Replace ReadOnlySpan<byte> properties with locals.

The same C# compiler optimisation works for locals, and they're now scoped more appropriately.

Author: bgrainger

src/MySqlConnector/Core/BatchedCommandPayloadCreator.cs

@@ -15,27 +15,26 @@ public bool WriteQueryCommand(ref CommandListPosition commandListPosition, IDict
 			writer.Write((byte) CommandKind.Multi);
 			bool? firstResult = default;
 			bool wroteCommand;
+			ReadOnlySpan<byte> padding = new byte[] { 0, 0, 0, 0, 0, 0, 0, 0, 0 };
 			do
 			{
 				// save room for command length
 				var position = writer.Position;
-				writer.Write(Padding);
+				writer.Write(padding);
 
 				wroteCommand = SingleCommandPayloadCreator.Instance.WriteQueryCommand(ref commandListPosition, cachedProcedures, writer);
 				firstResult ??= wroteCommand;
 
 				// write command length
-				var commandLength = writer.Position - position - Padding.Length;
+				var commandLength = writer.Position - position - padding.Length;
 				var span = writer.ArraySegment.AsSpan().Slice(position);
 				span[0] = 0xFE;
 				BinaryPrimitives.WriteUInt64LittleEndian(span.Slice(1), (ulong) commandLength);
 			} while (wroteCommand);
 
 			// remove the padding that was saved for the final command (which wasn't written)
-			writer.TrimEnd(Padding.Length);
+			writer.TrimEnd(padding.Length);
 			return firstResult.Value;
 		}
-
-		static ReadOnlySpan<byte> Padding => new byte[] { 0, 0, 0, 0, 0, 0, 0, 0, 0 };
 	}
 }

src/MySqlConnector/Core/ServerVersion.cs

@@ -27,7 +27,8 @@ public ServerVersion(ReadOnlySpan<byte> versionString)
 			if (versionString.Length != 0 && versionString[0] == 0x2D)
 			{
 				versionString = versionString.Slice(1);
-				var mariaDbIndex = versionString.IndexOf(MariaDb);
+				ReadOnlySpan<byte> mariaDb = new byte[] { 0x2D, 0x4D, 0x61, 0x72, 0x69, 0x61, 0x44, 0x42 }; // -MariaDB
+				var mariaDbIndex = versionString.IndexOf(mariaDb);
 				if (mariaDbIndex != -1)
 				{
 					var totalBytesRead = 0;
@@ -62,7 +63,5 @@ private ServerVersion()
 			OriginalString = "";
 			Version = new Version(0, 0);
 		}
-
-		static ReadOnlySpan<byte> MariaDb => new byte[] { 0x2D, 0x4D, 0x61, 0x72, 0x69, 0x61, 0x44, 0x42 }; // -MariaDB
 	}
 }

src/MySqlConnector/Core/SingleCommandPayloadCreator.cs

@@ -193,19 +193,25 @@ private static bool WriteCommand(IMySqlCommand command, ByteBufferWriter writer)
 			var isSchemaOnly = (command.CommandBehavior & CommandBehavior.SchemaOnly) != 0;
 			var isSingleRow = (command.CommandBehavior & CommandBehavior.SingleRow) != 0;
 			if (isSchemaOnly)
-				writer.Write(SetSqlSelectLimit0);
+			{
+				ReadOnlySpan<byte> setSqlSelectLimit0 = new byte[] { 83, 69, 84, 32, 115, 113, 108, 95, 115, 101, 108, 101, 99, 116, 95, 108, 105, 109, 105, 116, 61, 48, 59, 10 }; // SET sql_select_limit=0;\n
+				writer.Write(setSqlSelectLimit0);
+			}
 			else if (isSingleRow)
-				writer.Write(SetSqlSelectLimit1);
+			{
+				ReadOnlySpan<byte> setSqlSelectLimit1 = new byte[] { 83, 69, 84, 32, 115, 113, 108, 95, 115, 101, 108, 101, 99, 116, 95, 108, 105, 109, 105, 116, 61, 49, 59, 10 }; // SET sql_select_limit=1;\n
+				writer.Write(setSqlSelectLimit1);
+			}
 			var preparer = new StatementPreparer(command.CommandText!, command.RawParameters, command.CreateStatementPreparerOptions());
 			var isComplete = preparer.ParseAndBindParameters(writer);
 			if (isComplete && (isSchemaOnly || isSingleRow))
-				writer.Write(ClearSqlSelectLimit);
+			{
+				ReadOnlySpan<byte> clearSqlSelectLimit = new byte[] { 10, 83, 69, 84, 32, 115, 113, 108, 95, 115, 101, 108, 101, 99, 116, 95, 108, 105, 109, 105, 116, 61, 100, 101, 102, 97, 117, 108, 116, 59 }; // \nSET sql_select_limit=default;
+				writer.Write(clearSqlSelectLimit);
+			}
 			return isComplete;
 		}
 
-		static ReadOnlySpan<byte> SetSqlSelectLimit0 => new byte[] { 83, 69, 84, 32, 115, 113, 108, 95, 115, 101, 108, 101, 99, 116, 95, 108, 105, 109, 105, 116, 61, 48, 59, 10 }; // SET sql_select_limit=0;\n
-		static ReadOnlySpan<byte> SetSqlSelectLimit1 => new byte[] { 83, 69, 84, 32, 115, 113, 108, 95, 115, 101, 108, 101, 99, 116, 95, 108, 105, 109, 105, 116, 61, 49, 59, 10 }; // SET sql_select_limit=1;\n
-		static ReadOnlySpan<byte> ClearSqlSelectLimit => new byte[] { 10, 83, 69, 84, 32, 115, 113, 108, 95, 115, 101, 108, 101, 99, 116, 95, 108, 105, 109, 105, 116, 61, 100, 101, 102, 97, 117, 108, 116, 59 }; // \nSET sql_select_limit=default;
 		static readonly IMySqlConnectorLogger Log = MySqlConnectorLogManager.CreateLogger(nameof(SingleCommandPayloadCreator));
 	}
 }

src/MySqlConnector/MySqlBulkCopy.cs

@@ -425,13 +425,14 @@ static bool WriteValue(MySqlConnection connection, object? value, ref int inputI
 
 				if (value is null || value == DBNull.Value)
 				{
-					if (output.Length < EscapedNull.Length)
+					ReadOnlySpan<byte> escapedNull = new byte[] { 0x5C, 0x4E };
+					if (output.Length < escapedNull.Length)
 					{
 						bytesWritten = 0;
 						return false;
 					}
-					EscapedNull.CopyTo(output);
-					bytesWritten = EscapedNull.Length;
+					escapedNull.CopyTo(output);
+					bytesWritten = escapedNull.Length;
 					return true;
 				}
 				else if (value is string stringValue)
@@ -648,7 +649,6 @@ static bool WriteBytes(ReadOnlySpan<byte> value, ref int inputIndex, Span<byte>
 			static void WriteNibble(int value, Span<byte> output) => output[0] = value < 10 ? (byte) (value + 0x30) : (byte) (value + 0x57);
 		}
 
-		private static ReadOnlySpan<byte> EscapedNull => new byte[] { 0x5C, 0x4E };
 		private static readonly char[] s_specialCharacters = new char[] { '\t', '\\', '\n' };
 		private static readonly IMySqlConnectorLogger Log = MySqlConnectorLogManager.CreateLogger(nameof(MySqlBulkCopy));
 

src/MySqlConnector/MySqlParameter.cs

@@ -214,7 +214,8 @@ internal void AppendSqlString(ByteBufferWriter writer, StatementPreparerOptions
 
 			if (Value is null || Value == DBNull.Value)
 			{
-				writer.Write(NullBytes);
+				ReadOnlySpan<byte> nullBytes = new byte[] { 0x4E, 0x55, 0x4C, 0x4C }; // NULL
+				writer.Write(nullBytes);
 			}
 			else if (Value is string stringValue)
 			{
@@ -309,7 +310,9 @@ internal void AppendSqlString(ByteBufferWriter writer, StatementPreparerOptions
 			}
 			else if (Value is bool boolValue)
 			{
-				writer.Write(boolValue ? TrueBytes : FalseBytes);
+				ReadOnlySpan<byte> trueBytes = new byte[] { 0x74, 0x72, 0x75, 0x65 }; // true
+				ReadOnlySpan<byte> falseBytes = new byte[] { 0x66, 0x61, 0x6C, 0x73, 0x65 }; // false
+				writer.Write(boolValue ? trueBytes : falseBytes);
 			}
 			else if (Value is float || Value is double)
 			{
@@ -681,9 +684,6 @@ private static void WriteTime(ByteBufferWriter writer, TimeSpan timeSpan)
 			}
 		}
 
-		static ReadOnlySpan<byte> NullBytes => new byte[] { 0x4E, 0x55, 0x4C, 0x4C }; // NULL
-		static ReadOnlySpan<byte> TrueBytes => new byte[] { 0x74, 0x72, 0x75, 0x65 }; // true
-		static ReadOnlySpan<byte> FalseBytes => new byte[] { 0x66, 0x61, 0x6C, 0x73, 0x65 }; // false
 		static ReadOnlySpan<byte> BinaryBytes => new byte[] { 0x5F, 0x62, 0x69, 0x6E, 0x61, 0x72, 0x79, 0x27 }; // _binary'
 
 		DbType m_dbType;

src/MySqlConnector/Protocol/Payloads/HandshakeResponse41Payload.cs

@@ -30,7 +30,11 @@ private static ByteBufferWriter CreateCapabilitiesPayload(ProtocolCapabilities s
 				additionalCapabilities));
 			writer.Write(0x4000_0000);
 			writer.Write((byte) characterSet);
-			writer.Write(Padding);
+
+			// NOTE: not new byte[19]; see https://github.com/dotnet/roslyn/issues/33088
+			ReadOnlySpan<byte> padding = new byte[] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
+			writer.Write(padding);
+
 			if ((serverCapabilities & ProtocolCapabilities.LongPassword) == 0)
 			{
 				// MariaDB writes extended capabilities at the end of the padding
@@ -67,8 +71,5 @@ public static PayloadData Create(InitialHandshakePayload handshake, ConnectionSe
 
 			return writer.ToPayloadData();
 		}
-
-		// NOTE: not new byte[19]; see https://github.com/dotnet/roslyn/issues/33088
-		static ReadOnlySpan<byte> Padding => new byte[] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
 	}
 }

src/MySqlConnector/Utilities/Utility.cs

@@ -118,9 +118,11 @@ private static RSAParameters GetRsaParameters(ReadOnlySpan<byte> data, bool isPr
 
 			if (!isPrivate)
 			{
-				if (!data.Slice(0, s_rsaOid.Length).SequenceEqual(s_rsaOid))
+				// encoded OID sequence for  PKCS #1 rsaEncryption szOID_RSA_RSA = "1.2.840.113549.1.1.1"
+				ReadOnlySpan<byte> rsaOid = new byte[] { 0x30, 0x0D, 0x06, 0x09, 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x01, 0x05, 0x00 };
+				if (!data.Slice(0, rsaOid.Length).SequenceEqual(rsaOid))
 					throw new FormatException("Expected RSA OID but read {0}".FormatInvariant(BitConverter.ToString(data.Slice(0, 15).ToArray())));
-				data = data.Slice(s_rsaOid.Length);
+				data = data.Slice(rsaOid.Length);
 
 				// BIT STRING (0x03) followed by length
 				if (data[0] != 0x03)
@@ -576,8 +578,5 @@ private static bool TryReadAsnInteger(ReadOnlySpan<byte> data, out ReadOnlySpan<
 
 			return true;
 		}
-
-		// encoded OID sequence for  PKCS #1 rsaEncryption szOID_RSA_RSA = "1.2.840.113549.1.1.1"
-		private static ReadOnlySpan<byte> s_rsaOid => new byte[] { 0x30, 0x0D, 0x06, 0x09, 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x01, 0x05, 0x00 };
 	}
 }