Unable to serialize double value

Elastic.Clients.Elasticsearch version: 8.1.1

Elasticsearch version: 8.7.1

.NET runtime version: .NET FW 4.7.2

Operating system version: Win10 22H2

Description of the problem including expected versus actual behavior: Cannot index an instance of a class containing a public property of type double. Elastic.Transport.UnexpectedTransportException: Unable to serialize double value.

Steps to reproduce:

1. Execute following code/unit test:

using System;
using System.Diagnostics;
using Elastic.Clients.Elasticsearch;
using Elastic.Transport;
using Xunit;

namespace SearchESSequenceResearch.V1
{
	public class MyDecimalClass
	{
		public decimal MyDecimal { get; set; }
	}

	public class MyDoubleClass
	{
		public double MyDouble { get; set; }
	}

	public class TestIndexDouble
	{
		private const string TestMachineUriString = "https://docker.mydomain.com:9280"; // ES 8 in docker
		private readonly Uri _testMachineUri = new Uri(TestMachineUriString);

		[Fact]
		public void TestIndexingDouble()
		{
			ElasticsearchClient client = GetClient();
			var decimalInstance = new MyDecimalClass
			{
				MyDecimal = 123.45m
			};
			try
			{
				client.Index(decimalInstance, "mytestindex");
			}
			catch (Exception e)
			{
				Debug.WriteLine(e);
				throw;
			}
			
			var doubleInstance = new MyDoubleClass
			{
				MyDouble = 123.45d
			};
			try
			{
				client.Index(doubleInstance, "mytestindex");
			}
			catch (Exception e)
			{
				Debug.WriteLine(e);
				throw;
			}
			
		}

		private ElasticsearchClient GetClient()
		{
			var settings = new ElasticsearchClientSettings(_testMachineUri)
				.Authentication(new BasicAuthentication("elastic", "passwordhere"))
				.ServerCertificateValidationCallback((o, cert, chain, errors) => true);
			settings.DisableDirectStreaming();
			var client = new ElasticsearchClient(settings);
			return client;
		}
	}
}```

**Expected behavior**
The item should be serialized and addet to the index.

**Provide `DebugInformation` (if relevant)**:
Elastic.Transport.UnexpectedTransportException: Unable to serialize double value.

Elastic.Transport.UnexpectedTransportException
Unable to serialize double value.
   bei Elastic.Transport.DefaultHttpTransport`1.ThrowUnexpectedTransportException[TResponse](Exception killerException, List`1 seenExceptions, RequestData requestData, TResponse response, RequestPipeline pipeline) in /home/runner/work/elastic-transport-net/elastic-transport-net/src/Elastic.Transport/DefaultHttpTransport.cs:Zeile 328.
   bei Elastic.Transport.DefaultHttpTransport`1.Request[TResponse](HttpMethod method, String path, PostData data, RequestParameters requestParameters) in /home/runner/work/elastic-transport-net/elastic-transport-net/src/Elastic.Transport/DefaultHttpTransport.cs:Zeile 176.
   bei Elastic.Clients.Elasticsearch.ElasticsearchClient.DoRequest[TRequest,TResponse,TRequestParameters](TRequest request, Action`1 forceConfiguration) in /_/src/Elastic.Clients.Elasticsearch/Client/ElasticsearchClient.cs:Zeile 217.

[karl-sjogren]

I submitted a PR for this last week, #7753. It is a bug that only happens when running .NET Framework, not .NET Core or later.

As a temporary workaround you can remove DoubleWithFractionalPortionConverter and FloatWithFractionalPortionConverter from the serializer converters list when constructing the client.

var elasticClientSettings = new ElasticsearchClientSettings(
    new SingleNodePool(new Uri("http://localhost:9200")),
    (defaultSerializer, settings) =>
    new DefaultSourceSerializer(
        settings,
        options => options.Converters.Remove(options.Converters.First(converter => converter.GetType().Name == "DoubleWithFractionalPortionConverter")))) // Need to match on type name since the actual type is internal

[karl-sjogren]

Yeah looking at this another minute shows that the .NET Framework code is completely broken (or rather, incomplete). Since there were not tests to verify it I missunderstood how severe this was. It didn’t just fall through to always throw an exception, the .NET Framework code copies the value into a Span<byte>, but it never writes it to the Utf8JsonWriter.

I can have a look at fixing this in the coming days and when #7769 is done we can add proper tests for this as well.