Low level client exception structure should match SimpleJson strategy

src/Elasticsearch.Net/Serialization/ElasticsearchNetFormatterResolver.cs

@@ -29,6 +29,7 @@ internal sealed class InnerResolver : IJsonFormatterResolver
 				ElasticsearchNetEnumResolver.Instance, // Specialized Enum handling
 				AttributeFormatterResolver.Instance, // [JsonFormatter]
 				DynamicGenericResolver.Instance, // T[], List<T>, etc...
+				ExceptionFormatterResolver.Instance
 			};
 
 			private readonly IJsonFormatterResolver _finalFormatter;

src/Elasticsearch.Net/Serialization/Formatters/ExceptionFormatter.cs

@@ -0,0 +1,118 @@
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Reflection;
+using System.Runtime.Serialization;
+
+namespace Elasticsearch.Net
+{
+	internal class ExceptionFormatterResolver : IJsonFormatterResolver
+	{
+		public static ExceptionFormatterResolver Instance = new ExceptionFormatterResolver();
+
+		private ExceptionFormatterResolver() { }
+
+		private static readonly ExceptionFormatter ExceptionFormatter = new ExceptionFormatter();
+
+		public IJsonFormatter<T> GetFormatter<T>()
+		{
+			if (typeof(Exception).IsAssignableFrom(typeof(T)))
+				return (IJsonFormatter<T>)ExceptionFormatter;
+
+			return null;
+		}
+	}
+
+	internal class ExceptionFormatter : IJsonFormatter<Exception>
+	{
+		private List<Dictionary<string, object>> FlattenExceptions(Exception e)
+		{
+			var maxExceptions = 20;
+			var exceptions = new List<Dictionary<string, object>>(maxExceptions);
+			var depth = 0;
+			do
+			{
+				var o = ToDictionary(e, depth);
+				exceptions.Add(o);
+				depth++;
+				e = e.InnerException;
+			} while (depth < maxExceptions && e != null);
+
+			return exceptions;
+		}
+
+		private static Dictionary<string, object> ToDictionary(Exception e, int depth)
+		{
+			var o = new Dictionary<string, object>(10);
+			var si = new SerializationInfo(e.GetType(), new FormatterConverter());
+			var sc = new StreamingContext();
+			e.GetObjectData(si, sc);
+
+			var helpUrl = si.GetString("HelpURL");
+			var stackTrace = si.GetString("StackTraceString");
+			var remoteStackTrace = si.GetString("RemoteStackTraceString");
+			var remoteStackIndex = si.GetInt32("RemoteStackIndex");
+			var exceptionMethod = si.GetString("ExceptionMethod");
+			var hresult = si.GetInt32("HResult");
+			var source = si.GetString("Source");
+			var className = si.GetString("ClassName");
+
+			o.Add("Depth", depth);
+			o.Add("ClassName", className);
+			o.Add("Message", e.Message);
+			o.Add("Source", source);
+			o.Add("StackTraceString", stackTrace);
+			o.Add("RemoteStackTraceString", remoteStackTrace);
+			o.Add("RemoteStackIndex", remoteStackIndex);
+			o.Add("HResult", hresult);
+			o.Add("HelpURL", helpUrl);
+
+			WriteStructuredExceptionMethod(o, exceptionMethod);
+			return o;
+		}
+
+		private static void WriteStructuredExceptionMethod(Dictionary<string,object> o, string exceptionMethodString)
+		{
+			if (string.IsNullOrWhiteSpace(exceptionMethodString)) return;
+
+			var args = exceptionMethodString.Split('\0', '\n');
+
+			if (args.Length != 5) return;
+
+			var memberType = int.Parse(args[0], CultureInfo.InvariantCulture);
+			var name = args[1];
+			var assemblyName = args[2];
+			var className = args[3];
+			var signature = args[4];
+			var an = new AssemblyName(assemblyName);
+			var exceptionMethod = new Dictionary<string, object>(7)
+			{
+				{ "Name", name },
+				{ "AssemblyName", an.Name },
+				{ "AssemblyVersion", an.Version.ToString() },
+				{ "AssemblyCulture", an.CultureName },
+				{ "ClassName", className },
+				{ "Signature", signature },
+				{ "MemberType", memberType }
+			};
+
+			o.Add("ExceptionMethod", exceptionMethod);
+		}
+
+		public void Serialize(ref JsonWriter writer, Exception value, IJsonFormatterResolver formatterResolver)
+		{
+			if (value == null)
+			{
+				writer.WriteNull();
+				return;
+			}
+
+			var flattenedExceptions = FlattenExceptions(value);
+			var formatter = formatterResolver.GetFormatter<List<Dictionary<string, object>>>();
+			formatter.Serialize(ref writer, flattenedExceptions, formatterResolver);
+		}
+
+		public Exception Deserialize(ref JsonReader reader, IJsonFormatterResolver formatterResolver) =>
+			throw new NotSupportedException();
+	}
+}

src/Elasticsearch.Net/Utf8Json/Resolvers/DynamicObjectResolver.cs

@@ -715,7 +715,7 @@ public static object BuildAnonymousFormatter(Type type, Func<string, string> nam
 			{
 				var ignoreSet = new HashSet<string>(new[]
 				{
-					"HelpLink", "TargetSite", "HResult", "Data", "ClassName", "InnerException"
+					"TargetSite", "ClassName", "InnerException"
 				}.Select(x => nameMutator(x)));
 
 				// special case for exception, modify

src/Tests/Tests/Framework/SerializationTests/ExceptionSerializationTests.cs

@@ -0,0 +1,71 @@
+using System;
+using Elastic.Xunit.XunitPlumbing;
+using Elasticsearch.Net;
+using FluentAssertions;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
+
+namespace Tests.Framework.SerializationTests
+{
+	public class ExceptionSerializationTests
+	{
+		private readonly IElasticsearchSerializer _elasticsearchNetSerializer;
+
+		private readonly Exception Exception = new Exception("outer_exception",
+			new InnerException("inner_exception",
+				new InnerInnerException("inner_inner_exception")));
+
+		public ExceptionSerializationTests()
+		{
+			var pool = new SingleNodeConnectionPool(new Uri("http://localhost:9200"));
+			var connection = new InMemoryConnection();
+			var values = new ConnectionConfiguration(pool, connection);
+			var lowlevelClient = new ElasticLowLevelClient(values);
+			_elasticsearchNetSerializer = lowlevelClient.Serializer;
+		}
+
+		[U]
+		public void LowLevelExceptionSerializationMatchesJsonNet()
+		{
+			var serialized = _elasticsearchNetSerializer.SerializeToString(Exception);
+
+			object CreateException(Type exceptionType, string message, int depth)
+			{
+				return new
+				{
+					Depth = depth,
+					ClassName = exceptionType.FullName,
+					Message = message,
+					Source = (object)null,
+					StackTraceString = (object)null,
+					RemoteStackTraceString = (object)null,
+					RemoteStackIndex = 0,
+					HResult = -2146233088,
+					HelpURL = (object)null
+				};
+			}
+
+			var simpleJsonException = new[]
+			{
+				CreateException(typeof(Exception), "outer_exception", 0),
+				CreateException(typeof(InnerException), "inner_exception", 1),
+				CreateException(typeof(InnerInnerException), "inner_inner_exception", 2),
+			};
+
+			var jArray = JArray.Parse(serialized);
+			var jArray2 = JArray.Parse(JsonConvert.SerializeObject(simpleJsonException));
+
+			JToken.DeepEquals(jArray, jArray2).Should().BeTrue();
+		}
+
+		public class InnerException : Exception
+		{
+			public InnerException(string message, Exception innerException) : base(message, innerException) { }
+		}
+
+		public class InnerInnerException : Exception
+		{
+			public InnerInnerException(string message) : base(message) { }
+		}
+	}
+}