//------------------------------------------------------------------------------
// <copyright file="SqlInternalConnectionTds.cs" company="Microsoft">
//     Copyright (c) Microsoft Corporation.  All rights reserved.
// </copyright>
// <owner current="true" primary="true">[....]</owner>
// <owner current="true" primary="false">[....]</owner>
//------------------------------------------------------------------------------

namespace System.Data.SqlClient
{
    using System;
    using System.Collections.Generic;
    using System.Data;
    using System.Data.Common;
    using System.Data.ProviderBase;
    using System.Diagnostics;
    using System.Globalization;
    using System.Reflection;
    using System.Runtime.CompilerServices;
    using System.Runtime.ConstrainedExecution;
    using System.Runtime.InteropServices;
    using System.Security;
    using System.Security.Permissions;
    using System.Text;
    using System.Threading;
    using SysTx = System.Transactions;
    using System.Diagnostics.CodeAnalysis;
    using System.Threading.Tasks;
    

    internal class SessionStateRecord  {
        internal bool _recoverable;
        internal UInt32 _version;
        internal Int32 _dataLength;
        internal byte[] _data;
    }

    internal class SessionData {
        internal const int _maxNumberOfSessionStates = 256;
        internal UInt32 _tdsVersion;
        internal bool _encrypted;

        internal string _database;
        internal SqlCollation _collation;
        internal string _language;

        internal string _initialDatabase;
        internal SqlCollation _initialCollation;
        internal string _initialLanguage;
        
        internal byte _unrecoverableStatesCount = 0;
        internal Dictionary<string, Tuple<string, string>> _resolvedAliases;

#if DEBUG
        internal bool _debugReconnectDataApplied;
#endif

        internal SessionStateRecord[] _delta = new SessionStateRecord[_maxNumberOfSessionStates];
        internal bool _deltaDirty = false;
        internal byte[][] _initialState = new byte[_maxNumberOfSessionStates][];

        public SessionData(SessionData recoveryData) {
            _initialDatabase = recoveryData._initialDatabase;
            _initialCollation = recoveryData._initialCollation;
            _initialLanguage = recoveryData._initialLanguage;
            _resolvedAliases = recoveryData._resolvedAliases;

            for (int i = 0; i < _maxNumberOfSessionStates; i++) {
                if (recoveryData._initialState[i] != null) {
                    _initialState[i] = (byte[])recoveryData._initialState[i].Clone();
                }
            }
        }

        public SessionData() {
            _resolvedAliases = new Dictionary<string, Tuple<string, string>>(2);
        }

        public void Reset() {
            _database = null;
            _collation = null;
            _language = null;
            if (_deltaDirty) {
                _delta = new SessionStateRecord[_maxNumberOfSessionStates];
                _deltaDirty = false;
            }
            _unrecoverableStatesCount = 0;
        }        

        [Conditional("DEBUG")]
        public void AssertUnrecoverableStateCountIsCorrect() {
            byte unrecoverableCount = 0;
            foreach (var state in _delta) {
                if (state != null && !state._recoverable)
                    unrecoverableCount++;
            }
            Debug.Assert(unrecoverableCount == _unrecoverableStatesCount, "Unrecoverable count does not match");
        }
    }

    sealed internal class SqlInternalConnectionTds : SqlInternalConnection, IDisposable {
        // CONNECTION AND STATE VARIABLES
        private readonly SqlConnectionPoolGroupProviderInfo _poolGroupProviderInfo; // will only be null when called for ChangePassword, or creating SSE User Instance
        private TdsParser                _parser;
        private SqlLoginAck              _loginAck;
        private SqlCredential            _credential;

        // Connection Resiliency
        private bool                     _sessionRecoveryRequested;
        internal bool                     _sessionRecoveryAcknowledged;
        internal SessionData             _currentSessionData; // internal for use from TdsParser only, otehr should use CurrentSessionData property that will fix database and language
        private SessionData              _recoverySessionData;

        internal SessionData CurrentSessionData {
            get {
                if (_currentSessionData != null) {
                    _currentSessionData._database = CurrentDatabase;
                    _currentSessionData._language = _currentLanguage;
                }
                return _currentSessionData;
            }
        }

        // FOR POOLING
        private bool                     _fConnectionOpen = false;

        // 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;
        private int                      _asyncCommandCount; // number of async Begins minus number of async Ends.

        // FOR SSE
        private string                   _instanceName = String.Empty;

        // FOR NOTIFICATIONS
        private DbConnectionPoolIdentity _identity; // Used to lookup info for notification matching Start().

        // FOR SYNCHRONIZATION IN TdsParser
        // How to use these locks:
        // 1. Whenever writing to the connection (with the exception of Cancellation) the _parserLock MUST be taken
        // 2. _parserLock will also be taken during close (to prevent closing in the middle of a write)
        // 3. Whenever you have the _parserLock and are calling a method that would cause the connection to close if it failed (with the exception of any writing method), you MUST set ThreadHasParserLockForClose to true
        //      * This is to prevent the connection deadlocking with itself (since you already have the _parserLock, and Closing the connection will attempt to re-take that lock)
        //      * It is safe to set ThreadHasParserLockForClose to true when writing as well, but it is unneccesary
        //      * If you have a method that takes _parserLock, it is a good idea check ThreadHasParserLockForClose first (if you don't expect _parserLock to be taken by something higher on the stack, then you should at least assert that it is false)
        // 4. ThreadHasParserLockForClose is thread-specific - this means that you must set it to false before returning a Task, and set it back to true in the continuation
        // 5. ThreadHasParserLockForClose should only be modified if you currently own the _parserLock
        // 6. Reading ThreadHasParserLockForClose is thread-safe
        internal class SyncAsyncLock
        {
            SemaphoreSlim semaphore = new SemaphoreSlim(1);

            internal void Wait(bool canReleaseFromAnyThread)
            {
                Monitor.Enter(semaphore); // semaphore is used as lock object, no relation to SemaphoreSlim.Wait/Release methods
                if (canReleaseFromAnyThread || semaphore.CurrentCount==0) {
                    semaphore.Wait();
                    if (canReleaseFromAnyThread) {                        
                        Monitor.Exit(semaphore);
                    }
                    else {
                        semaphore.Release();
                    }
                }
            }
           
            internal void Wait(bool canReleaseFromAnyThread, int timeout, ref bool lockTaken) {
                lockTaken = false;
                bool hasMonitor = false;
                try {
                    Monitor.TryEnter(semaphore, timeout, ref hasMonitor); // semaphore is used as lock object, no relation to SemaphoreSlim.Wait/Release methods
                    if (hasMonitor) {
                        if ((canReleaseFromAnyThread) || (semaphore.CurrentCount == 0)) {
                            if (semaphore.Wait(timeout)) {
                                if (canReleaseFromAnyThread) {                        
                                    Monitor.Exit(semaphore);
                                    hasMonitor = false;
                                }
                                else {
                                    semaphore.Release();
                                }
                                lockTaken = true;
                            }
                        }
                        else {
                            lockTaken = true;
                        }
                    }
                }
                finally
                {
                    if ((!lockTaken) && (hasMonitor)) {
                        Monitor.Exit(semaphore);
                    }
                }
            }

            internal void Release()
            {
                if (semaphore.CurrentCount==0) {  //  semaphore methods were used for locking                   
                    semaphore.Release();
                }
                else {
                    Monitor.Exit(semaphore);
                }
            }


            internal bool CanBeReleasedFromAnyThread {
                get {
                    return semaphore.CurrentCount==0;
                }
            }

            // Necessary but not sufficient condition for thread to have lock (since sempahore may be obtained by any thread)            
            internal bool ThreadMayHaveLock() {
                   return Monitor.IsEntered(semaphore) || semaphore.CurrentCount == 0;
            }
        }


        internal SyncAsyncLock _parserLock = new SyncAsyncLock();
        private int _threadIdOwningParserLock = -1;                                          

        private SqlConnectionTimeoutErrorInternal timeoutErrorInternal;

        internal SqlConnectionTimeoutErrorInternal TimeoutErrorInternal
        {
            get { return timeoutErrorInternal; }
        }
 
        // OTHER STATE VARIABLES AND REFERENCES

        internal Guid _clientConnectionId = Guid.Empty;

        // Routing information (ROR)
        RoutingInfo _routingInfo = null;
        private Guid _originalClientConnectionId = Guid.Empty;
        private string _routingDestination = null;

        // although the new password is generally not used it must be passed to the c'tor
        // the new Login7 packet will always write out the new password (or a length of zero and no bytes if not present)
        //
        internal SqlInternalConnectionTds(
                DbConnectionPoolIdentity    identity, 
                SqlConnectionString         connectionOptions,
                SqlCredential               credential,
                object                      providerInfo, 
                string                      newPassword,
                SecureString                newSecurePassword,
                bool                        redirectedUserInstance,
                SqlConnectionString         userConnectionOptions = null, // NOTE: userConnectionOptions may be different to connectionOptions if the connection string has been expanded (see SqlConnectionString.Expand)
                SessionData                 reconnectSessionData = null) : base(connectionOptions) {

#if DEBUG
            if (reconnectSessionData != null) {
                reconnectSessionData._debugReconnectDataApplied = true;
            }
            try { // use this to help validate this object is only created after the following permission has been previously demanded in the current codepath
                if (userConnectionOptions != null) {
                    // As mentioned above, userConnectionOptions may be different to connectionOptions, so we need to demand on the correct connection string
                    userConnectionOptions.DemandPermission();
                }
                else {
                    connectionOptions.DemandPermission();
                }
            }
            catch(System.Security.SecurityException) {
                System.Diagnostics.Debug.Assert(false, "unexpected SecurityException for current codepath");
                throw;
            }
#endif
            Debug.Assert(reconnectSessionData == null || connectionOptions.ConnectRetryCount > 0, "Reconnect data supplied with CR turned off");
  
            if (connectionOptions.ConnectRetryCount > 0) {
                _recoverySessionData = reconnectSessionData;          
                if (reconnectSessionData == null) {
                    _currentSessionData = new SessionData();
                }
                else {
                    _currentSessionData = new SessionData(_recoverySessionData);
                    _originalDatabase = _recoverySessionData._initialDatabase;
                    _originalLanguage = _recoverySessionData._initialLanguage;
                }
            }

            if (connectionOptions.UserInstance && InOutOfProcHelper.InProc) {
                throw SQL.UserInstanceNotAvailableInProc();
            }

            _identity = identity;
            Debug.Assert(newSecurePassword != null || newPassword != null, "cannot have both new secure change password and string based change password to be null");
            Debug.Assert(credential == null || (String.IsNullOrEmpty(connectionOptions.UserID) && String.IsNullOrEmpty(connectionOptions.Password)), "cannot mix the new secure password system and the connection string based password");

            Debug.Assert(credential == null || !connectionOptions.IntegratedSecurity, "Cannot use SqlCredential and Integrated Security");
            Debug.Assert(credential == null || !connectionOptions.ContextConnection, "Cannot use SqlCredential with context connection");

            _poolGroupProviderInfo = (SqlConnectionPoolGroupProviderInfo)providerInfo;
            _fResetConnection = connectionOptions.ConnectionReset;
            if (_fResetConnection && _recoverySessionData == null) {
                _originalDatabase = connectionOptions.InitialCatalog;
                _originalLanguage = connectionOptions.CurrentLanguage;
            }

            timeoutErrorInternal = new SqlConnectionTimeoutErrorInternal();
            _credential = credential;

            _parserLock.Wait(canReleaseFromAnyThread:false);
            ThreadHasParserLockForClose = true;   // In case of error, let ourselves know that we already own the parser lock
            RuntimeHelpers.PrepareConstrainedRegions();
            try {
#if DEBUG
                TdsParser.ReliabilitySection tdsReliabilitySection = new TdsParser.ReliabilitySection();

                RuntimeHelpers.PrepareConstrainedRegions();
                try {
                    tdsReliabilitySection.Start();
#else
                {
#endif //DEBUG
                    var timeout = TimeoutTimer.StartSecondsTimeout(connectionOptions.ConnectTimeout);
                    OpenLoginEnlist(timeout, connectionOptions, credential, newPassword, newSecurePassword, redirectedUserInstance);
                }
#if DEBUG
                finally {
                    tdsReliabilitySection.Stop();
                }
#endif //DEBUG
            }
            catch (System.OutOfMemoryException) {
                DoomThisConnection();
                throw;
            }
            catch (System.StackOverflowException) {
                DoomThisConnection();
                throw;
            }
            catch (System.Threading.ThreadAbortException) {
                DoomThisConnection();
                throw;
            }
            finally {
                ThreadHasParserLockForClose = false;
                _parserLock.Release();
            }
            if (Bid.AdvancedOn) {
                Bid.Trace("<sc.SqlInternalConnectionTds.ctor|ADV> %d#, constructed new TDS internal connection\n", ObjectID);
            }
        }
       
        internal Guid ClientConnectionId {
            get {
                return _clientConnectionId;
            }
        }
       
        internal Guid OriginalClientConnectionId {
            get {
                return _originalClientConnectionId;
            }
        }
       
        internal string RoutingDestination {
            get {
                return _routingDestination;
            }
        }

        override internal SqlInternalTransaction CurrentTransaction {
            get {
                return _parser.CurrentTransaction;
            }
        }

        override internal SqlInternalTransaction AvailableInternalTransaction {
            get {
                return _parser._fResetConnection ? null : CurrentTransaction;
            }
        }


        override internal SqlInternalTransaction PendingTransaction {
            get {
                return _parser.PendingTransaction;
            }
        }
        
        internal DbConnectionPoolIdentity Identity {
            get {
                return _identity;
            }
        }

        internal string InstanceName {
            get {
                return _instanceName;
            }
        }

        override internal bool IsLockedForBulkCopy {
            get {
                return (!Parser.MARSOn && Parser._physicalStateObj.BcpLock);
            }
        }

        override protected internal bool IsNonPoolableTransactionRoot {
            get {
                return IsTransactionRoot && (!IsKatmaiOrNewer || null == Pool);
            }
        }

        override internal bool IsShiloh {
            get {
                return _loginAck.isVersion8;
            }
        }

        override internal bool IsYukonOrNewer {
            get {
                return _parser.IsYukonOrNewer;
            }
        }

        override internal bool IsKatmaiOrNewer {
            get {
                return _parser.IsKatmaiOrNewer;
            }
        }

        internal int PacketSize {
            get {
                return _currentPacketSize;
            }
        }

        internal TdsParser Parser {
            get {
                return _parser;
            }
        }

        internal string ServerProvidedFailOverPartner {
            get {
                return  _currentFailoverPartner;
            }
        }

        internal SqlConnectionPoolGroupProviderInfo PoolGroupProviderInfo {
            get {
                return _poolGroupProviderInfo;
            }
        }
        
        override protected bool ReadyToPrepareTransaction {
            get {
                // 
                bool result = (null == FindLiveReader(null)); // can't prepare with a live data reader...
                return result;
            }
        }

        override public string ServerVersion {
            get {
                return(String.Format((IFormatProvider)null, "{0:00}.{1:00}.{2:0000}", _loginAck.majorVersion,
                       (short) _loginAck.minorVersion, _loginAck.buildNum));
            }
        }

        /// <summary>
        /// Get boolean that specifies whether an enlisted transaction can be unbound from 
        /// the connection when that transaction completes.
        /// </summary>
        /// <value>
        /// This override always returns false.
        /// </value>
        /// <remarks>
        /// The SqlInternalConnectionTds.CheckEnlistedTransactionBinding method handles implicit unbinding for disposed transactions.
        /// </remarks>
        protected override bool UnbindOnTransactionCompletion
        {
            get
            {
                return false;
            }
        }


        ////////////////////////////////////////////////////////////////////////////////////////
        // GENERAL METHODS
        ////////////////////////////////////////////////////////////////////////////////////////
        [SuppressMessage("Microsoft.Globalization", "CA1303:DoNotPassLiteralsAsLocalizedParameters")] // copied from Triaged.cs
        override protected void ChangeDatabaseInternal(string database) {
            // MDAC 73598 - add brackets around database
            database = SqlConnection.FixupDatabaseTransactionName(database);
            Threading.Tasks.Task executeTask = _parser.TdsExecuteSQLBatch("use " + database, ConnectionOptions.ConnectTimeout, null, _parser._physicalStateObj, sync: true);
            Debug.Assert(executeTask == null, "Shouldn't get a task when doing sync writes");
            _parser.Run(RunBehavior.UntilDone, null, null, null, _parser._physicalStateObj);
        }

        override public void Dispose() {
            if (Bid.AdvancedOn) {
                Bid.Trace("<sc.SqlInternalConnectionTds.Dispose|ADV> %d# disposing\n", base.ObjectID);
            }
            try {
                TdsParser parser = Interlocked.Exchange(ref _parser, null);  // guard against multiple concurrent dispose calls -- Delegated Transactions might cause this.
                    
                Debug.Assert(parser != null && _fConnectionOpen || parser == null && !_fConnectionOpen, "Unexpected state on dispose");
                if (null != parser) {
                    parser.Disconnect();
                }
            }
            finally { // UNDONE: MDAC 77928
                // close will always close, even if exception is thrown
                // remember to null out any object references
                _loginAck          = null;
                _fConnectionOpen   = false; // mark internal connection as closed
            }
            base.Dispose();
        }

        override internal void ValidateConnectionForExecute(SqlCommand command) {
            TdsParser parser = _parser;
            if ((parser == null) || (parser.State == TdsParserState.Broken) || (parser.State == TdsParserState.Closed)) {
                throw ADP.ClosedConnectionError();
            }
            else {
                SqlDataReader reader = null;
                if (parser.MARSOn) {
                    if (null != command) { // command can't have datareader already associated with it
                        reader = FindLiveReader(command);
                    }
                }
                else { // single execution/datareader per connection
                    if (_asyncCommandCount > 0) {
                        throw SQL.MARSUnspportedOnConnection();
                    }

                    reader = FindLiveReader(null);
                }
                if (null != reader) {
                    // if MARS is on, then a datareader associated with the command exists
                    // or if MARS is off, then a datareader exists
                    throw ADP.OpenReaderExists(); // MDAC 66411
                }
                else if (!parser.MARSOn && parser._physicalStateObj._pendingData) {
                    parser.DrainData(parser._physicalStateObj);
                }
                Debug.Assert(!parser._physicalStateObj._pendingData, "Should not have a busy physicalStateObject at this point!");

                parser.RollbackOrphanedAPITransactions();
            }
        }

        /// <summary>
        /// Validate the enlisted transaction state, taking into consideration the ambient transaction and transaction unbinding mode.
        /// If there is no enlisted transaction, this method is a nop.
        /// </summary>
        /// <remarks>
        /// <para>
        /// This method must be called while holding a lock on the SqlInternalConnection instance,
        /// to ensure we don't accidentally execute after the transaction has completed on a different thread, 
        /// causing us to unwittingly execute in auto-commit mode.
        /// </para>
        /// 
        /// <para>
        /// When using Explicit transaction unbinding, 
        /// verify that the enlisted transaction is active and equal to the current ambient transaction.
        /// </para>
        /// 
        /// <para>
        /// When using Implicit transaction unbinding,
        /// verify that the enlisted transaction is active.
        /// If it is not active, and the transaction object has been diposed, unbind from the transaction.
        /// If it is not active and not disposed, throw an exception.
        /// </para>
        /// </remarks>
        internal void CheckEnlistedTransactionBinding()
        {
            // If we are enlisted in a transaction, check that transaction is active.
            // When using explicit transaction unbinding, also verify that the enlisted transaction is the current transaction.
            SysTx.Transaction enlistedTransaction = EnlistedTransaction;

            if (enlistedTransaction != null)
            {
                bool requireExplicitTransactionUnbind = ConnectionOptions.TransactionBinding == SqlConnectionString.TransactionBindingEnum.ExplicitUnbind;

                if (requireExplicitTransactionUnbind)
                {
                    SysTx.Transaction currentTransaction = SysTx.Transaction.Current;

                    if (SysTx.TransactionStatus.Active != enlistedTransaction.TransactionInformation.Status || !enlistedTransaction.Equals(currentTransaction))
                    {
                        throw ADP.TransactionConnectionMismatch();
                    }
                }
                else // implicit transaction unbind
                {
                    if (SysTx.TransactionStatus.Active != enlistedTransaction.TransactionInformation.Status)
                    {
                        if (EnlistedTransactionDisposed)
                        {
                            DetachTransaction(enlistedTransaction, true);
                        }
                        else
                        {
                            throw ADP.TransactionCompletedButNotDisposed();
                        }
                    }
                }
            }
        }

        internal override bool IsConnectionAlive(bool throwOnException)
        {
            bool isAlive = false;
#if DEBUG
            TdsParser.ReliabilitySection tdsReliabilitySection = new TdsParser.ReliabilitySection();

            RuntimeHelpers.PrepareConstrainedRegions();
            try
            {
                tdsReliabilitySection.Start();
#endif //DEBUG

                isAlive = _parser._physicalStateObj.IsConnectionAlive(throwOnException);

#if DEBUG
            }
            finally
            {
                tdsReliabilitySection.Stop();
            }
#endif //DEBUG
            return isAlive;
        }

        ////////////////////////////////////////////////////////////////////////////////////////
        // POOLING METHODS
        ////////////////////////////////////////////////////////////////////////////////////////

        override protected void Activate(SysTx.Transaction transaction) {
            FailoverPermissionDemand(); // Demand for unspecified failover pooled connections

            // When we're required to automatically enlist in transactions and
            // there is one we enlist in it. On the other hand, if there isn't a
            // transaction and we are currently enlisted in one, then we
            // unenlist from it.
            //
            // Regardless of whether we're required to automatically enlist,
            // when there is not a current transaction, we cannot leave the
            // connection enlisted in a transaction.
            if (null != transaction){
                if (ConnectionOptions.Enlist) {
                   Enlist(transaction);
                }
            }
            else {
                Enlist(null);
            }                           
        }
        
        override protected void InternalDeactivate() {
            // When we're deactivated, the user must have called End on all
            // the async commands, or we don't know that we're in a state that
            // we can recover from.  We doom the connection in this case, to
            // prevent odd cases when we go to the wire.
            if (0 != _asyncCommandCount) {
                DoomThisConnection();
            }

            // If we're deactivating with a delegated transaction, we 
            // should not be cleaning up the parser just yet, that will
            // cause our transaction to be rolled back and the connection
            // to be reset.  We'll get called again once the delegated
            // transaction is completed and we can do it all then.
            if (!IsNonPoolableTransactionRoot) {
                Debug.Assert(null != _parser || IsConnectionDoomed, "Deactivating a disposed connection?");
                if (_parser != null) {

                    _parser.Deactivate(IsConnectionDoomed);

                    if (!IsConnectionDoomed) {
                        ResetConnection();
                    }
                }
            }
        }

        [SuppressMessage("Microsoft.Globalization", "CA1303:DoNotPassLiteralsAsLocalizedParameters")] // copied from Triaged.cs
        private void ResetConnection() {
            // For implicit pooled connections, if connection reset behavior is specified,
            // reset the database and language properties back to default.  It is important
            // to do this on activate so that the hashtable is correct before SqlConnection
            // obtains a clone.

            Debug.Assert(!HasLocalTransactionFromAPI, "Upon ResetConnection SqlInternalConnectionTds has a currently ongoing local transaction.");
            Debug.Assert(!_parser._physicalStateObj._pendingData, "Upon ResetConnection SqlInternalConnectionTds has pending data.");

            if (_fResetConnection) {
                // Ensure we are either going against shiloh, or we are not enlisted in a
                // distributed transaction - otherwise don't reset!
                if (IsShiloh) {
                    // Prepare the parser for the connection reset - the next time a trip
                    // to the server is made.
                    _parser.PrepareResetConnection(IsTransactionRoot && !IsNonPoolableTransactionRoot);
                }
                else if (!IsEnlistedInTransaction) {
                    // If not Shiloh, we are going against Sphinx.  On Sphinx, we
                    // may only reset if not enlisted in a distributed transaction.
                    try {
                        // execute sp
                        Threading.Tasks.Task executeTask = _parser.TdsExecuteSQLBatch("sp_reset_connection", 30, null, _parser._physicalStateObj, sync: true);
                        Debug.Assert(executeTask == null, "Shouldn't get a task when doing sync writes");
                        _parser.Run(RunBehavior.UntilDone, null, null, null, _parser._physicalStateObj);
                    }
                    catch (Exception e) {
                        // 
                        if (!ADP.IsCatchableExceptionType(e)) {
                            throw;
                        }

                        DoomThisConnection();
                        ADP.TraceExceptionWithoutRethrow(e);
                    }
                }

                // Reset hashtable values, since calling reset will not send us env_changes.
                CurrentDatabase = _originalDatabase;
                _currentLanguage = _originalLanguage;
            }
        }

        internal void DecrementAsyncCount() {
            Interlocked.Decrement(ref _asyncCommandCount);
        }

        internal void IncrementAsyncCount() {
            Interlocked.Increment(ref _asyncCommandCount);
        }


        ////////////////////////////////////////////////////////////////////////////////////////
        // LOCAL TRANSACTION METHODS
        ////////////////////////////////////////////////////////////////////////////////////////

        override internal void DisconnectTransaction(SqlInternalTransaction internalTransaction) {
            TdsParser parser = Parser;

            if (null != parser) {
                parser.DisconnectTransaction(internalTransaction);
            }
        }

        internal void ExecuteTransaction(TransactionRequest transactionRequest, string name, IsolationLevel iso) {
            ExecuteTransaction(transactionRequest, name, iso, null, false);
        }

        override internal void ExecuteTransaction(TransactionRequest transactionRequest, string name, IsolationLevel iso, SqlInternalTransaction internalTransaction, bool isDelegateControlRequest) {
            if (IsConnectionDoomed) {  // doomed means we can't do anything else...
                if (transactionRequest == TransactionRequest.Rollback
                 || transactionRequest == TransactionRequest.IfRollback) {
                    return;
                }
                throw SQL.ConnectionDoomed();
            }

            if (transactionRequest == TransactionRequest.Commit
             || transactionRequest == TransactionRequest.Rollback
             || transactionRequest == TransactionRequest.IfRollback) {
                if (!Parser.MARSOn && Parser._physicalStateObj.BcpLock) {
                    throw SQL.ConnectionLockedForBcpEvent();
                }
            }

            string transactionName = (null == name) ? String.Empty : name;

            if (!_parser.IsYukonOrNewer) {
                ExecuteTransactionPreYukon(transactionRequest, transactionName, iso, internalTransaction);
            }
            else {
                ExecuteTransactionYukon(transactionRequest, transactionName, iso, internalTransaction, isDelegateControlRequest);
            }
        }

        // This function will not handle idle connection resiliency, as older servers will not support it
        internal void ExecuteTransactionPreYukon(
                    TransactionRequest      transactionRequest, 
                    string                  transactionName, 
                    IsolationLevel          iso, 
                    SqlInternalTransaction  internalTransaction) {
            StringBuilder sqlBatch = new StringBuilder();

            switch (iso) {
                case IsolationLevel.Unspecified:
                    break;
                case IsolationLevel.ReadCommitted:
                    sqlBatch.Append(TdsEnums.TRANS_READ_COMMITTED);
                    sqlBatch.Append(";");
                    break;
                case IsolationLevel.ReadUncommitted:
                    sqlBatch.Append(TdsEnums.TRANS_READ_UNCOMMITTED);
                    sqlBatch.Append(";");
                    break;
                case IsolationLevel.RepeatableRead:
                    sqlBatch.Append(TdsEnums.TRANS_REPEATABLE_READ);
                    sqlBatch.Append(";");
                    break;
                case IsolationLevel.Serializable:
                    sqlBatch.Append(TdsEnums.TRANS_SERIALIZABLE);
                    sqlBatch.Append(";");
                    break;
                case IsolationLevel.Snapshot:
                    throw SQL.SnapshotNotSupported(IsolationLevel.Snapshot);

                case IsolationLevel.Chaos:
                    throw SQL.NotSupportedIsolationLevel(iso);

                default:
                    throw ADP.InvalidIsolationLevel(iso);
            }

            if (!ADP.IsEmpty(transactionName)) {
                transactionName = " " + SqlConnection.FixupDatabaseTransactionName(transactionName);
            }
                
            switch (transactionRequest) {
                case TransactionRequest.Begin:
                    sqlBatch.Append(TdsEnums.TRANS_BEGIN);
                    sqlBatch.Append(transactionName);
                    break;
                case TransactionRequest.Promote:
                    Debug.Assert(false, "Promote called with transaction name or on pre-Yukon!");
                    break;
                case TransactionRequest.Commit:
                    sqlBatch.Append(TdsEnums.TRANS_COMMIT);
                    sqlBatch.Append(transactionName);
                    break;
                case TransactionRequest.Rollback:
                    sqlBatch.Append(TdsEnums.TRANS_ROLLBACK);
                    sqlBatch.Append(transactionName);
                    break;
                case TransactionRequest.IfRollback:
                    sqlBatch.Append(TdsEnums.TRANS_IF_ROLLBACK);
                    sqlBatch.Append(transactionName);
                    break;
                case TransactionRequest.Save:
                    sqlBatch.Append(TdsEnums.TRANS_SAVE);
                    sqlBatch.Append(transactionName);
                    break;
                default:
                    Debug.Assert(false, "Unknown transaction type");
                    break;
            }

            Threading.Tasks.Task executeTask = _parser.TdsExecuteSQLBatch(sqlBatch.ToString(), ConnectionOptions.ConnectTimeout, null, _parser._physicalStateObj, sync: true);
            Debug.Assert(executeTask == null, "Shouldn't get a task when doing sync writes");            
            _parser.Run(RunBehavior.UntilDone, null, null, null, _parser._physicalStateObj);

            // Prior to Yukon, we didn't have any transaction tokens to manage,
            // or any feedback to know when one was created, so we just presume
            // that successful execution of the request caused the transaction
            // to be created, and we set that on the parser.
            if (TransactionRequest.Begin == transactionRequest) {
                Debug.Assert(null != internalTransaction, "Begin Transaction request without internal transaction");
                _parser.CurrentTransaction = internalTransaction;
            }
        }
        

        internal void ExecuteTransactionYukon(
                    TransactionRequest      transactionRequest, 
                    string                  transactionName, 
                    IsolationLevel          iso, 
                    SqlInternalTransaction  internalTransaction, 
                    bool                    isDelegateControlRequest) {
            TdsEnums.TransactionManagerRequestType    requestType = TdsEnums.TransactionManagerRequestType.Begin;
            TdsEnums.TransactionManagerIsolationLevel isoLevel    = TdsEnums.TransactionManagerIsolationLevel.ReadCommitted;

            switch (iso) {
                case IsolationLevel.Unspecified:
                    isoLevel = TdsEnums.TransactionManagerIsolationLevel.Unspecified;
                    break;
                case IsolationLevel.ReadCommitted:
                    isoLevel = TdsEnums.TransactionManagerIsolationLevel.ReadCommitted;
                    break;
                case IsolationLevel.ReadUncommitted:
                    isoLevel = TdsEnums.TransactionManagerIsolationLevel.ReadUncommitted;
                    break;
                case IsolationLevel.RepeatableRead:
                    isoLevel = TdsEnums.TransactionManagerIsolationLevel.RepeatableRead;
                    break;
                case IsolationLevel.Serializable:
                    isoLevel = TdsEnums.TransactionManagerIsolationLevel.Serializable;
                    break;
                case IsolationLevel.Snapshot:
                    isoLevel = TdsEnums.TransactionManagerIsolationLevel.Snapshot;
                    break;
                case IsolationLevel.Chaos:
                    throw SQL.NotSupportedIsolationLevel(iso);
                default:
                    throw ADP.InvalidIsolationLevel(iso);
            }

            TdsParserStateObject stateObj = _parser._physicalStateObj;
            TdsParser parser = _parser;
            bool mustPutSession = false;
            bool releaseConnectionLock = false;

            Debug.Assert(!ThreadHasParserLockForClose || _parserLock.ThreadMayHaveLock(), "Thread claims to have parser lock, but lock is not taken");           
            if (!ThreadHasParserLockForClose) {
                _parserLock.Wait(canReleaseFromAnyThread:false);
                ThreadHasParserLockForClose = true;   // In case of error, let the connection know that we already own the parser lock
                releaseConnectionLock = true;
            }
            try {
                switch (transactionRequest) {
                    case TransactionRequest.Begin:
                        requestType = TdsEnums.TransactionManagerRequestType.Begin;
                        break;
                    case TransactionRequest.Promote:
                        requestType = TdsEnums.TransactionManagerRequestType.Promote;
                        break;
                    case TransactionRequest.Commit:
                        requestType = TdsEnums.TransactionManagerRequestType.Commit;
                        break;
                    case TransactionRequest.IfRollback:
                        // Map IfRollback to Rollback since with Yukon and beyond we should never need
                        // the if since the server will inform us when transactions have completed
                        // as a result of an error on the server.
                    case TransactionRequest.Rollback:
                        requestType = TdsEnums.TransactionManagerRequestType.Rollback;
                        break;
                    case TransactionRequest.Save:
                        requestType = TdsEnums.TransactionManagerRequestType.Save;
                        break;
                    default:
                        Debug.Assert(false, "Unknown transaction type");
                        break;
                }

                // only restore if connection lock has been taken within the function
                if (internalTransaction != null && internalTransaction.RestoreBrokenConnection && releaseConnectionLock) {
                    Task reconnectTask = internalTransaction.Parent.Connection.ValidateAndReconnect(() => {                      
                        ThreadHasParserLockForClose = false;
                        _parserLock.Release();
                        releaseConnectionLock = false;
                    }, 0);
                    if (reconnectTask != null) {
                        AsyncHelper.WaitForCompletion(reconnectTask, 0); // there is no specific timeout for BeginTransaction, uses ConnectTimeout
                        internalTransaction.ConnectionHasBeenRestored = true;
                        return;
                    }
                }
                    


                // SQLBUDT #20010853 - Promote, Commit and Rollback requests for
                // delegated transactions often happen while there is an open result
                // set, so we need to handle them by using a different MARS session, 
                // otherwise we'll write on the physical state objects while someone
                // else is using it.  When we don't have MARS enabled, we need to 
                // lock the physical state object to syncronize it's use at least 
                // until we increment the open results count.  Once it's been 
                // incremented the delegated transaction requests will fail, so they
                // won't stomp on anything.
                // 
                // We need to keep this lock through the duration of the TM reqeuest
                // so that we won't hijack a different request's data stream and a
                // different request won't hijack ours, so we have a lock here on 
                // an object that the ExecTMReq will also lock, but since we're on
                // the same thread, the lock is a no-op.

                if (null != internalTransaction && internalTransaction.IsDelegated) {
                    if (_parser.MARSOn) {
                        stateObj = _parser.GetSession(this);
                        mustPutSession = true;
                    }
                    else if (internalTransaction.OpenResultsCount != 0) {
                        throw SQL.CannotCompleteDelegatedTransactionWithOpenResults(this);
                    }
                }               

                // SQLBU #406778 - _parser may be nulled out during TdsExecuteTrannsactionManagerRequest.
                //  Only use local variable after this call.
                _parser.TdsExecuteTransactionManagerRequest(null, requestType, transactionName, isoLevel,
                    ConnectionOptions.ConnectTimeout, internalTransaction, stateObj, isDelegateControlRequest);
            }   
            finally {
                if (mustPutSession) {
                    parser.PutSession(stateObj);
                }

                if (releaseConnectionLock) {
                    ThreadHasParserLockForClose = false;
                    _parserLock.Release();
                }
            }
        }

        ////////////////////////////////////////////////////////////////////////////////////////
        // DISTRIBUTED TRANSACTION METHODS
        ////////////////////////////////////////////////////////////////////////////////////////

        override internal void DelegatedTransactionEnded() {
            // 
            base.DelegatedTransactionEnded();
        }
        
        override protected byte[] GetDTCAddress() {
            byte[] dtcAddress = _parser.GetDTCAddress(ConnectionOptions.ConnectTimeout, _parser.GetSession(this));
            Debug.Assert(null != dtcAddress, "null dtcAddress?");
            return dtcAddress;
        }

        override protected void PropagateTransactionCookie(byte[] cookie) {
            _parser.PropagateDistributedTransaction(cookie, ConnectionOptions.ConnectTimeout, _parser._physicalStateObj);
        }
      
        ////////////////////////////////////////////////////////////////////////////////////////
        // LOGIN-RELATED METHODS
        ////////////////////////////////////////////////////////////////////////////////////////

        private void CompleteLogin(bool enlistOK) {
            _parser.Run(RunBehavior.UntilDone, null, null, null, _parser._physicalStateObj);

            if (_routingInfo == null) { // ROR should not affect state of connection recovery
                if (!_sessionRecoveryAcknowledged) {
                    _currentSessionData = null;
                    if (_recoverySessionData != null) {
                        throw SQL.CR_NoCRAckAtReconnection(this);
                    }
                }
                if (_currentSessionData != null && _recoverySessionData==null) {
                        _currentSessionData._initialDatabase = CurrentDatabase;
                        _currentSessionData._initialCollation = _currentSessionData._collation;
                        _currentSessionData._initialLanguage = _currentLanguage;                        
                }
                bool isEncrypted = _parser.EncryptionOptions == EncryptionOptions.ON;
                if (_recoverySessionData != null) {
                    if (_recoverySessionData._encrypted != isEncrypted) {
                        throw SQL.CR_EncryptionChanged(this);
                    }                                      
                }
                if (_currentSessionData != null) {
                    _currentSessionData._encrypted = isEncrypted;
                }
                _recoverySessionData = null;
            }

            Debug.Assert(SniContext.Snix_Login == Parser._physicalStateObj.SniContext, String.Format((IFormatProvider)null, "SniContext should be Snix_Login; actual Value: {0}", Parser._physicalStateObj.SniContext));
            _parser._physicalStateObj.SniContext = SniContext.Snix_EnableMars;
            _parser.EnableMars();

            _fConnectionOpen = true; // mark connection as open

            if (Bid.AdvancedOn) {
                Bid.Trace("<sc.SqlInternalConnectionTds.CompleteLogin|ADV> Post-Login Phase: Server connection obtained.\n");
            }

            // for non-pooled connections, enlist in a distributed transaction
            // if present - and user specified to enlist
            if(enlistOK && ConnectionOptions.Enlist) {
                _parser._physicalStateObj.SniContext = SniContext.Snix_AutoEnlist;
                SysTx.Transaction tx = ADP.GetCurrentTransaction();
                Enlist(tx);
            }
            _parser._physicalStateObj.SniContext=SniContext.Snix_Login;
        }

        private void Login(ServerInfo server, TimeoutTimer timeout, string newPassword, SecureString newSecurePassword) {
            // create a new login record
            SqlLogin login = new SqlLogin();

            // gather all the settings the user set in the connection string or
            // properties and do the login
            CurrentDatabase   = server.ResolvedDatabaseName;
            _currentPacketSize = ConnectionOptions.PacketSize;
            _currentLanguage   = ConnectionOptions.CurrentLanguage;

            int timeoutInSeconds = 0;

            // If a timeout tick value is specified, compute the timeout based
            // upon the amount of time left in seconds.
            if (!timeout.IsInfinite)
            {
                long t = timeout.MillisecondsRemaining/1000;
                if ((long)Int32.MaxValue > t)
                {
                    timeoutInSeconds = (int)t;
                }
            }

            login.timeout = timeoutInSeconds;
            login.userInstance     = ConnectionOptions.UserInstance;
            login.hostName         = ConnectionOptions.ObtainWorkstationId();
            login.userName         = ConnectionOptions.UserID;
            login.password         = ConnectionOptions.Password;
            login.applicationName  = ConnectionOptions.ApplicationName;

            login.language         = _currentLanguage;
            if (!login.userInstance) { // Do not send attachdbfilename or database to SSE primary instance
                login.database         = CurrentDatabase;;
                login.attachDBFilename = ConnectionOptions.AttachDBFilename;
            }

            // VSTS#795621 - Ensure ServerName is Sent During TdsLogin To Enable Sql Azure Connectivity.
            // Using server.UserServerName (versus ConnectionOptions.DataSource) since TdsLogin requires 
            // serverName to always be non-null.
            login.serverName = server.UserServerName;

            login.useReplication   = ConnectionOptions.Replication;
            login.useSSPI          = ConnectionOptions.IntegratedSecurity;
            login.packetSize       = _currentPacketSize;
            login.newPassword      = newPassword;
            login.readOnlyIntent   = ConnectionOptions.ApplicationIntent == ApplicationIntent.ReadOnly;
            login.credential       = _credential;
            if (newSecurePassword != null) {
                login.newSecurePassword = newSecurePassword;
            }

            TdsEnums.FeatureExtension requestedFeatures = TdsEnums.FeatureExtension.None;
            if (ConnectionOptions.ConnectRetryCount>0) {
                requestedFeatures |= TdsEnums.FeatureExtension.SessionRecovery;
                _sessionRecoveryRequested = true;
            }

            _parser.TdsLogin(login, requestedFeatures, _recoverySessionData);
        }

        private void LoginFailure() {
            Bid.Trace("<sc.SqlInternalConnectionTds.LoginFailure|RES|CPOOL> %d#\n", ObjectID);

            // If the parser was allocated and we failed, then we must have failed on
            // either the Connect or Login, either way we should call Disconnect.
            // Disconnect can be called if the connection is already closed - becomes
            // no-op, so no issues there.
            if (_parser != null) {

                _parser.Disconnect();
            }
            // 
        }

        private void OpenLoginEnlist(TimeoutTimer timeout, SqlConnectionString connectionOptions, SqlCredential credential,
                    string newPassword, SecureString newSecurePassword, bool redirectedUserInstance) {
            bool useFailoverPartner; // should we use primary or secondary first
            ServerInfo dataSource = new ServerInfo(connectionOptions);
            string failoverPartner;

            if (null != PoolGroupProviderInfo) {
                useFailoverPartner = PoolGroupProviderInfo.UseFailoverPartner;
                failoverPartner = PoolGroupProviderInfo.FailoverPartner;
            }
            else {
                // Only ChangePassword or SSE User Instance comes through this code path.
                useFailoverPartner = false;
                failoverPartner = ConnectionOptions.FailoverPartner; 
            }

            timeoutErrorInternal.SetInternalSourceType(useFailoverPartner ? SqlConnectionInternalSourceType.Failover : SqlConnectionInternalSourceType.Principle);

            bool hasFailoverPartner = !ADP.IsEmpty(failoverPartner);

            // Open the connection and Login
            try {
                timeoutErrorInternal.SetAndBeginPhase(SqlConnectionTimeoutErrorPhase.PreLoginBegin);
                if (hasFailoverPartner) {
                    timeoutErrorInternal.SetFailoverScenario(true); // this is a failover scenario
                    LoginWithFailover(
                                useFailoverPartner, 
                                dataSource, 
                                failoverPartner, 
                                newPassword,
                                newSecurePassword,
                                redirectedUserInstance, 
                                connectionOptions,
                                credential,
                                timeout);
                }
                else {
                    timeoutErrorInternal.SetFailoverScenario(false); // not a failover scenario
                    LoginNoFailover(dataSource, newPassword, newSecurePassword, redirectedUserInstance, 
                            connectionOptions, credential, timeout);
                }
                timeoutErrorInternal.EndPhase(SqlConnectionTimeoutErrorPhase.PostLogin);
            }
            catch (Exception e) {
                // 
                if (ADP.IsCatchableExceptionType(e)) {
                    LoginFailure();
                }
                throw;
            }
            timeoutErrorInternal.SetAllCompleteMarker();

#if DEBUG
            _parser._physicalStateObj.InvalidateDebugOnlyCopyOfSniContext();
#endif
        }

    // Is the given Sql error one that should prevent retrying
    //   to connect.
    private bool IsDoNotRetryConnectError(SqlException exc) {

        return (TdsEnums.LOGON_FAILED == exc.Number) // actual logon failed, i.e. bad password
            || (TdsEnums.PASSWORD_EXPIRED == exc.Number) // actual logon failed, i.e. password isExpired
            || (TdsEnums.IMPERSONATION_FAILED == exc.Number)  // Insuficient privelege for named pipe, among others
            || exc._doNotReconnect; // Exception explicitly supressed reconnection attempts
    }

    // Attempt to login to a host that does not have a failover partner
    //
    //  Will repeatedly attempt to connect, but back off between each attempt so as not to clog the network.
    //  Back off period increases for first few failures: 100ms, 200ms, 400ms, 800ms, then 1000ms for subsequent attempts
    //
    // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
    //  DEVNOTE: The logic in this method is paralleled by the logic in LoginWithFailover.
    //           Changes to either one should be examined to see if they need to be reflected in the other
    // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
    private void LoginNoFailover(ServerInfo serverInfo, string newPassword, SecureString newSecurePassword, bool redirectedUserInstance, 
                SqlConnectionString connectionOptions, SqlCredential credential, TimeoutTimer timeout) {

        Debug.Assert(object.ReferenceEquals(connectionOptions, this.ConnectionOptions), "ConnectionOptions argument and property must be the same"); // consider removing the argument
        int routingAttempts = 0;
        ServerInfo originalServerInfo = serverInfo; // serverInfo may end up pointing to new object due to routing, original object is used to set CurrentDatasource

        if (Bid.AdvancedOn) {
            Bid.Trace("<sc.SqlInternalConnectionTds.LoginNoFailover|ADV> %d#, host=%ls\n", ObjectID, serverInfo.UserServerName);
        }
        int  sleepInterval = 100;  //milliseconds to sleep (back off) between attempts.

        ResolveExtendedServerName(serverInfo, !redirectedUserInstance, connectionOptions);

        long timeoutUnitInterval = 0;

        if (connectionOptions.MultiSubnetFailover) {
            // Determine unit interval
            if (timeout.IsInfinite) {
                timeoutUnitInterval = checked((long)(ADP.FailoverTimeoutStep * (1000L * ADP.DefaultConnectionTimeout)));
            }
            else {
                timeoutUnitInterval = checked((long)(ADP.FailoverTimeoutStep * timeout.MillisecondsRemaining));
            }
        }
        // Only three ways out of this loop:
        //  1) Successfully connected
        //  2) Parser threw exception while main timer was expired
        //  3) Parser threw logon failure-related exception 
        //  4) Parser threw exception in post-initial connect code,
        //      such as pre-login handshake or during actual logon. (parser state != Closed)
        //
        //  Of these methods, only #1 exits normally. This preserves the call stack on the exception 
        //  back into the parser for the error cases.
        int attemptNumber = 0;
        TimeoutTimer intervalTimer = null;
        while(true) {

            if (connectionOptions.MultiSubnetFailover) {
                attemptNumber++;
                // Set timeout for this attempt, but don't exceed original timer                
                long nextTimeoutInterval = checked(timeoutUnitInterval * attemptNumber);
                long milliseconds = timeout.MillisecondsRemaining;
                if (nextTimeoutInterval > milliseconds) {
                    nextTimeoutInterval = milliseconds;
                }
                intervalTimer = TimeoutTimer.StartMillisecondsTimeout(nextTimeoutInterval);
            }

            // Re-allocate parser each time to make sure state is known
            // RFC 50002652 - if parser was created by previous attempt, dispose it to properly close the socket, if created
            if (_parser != null)
                _parser.Disconnect();
 
            _parser = new TdsParser(ConnectionOptions.MARS, ConnectionOptions.Asynchronous);
            Debug.Assert(SniContext.Undefined== Parser._physicalStateObj.SniContext, String.Format((IFormatProvider)null, "SniContext should be Undefined; actual Value: {0}", Parser._physicalStateObj.SniContext));

            try {
                // 


                AttemptOneLogin(    serverInfo, 
                                    newPassword,
                                    newSecurePassword,
                                    !connectionOptions.MultiSubnetFailover,    // ignore timeout for SniOpen call unless MSF 
                                    connectionOptions.MultiSubnetFailover ? intervalTimer : timeout);
                
                if (connectionOptions.MultiSubnetFailover && null != ServerProvidedFailOverPartner) {
                    // connection succeeded: trigger exception if server sends failover partner and MultiSubnetFailover is used
                    throw SQL.MultiSubnetFailoverWithFailoverPartner(serverProvidedFailoverPartner: true, internalConnection: this);
                }

                if (_routingInfo != null) {
                    Bid.Trace("<sc.SqlInternalConnectionTds.LoginNoFailover> Routed to %ls", serverInfo.ExtendedServerName);

                    if (routingAttempts > 0) {
                        throw SQL.ROR_RecursiveRoutingNotSupported(this);
                    }

                    if (timeout.IsExpired) {
                        throw SQL.ROR_TimeoutAfterRoutingInfo(this);
                    }                    

                    serverInfo = new ServerInfo(ConnectionOptions, _routingInfo, serverInfo.ResolvedServerName);
                    timeoutErrorInternal.SetInternalSourceType(SqlConnectionInternalSourceType.RoutingDestination);
                    _originalClientConnectionId = _clientConnectionId;
                    _routingDestination = serverInfo.UserServerName;

                    // restore properties that could be changed by the environment tokens
                    _currentPacketSize = ConnectionOptions.PacketSize;
                    _currentLanguage = _originalLanguage = ConnectionOptions.CurrentLanguage;
                    CurrentDatabase = _originalDatabase = ConnectionOptions.InitialCatalog;
                    _currentFailoverPartner = null;
                    _instanceName = String.Empty;

                    routingAttempts++;

                    continue; // repeat the loop, but skip code reserved for failed connections (after the catch)
                }
                else {
                    break; // leave the while loop -- we've successfully connected
                }
            }
            catch (SqlException sqlex) {
                if (null == _parser
                        || TdsParserState.Closed != _parser.State
                        || IsDoNotRetryConnectError(sqlex)
                        || timeout.IsExpired) {       // no more time to try again
                    throw;  // Caller will call LoginFailure()
                }

                // Check sleep interval to make sure we won't exceed the timeout
                //  Do this in the catch block so we can re-throw the current exception
                if (timeout.MillisecondsRemaining <= sleepInterval) {
                    throw;
                }

                // 
            }

            // 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 (connectionOptions.MultiSubnetFailover) {
                    // connection failed: do not allow failover to server-provided failover partner if MultiSubnetFailover is set
                    throw SQL.MultiSubnetFailoverWithFailoverPartner(serverProvidedFailoverPartner: true, internalConnection: this);
                }
                Debug.Assert(ConnectionOptions.ApplicationIntent != ApplicationIntent.ReadOnly, "FAILOVER+AppIntent=RO: Should already fail (at LOGSHIPNODE in OnEnvChange)");

                timeoutErrorInternal.ResetAndRestartPhase();
                timeoutErrorInternal.SetAndBeginPhase(SqlConnectionTimeoutErrorPhase.PreLoginBegin);
                timeoutErrorInternal.SetInternalSourceType(SqlConnectionInternalSourceType.Failover);
                timeoutErrorInternal.SetFailoverScenario(true); // this is a failover scenario
                LoginWithFailover(
                            true,   // start by using failover partner, since we already failed to connect to the primary
                            serverInfo,
                            ServerProvidedFailOverPartner,
                            newPassword,
                            newSecurePassword,
                            redirectedUserInstance,
                            connectionOptions,
                            credential,
                            timeout);
                return; // LoginWithFailover successfully connected and handled entire connection setup
            }

            // Sleep for a bit to prevent clogging the network with requests, 
            //  then update sleep interval for next iteration (max 1 second interval)
            if (Bid.AdvancedOn) {
                Bid.Trace("<sc.SqlInternalConnectionTds.LoginNoFailover|ADV> %d#, sleeping %d{milisec}\n", ObjectID, sleepInterval);
            }
            Thread.Sleep(sleepInterval);
            sleepInterval = (sleepInterval < 500) ? sleepInterval * 2 : 1000;
        }

        if (null != PoolGroupProviderInfo) {
            // 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(this, false, connectionOptions, ServerProvidedFailOverPartner);
        }
        CurrentDataSource = originalServerInfo.UserServerName;
    }

    // Attempt to login to a host that has a failover partner
    //
    // Connection & timeout sequence is
    //      First target, timeout = interval * 1
    //      second target, timeout = interval * 1
    //      sleep for 100ms
    //      First target, timeout = interval * 2
    //      Second target, timeout = interval * 2
    //      sleep for 200ms
    //      First Target, timeout = interval * 3
    //      etc.
    //
    // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
    //  DEVNOTE: The logic in this method is paralleled by the logic in LoginNoFailover.
    //           Changes to either one should be examined to see if they need to be reflected in the other
    // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
    private void LoginWithFailover(
            bool                useFailoverHost, 
            ServerInfo          primaryServerInfo, 
            string              failoverHost, 
            string              newPassword,
            SecureString        newSecurePassword,
            bool                redirectedUserInstance, 
            SqlConnectionString connectionOptions,
            SqlCredential       credential,
            TimeoutTimer        timeout
        ) {

        Debug.Assert(!connectionOptions.MultiSubnetFailover, "MultiSubnetFailover should not be set if failover partner is used");

        if (Bid.AdvancedOn) {
            Bid.Trace("<sc.SqlInternalConnectionTds.LoginWithFailover|ADV> %d#, useFailover=%d{bool}, primary=", ObjectID, useFailoverHost);
            Bid.PutStr(primaryServerInfo.UserServerName);
            Bid.PutStr(", failover=");
            Bid.PutStr(failoverHost);
            Bid.PutStr("\n");
        }
        int  sleepInterval = 100;  //milliseconds to sleep (back off) between attempts.
        long timeoutUnitInterval;

        string     protocol = ConnectionOptions.NetworkLibrary;
        ServerInfo failoverServerInfo = new ServerInfo(connectionOptions, failoverHost);

        ResolveExtendedServerName(primaryServerInfo, !redirectedUserInstance, connectionOptions);
        if (null == ServerProvidedFailOverPartner) {// No point in resolving the failover partner when we're going to override it below
            // Don't resolve aliases if failover == primary // 
            ResolveExtendedServerName(failoverServerInfo, !redirectedUserInstance && failoverHost != primaryServerInfo.UserServerName, connectionOptions);
        }

        // Determine unit interval
        if (timeout.IsInfinite) {
            timeoutUnitInterval = checked((long) ADP.FailoverTimeoutStep * ADP.TimerFromSeconds(ADP.DefaultConnectionTimeout));
        }
        else {
            timeoutUnitInterval = checked((long) (ADP.FailoverTimeoutStep * timeout.MillisecondsRemaining));
        }

        // Initialize loop variables
        bool failoverDemandDone = false; // have we demanded for partner information yet (as necessary)?
        int attemptNumber = 0;

        // Only three ways out of this loop:
        //  1) Successfully connected
        //  2) Parser threw exception while main timer was expired
        //  3) Parser threw logon failure-related exception (LOGON_FAILED, PASSWORD_EXPIRED, etc)
        //
        //  Of these methods, only #1 exits normally. This preserves the call stack on the exception 
        //  back into the parser for the error cases.
        while (true) {
            // Set timeout for this attempt, but don't exceed original timer
            long nextTimeoutInterval = checked(timeoutUnitInterval * ((attemptNumber / 2) + 1));
            long milliseconds = timeout.MillisecondsRemaining;
            if (nextTimeoutInterval > milliseconds) {
                nextTimeoutInterval = milliseconds;
            }

            TimeoutTimer intervalTimer = TimeoutTimer.StartMillisecondsTimeout(nextTimeoutInterval);

            // Re-allocate parser each time to make sure state is known
            // RFC 50002652 - if parser was created by previous attempt, dispose it to properly close the socket, if created
            if (_parser != null)
                _parser.Disconnect();

            _parser = new TdsParser(ConnectionOptions.MARS, ConnectionOptions.Asynchronous);
            Debug.Assert(SniContext.Undefined== Parser._physicalStateObj.SniContext, String.Format((IFormatProvider)null, "SniContext should be Undefined; actual Value: {0}", Parser._physicalStateObj.SniContext));

            ServerInfo currentServerInfo;
            if (useFailoverHost) {
                if (!failoverDemandDone) {
                    FailoverPermissionDemand();
                    failoverDemandDone = true;
                }

                // Primary server may give us a different failover partner than the connection string indicates.  Update it
                if (null != ServerProvidedFailOverPartner && failoverServerInfo.ResolvedServerName != ServerProvidedFailOverPartner) {
                    if (Bid.AdvancedOn) {
                        Bid.Trace("<sc.SqlInternalConnectionTds.LoginWithFailover|ADV> %d#, new failover partner=%ls\n", ObjectID, ServerProvidedFailOverPartner);
                    }
                    failoverServerInfo.SetDerivedNames(protocol, ServerProvidedFailOverPartner);
                }
                currentServerInfo = failoverServerInfo;
                timeoutErrorInternal.SetInternalSourceType(SqlConnectionInternalSourceType.Failover);
            }
            else {
                currentServerInfo = primaryServerInfo;
                timeoutErrorInternal.SetInternalSourceType(SqlConnectionInternalSourceType.Principle);
            }

            try {
                // Attempt login.  Use timerInterval for attempt timeout unless infinite timeout was requested.
                AttemptOneLogin(
                        currentServerInfo,
                        newPassword,
                        newSecurePassword,
                        false,          // Use timeout in SniOpen
                        intervalTimer,
                        withFailover:true
                        );

                if (_routingInfo != null) {
                    // We are in login with failover scenation and server sent routing information
                    // If it is read-only routing - we did not supply AppIntent=RO (it should be checked before)
                    // If it is something else, not known yet (future server) - this client is not designed to support this.                    
                    // In any case, server should not have sent the routing info.
                    Bid.Trace("<sc.SqlInternalConnectionTds.LoginWithFailover> Routed to %ls", _routingInfo.ServerName);
                    throw SQL.ROR_UnexpectedRoutingInfo(this);
                }

                break; // leave the while loop -- we've successfully connected
            }
            catch (SqlException sqlex) {
                if (IsDoNotRetryConnectError(sqlex)
                        || timeout.IsExpired)
                {       // no more time to try again
                    throw;  // Caller will call LoginFailure()
                }

                if (IsConnectionDoomed) {
                    throw;
                }

                if (1 == attemptNumber % 2) {
                    // Check sleep interval to make sure we won't exceed the original timeout
                    //  Do this in the catch block so we can re-throw the current exception
                    if (timeout.MillisecondsRemaining <= sleepInterval) {
                        throw;
                    }
                }

                // 
            }

            // We only get here when we failed to connect, but are going to re-try

            // After trying to connect to both servers fails, sleep for a bit to prevent clogging 
            //  the network with requests, then update sleep interval for next iteration (max 1 second interval)
            if (1 == attemptNumber % 2) {
                if (Bid.AdvancedOn) {
                    Bid.Trace("<sc.SqlInternalConnectionTds.LoginWithFailover|ADV> %d#, sleeping %d{milisec}\n", ObjectID, sleepInterval);
                }
                Thread.Sleep(sleepInterval);
                sleepInterval = (sleepInterval < 500) ? sleepInterval * 2 : 1000;
            }

            // Update attempt number and target host
            attemptNumber++;
            useFailoverHost = !useFailoverHost;
        }

        // If we get here, connection/login succeeded!  Just a few more checks & record-keeping

        // if connected to failover host, but said host doesn't have DbMirroring set up, throw an error
        if (useFailoverHost && null == ServerProvidedFailOverPartner) {
            throw SQL.InvalidPartnerConfiguration(failoverHost, CurrentDatabase);
        }

        if (null != PoolGroupProviderInfo) {
            // 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(this, useFailoverHost, connectionOptions, ServerProvidedFailOverPartner);
        }
        CurrentDataSource = (useFailoverHost ? failoverHost : primaryServerInfo.UserServerName);
    }

    private void ResolveExtendedServerName(ServerInfo serverInfo, bool aliasLookup, SqlConnectionString options) {
        if (serverInfo.ExtendedServerName == null) {
            string host = serverInfo.UserServerName;
            string protocol = serverInfo.UserProtocol;

            if (aliasLookup) { // We skip this for UserInstances...
                // Perform registry lookup to see if host is an alias.  It will appropriately set host and protocol, if an Alias.
                // Check if it was already resolved, during CR reconnection _currentSessionData values will be copied from
                // _reconnectSessonData of the previous connection
                if (_currentSessionData != null && !string.IsNullOrEmpty(host)) {
                    Tuple<string, string> hostPortPair;
                    if (_currentSessionData._resolvedAliases.TryGetValue(host, out hostPortPair)) {
                        host = hostPortPair.Item1;
                        protocol = hostPortPair.Item2;
                    }
                    else {
                        TdsParserStaticMethods.AliasRegistryLookup(ref host, ref protocol);
                        _currentSessionData._resolvedAliases.Add(serverInfo.UserServerName, new Tuple<string, string>(host, protocol));
                    }
                }
                else {
                    TdsParserStaticMethods.AliasRegistryLookup(ref host, ref protocol);
                }

                //
                if (options.EnforceLocalHost) {
                    // verify LocalHost for |DataDirectory| usage
                    SqlConnectionString.VerifyLocalHostAndFixup(ref host, true, true /*fix-up to "."*/);
                }
            }

            serverInfo.SetDerivedNames(protocol, host);
        }
    }

    // Common code path for making one attempt to establish a connection and log in to server.
    private void AttemptOneLogin(ServerInfo serverInfo, string newPassword, SecureString newSecurePassword, bool ignoreSniOpenTimeout, TimeoutTimer timeout, bool withFailover = false) {
        if (Bid.AdvancedOn) {
            Bid.Trace("<sc.SqlInternalConnectionTds.AttemptOneLogin|ADV> %d#, timout=%I64d{msec}, server=", ObjectID, timeout.MillisecondsRemaining);
            Bid.PutStr(serverInfo.ExtendedServerName);
            Bid.Trace("\n");
        }

        _routingInfo = null; // forget routing information 

        _parser._physicalStateObj.SniContext = SniContext.Snix_Connect;

        _parser.Connect(serverInfo,
                        this,
                        ignoreSniOpenTimeout,
                        timeout.LegacyTimerExpire,
                        ConnectionOptions.Encrypt,
                        ConnectionOptions.TrustServerCertificate,
                        ConnectionOptions.IntegratedSecurity,
                        withFailover);

        timeoutErrorInternal.EndPhase(SqlConnectionTimeoutErrorPhase.ConsumePreLoginHandshake);
        timeoutErrorInternal.SetAndBeginPhase(SqlConnectionTimeoutErrorPhase.LoginBegin);

        _parser._physicalStateObj.SniContext = SniContext.Snix_Login;
        this.Login(serverInfo, timeout, newPassword, newSecurePassword);

        timeoutErrorInternal.EndPhase(SqlConnectionTimeoutErrorPhase.ProcessConnectionAuth);
        timeoutErrorInternal.SetAndBeginPhase(SqlConnectionTimeoutErrorPhase.PostLogin);

        CompleteLogin(!ConnectionOptions.Pooling);

        timeoutErrorInternal.EndPhase(SqlConnectionTimeoutErrorPhase.PostLogin);
    }


    internal void FailoverPermissionDemand() {
        if (null != PoolGroupProviderInfo) {
            PoolGroupProviderInfo.FailoverPermissionDemand();
        }
    }

        ////////////////////////////////////////////////////////////////////////////////////////
        // PREPARED COMMAND METHODS
        ////////////////////////////////////////////////////////////////////////////////////////
        
        protected override object ObtainAdditionalLocksForClose() {
            bool obtainParserLock = !ThreadHasParserLockForClose;
            Debug.Assert(obtainParserLock || _parserLock.ThreadMayHaveLock(), "Thread claims to have lock, but lock is not taken");
            if (obtainParserLock) {
                _parserLock.Wait(canReleaseFromAnyThread: false);
                ThreadHasParserLockForClose = true;
            }
            return obtainParserLock;
        }

        protected override void ReleaseAdditionalLocksForClose(object lockToken) {
            Debug.Assert(lockToken is bool, "Lock token should be boolean");
            if ((bool)lockToken) {
                ThreadHasParserLockForClose = false;
                _parserLock.Release();
            }
        }

        // called by SqlConnection.RepairConnection which is a relatevly expensive way of repair inner connection
        // prior to execution of request, used from EnlistTransaction, EnlistDistributedTransaction and ChangeDatabase
        internal bool GetSessionAndReconnectIfNeeded(SqlConnection parent, int timeout = 0) {

            Debug.Assert(!ThreadHasParserLockForClose, "Cannot call this method if caller has parser lock");
            if (ThreadHasParserLockForClose) {
                return false; // we cannot restore if we cannot release lock
            }

            _parserLock.Wait(canReleaseFromAnyThread: false);
            ThreadHasParserLockForClose = true;   // In case of error, let the connection know that we already own the parser lock
            bool releaseConnectionLock = true;

            try {
                RuntimeHelpers.PrepareConstrainedRegions();
                try {
#if DEBUG
                    TdsParser.ReliabilitySection tdsReliabilitySection = new TdsParser.ReliabilitySection();
                    RuntimeHelpers.PrepareConstrainedRegions();
                    try {
                        tdsReliabilitySection.Start();
#endif //DEBUG
                        Task reconnectTask = parent.ValidateAndReconnect(() => {
                            ThreadHasParserLockForClose = false;
                            _parserLock.Release();
                            releaseConnectionLock = false;
                        }, timeout);
                        if (reconnectTask != null) {
                            AsyncHelper.WaitForCompletion(reconnectTask, timeout);
                            return true;
                        }
                        return false;
#if DEBUG
                    }
                    finally {
                        tdsReliabilitySection.Stop();
                    }
#endif //DEBUG
                }
                catch (System.OutOfMemoryException) {
                    DoomThisConnection();
                    throw;
                }
                catch (System.StackOverflowException) {
                    DoomThisConnection();
                    throw;
                }
                catch (System.Threading.ThreadAbortException) {
                    DoomThisConnection();
                    throw;
                }
            }
            finally {
                if (releaseConnectionLock) {
                    ThreadHasParserLockForClose = false;
                    _parserLock.Release();
                }
            }
        }

        ////////////////////////////////////////////////////////////////////////////////////////
        // PARSER CALLBACKS
        ////////////////////////////////////////////////////////////////////////////////////////

        internal void BreakConnection() {
            var connection = Connection;
            Bid.Trace("<sc.SqlInternalConnectionTds.BreakConnection|RES|CPOOL> %d#, Breaking connection.\n", ObjectID);
            DoomThisConnection();   // Mark connection as unusable, so it will be destroyed
            if (null != connection) {
                connection.Close();                
            }
        }

        internal bool IgnoreEnvChange { // true if we are only draining environment change tokens, used by TdsParser
            get {
                return _routingInfo != null; // connection was routed, ignore rest of env change
            }
        }

        internal void OnEnvChange(SqlEnvChange rec) {
            Debug.Assert(!IgnoreEnvChange,"This function should not be called if IgnoreEnvChange is set!");
            switch (rec.type) {
                case TdsEnums.ENV_DATABASE:
                    // If connection is not open and recovery is not in progresss, store the server value as the original.
                    if (!_fConnectionOpen && _recoverySessionData == null) {
                        _originalDatabase = rec.newValue;
                    }

                    CurrentDatabase = rec.newValue;
                    break;

                case TdsEnums.ENV_LANG:
                    // If connection is not open and recovery is not in progresss, store the server value as the original.
                    if (!_fConnectionOpen && _recoverySessionData == null) {
                        _originalLanguage = rec.newValue;
                    }

                    _currentLanguage = rec.newValue; // TODO: finish this.
                    break;

                case TdsEnums.ENV_PACKETSIZE:
                    _currentPacketSize = Int32.Parse(rec.newValue, CultureInfo.InvariantCulture);
                    break;

                case TdsEnums.ENV_COLLATION:
                    if (_currentSessionData != null) {
                        _currentSessionData._collation = rec.newCollation;
                    }
                    break;

                case TdsEnums.ENV_CHARSET:
                case TdsEnums.ENV_LOCALEID:
                case TdsEnums.ENV_COMPFLAGS:
                case TdsEnums.ENV_BEGINTRAN:
                case TdsEnums.ENV_COMMITTRAN:
                case TdsEnums.ENV_ROLLBACKTRAN:
                case TdsEnums.ENV_ENLISTDTC:
                case TdsEnums.ENV_DEFECTDTC:
                    // only used on parser
                    break;

                case TdsEnums.ENV_LOGSHIPNODE:
                    if (ConnectionOptions.ApplicationIntent == ApplicationIntent.ReadOnly) {
                        throw SQL.ROR_FailoverNotSupportedServer(this);
                    }
                    _currentFailoverPartner = rec.newValue;
                    break;

                case TdsEnums.ENV_PROMOTETRANSACTION:
                    PromotedDTCToken = rec.newBinValue;
                    break;

                case TdsEnums.ENV_TRANSACTIONENDED:
                    break;

                case TdsEnums.ENV_TRANSACTIONMANAGERADDRESS:
                    // For now we skip these Yukon only env change notifications
                    break;

                case TdsEnums.ENV_SPRESETCONNECTIONACK:
                    // connection is being reset 
                    if (_currentSessionData != null) {
                        _currentSessionData.Reset();
                    }                    
                    break;

                case TdsEnums.ENV_USERINSTANCE:
                    _instanceName = rec.newValue;
                    break;

                case TdsEnums.ENV_ROUTING:
                    if (string.IsNullOrEmpty(rec.newRoutingInfo.ServerName) || rec.newRoutingInfo.Protocol != 0 || rec.newRoutingInfo.Port == 0) {
                        throw SQL.ROR_InvalidRoutingInfo(this);
                    }
                    _routingInfo = rec.newRoutingInfo;
                    break;

                default:
                    Debug.Assert(false, "Missed token in EnvChange!");
                    break;
            }
        }

        internal void OnLoginAck(SqlLoginAck rec) {
            _loginAck = rec;
            // 
            if (_recoverySessionData != null) {
                if (_recoverySessionData._tdsVersion != rec.tdsVersion) {
                    throw SQL.CR_TDSVersionNotPreserved(this);
                }
            }
            if (_currentSessionData != null) {
                _currentSessionData._tdsVersion = rec.tdsVersion;
            }
        }

        internal void OnFeatureExtAck(int featureId, byte[] data) {
            if (_routingInfo != null) {
                return;
            }
            switch (featureId) {
                case TdsEnums.FEATUREEXT_SRECOVERY: {
                        // Session recovery not requested
                        if (!_sessionRecoveryRequested) {
                            throw SQL.ParsingError();
                        }
                        _sessionRecoveryAcknowledged = true;

#if DEBUG
                        foreach (var s in _currentSessionData._delta) {
                            Debug.Assert(s==null, "Delta should be null at this point");
                        }
#endif
                        Debug.Assert(_currentSessionData._unrecoverableStatesCount == 0, "Unrecoverable states count should be 0");

                        int i = 0;
                        while (i < data.Length) {
                            byte stateId = data[i]; i++;
                            int len;
                            byte bLen = data[i]; i++;
                            if (bLen == 0xFF) {
                                len = BitConverter.ToInt32(data, i); i += 4;
                            }
                            else {
                                len = bLen;
                            }
                            byte[] stateData = new byte[len];
                            Buffer.BlockCopy(data, i, stateData, 0, len); i += len;
                            if (_recoverySessionData == null) {
                                _currentSessionData._initialState[stateId] = stateData;
                            }
                            else {
                                _currentSessionData._delta[stateId] = new SessionStateRecord { _data = stateData, _dataLength = len, _recoverable = true, _version = 0 };
                                _currentSessionData._deltaDirty = true;
                            }
                        }
                        break;
                    }
                default: {
                        // Unknown feature ack 
                        throw SQL.ParsingError();
                    }
            }
        }

        ////////////////////////////////////////////////////////////////////////////////////////
        // Helper methods for Locks
        ////////////////////////////////////////////////////////////////////////////////////////
        
        // Indicates if the current thread claims to hold the parser lock
        internal bool ThreadHasParserLockForClose {
            get {
                return _threadIdOwningParserLock == Thread.CurrentThread.ManagedThreadId;
            }
            set {
                Debug.Assert(_parserLock.ThreadMayHaveLock(), "Should not modify ThreadHasParserLockForClose without taking the lock first");
                Debug.Assert(_threadIdOwningParserLock == -1 || _threadIdOwningParserLock == Thread.CurrentThread.ManagedThreadId, "Another thread already claims to own the parser lock");

                if (value) {
                    // If setting to true, then the thread owning the lock is the current thread
                    _threadIdOwningParserLock = Thread.CurrentThread.ManagedThreadId;
                }
                else if (_threadIdOwningParserLock == Thread.CurrentThread.ManagedThreadId) {
                    // If setting to false and currently owns the lock, then no-one owns the lock
                    _threadIdOwningParserLock = -1;
                }
                // else This thread didn't own the parser lock and doesn't claim to own it, so do nothing
            }
        }

        internal override bool TryReplaceConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource<DbConnectionInternal> retry, DbConnectionOptions userOptions) {
            return base.TryOpenConnectionInternal(outerConnection, connectionFactory, retry, userOptions);
        }
    }

    internal sealed class ServerInfo {
        internal string ExtendedServerName   { get; private set; } // the resolved servername with protocol
        internal string ResolvedServerName   { get; private set; } // the resolved servername only
        internal string ResolvedDatabaseName { get; private set; } // name of target database after resolution
        internal string UserProtocol         { get; private set; } // the user specified protocol        

        // The original user-supplied server name from the connection string.
        // If connection string has no Data Source, the value is set to string.Empty.
        // In case of routing, will be changed to routing destination
        internal string UserServerName
        {
            get
            {
                return m_userServerName;
            }
            private set
            {
                m_userServerName = value;
            }
        } private string m_userServerName;

        internal readonly string PreRoutingServerName;
        
        // Initialize server info from connection options, 
        internal ServerInfo(SqlConnectionString userOptions) : this(userOptions, userOptions.DataSource) {}

        // Initialize server info from connection options, but override DataSource with given server name
        internal ServerInfo (SqlConnectionString userOptions, string serverName) {
            //-----------------
            // Preconditions
            Debug.Assert(null != userOptions);

            //-----------------
            //Method body
             
            Debug.Assert(serverName != null, "server name should never be null");
            UserServerName  = (serverName ?? string.Empty); // ensure user server name is not null

            UserProtocol = userOptions.NetworkLibrary;
            ResolvedDatabaseName = userOptions.InitialCatalog;
            PreRoutingServerName = null;
        }


        // Initialize server info from connection options, but override DataSource with given server name
        internal ServerInfo(SqlConnectionString userOptions, RoutingInfo routing, string preRoutingServerName) {
            //-----------------
            // Preconditions
            Debug.Assert(null != userOptions && null!=routing);

            //-----------------
            //Method body
            Debug.Assert(routing.ServerName != null, "server name should never be null");
            if (routing == null || routing.ServerName == null) {
                UserServerName = string.Empty; // ensure user server name is not null
            }
            else {
                UserServerName = string.Format(CultureInfo.InvariantCulture, "{0},{1}", routing.ServerName, routing.Port);
            }
            PreRoutingServerName = preRoutingServerName;
            UserProtocol = TdsEnums.TCP;
            SetDerivedNames(UserProtocol, UserServerName);
            ResolvedDatabaseName = userOptions.InitialCatalog;
        }

        internal void SetDerivedNames(string protocol, string serverName) {
            // The following concatenates the specified netlib network protocol to the host string, if netlib is not null
            // and the flag is on.  This allows the user to specify the network protocol for the connection - but only
            // when using the Dbnetlib dll.  If the protocol is not specified, the netlib will
            // try all protocols in the order listed in the Client Network Utility.  Connect will
            // then fail if all protocols fail.
            if (!ADP.IsEmpty(protocol)) {
                ExtendedServerName = protocol + ":" + serverName;
            }
            else {
                ExtendedServerName = serverName;
            }
            ResolvedServerName = serverName;
        }
    }
}