How do I get ASP.NET Web API to return JSON instead of XML using Chrome?

Answer 1

Some time has passed since this question was asked (and answered) but another option is to override the Accept header on the server during request processing using a MessageHandler as below:

public class ForceableContentTypeDelegationHandler : DelegatingHandler
{
    protected async override Task SendAsync(
                HttpRequestMessage request,
                CancellationToken cancellationToken)
    {
        var someOtherCondition = false;
        var accHeader = request.Headers.GetValues("Accept").FirstOrDefault();
        if (someOtherCondition && accHeader.Contains("application/xml"))
        {
            request.Headers.Remove("Accept");
            request.Headers.Add("Accept", "application/json");
        }
        return await base.SendAsync(request, cancellationToken);
    }
}

Where someOtherCondition can be anything including browser type, etc. This would be for conditional cases where only sometimes do we want to override the default content negotiation. Otherwise as per other answers, you would simply remove an unnecessary formatter from the configuration.

You'll need to register it of course. You can either do this globally:

  public static void Register(HttpConfiguration config) {
      config.MessageHandlers.Add(new ForceableContentTypeDelegationHandler());
  }

or on a route by route basis:

config.Routes.MapHttpRoute(
   name: "SpecialContentRoute",
   routeTemplate: "api/someUrlThatNeedsSpecialTreatment/{id}",
   defaults: new { controller = "SpecialTreatment" id = RouteParameter.Optional },
   constraints: null,
   handler: new ForceableContentTypeDelegationHandler()
);

And since this is a message handler it will run on both the request and response ends of the pipeline much like an HttpModule. So you could easily acknowledge the override with a custom header:

public class ForceableContentTypeDelegationHandler : DelegatingHandler
{
    protected async override Task SendAsync(
                HttpRequestMessage request,
                CancellationToken cancellationToken)
    {
        var wasForced = false;
        var someOtherCondition = false;
        var accHeader = request.Headers.GetValues("Accept").FirstOrDefault();
        if (someOtherCondition && accHeader.Contains("application/xml"))
        {
            request.Headers.Remove("Accept");
            request.Headers.Add("Accept", "application/json");
            wasForced = true;
        }

        var response =  await base.SendAsync(request, cancellationToken);
        if (wasForced){
          response.Headers.Add("X-ForcedContent", "We overrode your content prefs, sorry");
        }
        return response;
    }
}