Rewrite server redirection loop.

This fixes a resource leak from the original session, at the cost of some potentially-unnecessary server initialisation happening on the first session.

The retry logic is only implemented for pooled connections.

Author: bgrainger

src/MySqlConnector/Core/ConnectionPool.cs

@@ -104,10 +104,7 @@ public async ValueTask<ServerSession> GetSessionAsync(MySqlConnection connection
 				}
 
 				// create a new session
-				session = new(this, m_generation, Interlocked.Increment(ref m_lastSessionId));
-				if (Log.IsInfoEnabled())
-					Log.Info("Pool{0} no pooled session available; created new Session{1}", m_logArguments[0], session.Id);
-				await session.ConnectAsync(ConnectionSettings, startTickCount, m_loadBalancer, ioBehavior, cancellationToken).ConfigureAwait(false);
+				session = await ConnectSessionAsync("Pool{0} no pooled session available; created new Session{1}", startTickCount, ioBehavior, cancellationToken).ConfigureAwait(false);
 				AdjustHostConnectionCount(session, 1);
 				session.OwningConnection = new(connection);
 				int leasedSessionsCountNew;
@@ -350,9 +347,7 @@ private async Task CreateMinimumPooledSessions(IOBehavior ioBehavior, Cancellati
 
 				try
 				{
-					var session = new ServerSession(this, m_generation, Interlocked.Increment(ref m_lastSessionId));
-					Log.Info("Pool{0} created Session{1} to reach minimum pool size", m_logArguments[0], session.Id);
-					await session.ConnectAsync(ConnectionSettings, Environment.TickCount, m_loadBalancer, ioBehavior, cancellationToken).ConfigureAwait(false);
+					var session = await ConnectSessionAsync("Pool{0} created Session{1} to reach minimum pool size", Environment.TickCount, ioBehavior, cancellationToken).ConfigureAwait(false);
 					AdjustHostConnectionCount(session, 1);
 					lock (m_sessions)
 						m_sessions.AddFirst(session);
@@ -365,6 +360,42 @@ private async Task CreateMinimumPooledSessions(IOBehavior ioBehavior, Cancellati
 			}
 		}
 
+		private async ValueTask<ServerSession> ConnectSessionAsync(string logMessage, int startTickCount, IOBehavior ioBehavior, CancellationToken cancellationToken)
+		{
+			var session = new ServerSession(this, m_generation, Interlocked.Increment(ref m_lastSessionId));
+			if (Log.IsInfoEnabled())
+				Log.Info(logMessage, m_logArguments[0], session.Id);
+			var statusInfo = await session.ConnectAsync(ConnectionSettings, startTickCount, m_loadBalancer, ioBehavior, cancellationToken).ConfigureAwait(false);
+
+			if (statusInfo is not null && statusInfo.StartsWith("Location: mysql://", StringComparison.Ordinal))
+			{
+				// server redirection string has the format "Location: mysql://{host}:{port}/user={userId}[&ttl={ttl}]"
+				Log.Info("Session{0} has server redirection header {1}", session.Id, statusInfo);
+
+				if (Utility.TryParseRedirectionHeader(statusInfo, out var host, out var port, out var user))
+				{
+					Log.Info("Session{0} found server redirection Host={1}; Port={2}; User={3}", session.Id, host, port, user);
+
+					if (host != ConnectionSettings.HostNames![0] || port != ConnectionSettings.Port || user != ConnectionSettings.UserID)
+					{
+						var redirectedSettings = ConnectionSettings.CloneWith(host, port, user);
+						Log.Info("Pool{0} opening new connection to Host={1}; Port={2}; User={3}", m_logArguments[0], host, port, user);
+						var redirectedSession = new ServerSession(this, m_generation, Interlocked.Increment(ref m_lastSessionId));
+						await redirectedSession.ConnectAsync(redirectedSettings, startTickCount, m_loadBalancer, ioBehavior, cancellationToken).ConfigureAwait(false);
+						Log.Info("Pool{0} closing Session{1} to use redirected Session{2} instead", m_logArguments[0], session.Id, redirectedSession.Id);
+						await session.DisposeAsync(ioBehavior, cancellationToken).ConfigureAwait(false);
+						return redirectedSession;
+					}
+					else
+					{
+						Log.Info("Session{0} is already connected to this server; ignoring redirection", session.Id);
+					}
+				}
+			}
+
+			return session;
+		}
+
 		public static ConnectionPool? GetPool(string connectionString)
 		{
 			// check single-entry MRU cache for this exact connection string; most applications have just one

src/MySqlConnector/Core/ConnectionSettings.cs

@@ -150,7 +150,7 @@ public ConnectionSettings(MySqlConnectionStringBuilder csb)
 			static int ToSigned(uint value) => value >= int.MaxValue ? int.MaxValue : (int) value;
 		}
 
-		public ConnectionSettings CloneWith(string host, int port, string userId, bool isRedirected) => new ConnectionSettings(this, host, port, userId, isRedirected);
+		public ConnectionSettings CloneWith(string host, int port, string userId) => new ConnectionSettings(this, host, port, userId);
 
 		private static MySqlGuidFormat GetEffectiveGuidFormat(MySqlGuidFormat guidFormat, bool oldGuids)
 		{
@@ -242,7 +242,6 @@ private static MySqlGuidFormat GetEffectiveGuidFormat(MySqlGuidFormat guidFormat
 		public bool UseXaTransactions { get; }
 
 		public byte[]? ConnectionAttributes { get; set; }
-		public bool IsRedirected { get; }
 
 		// Helper Functions
 		int? m_connectionTimeoutMilliseconds;
@@ -268,7 +267,7 @@ public int ConnectionTimeoutMilliseconds
 			}
 		}
 
-		private ConnectionSettings(ConnectionSettings other, string host, int port, string userId, bool isRedirected)
+		private ConnectionSettings(ConnectionSettings other, string host, int port, string userId)
 		{
 			ConnectionStringBuilder = other.ConnectionStringBuilder;
 			ConnectionString = other.ConnectionString;
@@ -324,8 +323,6 @@ private ConnectionSettings(ConnectionSettings other, string host, int port, stri
 			UseAffectedRows = other.UseAffectedRows;
 			UseCompression = other.UseCompression;
 			UseXaTransactions = other.UseXaTransactions;
-
-			IsRedirected = isRedirected;
 		}
 
 		static readonly string[] s_localhostPipeServer = { "." };

src/MySqlConnector/Core/ServerSession.cs

@@ -340,8 +340,10 @@ public async Task DisposeAsync(IOBehavior ioBehavior, CancellationToken cancella
 				m_state = State.Closed;
 		}
 
-		public async Task ConnectAsync(ConnectionSettings cs, int startTickCount, ILoadBalancer? loadBalancer, IOBehavior ioBehavior, CancellationToken cancellationToken)
+		public async Task<string?> ConnectAsync(ConnectionSettings cs, int startTickCount, ILoadBalancer? loadBalancer, IOBehavior ioBehavior, CancellationToken cancellationToken)
 		{
+			string? statusInfo = null;
+
 			try
 			{
 				lock (m_lock)
@@ -350,7 +352,6 @@ public async Task ConnectAsync(ConnectionSettings cs, int startTickCount, ILoadB
 					m_state = State.Connecting;
 				}
 
-serverRedirection:
 				// TLS negotiation should automatically fall back to the best version supported by client and server. However,
 				// Windows Schannel clients will fail to connect to a yaSSL-based MySQL Server if TLS 1.2 is requested and
 				// have to use only TLS 1.1: https://github.com/mysql-net/MySqlConnector/pull/101
@@ -467,34 +468,7 @@ public async Task ConnectAsync(ConnectionSettings cs, int startTickCount, ILoadB
 				}
 
 				var ok = OkPayload.Create(payload.Span, SupportsDeprecateEof, SupportsSessionTrack);
-				if (ok.StatusInfo is not null && ok.StatusInfo.StartsWith("Location: mysql://", StringComparison.Ordinal))
-				{
-					// server redirection string has the format "Location: mysql://{host}:{port}/user={userId}[&ttl={ttl}]"
-					m_logArguments[1] = ok.StatusInfo;
-					Log.Info("Session{0} has server redirection header {1}", m_logArguments);
-
-					if (cs.IsRedirected)
-					{
-						Log.Info("Session{0} is already redirected; ignoring it.", m_logArguments);
-					}
-					else if (Utility.TryParseRedirectionHeader(ok.StatusInfo, out var host, out var port, out var user))
-					{
-						Log.Info("Session{0} found server redirection Host={1}; Port={2}; User={3}", m_logArguments[0], host, port, user);
-
-						if (host != cs.HostNames![0] || port != cs.Port || user != cs.UserID)
-						{
-							Log.Info("Session{0} closing existing connection", m_logArguments);
-							await SendAsync(QuitPayload.Instance, ioBehavior, cancellationToken).ConfigureAwait(false);
-							Log.Info("Session{0} opening new connection to Host={1}; Port={2}; User={3}", m_logArguments[0], host, port, user);
-							cs = cs.CloneWith(host, port, user, isRedirected: true);
-							goto serverRedirection;
-						}
-						else
-						{
-							Log.Info("Session{0} is already connected to this server; ignoring redirection", m_logArguments);
-						}
-					}
-				}
+				statusInfo = ok.StatusInfo;
 
 				if (m_useCompression)
 					m_payloadHandler = new CompressedPayloadHandler(m_payloadHandler.ByteHandler);
@@ -519,6 +493,8 @@ public async Task ConnectAsync(ConnectionSettings cs, int startTickCount, ILoadB
 				Log.Error(ex, "Session{0} couldn't connect to server", m_logArguments);
 				throw new MySqlException(MySqlErrorCode.UnableToConnectToHost, "Couldn't connect to server", ex);
 			}
+
+			return statusInfo;
 		}
 
 		public async Task<bool> TryResetConnectionAsync(ConnectionSettings cs, IOBehavior ioBehavior, CancellationToken cancellationToken)