Use Stream buffer (#3730)

Forward port of b75271d

Author: russcam

src/Elasticsearch.Net/Extensions/Extensions.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Globalization;
+using System.IO;
 using System.Linq;
 using System.Text;
 
@@ -11,11 +12,22 @@ internal static class Extensions
 		private const long MillisecondsInAWeek = MillisecondsInADay * 7;
 		private const long MillisecondsInADay = MillisecondsInAnHour * 24;
 		private const long MillisecondsInAnHour = MillisecondsInAMinute * 60;
-
-		internal static string Utf8String(this byte[] bytes) => bytes == null ? null : Encoding.UTF8.GetString(bytes, 0, bytes.Length);
 		private const long MillisecondsInAMinute = MillisecondsInASecond * 60;
 		private const long MillisecondsInASecond = 1000;
 
+		internal static string Utf8String(this byte[] bytes) => bytes == null ? null : Encoding.UTF8.GetString(bytes, 0, bytes.Length);
+
+		internal static string Utf8String(this MemoryStream ms)
+		{
+			if (ms is null)
+				return null;
+
+			if (!ms.TryGetBuffer(out ArraySegment<byte> buffer) || buffer.Array is null)
+				return Encoding.UTF8.GetString(ms.ToArray());
+
+			return Encoding.UTF8.GetString(buffer.Array, buffer.Offset, buffer.Count);
+		}
+
 		internal static byte[] Utf8Bytes(this string s) => s.IsNullOrEmpty() ? null : Encoding.UTF8.GetBytes(s);
 
 		internal static string NotNull(this string @object, string parameterName)

src/Elasticsearch.Net/Serialization/IElasticsearchSerializer.cs

@@ -44,7 +44,14 @@ public static string SerializeToString<T>(
 			T data,
 			IMemoryStreamFactory memoryStreamFactory = null,
 			SerializationFormatting formatting = SerializationFormatting.Indented
-		) =>
-			serializer.SerializeToBytes(data, memoryStreamFactory, formatting).Utf8String();
+		)
+		{
+			memoryStreamFactory = memoryStreamFactory ?? RecyclableMemoryStreamFactory.Default;
+			using (var ms = memoryStreamFactory.Create())
+			{
+				serializer.Serialize(data, ms, formatting);
+				return ms.Utf8String();
+			}
+		}
 	}
 }