[5.1] Backport BAG failover fix. Ignore server provided failover partner. (#3704)

* Fix #3400, ignore server-provided failover partner (#3625)

* Add IgnoreServerProvidedFailoverPartner app context switch.

* Add behavior skip to netfx.

* Consolidate to single property for failover partner value.

* Rework checks to preserve server provided value, but ignore it.

* Fix import.

* Skip server failover partner override in �LoginNoFailover method. Add simulated server test coverage.

* Fix compilation issues.

* Clean up duplicate line. Adjust app context switch logic to match existing.

* Review changes.

* Add test case. Doesn't compile.

* Adjust usage of test servers and app context.

* Add failover and prelogin count capabilities to test server. Update test case.

* Set backing field using reflection.

* Try clearing pool to make test more reliable.

* Use string.Empty

Author: mdaigle

src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/SqlCommand.cs

@@ -3431,7 +3431,7 @@ private void CheckNotificationStateAndAutoEnlist()
                         }
 
                         Notification.Options = SqlDependency.GetDefaultComposedOptions(_activeConnection.DataSource,
-                                                             InternalTdsConnection.ServerProvidedFailOverPartner,
+                                                             InternalTdsConnection.ServerProvidedFailoverPartner,
                                                              identityUserName, _activeConnection.Database);
                     }
 

src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/SqlInternalConnectionTds.cs

@@ -300,7 +300,6 @@ internal SessionData CurrentSessionData
         // FOR CONNECTION RESET MANAGEMENT
         private bool _fResetConnection;
         private string _originalDatabase;
-        private string _currentFailoverPartner;                     // only set by ENV change from server
         private string _originalLanguage;
         private string _currentLanguage;
         private int _currentPacketSize;
@@ -667,13 +666,7 @@ internal TdsParser Parser
             }
         }
 
-        internal string ServerProvidedFailOverPartner
-        {
-            get
-            {
-                return _currentFailoverPartner;
-            }
-        }
+        internal string ServerProvidedFailoverPartner { get; private set; }
 
         internal SqlConnectionPoolGroupProviderInfo PoolGroupProviderInfo
         {
@@ -1533,7 +1526,7 @@ private void LoginNoFailover(ServerInfo serverInfo,
                                     !connectionOptions.MultiSubnetFailover,    // ignore timeout for SniOpen call unless MSF
                                     connectionOptions.MultiSubnetFailover ? intervalTimer : timeout);
 
-                    if (connectionOptions.MultiSubnetFailover && null != ServerProvidedFailOverPartner)
+                    if (connectionOptions.MultiSubnetFailover && ServerProvidedFailoverPartner != null)
                     {
                         // connection succeeded: trigger exception if server sends failover partner and MultiSubnetFailover is used
                         throw SQL.MultiSubnetFailoverWithFailoverPartner(serverProvidedFailoverPartner: true, internalConnection: this);
@@ -1561,7 +1554,7 @@ private void LoginNoFailover(ServerInfo serverInfo,
                         _currentPacketSize = ConnectionOptions.PacketSize;
                         _currentLanguage = _originalLanguage = ConnectionOptions.CurrentLanguage;
                         CurrentDatabase = _originalDatabase = ConnectionOptions.InitialCatalog;
-                        _currentFailoverPartner = null;
+                        ServerProvidedFailoverPartner = null;
                         _instanceName = string.Empty;
 
                         routingAttempts++;
@@ -1599,7 +1592,7 @@ private void LoginNoFailover(ServerInfo serverInfo,
                 // We only get here when we failed to connect, but are going to re-try
 
                 // Switch to failover logic if the server provided a partner
-                if (null != ServerProvidedFailOverPartner)
+                if (ServerProvidedFailoverPartner != null)
                 {
                     if (connectionOptions.MultiSubnetFailover)
                     {
@@ -1615,7 +1608,7 @@ private void LoginNoFailover(ServerInfo serverInfo,
                     LoginWithFailover(
                                 true,   // start by using failover partner, since we already failed to connect to the primary
                                 serverInfo,
-                                ServerProvidedFailOverPartner,
+                                ServerProvidedFailoverPartner,
                                 newPassword,
                                 newSecurePassword,
                                 redirectedUserInstance,
@@ -1637,8 +1630,13 @@ private void LoginNoFailover(ServerInfo serverInfo,
             {
                 // We must wait for CompleteLogin to finish for to have the
                 // env change from the server to know its designated failover
-                // partner; save this information in _currentFailoverPartner.
-                PoolGroupProviderInfo.FailoverCheck(false, connectionOptions, ServerProvidedFailOverPartner);
+                // partner; save this information in ServerProvidedFailoverPartner.
+
+                // When ignoring server provided failover partner, we must pass in the original failover partner from the connection string.
+                // Otherwise the pool group's failover partner designation will be updated to point to the server provided value.
+                string actualFailoverPartner = LocalAppContextSwitches.IgnoreServerProvidedFailoverPartner ? string.Empty : ServerProvidedFailoverPartner;
+
+                PoolGroupProviderInfo.FailoverCheck(false, connectionOptions, actualFailoverPartner);
             }
             CurrentDataSource = originalServerInfo.UserServerName;
         }
@@ -1699,7 +1697,7 @@ TimeoutTimer timeout
             ServerInfo failoverServerInfo = new ServerInfo(connectionOptions, failoverHost, connectionOptions.FailoverPartnerSPN);
 
             ResolveExtendedServerName(primaryServerInfo, !redirectedUserInstance, connectionOptions);
-            if (null == ServerProvidedFailOverPartner)
+            if (ServerProvidedFailoverPartner == null)
             {
                 ResolveExtendedServerName(failoverServerInfo, !redirectedUserInstance && failoverHost != primaryServerInfo.UserServerName, connectionOptions);
             }
@@ -1747,12 +1745,21 @@ TimeoutTimer timeout
                 ServerInfo currentServerInfo;
                 if (useFailoverHost)
                 {
-                    // Primary server may give us a different failover partner than the connection string indicates.  Update it
-                    if (null != ServerProvidedFailOverPartner && failoverServerInfo.ResolvedServerName != ServerProvidedFailOverPartner)
+                    // Primary server may give us a different failover partner than the connection string indicates.
+                    // Update it only if we are respecting server-provided failover partner values.
+                    if (ServerProvidedFailoverPartner != null && failoverServerInfo.ResolvedServerName != ServerProvidedFailoverPartner)
                     {
-                        SqlClientEventSource.Log.TryAdvancedTraceEvent("<sc.SqlInternalConnectionTds.LoginWithFailover|ADV> {0}, new failover partner={1}", ObjectID, ServerProvidedFailOverPartner);
-                        failoverServerInfo.SetDerivedNames(string.Empty, ServerProvidedFailOverPartner);
+                        if (LocalAppContextSwitches.IgnoreServerProvidedFailoverPartner)
+                        {
+                            SqlClientEventSource.Log.TryTraceEvent("<sc.SqlInternalConnectionTds.LoginWithFailover|ADV> {0}, Ignoring server provided failover partner '{1}' due to IgnoreServerProvidedFailoverPartner AppContext switch.", ObjectID, ServerProvidedFailoverPartner);
+                        }
+                        else
+                        {
+                            SqlClientEventSource.Log.TryAdvancedTraceEvent("<sc.SqlInternalConnectionTds.LoginWithFailover|ADV> {0}, new failover partner={1}", ObjectID, ServerProvidedFailoverPartner);
+                            failoverServerInfo.SetDerivedNames(string.Empty, ServerProvidedFailoverPartner);
+                        }
                     }
+
                     currentServerInfo = failoverServerInfo;
                     _timeoutErrorInternal.SetInternalSourceType(SqlConnectionInternalSourceType.Failover);
                 }
@@ -1834,7 +1841,7 @@ TimeoutTimer timeout
             _activeDirectoryAuthTimeoutRetryHelper.State = ActiveDirectoryAuthenticationTimeoutRetryState.HasLoggedIn;
 
             // if connected to failover host, but said host doesn't have DbMirroring set up, throw an error
-            if (useFailoverHost && null == ServerProvidedFailOverPartner)
+            if (useFailoverHost && ServerProvidedFailoverPartner == null)
             {
                 throw SQL.InvalidPartnerConfiguration(failoverHost, CurrentDatabase);
             }
@@ -1843,8 +1850,13 @@ TimeoutTimer timeout
             {
                 // We must wait for CompleteLogin to finish for to have the
                 // env change from the server to know its designated failover
-                // partner; save this information in _currentFailoverPartner.
-                PoolGroupProviderInfo.FailoverCheck(useFailoverHost, connectionOptions, ServerProvidedFailOverPartner);
+                // partner.
+
+                // When ignoring server provided failover partner, we must pass in the original failover partner from the connection string.
+                // Otherwise the pool group's failover partner designation will be updated to point to the server provided value.
+                string actualFailoverPartner = LocalAppContextSwitches.IgnoreServerProvidedFailoverPartner ? failoverHost : ServerProvidedFailoverPartner;
+
+                PoolGroupProviderInfo.FailoverCheck(useFailoverHost, connectionOptions, actualFailoverPartner);
             }
             CurrentDataSource = (useFailoverHost ? failoverHost : primaryServerInfo.UserServerName);
         }
@@ -2068,7 +2080,8 @@ internal void OnEnvChange(SqlEnvChange rec)
                     {
                         throw SQL.ROR_FailoverNotSupportedServer(this);
                     }
-                    _currentFailoverPartner = rec._newValue;
+
+                    ServerProvidedFailoverPartner = rec._newValue;
                     break;
 
                 case TdsEnums.ENV_PROMOTETRANSACTION:

src/Microsoft.Data.SqlClient/netfx/src/Microsoft/Data/SqlClient/SqlCommand.cs

@@ -3814,7 +3814,7 @@ private void CheckNotificationStateAndAutoEnlist()
                         }
 
                         Notification.Options = SqlDependency.GetDefaultComposedOptions(_activeConnection.DataSource,
-                                                             InternalTdsConnection.ServerProvidedFailOverPartner,
+                                                             InternalTdsConnection.ServerProvidedFailoverPartner,
                                                              identityUserName, _activeConnection.Database);
                     }