More lenient extended_stats deserialization

This commit updates the deserialization of
ExtendedStatsAggregate to make it more lenient to
the introduction of new fields.

Closes #4773

Author: russcam

src/Nest/Aggregations/AggregateFormatter.cs

@@ -68,6 +68,13 @@ internal class AggregateFormatter : IJsonFormatter<IAggregate>
 			{ Parser.Hits, 2 },
 		};
 
+		private static readonly AutomataDictionary ExtendedStatsFields = new AutomataDictionary
+		{
+			{ "variance", 0 },
+			{ "std_deviation", 1 },
+			{ "std_deviation_bounds", 2 }
+		};
+
 		private static readonly byte[] ValueAsStringField = JsonWriter.GetEncodedPropertyNameWithoutQuotation(Parser.ValueAsString);
 
 		static AggregateFormatter()
@@ -547,10 +554,10 @@ private IAggregate GetStatsAggregate(ref JsonReader reader, IJsonFormatterResolv
 			if (reader.GetCurrentJsonToken() == JsonToken.EndObject)
 				return statsMetric;
 
-			return GetExtendedStatsAggregate(ref reader, statsMetric, meta);
+			return GetExtendedStatsAggregate(ref reader, formatterResolver, statsMetric, meta);
 		}
 
-		private IAggregate GetExtendedStatsAggregate(ref JsonReader reader, StatsAggregate statsMetric, IReadOnlyDictionary<string, object> meta)
+		private IAggregate GetExtendedStatsAggregate(ref JsonReader reader, IJsonFormatterResolver formatterResolver, StatsAggregate statsMetric, IReadOnlyDictionary<string, object> meta)
 		{
 			var extendedStatsMetric = new ExtendedStatsAggregate
 			{
@@ -564,35 +571,31 @@ private IAggregate GetExtendedStatsAggregate(ref JsonReader reader, StatsAggrega
 
 			extendedStatsMetric.SumOfSquares = reader.ReadNullableDouble();
 			reader.ReadNext(); // ,
-			reader.ReadNext(); // "variance"
-			reader.ReadNext(); // :
-			extendedStatsMetric.Variance = reader.ReadNullableDouble();
-			reader.ReadNext(); // ,
-			reader.ReadNext(); // "std_deviation"
-			reader.ReadNext(); // :
-			extendedStatsMetric.StdDeviation = reader.ReadNullableDouble();
 
-			if (reader.GetCurrentJsonToken() != JsonToken.EndObject)
+			while (reader.GetCurrentJsonToken() != JsonToken.EndObject)
 			{
-				var bounds = new StandardDeviationBounds();
-				reader.ReadNext(); // ,
-				reader.ReadNext(); // "std_deviation_bounds"
-				reader.ReadNext(); // :
-				reader.ReadNext(); // {
-				reader.ReadNext(); // "upper"
-				reader.ReadNext(); // :
-				bounds.Upper = reader.ReadNullableDouble();
-				reader.ReadNext(); // ,
-				reader.ReadNext(); // "lower"
-				reader.ReadNext(); // :
-				bounds.Lower = reader.ReadNullableDouble();
-				reader.ReadNext(); // }
-				extendedStatsMetric.StdDeviationBounds = bounds;
-			}
+				var propertyName = reader.ReadPropertyNameSegmentRaw();
+				if (ExtendedStatsFields.TryGetValue(propertyName, out var value))
+				{
+					switch (value)
+					{
+						case 0:
+							extendedStatsMetric.Variance = reader.ReadNullableDouble();
+							break;
+						case 1:
+							extendedStatsMetric.StdDeviation = reader.ReadNullableDouble();
+							break;
+						case 2:
+							extendedStatsMetric.StdDeviationBounds =
+								formatterResolver.GetFormatter<StandardDeviationBounds>().Deserialize(ref reader, formatterResolver);
+							break;
+					}
+				}
+				else
+					reader.ReadNextBlock();
 
-			// read any remaining _as_string fields
-			while (reader.GetCurrentJsonToken() != JsonToken.EndObject)
-				reader.ReadNextBlock();
+				reader.ReadIsValueSeparator();
+			}
 
 			return extendedStatsMetric;
 		}

src/Nest/Aggregations/Metric/ExtendedStats/ExtendedStatsAggregate.cs

@@ -2,7 +2,9 @@
 // Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
 // See the LICENSE file in the project root for more information
 
-namespace Nest
+using System.Runtime.Serialization;
+
+namespace Nest
 {
 	public class ExtendedStatsAggregate : StatsAggregate
 	{
@@ -12,9 +14,13 @@ public class ExtendedStatsAggregate : StatsAggregate
 		public double? Variance { get; set; }
 	}
 
+	[DataContract]
 	public class StandardDeviationBounds
 	{
+		[DataMember(Name = "lower")]
 		public double? Lower { get; set; }
+
+		[DataMember(Name = "upper")]
 		public double? Upper { get; set; }
 	}
 }