIds.NoServerIdentificationForVerification, LogLevel.Debug, "Session {SessionId} and kill session {KillSessionId} have no server identification available for verification")]
-	public static partial void NoServerIdentificationForVerification(ILogger logger, string sessionId, string killSessionId);
+	[LoggerMessage(EventIds.IgnoringCancellationForDifferentServer, LogLevel.Warning, "Session {SessionId} ignoring cancellation from session {KillSessionId}: server hostname mismatch (this hostname={ServerHostname}, kill hostname={KillServerHostname})")]
+	public static partial void IgnoringCancellationForDifferentServer(ILogger logger, string sessionId, string killSessionId, string? serverHostname, string? killServerHostname);
 
 	[LoggerMessage(EventIds.ClosingStreamSocket, LogLevel.Debug, "Session {SessionId} closing stream/socket")]
 	public static partial void ClosingStreamSocket(ILogger logger, string sessionId);

tests/IntegrationTests/ServerIdentificationTests.cs

@@ -39,34 +39,17 @@ public void CancelCommand_WithServerVerification()
 	}
 
 	[SkippableFact(ServerFeatures.KnownCertificateAuthority)]  
-	public void ServerHasServerIdentification()
+	public void ServerHasServerHostname()
 	{
 		using var connection = new MySqlConnection(AppConfig.ConnectionString);
 		connection.Open();
 
-		// Test that we can query server identification manually
-		using var cmd = new MySqlCommand("SELECT @@server_id", connection);
-		var serverId = cmd.ExecuteScalar();
-		Assert.NotNull(serverId);
-		TestUtilities.LogInfo($"Server ID: {serverId}");
-
-		// Test server UUID if available (MySQL 5.6+)
-		if (connection.ServerVersion.Version.Major > 5 || 
-			(connection.ServerVersion.Version.Major == 5 && connection.ServerVersion.Version.Minor >= 6))
-		{
-			try
-			{
-				using var uuidCmd = new MySqlCommand("SELECT @@server_uuid", connection);
-				var serverUuid = uuidCmd.ExecuteScalar();
-				Assert.NotNull(serverUuid);
-				TestUtilities.LogInfo($"Server UUID: {serverUuid}");
-			}
-			catch (MySqlException ex) when (ex.ErrorCode == MySqlErrorCode.UnknownSystemVariable)
-			{
-				// Some MySQL-compatible servers might not support server_uuid
-				TestUtilities.LogInfo("Server UUID not supported on this server");
-			}
-		}
+		// Test that we can query server hostname
+		using var cmd = new MySqlCommand("SELECT @@hostname", connection);
+		var hostname = cmd.ExecuteScalar();
+		
+		// Hostname might be null on some server configurations, but the query should succeed
+		TestUtilities.LogInfo($"Server hostname: {hostname ?? "null"}");
 	}
 
 	private readonly DatabaseFixture m_database;