Question

I’m working on an API where I’d like to be able to customize the response structure based on a parameter from the client. Response filters seem like a good place to do this in order to avoid doing so in each service or action. The problem is that while I have access to the response DTO returned by the action, and could change its properties, I can’t find how or where to replace the object entirely.

Naively replacing the object in the response filter did not work, but this help illustrate what I’m trying to do:

public class ChangeResponseAttribute : ResponseFilterAttribute
{
    public override void Execute(IHttpRequest req, IHttpResponse res, object responseDto)
    {
        var overrideText = req.QueryString["override"];
        if (!String.IsNullOrEmpty(overrideText))
            responseDto = new { Message = overrideText };
    }
}

[ChangeResponse]
public class TodosService : Service
{
    public object Get(Todos request)
    {
        return new object[0];
    }
}

It looks like another option would be to write the custom response directly & end the request, but that would bypass any other processing left to do by ServiceStack.

Is there a better place to do this than a response filter? Or do I need to bite the bullet and return the optimal DTO in each action?

Answer 1

You can’t change the Response DTO in a filter, but yes one option is to write the response in the filter itself (see this answer for an example of how to do this).

The other option is to use a ServiceRunner and override the OnAfterExecute() custom hook which does let you modify the response returned, e.g:

public class MyServiceRunner<T> : ServiceRunner<T> 
{
    public override object OnAfterExecute(
        IRequestContext requestContext, object response) 
    {
        // Called just after any Action is executed
        var overrideText = req.Get<IHttpRequest>().QueryString["override"];
        return !string.IsNullOrEmpty(overrideText) 
            ? new { Message = overrideText } : null;
    }
}

To get ServiceStack to use it you need to override the CreateServiceRunner method in your AppHost, e.g:

public override IServiceRunner<TRequest> CreateServiceRunner<TRequest>(
    ActionContext actionContext)
{           
    return new MyServiceRunner<TRequest>(this, actionContext); 
}