System.Text.Json exception when trying to serialize NaN - problem with NTSTopologySuite

[fededim]

I am working on a project based asp.net core 3.1, EF Code First and NTSTopologySuite. I do have Point properties in my entites to specify geographic location, however when I try to return the entity from a standard WebApi2 controller the serialization fails with the following error:

System.ArgumentException: .NET number values such as positive and negative infinity cannot be written as valid JSON. at System.Text.Json.ThrowHelper.ThrowArgumentException_ValueNotSupported() at System.Text.Json.Utf8JsonWriter.WriteNumberValue(Double value) at System.Text.Json.Serialization.Converters.JsonConverterDouble.Write(Utf8JsonWriter writer, Double value, JsonSerializerOptions options) at System.Text.Json.JsonPropertyInfoNotNullable`4.OnWrite(WriteStackFrame& current, Utf8JsonWriter writer) at System.Text.Json.JsonPropertyInfo.Write(WriteStack& state, Utf8JsonWriter writer) at System.Text.Json.JsonSerializer.Write(Utf8JsonWriter writer, Int32 originalWriterDepth, Int32 flushThreshold, JsonSerializerOptions options, WriteStack& state) at System.Text.Json.JsonSerializer.WriteAsyncCore(Stream utf8Json, Object value, Type inputType, JsonSerializerOptions options, CancellationToken cancellationToken) at Microsoft.AspNetCore.Mvc.Formatters.SystemTextJsonOutputFormatter.WriteResponseBodyAsync(OutputFormatterWriteContext context, Encoding selectedEncoding) at Microsoft.AspNetCore.Mvc.Formatters.SystemTextJsonOutputFormatter.WriteResponseBodyAsync(OutputFormatterWriteContext context, Encoding selectedEncoding) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.gAwaited|27_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g__Awaited|19_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.gAwaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope) at Microsoft.AspNetCore.Routing.EndpointMiddleware.g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger) at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context) at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)

The problem is that the Point class has some properties with NaN values. I could skip the serialization of Point properties with JsonIgnore attribute, but that's not what I need (I need to have the geographic location). Any plan to support NaN values in JSON serialization of Double ? As a matter of fact, double datatype has also this possible value and I do not see why it can't be serialized.

[layomia]

NaN and other floating point constants (infinity, negative infinity) are not valid for (de)serialization using System.Text.Json In ASP.NET 3.1, hence the error you are seeing.

For .NET 5.0, we've added a "number handling" feature that allows you to opt in to read and write these floating point constants - https://github.com/dotnet/runtime/pull/39363. This feature will be available in .NET preview 8, but will not be ported to 3.1

The work around for 3.1 is to add a custom converter for the double type to a JsonSerializerOptions instance, or on each property that requires this handling.

public class DoubleConverter : JsonConverter<double>
{
    public override double Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        if (reader.TokenType == JsonTokenType.String && reader.GetString() == "NaN")
        {
            return double.NaN;
        }

        return reader.GetDouble(); // JsonException thrown if reader.TokenType != JsonTokenType.Number
    }

    public override void Write(Utf8JsonWriter writer, double value, JsonSerializerOptions options)
    {
        if (double.IsNaN(value))
        {
            writer.WriteStringValue("NaN");    
        }
        else
        {
            writer.WriteNumberValue(value);
        }
    }
}