在ActionFilterAttribute中从.NET Core Web API上的请求正文获取JSON数据

Question

I am writing a custom ActionFilterAttribute in order to handle some business logic before the request hits the action in .Net Core Web API. (Core v1.1) The handler is being successfully hit by OnActionExecuting, but I am not able to extract its data sent in JSON format that is coming from the request body.

I have tried in few ways, like reading the ActionExecutingContext stream body (which comes empty), accesing the Form property (but as it is json, it does not work), and some other solutions but no luck on that.

This is the code for my ActionFilter, which is empty, since the issue here is basically the need to extract its data, so further code would be irrelevant.

public class AccountRestrictionAttribute : ActionFilterAttribute
{
     public override async void OnActionExecuting(ActionExecutingContext context)
     {      
     }
}

Answer 1

Answer credit goes to rynowak, I found it here https://github.com/aspnet/Mvc/issues/5260

ModelBinding runs before action filters so if you have form data or a [FromBody] parameter, we've already read it.

Yes, if you're inside an action filter then context.ActionArguments will contain all of the model objects we created. So if you have:

public IActionResult Edit(int id, [FromBody] Widget widget) { }

Then context.ActionArguments["widget"] will return the Widget object. If you're trying to do this in a generic way, look at context.ActionDescriptor.Parameters - this will contain all of the parameter definitions and metadata.