Convert small classes to structs to reduce allocations.

Author: bgrainger

src/MySqlConnector/ByteArrayReader.cs

@@ -2,7 +2,7 @@
 
 namespace MySql.Data
 {
-	internal sealed class ByteArrayReader
+	internal struct ByteArrayReader
 	{
 		public ByteArrayReader(byte[] buffer, int offset, int length)
 		{
@@ -118,6 +118,8 @@ public ulong ReadLengthEncodedInteger()
 			byte encodedLength = m_buffer[m_offset++];
 			switch (encodedLength)
 			{
+			case 0xFB:
+				throw new FormatException("Length-encoded integer cannot have 0xFB prefix byte.");
 			case 0xFC:
 				return ReadFixedLengthUInt32(2);
 			case 0xFD:
@@ -131,6 +133,17 @@ public ulong ReadLengthEncodedInteger()
 			}
 		}
 
+		public int ReadLengthEncodedIntegerOrNull()
+		{
+			if (m_buffer[m_offset] == 0xFB)
+			{
+				// "NULL is sent as 0xfb" (https://dev.mysql.com/doc/internals/en/com-query-response.html#packet-ProtocolText::ResultsetRow)
+				m_offset++;
+				return -1;
+			}
+			return checked((int) ReadLengthEncodedInteger());
+		}
+
 		public ArraySegment<byte> ReadLengthEncodedByteString()
 		{
 			var length = checked((int) ReadLengthEncodedInteger());

src/MySqlConnector/MySqlClient/Results/ResultSet.cs

@@ -197,7 +197,7 @@ Row ScanRowAsyncRemainder(PayloadData payload)
 				var reader = new ByteArrayReader(payload.ArraySegment);
 				for (var column = 0; column < m_dataOffsets.Length; column++)
 				{
-					var length = checked((int) ReadFieldLength(reader));
+					var length = reader.ReadLengthEncodedIntegerOrNull();
 					m_dataLengths[column] = length == -1 ? 0 : length;
 					m_dataOffsets[column] = length == -1 ? -1 : reader.Offset;
 					reader.Offset += m_dataLengths[column];
@@ -211,24 +211,6 @@ Row ScanRowAsyncRemainder(PayloadData payload)
 			}
 		}
 
-		private static long ReadFieldLength(ByteArrayReader reader)
-		{
-			var leadByte = reader.ReadByte();
-			switch (leadByte)
-			{
-				case 0xFB:
-					return -1;
-				case 0xFC:
-					return reader.ReadFixedLengthUInt32(2);
-				case 0xFD:
-					return reader.ReadFixedLengthUInt32(3);
-				case 0xFE:
-					return checked((long) reader.ReadFixedLengthUInt64(8));
-				default:
-					return leadByte;
-			}
-		}
-
 		public string GetName(int ordinal)
 		{
 			if (ColumnDefinitions == null)

src/MySqlConnector/Serialization/PayloadData.cs

@@ -1,8 +1,8 @@
-using System;
+using System;
 
 namespace MySql.Data.Serialization
 {
-	internal class PayloadData
+	internal struct PayloadData
 	{
 		public PayloadData(ArraySegment<byte> data)
 		{