Azure functions HttpTriggers Json deserialization failure should return BadRequest instead of Internal Server error

[Duranom]

Description

Feature request
When using HttpTrigger and a Json de-serialization fails there is a InvalidOperationException and it will result in Internal Server Error.
When you compare it to ASP.NET Core, especially when migrating from it to azure functions, this is an unexpected behavior as there it would result in BadRequest with ValidationProblemDetails.

Details
This example uses ASP.NET Core integration, however same happens with native one.
Assumed: JsonSerializerOptions has been set to use JsonStringEnumConverter.

public class HttpFunction
{
    [Function("Sample")]
    public async Task<IActionResult> SampleAsync(
        [HttpTrigger(AuthorizationLevel.Function, "post", Route = "sample")] HttpRequest request,
        [FromBody] Sample model
    )
    {
        return Task.FromResult(new OkResult());
    }
}
public class Sample
{
    public SampleEnum Value { get; set; }
}
public enum SampleEnum
{
    A,
    B
}

When invoked with a json payload that has a value not in the enum get an exception because "Error" is not the deserialization, with the message System.InvalidOperationException: The Json value could not be converted ....

{
   "value":"Error"
}

Additional Information
A few points regarding the feature request:

• Because it throws InvalidOperationException a middleware cannot help determine if it was a json exception without interpreting the message.
  • An unique exception only thrown by the FromBodyConversionFeature would be needed, because a non-unique one like JsonException or so just means you still have to find out if the input deserialization is the cause or some other layer that leaked.
• The FromBodyuConversionFeature has a model state with results, so even a BadRequest with proper ValidationProblemsDetails would be expected.
• During an attempt to create and use a custom IInputConverter and a copy of DefaultFromBodyConversion, it was noticed that ussing ConversionResult.Failed(exception) actually has no use, as the GeneratedFunctionExecutor.g.cs just perform as BindFunctionInputAsync and even if that returns a failed type it means the result is null. (Seems weird)
• It is not only with in regard with the JsonStringEnumConverter, but will all forms of json that fail, it is just used in the example as it is the fastest way to reproduce.

Currently the only way to have this into a badrequest is either:

• Not use FromBody and deserialize manually from HttpRequest(Data), however that does feel like a step back
• Create custom FromBodyAttribute and either catch the exception from FromBodyConversionFeature to a custom one or have copy from FromBodyConversionFeature and have it in there thrown
  • Replacing IFromBodyConversionFeature in FunctionContext features is also an option if possible, though not checked nore sure about side effects

The first option would mean that you potentially have to do that for a lot of http function triggers, while it would feel more out-of-box feature.
The second/third are an option, however you are very dependent on what the sdk will do and very upgrade dependent breaking.