4. Merging "Buffer read" methods of TdsParserStateObject, port dotnet…

…#285 to netfx.

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

@@ -2411,10 +2411,5 @@ internal void CloneCleanupAltMetaDataSetArray()
                 _snapshot.CloneCleanupAltMetaDataSetArray();
             }
         }
-
-        sealed partial class StateSnapshot
-        {
-            internal byte[] _plpBuffer;
-        }
     }
 }

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

@@ -393,7 +393,7 @@ internal bool TryReadPlpBytes(ref byte[] buff, int offset, int len, out int tota
                 Debug.Assert(_longlenleft == 0);
                 if (buff == null)
                 {
-                    buff = new byte[0];
+                    buff = Array.Empty<byte>();
                 }
 
                 AssertValidState();
@@ -409,7 +409,19 @@ internal bool TryReadPlpBytes(ref byte[] buff, int offset, int len, out int tota
             // If total length is known up front, allocate the whole buffer in one shot instead of realloc'ing and copying over each time
             if (buff == null && _longlen != TdsEnums.SQL_PLP_UNKNOWNLEN)
             {
-                buff = new byte[(Math.Min((int)_longlen, len))];
+                if (_snapshot != null)
+                {
+                    // if there is a snapshot and it contains a stored plp buffer take it
+                    // and try to use it if it is the right length
+                    buff = _snapshot._plpBuffer;
+                    _snapshot._plpBuffer = null;
+                }
+
+                if ((ulong)(buff?.Length ?? 0) != _longlen)
+                {
+                    // if the buffer is null or the wrong length create one to use
+                    buff = new byte[(Math.Min((int)_longlen, len))];
+                }
             }
 
             if (_longlenleft == 0)
@@ -454,6 +466,12 @@ internal bool TryReadPlpBytes(ref byte[] buff, int offset, int len, out int tota
                 _longlenleft -= (ulong)bytesRead;
                 if (!result)
                 {
+                    if (_snapshot != null)
+                    {
+                        // a partial read has happened so store the target buffer in the snapshot
+                        // so it can be re-used when another packet arrives and we read again
+                        _snapshot._plpBuffer = buff;
+                    }
                     return false;
                 }
 
@@ -462,6 +480,12 @@ internal bool TryReadPlpBytes(ref byte[] buff, int offset, int len, out int tota
                     // Read the next chunk or cleanup state if hit the end
                     if (!TryReadPlpLength(false, out _))
                     {
+                        if (_snapshot != null)
+                        {
+                            // a partial read has happened so store the target buffer in the snapshot
+                            // so it can be re-used when another packet arrives and we read again
+                            _snapshot._plpBuffer = buff;
+                        }
                         return false;
                     }
                 }

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

@@ -2030,6 +2030,8 @@ internal void Restore(TdsParserStateObject stateObj)
             private TdsParserStateObject _stateObj;
             private StateObjectData _replayStateData;
 
+            internal byte[] _plpBuffer;
+
             private PacketData _lastPacket;
             private PacketData _firstPacket;
             private PacketData _current;
@@ -2149,7 +2151,7 @@ internal bool MoveNext()
                     _stateObj._inBuff = _current.Buffer;
                     _stateObj._inBytesUsed = 0;
                     _stateObj._inBytesRead = _current.Read;
-                    _stateObj._snapshotReplay = true;
+                _stateObj._snapshotReplay = true;
                     retval = true;
                 }