How can I wrap Web API responses(in .net core) for consistency?

Question

I need to return a consistent response with a similar structure returned for all requests. In the previous .NET web api, I was able to achieve this using DelegatingHandler (

Answer 1

This is an old question but maybe this will help others.

In AspNetCore 2(not sure if it applies to previous versions) you can add a Custom OutputFormatter. Below is an implementation using the builtin JsonOutputFormatter.

Note that this wasn't tested thoroughly and I'm not 100% that changing the context is ok. I looked in the aspnet source code and it didn't seem to matter but I might be wrong.

public class CustomJsonOutputFormatter : JsonOutputFormatter
{
    public CustomJsonOutputFormatter(JsonSerializerSettings serializerSettings, ArrayPool charPool)
        : base(serializerSettings, charPool)
    { }

    public override Task WriteResponseBodyAsync(OutputFormatterWriteContext context, Encoding selectedEncoding)
    {
        if (context.HttpContext.Response.StatusCode == (int)HttpStatusCode.OK)
        {
            var @object = new ApiResponse { Data = context.Object };

            var newContext = new OutputFormatterWriteContext(context.HttpContext, context.WriterFactory, typeof(ApiResponse), @object);
            newContext.ContentType = context.ContentType;
            newContext.ContentTypeIsServerDefined = context.ContentTypeIsServerDefined;

            return base.WriteResponseBodyAsync(newContext, selectedEncoding);
        }

        return base.WriteResponseBodyAsync(context, selectedEncoding);
    }
}

and then register it in your Startup class

public void ConfigureServices(IServiceCollection services)
{

        var jsonSettings = new JsonSerializerSettings
        {
            NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore,
            ContractResolver = new CamelCasePropertyNamesContractResolver()
        };

        options.OutputFormatters.RemoveType();
        options.OutputFormatters.Add(new WrappedJsonOutputFormatter(jsonSettings, ArrayPool.Shared));
}