Swagger JSON including null values which is breaking the UI

[domaindrivendev]

Moving the problem described by @replaysMike in issue #184 here as it's a different problem.

For some reason, he is seeing the returned Swagger JSON include null values. This should not happen and is causing the swagger-ui to break. Looking at the following snippet ...

private HttpContent ContentFor(HttpRequestMessage request, SwaggerDocument swaggerDoc)
{
    var negotiator = request.GetConfiguration().Services.GetContentNegotiator();
    var result = negotiator.Negotiate(typeof(SwaggerDocument), request, GetSupportedSwaggerFormatters());

    return new ObjectContent(typeof(SwaggerDocument), swaggerDoc, result.Formatter, result.MediaType);
}

private IEnumerable<MediaTypeFormatter> GetSupportedSwaggerFormatters()
{
    var jsonFormatter = new JsonMediaTypeFormatter
    {
        SerializerSettings = new JsonSerializerSettings
        {
            NullValueHandling = NullValueHandling.Ignore,
            Converters = new[] { new VendorExtensionsConverter() }
        }
    };
    // NOTE: The custom converter would not be neccessary in Newtonsoft.Json >= 5.0.5 as JsonExtensionData
    // provides similar functionality. But, need to stick with older version for WebApi 5.0.0 compatibility 
    return new[] { jsonFormatter };
}

It's clear that the Swagger JSON should be created with a formatter that explicitly sets NullValueHandling.Ignore. Up until this issue, I've never seen this fail so it must be a very specific WebApi configuration that causes the problem.

@replaysMike - I wonder if by any chance you're using a custom IContentNegotiator?

[replaysMike]

I am indeed ;) I use a JsonContentNegotiator to improve performance of json serialization (caches the media type formatter, as outlined here link)

I'll remove that and test again.

[domaindrivendev]

Bingo!

It's an interesting one this. On the one hand the JsonContentNegotiator breaking the semantics of the negotiator interface. When a consumer (e.g. SB) asks to negotiate for a request based on a supplied set of supported formats it doesn't do that. Hence the issue you've uncovered.

Then on the other hand the use of the IContentNegotiator in SB is overkill here - I could easily achieve the same result without it and reduce the dependency on specific app configurations.

I'm leaning toward the latter but would be interested to hear your thoughts?

Thanks

[replaysMike]

Yup! This was the problem. Removing the content negotiator completely resolves the problem. I would agree, it's probably overkill. However it's also not the norm to be using an IContentNegotiator in the manner I did, since the performance increase is probably negligible. Reducing the dependency would be a smart move unless there is a compelling reason for using it, I'm afraid I'm not familiar enough with the pipeline yet to know why. Less brittle is better :)

Thanks dude.

[domaindrivendev]

I'm going to leave the current code in place for now ...

As a side note, the next major version of SB (targeted to AspNet 6.0 and currently in beta) will address this issue fully.