Add and use TryReadChars method (#1544)

Author: Wraith2

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

@@ -12501,18 +12501,18 @@ private bool TryReadPlpUnicodeCharsChunk(char[] buff, int offst, int len, TdsPar
                 return true;
             }
 
-            charsRead = len;
+            int charsToRead = len;
 
             // stateObj._longlenleft is in bytes
-            if ((stateObj._longlenleft >> 1) < (ulong)len)
-                charsRead = (int)(stateObj._longlenleft >> 1);
+            if ((stateObj._longlenleft / 2) < (ulong)len)
+            {
+                charsToRead = (int)(stateObj._longlenleft >> 1);
+            }
 
-            for (int ii = 0; ii < charsRead; ii++)
+            if (!stateObj.TryReadChars(buff, offst, charsToRead, out charsRead))
             {
-                if (!stateObj.TryReadChar(out buff[offst + ii]))
-                {
-                    return false;
-                }
+                charsRead = 0;
+                return false;
             }
 
             stateObj._longlenleft -= ((ulong)charsRead << 1);

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

@@ -3,12 +3,9 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
-using System.Collections.Generic;
 using System.Diagnostics;
-using System.Linq;
 using System.Runtime.InteropServices;
 using System.Security;
-using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.Data.Common;
@@ -487,6 +484,7 @@ internal bool TryReadChar(out char value)
 
             AssertValidState();
             value = (char)((buffer[1] << 8) + buffer[0]);
+            
             return true;
         }
 

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

@@ -13528,7 +13528,6 @@ internal void WriteParameterVarLen(MetaType type, int size, bool isNull, TdsPars
         // Returns the actual chars read
         private bool TryReadPlpUnicodeCharsChunk(char[] buff, int offst, int len, TdsParserStateObject stateObj, out int charsRead)
         {
-
             Debug.Assert((buff == null && len == 0) || (buff.Length >= offst + len), "Invalid length sent to ReadPlpUnicodeChars()!");
             Debug.Assert((stateObj._longlen != 0) && (stateObj._longlen != TdsEnums.SQL_PLP_NULL),
                         "Out of sync plp read request");
@@ -13539,18 +13538,18 @@ private bool TryReadPlpUnicodeCharsChunk(char[] buff, int offst, int len, TdsPar
                 return true;
             }
 
-            charsRead = len;
+            int charsToRead = len;
 
             // stateObj._longlenleft is in bytes
-            if ((stateObj._longlenleft >> 1) < (ulong)len)
-                charsRead = (int)(stateObj._longlenleft >> 1);
+            if ((stateObj._longlenleft / 2) < (ulong)len)
+            {
+                charsToRead = (int)(stateObj._longlenleft >> 1);
+            }
 
-            for (int ii = 0; ii < charsRead; ii++)
+            if (!stateObj.TryReadChars(buff, offst, charsToRead, out charsRead))
             {
-                if (!stateObj.TryReadChar(out buff[offst + ii]))
-                {
-                    return false;
-                }
+                charsRead = 0;
+                return false;
             }
 
             stateObj._longlenleft -= ((ulong)charsRead << 1);

src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/TdsParserStateObject.cs

@@ -436,6 +436,51 @@ internal bool TryStartNewRow(bool isNullCompressed, int nullBitmapColumnsCount =
             return true;
         }
 
+        internal bool TryReadChars(char[] chars, int charsOffset, int charsCount, out int charsCopied)
+        {
+            charsCopied = 0;
+            while (charsCopied < charsCount)
+            {
+                // check if the current buffer contains some bytes we need to copy and copy them
+                //  in a block
+                int bytesToRead = Math.Min(
+                    (charsCount - charsCopied) * 2,
+                    unchecked((_inBytesRead - _inBytesUsed) & (int)0xFFFFFFFE) // it the result is odd take off the 0 to make it even
+                );
+                if (bytesToRead > 0)
+                {
+                    Buffer.BlockCopy(
+                        _inBuff,
+                        _inBytesUsed,
+                        chars,
+                        (charsOffset + charsCopied) * 2, // offset in bytes,
+                        bytesToRead
+                    );
+                    charsCopied += (bytesToRead / 2);
+                    _inBytesUsed += bytesToRead;
+                    _inBytesPacket -= bytesToRead;
+                }
+
+                // if the number of chars requested is lower than the number copied then we need
+                //  to request a new packet, use TryReadChar() to do this then loop back to see
+                //  if we can copy another bulk of chars from the new buffer
+
+                if (charsCopied < charsCount)
+                {
+                    bool result = TryReadChar(out chars[charsOffset + charsCopied]);
+                    if (result)
+                    {
+                        charsCopied += 1;
+                    }
+                    else
+                    {
+                        return false;
+                    }
+                }
+            }
+            return true;
+        }
+
         internal bool IsRowTokenReady()
         {
             // Removing one byte since TryReadByteArray\TryReadByte will aggressively read the next packet if there is no data left - so we need to ensure there is a spare byte