Add ArraySegment.Slice extension method.

API modelled off proposed Span<T> API: https://github.com/dotnet/corefxlab/blob/master/docs/Span.md#api-surface

Author: bgrainger

src/MySqlConnector/Protocol/Serialization/BufferedByteReader.cs

@@ -9,8 +9,8 @@ public ValueTask<ArraySegment<byte>> ReadBytesAsync(IByteHandler byteHandler, in
 		{
 			if (m_remainingData.Count >= count)
 			{
-				var readBytes = new ArraySegment<byte>(m_remainingData.Array, m_remainingData.Offset, count);
-				m_remainingData = new ArraySegment<byte>(m_remainingData.Array, m_remainingData.Offset + count, m_remainingData.Count - count);
+				var readBytes = m_remainingData.Slice(0, count);
+				m_remainingData = m_remainingData.Slice(count);
 				return new ValueTask<ArraySegment<byte>>(readBytes);
 			}
 
@@ -35,8 +35,8 @@ private ValueTask<ArraySegment<byte>> ReadBytesAsync(IByteHandler byteHandler, A
 
 					if (previousReadBytes.Array == null && readBytes.Count >= count)
 					{
-						m_remainingData = new ArraySegment<byte>(readBytes.Array, readBytes.Offset + count, readBytes.Count - count);
-						return new ValueTask<ArraySegment<byte>>(new ArraySegment<byte>(readBytes.Array, readBytes.Offset, count));
+						m_remainingData = readBytes.Slice(count);
+						return new ValueTask<ArraySegment<byte>>(readBytes.Slice(0, count));
 					}
 
 					var previousReadBytesArray = previousReadBytes.Array;
@@ -50,8 +50,8 @@ private ValueTask<ArraySegment<byte>> ReadBytesAsync(IByteHandler byteHandler, A
 
 					if (previousReadBytes.Count >= count)
 					{
-						m_remainingData = new ArraySegment<byte>(previousReadBytes.Array, previousReadBytes.Offset + count, previousReadBytes.Count - count);
-						return new ValueTask<ArraySegment<byte>>(new ArraySegment<byte>(previousReadBytes.Array, previousReadBytes.Offset, count));
+						m_remainingData = previousReadBytes.Slice(count);
+						return new ValueTask<ArraySegment<byte>>(previousReadBytes.Slice(0, count));
 					}
 
 					return ReadBytesAsync(byteHandler, previousReadBytes, count, ioBehavior);

src/MySqlConnector/Protocol/Serialization/CompressedPayloadHandler.cs

@@ -60,7 +60,7 @@ private ValueTask<ArraySegment<byte>> ReadBytesAsync(int count, ProtocolErrorBeh
 			{
 				int bytesToRead = Math.Min(m_remainingData.Count, count);
 				var result = new ArraySegment<byte>(m_remainingData.Array, m_remainingData.Offset, bytesToRead);
-				m_remainingData = new ArraySegment<byte>(m_remainingData.Array, m_remainingData.Offset + bytesToRead, m_remainingData.Count - bytesToRead);
+				m_remainingData = m_remainingData.Slice(bytesToRead);
 				return new ValueTask<ArraySegment<byte>>(result);
 			}
 
@@ -155,8 +155,8 @@ private ValueTask<ArraySegment<byte>> ReadBytesAsync(int count, ProtocolErrorBeh
 								}
 							}
 
-							var result = new ArraySegment<byte>(m_remainingData.Array, m_remainingData.Offset, count);
-							m_remainingData = new ArraySegment<byte>(m_remainingData.Array, m_remainingData.Offset + count, m_remainingData.Count - count);
+							var result = m_remainingData.Slice(0, count);
+							m_remainingData = m_remainingData.Slice(count);
 							return new ValueTask<ArraySegment<byte>>(result);
 						});
 				});
@@ -202,7 +202,7 @@ private ValueTask<int> CompressAndWrite(ArraySegment<byte> remainingUncompressed
 			{
 				// setting the length to 0 indicates sending uncompressed data
 				uncompressedLength = 0;
-				compressedData = new ArraySegment<byte>(remainingUncompressedData.Array, remainingUncompressedData.Offset, remainingUncompressedBytes);
+				compressedData = remainingUncompressedData.Slice(0, remainingUncompressedBytes);
 			}
 
 			var buffer = new byte[compressedData.Count + 7];
@@ -211,7 +211,7 @@ private ValueTask<int> CompressAndWrite(ArraySegment<byte> remainingUncompressed
 			SerializationUtility.WriteUInt32(uncompressedLength, buffer, 4, 3);
 			Buffer.BlockCopy(compressedData.Array, compressedData.Offset, buffer, 7, compressedData.Count);
 
-			remainingUncompressedData = new ArraySegment<byte>(remainingUncompressedData.Array, remainingUncompressedData.Offset + remainingUncompressedBytes, remainingUncompressedData.Count - remainingUncompressedBytes);
+			remainingUncompressedData = remainingUncompressedData.Slice(remainingUncompressedBytes);
 			return m_byteHandler.WriteBytesAsync(new ArraySegment<byte>(buffer, 0, buffer.Length), ioBehavior)
 				.ContinueWith(_ => remainingUncompressedData.Count == 0 ? default(ValueTask<int>) :
 					CompressAndWrite(remainingUncompressedData, ioBehavior));

src/MySqlConnector/Utility.cs

@@ -25,6 +25,25 @@ public static string FormatInvariant(this string format, params object[] args)
 		public static string GetString(this Encoding encoding, ArraySegment<byte> arraySegment)
 			=> encoding.GetString(arraySegment.Array, arraySegment.Offset, arraySegment.Count);
 
+		/// <summary>
+		/// Returns a new <see cref="ArraySegment{T}"/> that starts at index <paramref name="index"/> into <paramref name="arraySegment"/>.
+		/// </summary>
+		/// <param name="arraySegment">The <see cref="ArraySegment{T}"/> from which to create a slice.</param>
+		/// <param name="index">The non-negative, zero-based starting index of the new slice (relative to <see cref="ArraySegment{T}.Offset"/> of <paramref name="arraySegment"/>.</param>
+		/// <returns>A new <see cref="ArraySegment{T}"/> starting at the <paramref name="index"/>th element of <paramref name="arraySegment"/> and continuing to the end of <paramref name="arraySegment"/>.</returns>
+		public static ArraySegment<T> Slice<T>(this ArraySegment<T> arraySegment, int index) =>
+			new ArraySegment<T>(arraySegment.Array, arraySegment.Offset + index, arraySegment.Count - index);
+
+		/// <summary>
+		/// Returns a new <see cref="ArraySegment{T}"/> that starts at index <paramref name="index"/> into <paramref name="arraySegment"/> and has a length of <paramref name="length"/>.
+		/// </summary>
+		/// <param name="arraySegment">The <see cref="ArraySegment{T}"/> from which to create a slice.</param>
+		/// <param name="index">The non-negative, zero-based starting index of the new slice (relative to <see cref="ArraySegment{T}.Offset"/> of <paramref name="arraySegment"/>.</param>
+		/// <param name="length">The non-negative length of the new slice.</param>
+		/// <returns>A new <see cref="ArraySegment{T}"/> of length <paramref name="length"/>, starting at the <paramref name="index"/>th element of <paramref name="arraySegment"/>.</returns>
+		public static ArraySegment<T> Slice<T>(this ArraySegment<T> arraySegment, int index, int length) =>
+			new ArraySegment<T>(arraySegment.Array, arraySegment.Offset + index, length);
+
 #if NET45
 		public static bool TryGetBuffer(this MemoryStream memoryStream, out ArraySegment<byte> buffer)
 		{