NewtonsoftJsonPatchInputFormatter not working for non generic JsonPatchDocument with System.Text.Json

[buslm]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

When using System.Text.Json, patches to dynamic objects using the non-generic type JsonPatchDocument are not processed correctly.

The CanRead method of the NewtonsoftJsonPatchInputFormatter class does not allow non-generic types.

With this behavior, patch requests are not handled correctly and the InputFormatter falls back to the default of System.Text.Json, which cannot deserialize this request into a suitable object.

public override bool CanRead(InputFormatterContext context)
{
    ArgumentNullException.ThrowIfNull(context);

    var modelType = context.ModelType;
    if (!typeof(IJsonPatchDocument).IsAssignableFrom(modelType) ||
        !modelType.IsGenericType)
    {
        return false;
    }

    return base.CanRead(context);
}

Expected Behavior

Perhaps the type should be treated explicitly

public override bool CanRead(InputFormatterContext context)
{
    ArgumentNullException.ThrowIfNull(context);

    var modelType = context.ModelType;
    if (!typeof(IJsonPatchDocument).IsAssignableFrom(modelType) ||
        !(modelType.IsGenericType && modelType.Equals(typeof(JsonPatchDocument))))
    {
        return false;
    }

    return base.CanRead(context);
}

Steps To Reproduce

1. Setup a project like described
2. Create Endpoint for dynamic objects
3. Send Request to Endpoint

Exceptions (if any)

No response

.NET Version

.NET 8.0

Anything else?

No response

[captainsafia]

@buslm Thanks for filing this issue!

Do you have a code repro of the issue? The repro steps that you provided indicate that the JsonPatchDocument input would succeed in this case since even though it is not generic it does implement the IJsonPathDocument interface expected here.

[buslm]

Hi @captainsafia,
thanks for your reply! I have just created an example project so that you can reproduce the error.

Because JsonPatchDocument implements the interface IJsonPathDocument, the first condition in if is fulfilled. However, by negating the expression, the next condition of the evaluation sequence - IsGenericType - is also taken into consideration.

In my original answer I had a mistake in the negation of the condition..

public override bool CanRead(InputFormatterContext context)
{
    ArgumentNullException.ThrowIfNull(context);

    var modelType = context.ModelType;
    if (!typeof(IJsonPatchDocument).IsAssignableFrom(modelType) ||
        (!modelType.IsGenericType && !modelType.Equals(typeof(JsonPatchDocument))))
    {
        return false;
    }

    return base.CanRead(context);
}