2010-06-21 Atsushi Enomoto <atsushi@ximian.com>

[mcs.git] / class / Mono.Data.Tds / Mono.Data.Tds.Protocol / Tds.cs

//
// Mono.Data.Tds.Protocol.Tds.cs
//
// Author:
//   Tim Coleman (tim@timcoleman.com)
//   Sebastien Pouliot (spouliot@motus.com)
//   Daniel Morgan (danielmorgan@verizon.net)
//       Veerapuram Varadhan  (vvaradhan@novell.com)
//
// Copyright (C) 2002 Tim Coleman
// Portions (C) 2003 Motus Technologies Inc. (http://www.motus.com)
// Portions (C) 2003,2005 Daniel Morgan
// Portions (C) 2008,2009 Novell Inc. 

//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
// 
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

using Mono.Security.Protocol.Ntlm;
using System;
using System.IO;
using System.Collections;
using System.ComponentModel;
using System.Diagnostics;
using System.Net.Sockets;
using System.Globalization;
using System.Text;

namespace Mono.Data.Tds.Protocol
{
        public abstract class Tds
        {
                #region Fields

                TdsComm comm;
                TdsVersion tdsVersion;
                
                protected internal TdsConnectionParameters connectionParms;
                protected readonly byte[] NTLMSSP_ID = new byte[] {0x4e, 0x54, 0x4c, 0x4d, 0x53, 0x53, 0x50, 0x00};

                int packetSize;
                string dataSource;
                string database;
                string originalDatabase = string.Empty;
                string databaseProductName;
                string databaseProductVersion;
                int databaseMajorVersion;
                CultureInfo locale = CultureInfo.InvariantCulture;

                string charset;
                string language;

                bool connected;
                bool moreResults;

                Encoding encoder;
//              bool autoCommit;

                bool doneProc;
                bool pooling = true;
                TdsDataRow currentRow;
                TdsDataColumnCollection columns;

                ArrayList tableNames;
                ArrayList columnNames;

                TdsMetaParameterCollection parameters = new TdsMetaParameterCollection ();

                bool queryInProgress;
                int cancelsRequested;
                int cancelsProcessed;

//              bool isDone;
//              bool isDoneInProc;

                ArrayList outputParameters = new ArrayList ();
                protected TdsInternalErrorCollection messages = new TdsInternalErrorCollection ();

                int recordsAffected = -1;

                long StreamLength;
                long StreamIndex;
                int StreamColumnIndex;

                bool sequentialAccess;
                bool isRowRead;
                bool isResultRead;
                bool LoadInProgress;
                byte [] collation;

                internal int poolStatus = 0;

                #endregion // Fields

                #region Properties

                protected string Charset {
                        get { return charset; }
                }

                protected CultureInfo Locale {
                        get { return locale; }
                }

                public bool DoneProc {
                        get { return doneProc; }
                }

                protected string Language {
                        get { return language; }
                }

                protected ArrayList ColumnNames {
                        get { return columnNames; }
                }

                public TdsDataRow ColumnValues {
                        get { return currentRow; }
                }

                internal TdsComm Comm {
                        get { return comm; }
                }

                public string Database {
                        get { return database; }
                }

                public string DataSource {
                        get { return dataSource; }
                }

                public bool IsConnected {
                        get { return connected && comm != null && comm.IsConnected (); }
                        set { connected = value; }
                }

                public bool Pooling {
                        get { return pooling; }
                        set { pooling = value; }
                }

                public bool MoreResults {
                        get { return moreResults; }
                        set { moreResults = value; }
                }

                public int PacketSize {
                        get { return packetSize; }
                }

                public int RecordsAffected {
                        get { return recordsAffected; }
                        set { recordsAffected = value; }
                }

                public string ServerVersion {
                        get { return databaseProductVersion; }
                }

                public TdsDataColumnCollection Columns {
                        get { return columns; }
                }

                public TdsVersion TdsVersion {
                        get { return tdsVersion; }
                }

                public ArrayList OutputParameters {
                        get { return outputParameters; }
                        set { outputParameters = value; }
                }

                protected TdsMetaParameterCollection Parameters {
                        get { return parameters; }
                        set { parameters = value; }
                }

                public bool SequentialAccess {
                        get { return sequentialAccess; }
                        set { sequentialAccess = value; }
                }

                public byte[] Collation {
                        get {return collation; }
                }

                public TdsVersion ServerTdsVersion {
                        get { 
                                switch (databaseMajorVersion) {
                                case 4: return TdsVersion.tds42;
                                case 5: return TdsVersion.tds50;
                                case 7: return TdsVersion.tds70;
                                case 8: return TdsVersion.tds80;
                                case 9: return TdsVersion.tds90;
                                case 10: return TdsVersion.tds100;
                                default: return tdsVersion; // return client's version
                                }
                        }
                }

                private void SkipRow ()
                {
                        SkipToColumnIndex (Columns.Count);

                        StreamLength = 0;
                        StreamColumnIndex = 0;
                        StreamIndex = 0;
                        LoadInProgress = false;
                }

                private void SkipToColumnIndex (int colIndex)
                {
                        if (LoadInProgress)
                                EndLoad ();

                        if (colIndex < StreamColumnIndex)
                                throw new Exception ("Cannot Skip to a colindex less than the curr index");

                        while (colIndex != StreamColumnIndex) {
#if NET_2_0
                                TdsColumnType? colType = Columns[StreamColumnIndex].ColumnType;
                                if (colType == null)
                                        throw new Exception ("Column type unset.");
#else
                                TdsColumnType colType = (TdsColumnType) Columns [StreamColumnIndex]["ColumnType"];
#endif
                                if (!(colType == TdsColumnType.Image ||
                                        colType == TdsColumnType.Text ||
                                        colType == TdsColumnType.NText)) {
                                        GetColumnValue (colType, false, StreamColumnIndex);
                                        StreamColumnIndex ++;
                                }
                                else {
                                        BeginLoad (colType);
                                        Comm.Skip (StreamLength);
                                        StreamLength = 0;
                                        EndLoad ();
                                }
                        }
                }

                public object GetSequentialColumnValue (int colIndex)
                {
                        if (colIndex < StreamColumnIndex)
                                throw new InvalidOperationException ("Invalid attempt tp read from column ordinal" + colIndex); 

                        if (LoadInProgress)
                                EndLoad ();

                        if (colIndex != StreamColumnIndex)
                                SkipToColumnIndex (colIndex);

#if NET_2_0
                        object o = GetColumnValue (Columns[colIndex].ColumnType, false, colIndex);
#else
                        object o = GetColumnValue ((TdsColumnType)Columns[colIndex]["ColumnType"], false, colIndex);
#endif
                        StreamColumnIndex++;
                        return o;
                }

                public long GetSequentialColumnValue (int colIndex, long fieldIndex, byte[] buffer, int bufferIndex, int size) 
                {
                        if (colIndex < StreamColumnIndex)
                                throw new InvalidOperationException ("Invalid attempt to read from column ordinal" + colIndex);
                        try {
                                if (colIndex != StreamColumnIndex)
                                        SkipToColumnIndex (colIndex);

                                if (!LoadInProgress) {
#if NET_2_0
                                        BeginLoad (Columns[colIndex].ColumnType);
#else
                                        BeginLoad ((TdsColumnType)Columns[colIndex]["ColumnType"]);
#endif
                                }

                                if (buffer == null)
                                        return StreamLength;
                                return LoadData (fieldIndex, buffer, bufferIndex, size);
                        } catch (IOException ex) {
                                connected = false;
                                throw new TdsInternalException ("Server closed the connection.", ex);
                        }
                }

                private void BeginLoad (
#if NET_2_0
                        TdsColumnType? colType
#else
                        TdsColumnType colType
#endif
                ) 
                {
                        if (LoadInProgress)
                                EndLoad ();

                        StreamLength = 0;

#if NET_2_0
                        if (colType == null)
                                throw new ArgumentNullException ("colType");
#endif

                        switch (colType) {
                        case TdsColumnType.Text :
                        case TdsColumnType.NText:
                        case TdsColumnType.Image:
                                if (Comm.GetByte () != 0) {
                                        Comm.Skip (24);
                                        StreamLength = Comm.GetTdsInt ();
                                } else {
                                        // use -2 to indicate that we're dealing
                                        // with a NULL value
                                        StreamLength = -2;
                                }
                                break;
                        case TdsColumnType.BigVarChar:
                        case TdsColumnType.BigChar:
                        case TdsColumnType.BigBinary:
                        case TdsColumnType.BigVarBinary:
                                Comm.GetTdsShort ();
                                StreamLength = Comm.GetTdsShort ();
                                break;
                        case TdsColumnType.VarChar :
                        case TdsColumnType.NVarChar :
                        case TdsColumnType.Char:
                        case TdsColumnType.NChar:
                        case TdsColumnType.Binary:
                        case TdsColumnType.VarBinary:
                                StreamLength = Comm.GetTdsShort ();
                                break;
                        default :
                                StreamLength = -1;
                                break;
                        }

                        StreamIndex = 0;
                        LoadInProgress = true;
                }

                private void EndLoad()
                {
                        if (StreamLength > 0)
                                Comm.Skip (StreamLength);
                        StreamLength = 0;
                        StreamIndex = 0;
                        StreamColumnIndex++;
                        LoadInProgress = false;
                }

                private long LoadData (long fieldIndex, byte[] buffer, int bufferIndex, int size)
                {
                        if (StreamLength <= 0)
                                return StreamLength;

                        if (fieldIndex < StreamIndex)
                                throw new InvalidOperationException (string.Format (
                                        "Attempting to read at dataIndex '{0}' is " +
                                        "not allowed as this is less than the " +
                                        "current position. You must read from " +
                                        "dataIndex '{1}' or greater.",
                                        fieldIndex, StreamIndex));

                        if (fieldIndex >= (StreamLength + StreamIndex))
                                return 0;

                        // determine number of bytes to skip
                        int skip = (int) (fieldIndex - StreamIndex);
                        // skip bytes
                        Comm.Skip (skip);
                        // update the current position
                        StreamIndex += (fieldIndex - StreamIndex);
                        // update the remaining length
                        StreamLength -= skip;

                        // Load the reqd amt of bytes
                        int loadlen = (int) ((size > StreamLength) ? StreamLength : size);
                        byte[] arr = Comm.GetBytes (loadlen, true);

                        // update the index and stream length
                        StreamIndex +=  loadlen + (fieldIndex - StreamIndex);
                        StreamLength -= loadlen;
                        arr.CopyTo (buffer, bufferIndex);

                        return arr.Length;
                }

                #endregion // Properties

                #region Events

                public event TdsInternalErrorMessageEventHandler TdsErrorMessage;
                public event TdsInternalInfoMessageEventHandler TdsInfoMessage;

                #endregion // Events

                #region Constructors

                public Tds (string dataSource, int port, int packetSize, int timeout, TdsVersion tdsVersion)
                {
                        this.tdsVersion = tdsVersion;
                        this.packetSize = packetSize;
                        this.dataSource = dataSource;
                        this.columns = new TdsDataColumnCollection ();

                        comm = new TdsComm (dataSource, port, packetSize, timeout, tdsVersion);
                }

                #endregion // Constructors

                #region Public Methods

                internal protected void InitExec () 
                {
                        // clean up
                        moreResults = true;
                        doneProc = false;

                        // Reset "read" status variables  - used in case of SequentialAccess
                        isResultRead = false;
                        isRowRead = false;
                        StreamLength = 0;
                        StreamIndex = 0;
                        StreamColumnIndex = 0;
                        LoadInProgress = false;
                        
                        // Reset more variables
                        queryInProgress = false;
                        cancelsRequested = 0;
                        cancelsProcessed = 0;
                        recordsAffected = -1;
                        
                        messages.Clear ();
                        outputParameters.Clear ();
                }

                public void Cancel ()
                {
                        if (queryInProgress) {
                                if (cancelsRequested == cancelsProcessed) {
                                        comm.StartPacket (TdsPacketType.Cancel);
                                        try {
                                                Comm.SendPacket ();
                                        } catch (IOException ex) {
                                                connected = false;
                                                throw new TdsInternalException ("Server closed the connection.", ex);
                                        }
                                        cancelsRequested += 1;
                                }
                        }
                }
        
                public abstract bool Connect (TdsConnectionParameters connectionParameters);

                public static TdsTimeoutException CreateTimeoutException (string dataSource, string method)
                {
                        string message = "Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding.";
                        return new TdsTimeoutException (0, 0, message, -2, method, dataSource, "Mono TdsClient Data Provider", 0);
                }

                public void Disconnect ()
                {
                        try {
                                comm.StartPacket (TdsPacketType.Logoff);
                                comm.Append ((byte) 0);
                                comm.SendPacket ();
                        } catch {
                                // We're closing the socket anyway
                        }
                        connected = false;
                        comm.Close ();
                }
                
                public virtual bool Reset ()
                {
                        database = originalDatabase;
                        return true;
                }

                protected virtual bool IsValidRowCount (byte status, byte op)
                {
                        return ((status & (0x10)) != 0) ;
                }

                public void Execute (string sql)
                {
                        Execute (sql, null, 0, false);
                }

                public void ExecProc (string sql)
                {
                        ExecProc (sql, null, 0, false);
                }

                public virtual void Execute (string sql, TdsMetaParameterCollection parameters, int timeout, bool wantResults)
                {
                        ExecuteQuery (sql, timeout, wantResults);       
                }

                public virtual void ExecProc (string sql, TdsMetaParameterCollection parameters, int timeout, bool wantResults)
                {
                        ExecuteQuery (String.Format ("exec {0}", sql), timeout, wantResults);
                }

                public virtual void ExecPrepared (string sql, TdsMetaParameterCollection parameters, int timeout, bool wantResults)
                {
                        throw new NotSupportedException ();
                }

                internal void ExecBulkCopyMetaData (int timeout, bool wantResults)
                {
                        moreResults = true;
                        try {
                                Comm.SendPacket ();
                                CheckForData (timeout);
                                if (!wantResults) 
                                        SkipToEnd ();
                        } catch (IOException ex) {
                                connected = false;
                                throw new TdsInternalException ("Server closed the connection.", ex);
                        }
                }

                internal void ExecBulkCopy (int timeout, bool wantResults)
                {
                        moreResults = true;
                        try {
                                Comm.SendPacket ();
                                CheckForData (timeout);
                                if (!wantResults) 
                                        SkipToEnd ();
                        } catch (IOException ex) {
                                connected = false;
                                throw new TdsInternalException ("Server closed the connection.", ex);
                        }
                }

                protected void ExecuteQuery (string sql, int timeout, bool wantResults)
                {
                        InitExec ();

                        Comm.StartPacket (TdsPacketType.Query);
                        Comm.Append (sql);
                        try {
                                Comm.SendPacket ();
                                CheckForData (timeout);
                                if (!wantResults) 
                                        SkipToEnd ();
                        } catch (IOException ex) {
                                connected = false;
                                throw new TdsInternalException ("Server closed the connection.", ex);
                        }
                }

                protected virtual void ExecRPC (string rpcName, TdsMetaParameterCollection parameters,
                                                int timeout, bool wantResults)
                {
                        Comm.StartPacket (TdsPacketType.DBRPC);

                        byte [] rpcNameBytes = Comm.Encoder.GetBytes (rpcName);
                        byte rpcNameLength = (byte) rpcNameBytes.Length;
                        ushort mask = 0x0000;
                        ushort packetLength =  (ushort) (sizeof (byte) + rpcNameLength +
                                                sizeof (ushort));

                        Comm.Append (packetLength);
                        Comm.Append (rpcNameLength);
                        Comm.Append (rpcNameBytes);
                        Comm.Append (mask);
                        
                        try {
                                Comm.SendPacket ();
                                CheckForData (timeout);
                                if (!wantResults) 
                                        SkipToEnd ();
                        } catch (IOException ex) {
                                connected = false;
                                throw new TdsInternalException ("Server closed the connection.", ex);
                        }
                }

                public bool NextResult ()
                {
                        if (SequentialAccess) {
                                if (isResultRead) {
                                        while (NextRow ()) {}
                                        isRowRead = false;
                                        isResultRead = false;
                                }
                        }
                        if (!moreResults)
                                return false;

                        TdsPacketSubType subType;

                        bool done = false;
                        bool outputParams = false;

                        while (!done) {
                                subType = ProcessSubPacket ();
                                if (outputParams) {
                                        moreResults = false;
                                        break;
                                }
                                switch (subType) {
                                case TdsPacketSubType.ColumnInfo:
                                case TdsPacketSubType.ColumnMetadata: 
                                case TdsPacketSubType.RowFormat:
                                        byte peek = Comm.Peek ();
                                        done = (peek != (byte) TdsPacketSubType.TableName);
                                        if (done && doneProc && peek == (byte) TdsPacketSubType.Row) {
                                                outputParams = true;
                                                done = false;
                                        }
                                        break;
                                case TdsPacketSubType.TableName:
                                //      done = true;
                                        peek = Comm.Peek ();
                                        done = (peek != (byte) TdsPacketSubType.ColumnDetail);
                                        break;
                                case TdsPacketSubType.ColumnDetail:
                                        done = true;
                                        break;
                                default:
                                        done = !moreResults;
                                        break;
                                }
                        }

                        return moreResults;
                }

                public bool NextRow ()
                {
                        if (SequentialAccess) {
                                if (isRowRead) {
                                        SkipRow ();
                                        isRowRead = false;
                                }
                        }

                        TdsPacketSubType subType;
                        bool done = false;
                        bool result = false;

                        do {
                                subType = ProcessSubPacket ();
                                switch (subType) {
                                case TdsPacketSubType.Row:
                                        result = true;
                                        done = true;
                                        break;
                                case TdsPacketSubType.Done:
                                case TdsPacketSubType.DoneProc:
                                case TdsPacketSubType.DoneInProc:
                                        result = false;
                                        done = true;
                                        break;
                                }
                        } while (!done);

                        return result;
                }

                public virtual string Prepare (string sql, TdsMetaParameterCollection parameters)
                {
                        throw new NotSupportedException ();
                }

                public void SkipToEnd ()
                {
                        try {
                                while (NextResult ()) { /* DO NOTHING */ }
                        } catch (IOException ex) {
                                connected = false;
                                throw new TdsInternalException ("Server closed the connection.", ex);
                        }
                }

                public virtual void Unprepare (string statementId) 
                {
                        throw new NotSupportedException ();
                }

                #endregion // Public Methods

                #region // Private Methods

                [MonoTODO ("Is cancel enough, or do we need to drop the connection?")]
                protected void CheckForData (int timeout) 
                {
                        if (timeout > 0 && !comm.Poll (timeout, SelectMode.SelectRead)) {
                                Cancel ();
                                throw CreateTimeoutException (dataSource, "CheckForData()");
                        }
                }
        
                protected TdsInternalInfoMessageEventArgs CreateTdsInfoMessageEvent (TdsInternalErrorCollection errors)
                {
                        return new TdsInternalInfoMessageEventArgs (errors);
                }

                protected TdsInternalErrorMessageEventArgs CreateTdsErrorMessageEvent (byte theClass, int lineNumber, string message, int number, string procedure, string server, string source, byte state)
                {
                        return new TdsInternalErrorMessageEventArgs (new TdsInternalError (theClass, lineNumber, message, number, procedure, server, source, state));
                }

                private Encoding GetEncodingFromColumnCollation (int lcid, int sortId)
                {
                        if (sortId != 0) 
                                return TdsCharset.GetEncodingFromSortOrder (sortId);
                        else
                                return TdsCharset.GetEncodingFromLCID (lcid);
                }
                
                protected object GetColumnValue (
#if NET_2_0
                        TdsColumnType? colType,
#else
                        TdsColumnType colType,
#endif
                        bool outParam)
                {
                        return GetColumnValue (colType, outParam, -1);
                }

                private object GetColumnValue (
#if NET_2_0
                        TdsColumnType? colType,
#else
                        TdsColumnType colType,
#endif
                        bool outParam, int ordinal)
                {
                        int len;
                        object element = null;
                        Encoding enc = null;
                        int lcid = 0, sortId = 0;

#if NET_2_0
                        if (colType == null)
                                throw new ArgumentNullException ("colType");
#endif
                        if (ordinal > -1 && tdsVersion > TdsVersion.tds70) {
#if NET_2_0
                                lcid = (int) columns[ordinal].LCID;
                                sortId = (int) columns[ordinal].SortOrder; 
#else
                                lcid = (int) columns[ordinal]["LCID"];
                                sortId = (int) columns[ordinal]["SortOrder"];
#endif                  
                        }
                        
                        switch (colType) {
                        case TdsColumnType.IntN :
                                if (outParam)
                                        comm.Skip (1);
                                element = GetIntValue (colType);
                                break;
                        case TdsColumnType.Int1 :
                        case TdsColumnType.Int2 :
                        case TdsColumnType.Int4 :
                        case TdsColumnType.BigInt :
                                element = GetIntValue (colType);
                                break;
                        case TdsColumnType.Image :
                                if (outParam)
                                        comm.Skip (1);
                                element = GetImageValue ();
                                break;
                        case TdsColumnType.Text :
                                enc = GetEncodingFromColumnCollation (lcid, sortId);                    
                                if (outParam) 
                                        comm.Skip (1);
                                element = GetTextValue (false, enc);
                                break;
                        case TdsColumnType.NText :
                                enc = GetEncodingFromColumnCollation (lcid, sortId);
                                if (outParam) 
                                        comm.Skip (1);
                                element = GetTextValue (true, enc);
                                break;
                        case TdsColumnType.Char :
                        case TdsColumnType.VarChar :
                                enc = GetEncodingFromColumnCollation (lcid, sortId);                    
                                if (outParam)
                                        comm.Skip (1);
                                element = GetStringValue (colType, false, outParam, enc);
                                break;
                        case TdsColumnType.BigVarBinary :
                                if (outParam)
                                        comm.Skip (1);
                                len = comm.GetTdsShort ();
                                element = comm.GetBytes (len, true);
                                break;
                                /*
                        case TdsColumnType.BigBinary :
                                if (outParam)
                                        comm.Skip (2);
                                len = comm.GetTdsShort ();
                                element = comm.GetBytes (len, true);
                                break;
                                */
                        case TdsColumnType.BigBinary :
                                if (outParam)
                                        comm.Skip (2);
                                element = GetBinaryValue ();
                                break;
                        case TdsColumnType.BigChar :
                        case TdsColumnType.BigVarChar :
                                enc = GetEncodingFromColumnCollation (lcid, sortId);                            
                                if (outParam)
                                        comm.Skip (2);
                                element = GetStringValue (colType, false, outParam, enc);
                                break;
                        case TdsColumnType.NChar :
                        case TdsColumnType.BigNVarChar :
                                enc = GetEncodingFromColumnCollation (lcid, sortId);                            
                                if (outParam)
                                        comm.Skip(2);
                                element = GetStringValue (colType, true, outParam, enc);
                                break;
                        case TdsColumnType.NVarChar :
                                enc = GetEncodingFromColumnCollation (lcid, sortId);                            
                                if (outParam) 
                                        comm.Skip (1);
                                element = GetStringValue (colType, true, outParam, enc);
                                break;
                        case TdsColumnType.Real :
                        case TdsColumnType.Float8 :
                                element = GetFloatValue (colType);
                                break;
                        case TdsColumnType.FloatN :
                                if (outParam) 
                                        comm.Skip (1);
                                element = GetFloatValue (colType);
                                break;
                        case TdsColumnType.SmallMoney :
                        case TdsColumnType.Money :
                                element = GetMoneyValue (colType);
                                break;
                        case TdsColumnType.MoneyN :
                                if (outParam)
                                        comm.Skip (1);
                                element = GetMoneyValue (colType);
                                break;
                        case TdsColumnType.Numeric :
                        case TdsColumnType.Decimal :
                                byte precision;
                                byte scale;
                                if (outParam) {
                                        comm.Skip (1);
                                        precision = comm.GetByte ();
                                        scale = comm.GetByte ();
                                }
                                else {
#if NET_2_0
                                        precision = (byte) columns[ordinal].NumericPrecision;
                                        scale = (byte) columns[ordinal].NumericScale;
#else
                                        precision = (byte) columns[ordinal]["NumericPrecision"];
                                        scale = (byte) columns[ordinal]["NumericScale"];
#endif
                                }

                                element = GetDecimalValue (precision, scale);
                                
                                // workaround for fact that TDS 7.0 returns
                                // bigint as decimal (19,0), and client code
                                // expects it to be returned as a long
                                if (scale == 0 && precision <= 19 && tdsVersion == TdsVersion.tds70) {
                                        if (!(element is System.DBNull))
                                                element = Convert.ToInt64 (element);
                                }
                                break;
                        case TdsColumnType.DateTimeN :
                                if (outParam) 
                                        comm.Skip (1);
                                element = GetDateTimeValue (colType);
                                break;
                        case TdsColumnType.DateTime4 :
                        case TdsColumnType.DateTime :
                                element = GetDateTimeValue (colType);
                                break;
                        case TdsColumnType.VarBinary :
                        case TdsColumnType.Binary :
                                if (outParam) 
                                        comm.Skip (1);
                                element = GetBinaryValue ();
                                break;
                        case TdsColumnType.BitN :
                                if (outParam) 
                                        comm.Skip (1);
                                if (comm.GetByte () == 0)
                                        element = DBNull.Value;
                                else
                                        element = (comm.GetByte() != 0);
                                break;
                        case TdsColumnType.Bit :
                                int columnSize = comm.GetByte ();
                                element = (columnSize != 0);
                                break;
                        case TdsColumnType.UniqueIdentifier :
                                if (comm.Peek () != 16) { // If it's null, then what to do?
                                        /*byte swallowed =*/ comm.GetByte();
                                        element = DBNull.Value;
                                        break;
                                }
                                if (outParam)
                                        comm.Skip (1);
                                
                                len = comm.GetByte () & 0xff;
                                if (len > 0) {
                                        byte[] guidBytes = comm.GetBytes (len, true);
                                        if (!BitConverter.IsLittleEndian) {
                                                byte[] swappedguidBytes = new byte[len];
                                                for (int i = 0; i < 4; i++)
                                                        swappedguidBytes[i] = guidBytes[4-i-1];
                                                for (int i = 4; i < 6; i++)
                                                        swappedguidBytes[i] = guidBytes[6-(i-4)-1];
                                                for (int i = 6; i < 8; i++)
                                                        swappedguidBytes[i] = guidBytes[8-(i-6)-1];
                                                for (int i = 8; i < 16; i++)
                                                        swappedguidBytes[i] = guidBytes[i];
                                                Array.Copy(swappedguidBytes, 0, guidBytes, 0, len);
                                        }
                                        element = new Guid (guidBytes);
                                }
                                break;
                        default :
                                return DBNull.Value;
                        }
                        return element;
                }

                private object GetBinaryValue ()
                {
                        int len;
                        object result = DBNull.Value;

                        if (tdsVersion >= TdsVersion.tds70) {
                                len = comm.GetTdsShort ();
                                if (len != 0xffff && len >= 0)
                                        result = comm.GetBytes (len, true);
                        } else {
                                len = (comm.GetByte () & 0xff);
                                if (len != 0)
                                        result = comm.GetBytes (len, true);
                        }

                        return result;
                }

                private object GetDateTimeValue (
#if NET_2_0
                        TdsColumnType? type
#else
                        TdsColumnType type
#endif
                )
                {
                        int len = 0;
                        object result;

#if NET_2_0
                        if (type == null)
                                throw new ArgumentNullException ("type");
#endif
                        switch (type) {
                        case TdsColumnType.DateTime4:
                                len = 4;
                                break;
                        case TdsColumnType.DateTime:
                                len = 8;
                                break;
                        case TdsColumnType.DateTimeN:
                                byte tmp = comm.Peek ();
                                if (tmp != 0 && tmp != 4 && tmp != 8)
                                        break;
                                len = comm.GetByte ();
                                break;
                        }
        
                        DateTime epoch = new DateTime (1900, 1, 1);
        
                        switch (len) {
                        case 8 :
                                result = epoch.AddDays (comm.GetTdsInt ());
                                int seconds = comm.GetTdsInt ();
                                long millis = (long) System.Math.Round (((((long) seconds) % 300L) * 1000L) / 300f);
                                if (seconds != 0 || millis != 0) {
                                        result = ((DateTime) result).AddSeconds (seconds / 300);
                                        result = ((DateTime) result).AddMilliseconds (millis);
                                }
                                break;
                        case 4 :
                                // MSDN says small datetime is stored in 2 bytes as no of days
                                // *after* 1/1/1900. so, cast to unsigned short
                                result = epoch.AddDays ((ushort) comm.GetTdsShort ());
                                short minutes = comm.GetTdsShort ();
                                if (minutes != 0) 
                                        result = ((DateTime) result).AddMinutes ((int) minutes);
                                break;
                        default:
                                result = DBNull.Value;
                                break;
                        }

                        return result;
                }

                private object GetDecimalValue (byte precision, byte scale)
                {
                        if (tdsVersion < TdsVersion.tds70)
                                return GetDecimalValueTds50 (precision, scale);
                        else
                                return GetDecimalValueTds70 (precision, scale);
                }
                
                private object GetDecimalValueTds70 (byte precision, byte scale)
                {
                        int[] bits = new int[4] {0,0,0,0};

                        int len = (comm.GetByte() & 0xff) - 1;
                        if (len < 0)
                                return DBNull.Value;
                        
                        bool positive = (comm.GetByte () == 1);
                        if (len > 16)
                                throw new OverflowException ();

                        for (int i = 0, index = 0; i < len && i < 16; i += 4, index += 1) 
                                bits[index] = comm.GetTdsInt ();
                        
                        if (bits [3] != 0) 
                                return new TdsBigDecimal (precision, scale, !positive, bits);
                        else
                                return new Decimal (bits[0], bits[1], bits[2], !positive, scale);
                }

                private object GetDecimalValueTds50 (byte precision, byte scale)
                {
                        int[] bits = new int[4] {0,0,0,0};

                        int len = (comm.GetByte() & 0xff);
                        if (len == 0)
                                return DBNull.Value;

                        byte[] dec_bytes=comm.GetBytes(len,false);
                
                        byte[] easy=new byte[4];

                        bool positive = dec_bytes[0]==1;

                        if (len > 17)
                                throw new OverflowException ();

                        for (int i = 1, index = 0; i < len && i < 16; i += 
                                4, index += 1) {
                                for(int j=0; j<4; j++)
                                        if(i+j<len)
                                                easy[j]=dec_bytes[len-
                                                        (i+j)];
                                        else
                                                easy[j]=0;
                                if(!BitConverter.IsLittleEndian)
                                        easy=comm.Swap(easy);
                                bits[index] = BitConverter.ToInt32(easy,0);
                        }
                        if (bits [3] != 0) 
                                return new TdsBigDecimal (precision, 
                                        scale, positive, bits);
                        else
                                return new Decimal(bits[0], bits[1], bits
                                        [2], positive, scale);
                        
                }

                private object GetFloatValue (
#if NET_2_0
                        TdsColumnType? columnType
#else
                        TdsColumnType columnType
#endif
                )
                {
#if NET_2_0
                        if (columnType == null)
                                throw new ArgumentNullException ("columnType");
#endif
                        int columnSize = 0;

                        switch (columnType) {
                        case TdsColumnType.Real:
                                columnSize = 4;
                                break;
                        case TdsColumnType.Float8:
                                columnSize = 8;
                                break;
                        case TdsColumnType.FloatN:
                                columnSize = comm.GetByte ();
                                break;
                        }

                        switch (columnSize) {
                        case 8 :
                                return BitConverter.Int64BitsToDouble (comm.GetTdsInt64 ());
                        case 4 :
                                return BitConverter.ToSingle (BitConverter.GetBytes (comm.GetTdsInt ()), 0);
                        default :
                                return DBNull.Value;
                        }
                }

                private object GetImageValue ()
                {
                        byte hasValue = comm.GetByte ();

                        if (hasValue == 0)
                                return DBNull.Value;
                        
                        comm.Skip (24);
                        int len = comm.GetTdsInt ();

                        if (len < 0)
                                return DBNull.Value;

                        return (comm.GetBytes (len, true));
                }

                private object GetIntValue (
#if NET_2_0
                        TdsColumnType? type
#else
                        TdsColumnType type
#endif
                )
                {
                        int len;

#if NET_2_0
                        if (type == null)
                                throw new ArgumentNullException ("type");
#endif
                        switch (type) {
                        case TdsColumnType.BigInt :
                                len = 8;
                                break;
                        case TdsColumnType.IntN :
                                len = comm.GetByte ();
                                break;
                        case TdsColumnType.Int4 :
                                len = 4; 
                                break;
                        case TdsColumnType.Int2 :
                                len = 2; 
                                break;
                        case TdsColumnType.Int1 :
                                len = 1; 
                                break;
                        default:
                                return DBNull.Value;
                        }

                        switch (len) {
                        case 8:
                                return (comm.GetTdsInt64 ());
                        case 4 :
                                return (comm.GetTdsInt ());
                        case 2 :
                                return (comm.GetTdsShort ());
                        case 1 :
                                return (comm.GetByte ());
                        default:
                                return DBNull.Value;
                        }
                }

                private object GetMoneyValue (
#if NET_2_0
                        TdsColumnType? type
#else
                        TdsColumnType type
#endif
                )
                {
                        int len;

#if NET_2_0
                        if (type == null)
                                throw new ArgumentNullException ("type");
#endif
                        switch (type) {
                        case TdsColumnType.SmallMoney :
                        case TdsColumnType.Money4 :
                                len = 4;
                                break;
                        case TdsColumnType.Money :
                                len = 8;
                                break;
                        case TdsColumnType.MoneyN :
                                len = comm.GetByte ();
                                break;
                        default:
                                return DBNull.Value;
                        }

                        switch (len) {
                        case 4: {
                                int val = Comm.GetTdsInt ();
                                bool negative = val < 0;
                                if (negative)
                                        val = ~(val - 1);
                                return new Decimal (val, 0, 0, negative, 4);
                        }
                        case 8: {
                                int hi = Comm.GetTdsInt ();
                                int lo = Comm.GetTdsInt ();
                                bool negative = hi < 0;

                                if (negative) {
                                        hi = ~hi;
                                        lo = ~(lo - 1);
                                }
                                return new Decimal (lo, hi, 0, negative, 4);
                        }
                        default:
                                return DBNull.Value;
                        }
                }

                protected object GetStringValue (
#if NET_2_0
                        TdsColumnType? colType,
#else
                        TdsColumnType colType,
#endif
                    bool wideChars, bool outputParam, Encoding encoder)
                {
                        bool shortLen = false;
                        Encoding enc = encoder;
                
                        if (tdsVersion > TdsVersion.tds70 && outputParam && 
                            (colType == TdsColumnType.BigChar || colType == TdsColumnType.BigNVarChar || 
                             colType == TdsColumnType.BigVarChar || colType == TdsColumnType.NChar ||
                                 colType == TdsColumnType.NVarChar)) {
                                // Read collation for SqlServer 2000 and beyond
                                byte[] collation;
                                collation = Comm.GetBytes (5, true);
                                enc = TdsCharset.GetEncoding (collation);
                                shortLen = true;
                        } else {
                                shortLen = (tdsVersion >= TdsVersion.tds70) && (wideChars || !outputParam);
                        }
                        
                        int len = shortLen ? comm.GetTdsShort () : (comm.GetByte () & 0xff);
                        return GetStringValue (wideChars, len, enc);
                }

                protected object GetStringValue (bool wideChars, int len, Encoding enc)
                {
                        if (tdsVersion < TdsVersion.tds70 && len == 0)
                                return DBNull.Value;
                        
                        else if (len >= 0) {
                                object result;
                                if (wideChars)
                                        result = comm.GetString (len / 2, enc);
                                else
                                        result = comm.GetString (len, false, enc);
                                if (tdsVersion < TdsVersion.tds70 && ((string) result).Equals (" "))
                                        result = string.Empty;
                                return result;
                        }
                        else
                                return DBNull.Value;
                }

                protected int GetSubPacketLength ()
                {
                        return comm.GetTdsShort ();
                }

                private object GetTextValue (bool wideChars, Encoding encoder)
                {
                        string result = null;
                        byte hasValue = comm.GetByte ();

                        if (hasValue != 16)
                                return DBNull.Value;

                        // 16 Byte TEXTPTR, 8 Byte TIMESTAMP
                        comm.Skip (24);

                        int len = comm.GetTdsInt ();

                        //if the len is 0 , then the string can be a '' string 
                        // this method is called only for Text and NText. Hence will
                        // return a empty string
                        if (len == 0)
                                return string.Empty;

                        if (wideChars)
                                result = comm.GetString (len / 2, encoder);
                        else
                                result = comm.GetString (len, false, encoder);
                                len /= 2;

                        if ((byte) tdsVersion < (byte) TdsVersion.tds70 && result == " ")
                                result = string.Empty;

                        return result;                  
                }
                
                internal bool IsBlobType (TdsColumnType columnType)
                {
                        return (columnType == TdsColumnType.Text || columnType == TdsColumnType.Image || columnType == TdsColumnType.NText);
                }

                internal bool IsLargeType (TdsColumnType columnType)
                {
                        return ((byte) columnType > 128);
                }

                protected bool IsWideType (TdsColumnType columnType)
                {
                        switch (columnType) {
                        case TdsColumnType.NChar:
                        case TdsColumnType.NText:
                        case TdsColumnType.NVarChar:
                                return true;
                        default:
                                return false;
                        }
                }

                internal static bool IsFixedSizeColumn (TdsColumnType columnType)
                {
                        switch (columnType) {
                                case TdsColumnType.Int1 :
                                case TdsColumnType.Int2 :
                                case TdsColumnType.Int4 :
                                case TdsColumnType.BigInt :
                                case TdsColumnType.Float8 :
                                case TdsColumnType.DateTime :
                                case TdsColumnType.Bit :
                                case TdsColumnType.Money :
                                case TdsColumnType.Money4 :
                                case TdsColumnType.SmallMoney :
                                case TdsColumnType.Real :
                                case TdsColumnType.DateTime4 :
                                  /*
                                case TdsColumnType.Decimal:
                                case TdsColumnType.Numeric:
                                  */
                                        return true;
                                default :
                                        return false;
                        }
                }

                protected void LoadRow ()
                {
                        if (SequentialAccess) {
                                if (isRowRead)
                                        SkipRow ();
                                isRowRead = true;
                                isResultRead = true;
                                return;
                        }

                        currentRow = new TdsDataRow ();

                        int i = 0;
                        foreach (TdsDataColumn column in columns) {
#if NET_2_0
                                object o = GetColumnValue (column.ColumnType, false, i);
#else
                                object o = GetColumnValue ((TdsColumnType)column["ColumnType"], false, i);
#endif
                                currentRow.Add (o);
                                if (doneProc)
                                        outputParameters.Add (o);

                                if (o is TdsBigDecimal && currentRow.BigDecimalIndex < 0) 
                                        currentRow.BigDecimalIndex = i;
                                i += 1;
                        }
                }

                internal static int LookupBufferSize (TdsColumnType columnType)
                {
                        switch (columnType) {
                                case TdsColumnType.Int1 :
                                case TdsColumnType.Bit :
                                        return 1;
                                case TdsColumnType.Int2 :
                                        return 2;
                                case TdsColumnType.Int4 :
                                case TdsColumnType.Real :
                                case TdsColumnType.DateTime4 :
                                case TdsColumnType.Money4 :
                                case TdsColumnType.SmallMoney :
                                        return 4;
                                case TdsColumnType.Float8 :
                                case TdsColumnType.DateTime :
                                case TdsColumnType.Money :
                                case TdsColumnType.BigInt :
                                        return 8;
                                default :
                                        return 0;
                        }
                }

                protected internal int ProcessAuthentication ()
                {
                        int pdu_size = Comm.GetTdsShort ();
                        byte[] msg2 = Comm.GetBytes (pdu_size, true);

                        Type2Message t2 = new Type2Message (msg2);
                        // 0x0001       Negotiate Unicode
                        // 0x0200       Negotiate NTLM
                        // 0x8000       Negotiate Always Sign

                        Type3Message t3 = new Type3Message ();
                        t3.Challenge = t2.Nonce;
                        
                        t3.Domain = this.connectionParms.DefaultDomain;
                        t3.Host = this.connectionParms.Hostname;
                        t3.Username = this.connectionParms.User;
                        t3.Password = this.connectionParms.Password;

                        Comm.StartPacket (TdsPacketType.SspAuth); // 0x11
                        Comm.Append (t3.GetBytes ());
                        try {
                                Comm.SendPacket ();
                        } catch (IOException ex) {
                                connected = false;
                                throw new TdsInternalException ("Server closed the connection.", ex);
                        }
                        return 1; // TDS_SUCCEED
                }

                protected void ProcessColumnDetail ()
                {
                        int len = GetSubPacketLength ();
                        byte[] values = new byte[3];
                        int columnNameLength;
                        string baseColumnName = String.Empty;
                        int position = 0;

                        while (position < len) {
                                for (int j = 0; j < 3; j += 1) 
                                        values[j] = comm.GetByte ();
                                position += 3;

                                bool isAlias = ((values[2] & (byte) TdsColumnStatus.Rename) != 0);
                                if (isAlias) {
                                        if (tdsVersion >= TdsVersion.tds70) {
                                                columnNameLength = comm.GetByte ();
                                                position += 2 * columnNameLength + 1;
                                        }
                                        else {
                                                columnNameLength = comm.GetByte ();
                                                position += columnNameLength + 1;
                                        }
                                        baseColumnName = comm.GetString (columnNameLength);
                                }

                                byte index = (byte) (values[0] - (byte) 1);
                                byte tableIndex = (byte) (values[1] - (byte) 1);
                                bool isExpression = ((values[2] & (byte) TdsColumnStatus.IsExpression) != 0);

                                TdsDataColumn column = columns [index];
#if NET_2_0
                                column.IsHidden = ((values[2] & (byte) TdsColumnStatus.Hidden) != 0);
                                column.IsExpression = isExpression;
                                column.IsKey = ((values[2] & (byte) TdsColumnStatus.IsKey) != 0);
                                column.IsAliased = isAlias;
                                column.BaseColumnName = ((isAlias) ? baseColumnName : null);
                                column.BaseTableName = ((!isExpression) ? (string) tableNames [tableIndex] : null);
#else
                                column ["IsHidden"] = ((values [2] & (byte) TdsColumnStatus.Hidden) != 0);
                                column ["IsExpression"] = isExpression;
                                column ["IsKey"] = ((values [2] & (byte) TdsColumnStatus.IsKey) != 0);
                                column ["IsAliased"] = isAlias;
                                column ["BaseColumnName"] = ((isAlias) ? baseColumnName : null);
                                column ["BaseTableName"] = ((!isExpression) ? tableNames [tableIndex] : null);
#endif
                        }
                }

                protected abstract void ProcessColumnInfo ();

                protected void ProcessColumnNames ()
                {
                        columnNames = new ArrayList ();

                        int totalLength = comm.GetTdsShort ();
                        int bytesRead = 0;
                        int i = 0;

                        while (bytesRead < totalLength) {
                                int columnNameLength = comm.GetByte ();
                                string columnName = comm.GetString (columnNameLength);
                                bytesRead = bytesRead + 1 + columnNameLength;
                                columnNames.Add (columnName);
                                i += 1;
                        }
                }

                [MonoTODO ("Make sure counting works right, especially with multiple resultsets.")]
                protected void ProcessEndToken (TdsPacketSubType type)
                {
                        byte status = Comm.GetByte ();
                        Comm.Skip (1);
                        byte op = comm.GetByte ();
                        Comm.Skip (1);

                        int rowCount = comm.GetTdsInt ();
                        bool validRowCount = IsValidRowCount (status,op);
                        moreResults = ((status & 0x01) != 0);
                        bool cancelled = ((status & 0x20) != 0);

                        switch (type) {
                        case TdsPacketSubType.DoneProc:
                                doneProc = true;
                                goto case TdsPacketSubType.Done;
                        case TdsPacketSubType.Done:
                        case TdsPacketSubType.DoneInProc:
                                if (validRowCount) {
                                        if (recordsAffected == -1) 
                                                recordsAffected = rowCount;
                                        else
                                                recordsAffected += rowCount;
                                }
                                break;
                        }

                        if (moreResults) 
                                queryInProgress = false;
                        if (cancelled)
                                cancelsProcessed += 1;
                        if (messages.Count > 0 && !moreResults) 
                                OnTdsInfoMessage (CreateTdsInfoMessageEvent (messages));
                }

                protected void ProcessEnvironmentChange ()
                {
                        // VARADHAN: TDS 8 Debugging
                        //Console.WriteLine ("In ProcessEnvironmentChange... entry");
                        int len = GetSubPacketLength ();
                        TdsEnvPacketSubType type = (TdsEnvPacketSubType) comm.GetByte ();
                        int cLen;

                        switch (type) {
                        case TdsEnvPacketSubType.BlockSize :
                                string blockSize;
                                cLen = comm.GetByte ();
                                blockSize = comm.GetString (cLen);

                                if (tdsVersion >= TdsVersion.tds70) 
                                        comm.Skip (len - 2 - cLen * 2);
                                else 
                                        comm.Skip (len - 2 - cLen);

                                packetSize = Int32.Parse (blockSize);   
                                comm.ResizeOutBuf (packetSize);
                                break;
                        case TdsEnvPacketSubType.CharSet :
                                cLen = comm.GetByte ();
                                if (tdsVersion == TdsVersion.tds70) {
                                        SetCharset (comm.GetString (cLen));
                                        comm.Skip (len - 2 - cLen * 2);
                                }
                                else {
                                        SetCharset (comm.GetString (cLen));
                                        comm.Skip (len - 2 - cLen);
                                }

                                break;
                        case TdsEnvPacketSubType.Locale :
                                cLen = comm.GetByte ();
                                int lcid = 0;
                                if (tdsVersion >= TdsVersion.tds70) {
                                        lcid = (int) Convert.ChangeType (comm.GetString (cLen), typeof (int));
                                        comm.Skip (len - 2 - cLen * 2);
                                }
                                else {
                                        lcid = (int) Convert.ChangeType (comm.GetString (cLen), typeof (int));
                                        comm.Skip (len - 2 - cLen);
                                }
                                locale = new CultureInfo (lcid);
                                break;
                        case TdsEnvPacketSubType.Database :
                                cLen = comm.GetByte ();
                                string newDB = comm.GetString (cLen);
                                cLen = comm.GetByte () & 0xff;
                                comm.GetString (cLen);
                                if (originalDatabase == string.Empty)
                                        originalDatabase = newDB;
                                database = newDB;
                                break;
                        case TdsEnvPacketSubType.CollationInfo:
                                //Console.WriteLine ("ProcessEnvironmentChange::Got collation info");
                                cLen = comm.GetByte ();
                                collation = comm.GetBytes (cLen, true);
                                lcid = TdsCollation.LCID (collation);
                                locale = new CultureInfo (lcid);
                                SetCharset (TdsCharset.GetEncoding (collation));
                                break;
                                
                        default:
                                comm.Skip (len - 1);
                                break;
                        }
                        // VARADHAN: TDS 8 Debugging
                        //Console.WriteLine ("In ProcessEnvironmentChange... exit");
                }

                protected void ProcessLoginAck ()
                {
                        uint srvVersion = 0;
                        GetSubPacketLength ();
                        
                        //Console.WriteLine ("ProcessLoginAck: B4 tdsVersion:{0}", tdsVersion);
                        // Valid only for a Login7 request
                        if (tdsVersion >= TdsVersion.tds70) {
                                comm.Skip (1);
                                srvVersion = (uint)comm.GetTdsInt ();

                                //Console.WriteLine ("srvVersion: {0}", srvVersion);
                                switch (srvVersion) {
                                case 0x00000007: 
                                        tdsVersion = TdsVersion.tds70;
                                        break;
                                case 0x00000107:
                                        tdsVersion = TdsVersion.tds80;
                                        break;
                                case 0x01000071:
                                        tdsVersion = TdsVersion.tds81;
                                        break;
                                case 0x02000972:
                                        tdsVersion = TdsVersion.tds90;
                                        break;
                                }
                                //Console.WriteLine ("ProcessLoginAck: after tdsVersion:{0}", tdsVersion);                              
                        }
                        
                        if (tdsVersion >= TdsVersion.tds70) {
                                int nameLength = comm.GetByte ();
                                databaseProductName = comm.GetString (nameLength);
                                databaseMajorVersion = comm.GetByte ();
                                databaseProductVersion = String.Format ("{0}.{1}.{2}", databaseMajorVersion.ToString("00"),
                                                                comm.GetByte ().ToString("00"), 
                                                                (256 * comm.GetByte () + comm.GetByte ()).ToString("0000"));
                        } else {
                                comm.Skip (5);
                                short nameLength = comm.GetByte ();
                                databaseProductName = comm.GetString (nameLength);
                                comm.Skip (1);
                                databaseMajorVersion = comm.GetByte ();
                                databaseProductVersion = String.Format ("{0}.{1}", databaseMajorVersion, comm.GetByte ());
                                comm.Skip (1);
                        }

                        if (databaseProductName.Length > 1 && -1 != databaseProductName.IndexOf ('\0')) {
                                int last = databaseProductName.IndexOf ('\0');
                                databaseProductName = databaseProductName.Substring (0, last);
                        }

                        connected = true;
                        //Console.WriteLine ("databaseProductVersion:{0}", databaseProductVersion);
                }

                protected void OnTdsErrorMessage (TdsInternalErrorMessageEventArgs e)
                {
                        if (TdsErrorMessage != null)
                                TdsErrorMessage (this, e);
                }

                protected void OnTdsInfoMessage (TdsInternalInfoMessageEventArgs e)
                {
                        if (TdsInfoMessage != null)
                                TdsInfoMessage (this, e);
                        messages.Clear ();
                }

                protected void ProcessMessage (TdsPacketSubType subType)
                {
                        GetSubPacketLength ();

                        int number = comm.GetTdsInt ();
                        byte state = comm.GetByte ();
                        byte theClass = comm.GetByte ();
                        string message;
                        string server;
                        string procedure;
                        byte lineNumber;
                        string source;
                        bool isError = false;

                        if (subType == TdsPacketSubType.EED) {
                                isError = (theClass > 10);
                                comm.Skip (comm.GetByte ()); // SQL State
                                comm.Skip (1);               // Status
                                comm.Skip (2);               // TranState
                        } else 
                                isError = (subType == TdsPacketSubType.Error);

                        message = comm.GetString (comm.GetTdsShort ());
                        server = comm.GetString (comm.GetByte ());
                        procedure = comm.GetString (comm.GetByte ());
                        lineNumber = comm.GetByte ();
                        comm.Skip (1);
                        source = String.Empty; // FIXME

                        if (isError)
                                OnTdsErrorMessage (CreateTdsErrorMessageEvent (theClass, lineNumber, message, number, procedure, server, source, state));
                        else
                                messages.Add (new TdsInternalError (theClass, lineNumber, message, number, procedure, server, source, state));
                }

                protected virtual void ProcessOutputParam ()
                {
                        GetSubPacketLength ();
                        /*string paramName = */comm.GetString (comm.GetByte () & 0xff);
                        comm.Skip (5);

                        TdsColumnType colType = (TdsColumnType) comm.GetByte ();
                        object value = GetColumnValue (colType, true);
                        outputParameters.Add (value);
                }

                protected void ProcessDynamic ()
                {
                        Comm.Skip (2);
                        /*byte type =*/ Comm.GetByte ();
                        /*byte status =*/ Comm.GetByte ();
                        /*string id =*/ Comm.GetString (Comm.GetByte ());
                }

                protected virtual TdsPacketSubType ProcessSubPacket ()
                {
                        // VARADHAN: TDS 8 Debugging
                        // Console.WriteLine ("In ProcessSubPacket... entry");
                        
                        TdsPacketSubType subType = (TdsPacketSubType) comm.GetByte ();

                        // VARADHAN: TDS 8 Debugging
                        //Console.WriteLine ("Subpacket type: {0}", subType);
                        switch (subType) {
                        case TdsPacketSubType.Dynamic2:
                                comm.Skip (comm.GetTdsInt ());
                                break;
                        case TdsPacketSubType.AltName:
                        case TdsPacketSubType.AltFormat:
                        case TdsPacketSubType.Capability:
                        case TdsPacketSubType.ParamFormat:
                                comm.Skip (comm.GetTdsShort ());
                                break;
                        case TdsPacketSubType.Dynamic:
                                ProcessDynamic ();
                                break;
                        case TdsPacketSubType.EnvironmentChange:
                                ProcessEnvironmentChange ();
                                break;
                        case TdsPacketSubType.Info:  // TDS 4.2/7.0
                        case TdsPacketSubType.EED:   // TDS 5.0
                        case TdsPacketSubType.Error: // TDS 4.2/7.0
                                ProcessMessage (subType);
                                break;
                        case TdsPacketSubType.Param:
                                ProcessOutputParam ();
                                break;
                        case TdsPacketSubType.LoginAck:
                                ProcessLoginAck ();
                                break;
                        case TdsPacketSubType.Authentication: // TDS 7.0
                                ProcessAuthentication ();
                                break;
                        case TdsPacketSubType.ReturnStatus :
                                ProcessReturnStatus ();
                                break;
                        case TdsPacketSubType.ProcId:
                                Comm.Skip (8);
                                break;
                        case TdsPacketSubType.Done:
                        case TdsPacketSubType.DoneProc:
                        case TdsPacketSubType.DoneInProc:
                                ProcessEndToken (subType);
                                break;
                        case TdsPacketSubType.ColumnName:
                                Comm.Skip (8);
                                ProcessColumnNames ();
                                break;
                        case TdsPacketSubType.ColumnInfo:      // TDS 4.2
                        case TdsPacketSubType.ColumnMetadata:  // TDS 7.0
                        case TdsPacketSubType.RowFormat:       // TDS 5.0
                                Columns.Clear ();
                                ProcessColumnInfo ();
                                break;
                        case TdsPacketSubType.ColumnDetail:
                                ProcessColumnDetail ();
                                break;
                        case TdsPacketSubType.TableName:
                                ProcessTableName ();
                                break;
                        case TdsPacketSubType.ColumnOrder:
                                comm.Skip (comm.GetTdsShort ());
                                break;
                        case TdsPacketSubType.Control:
                                comm.Skip (comm.GetTdsShort ());
                                break;
                        case TdsPacketSubType.Row:
                                LoadRow ();
                                break;
                        }

                        // VARADHAN: TDS 8 Debugging
                        //Console.WriteLine ("In ProcessSubPacket... exit");
                        return subType;
                }

                protected void ProcessTableName ()
                {
                        tableNames = new ArrayList ();
                        int totalLength = comm.GetTdsShort ();
                        int position = 0;
                        int len;

                        while (position < totalLength) {
                                if (tdsVersion >= TdsVersion.tds70) {
                                        len = comm.GetTdsShort ();
                                        position += 2 * (len + 1);
                                }
                                else {
                                        len = comm.GetByte ();
                                        position += len + 1;
                                }
                                tableNames.Add (comm.GetString (len));
                        }
                }

                protected void SetCharset (Encoding encoder)
                {
                        comm.Encoder = encoder;
                }
                
                protected void SetCharset (string charset)
                {
                        if (charset == null || charset.Length > 30)
                                charset = "iso_1";

                        if (this.charset != null && this.charset == charset)
                                return;

                        if (charset.StartsWith ("cp")) {
                                encoder = Encoding.GetEncoding (Int32.Parse (charset.Substring (2)));
                                this.charset = charset;
                        }
                        else {
                                encoder = Encoding.GetEncoding ("iso-8859-1");
                                this.charset = "iso_1";
                        }
                        SetCharset (encoder);
                }

                protected void SetLanguage (string language)
                {
                        if (language == null || language.Length > 30)
                                language = "us_english";

                        this.language = language;
                }

                protected virtual void ProcessReturnStatus () 
                {
                        comm.Skip(4);
                }

                #endregion // Private Methods

#if NET_2_0
                #region asynchronous methods
                protected IAsyncResult BeginExecuteQueryInternal (string sql, bool wantResults, 
                                                          AsyncCallback callback, object state)
                {
                        InitExec ();

                        TdsAsyncResult ar = new TdsAsyncResult (callback, state);
                        ar.TdsAsyncState.WantResults = wantResults;

                        Comm.StartPacket (TdsPacketType.Query);
                        Comm.Append (sql);
                        try {
                                Comm.SendPacket ();
                                Comm.BeginReadPacket (new AsyncCallback(OnBeginExecuteQueryCallback), 
                                                      ar);
                        } catch (IOException ex) {
                                connected = false;
                                throw new TdsInternalException ("Server closed the connection.", ex);
                        }

                        return ar;
                }
                
                protected void EndExecuteQueryInternal (IAsyncResult ar)
                {
                        if (!ar.IsCompleted)
                                ar.AsyncWaitHandle.WaitOne ();
                        TdsAsyncResult result = (TdsAsyncResult) ar;
                        if (result.IsCompletedWithException)
                                throw result.Exception;
                }

                protected void OnBeginExecuteQueryCallback (IAsyncResult ar)
                {
                        TdsAsyncResult result = (TdsAsyncResult) ar.AsyncState;
                        TdsAsyncState tdsState = (TdsAsyncState) result.TdsAsyncState;

                        try {
                                Comm.EndReadPacket (ar);
                                if (!tdsState.WantResults)
                                        SkipToEnd ();
                        } catch (Exception e) {
                                result.MarkComplete (e);
                                return;
                        }
                        result.MarkComplete ();
                }
                

                public virtual IAsyncResult BeginExecuteNonQuery (string sql,
                                                                  TdsMetaParameterCollection parameters,
                                                                  AsyncCallback callback,
                                                                  object state)
                {
                        // abstract, kept to be backward compatiable.
                        throw new NotImplementedException ("should not be called!");
                }
                
                public virtual void EndExecuteNonQuery (IAsyncResult ar)
                {
                        // abstract method
                        throw new NotImplementedException ("should not be called!");
                }
                
                public virtual IAsyncResult BeginExecuteQuery (string sql,
                                                                  TdsMetaParameterCollection parameters,
                                                                  AsyncCallback callback,
                                                                  object state)
                {
                        // abstract, kept to be backward compatiable.
                        throw new NotImplementedException ("should not be called!");
                }
                
                public virtual void EndExecuteQuery (IAsyncResult ar)
                {
                        // abstract method
                        throw new NotImplementedException ("should not be called!");
                }

                public virtual IAsyncResult BeginExecuteProcedure (string prolog,
                                                                    string epilog,
                                                                    string cmdText,
                                                                    bool IsNonQuery,
                                                                    TdsMetaParameterCollection parameters,
                                                                    AsyncCallback callback,
                                                                    object state)
                {
                        throw new NotImplementedException ("should not be called!");
                }
                
                public virtual void EndExecuteProcedure (IAsyncResult ar)
                {
                        // abstract method
                        throw new NotImplementedException ("should not be called!");
                }
                
                public void WaitFor (IAsyncResult ar)
                {
                        if (! ar.IsCompleted)
                                ar.AsyncWaitHandle.WaitOne ();
                }

                public void CheckAndThrowException (IAsyncResult ar)
                {
                        TdsAsyncResult result = (TdsAsyncResult) ar;
                        if (result.IsCompleted && result.IsCompletedWithException)
                                throw result.Exception;
                }

                #endregion // asynchronous methods
#endif // NET_2_0


        }
}