Mvc: Recommended way to read the Request.Body in an ActionFilter

[damienbod]

What's the recommended way to read the request body inside an Actionfilter

The Body property in the ActionExecutingContext cannot be read.

Thanks Damien

[davidfowl]

What are you trying to do with the body?

[damienbod]

I want to validate the model with custom validation which is not possible using the ModelState

[damienbod]

Are you trying to prevent developers from implementing validation logic in Filters? After reading the docs, this is not one of the use cases for ActionFilters.

https://docs.asp.net/en/latest/mvc/controllers/filters.html#selecting-a-filter

Greetings Damien

[rynowak]

If you must do this inside an action filter then you'll need to buffer the body (new up a memory stream and copy to it, replace the body). ModelBinding runs before action filters so if you have form data or a [FromBody] parameter, we've already read it.

If you can tell us more about what you need to accomplish we can suggest alternatives

[damienbod]

Hi @rynowak thanks for your answer. I don't have to validate in the ActionFilter, I just though this would be a good place to put the validation logic before I call the controller method. I use the FromBody in the Controller class to get the data. Can I access this in an ActionFilter?

If not I can always do the validation from the controller class inside the method.

Thanks Damien

[rynowak]

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.

[damienbod]

Cool thanks, works perfect. Thanks a million for the tip.

Greetings Damien

[damienbod]

Created a blog about this. thanks
https://damienbod.com/2016/09/09/asp-net-core-action-arguments-validation-using-an-actionfilter/

[nhwilly]

Interestingly, if you try to update the model (as I am doing with inbound open id connect claims), the validation has already occurred. You have to force it to validate again.

I tried using a resource filter so I could catch it first, but I couldn't figure out how to determine the object type (which would tell me I needed to insert the data into the model). I can't always assume there is just one model coming in, right? One of the incoming models might not have the properties I need to update.

So I loop through, find the models that need updating, make the updates and then force validation again.

Doesn't sound very efficient, but I can't figure another way to do it. Any suggestions/pointers would be great.

Thanks for the articles and the answers here. Huge help.

[rynowak]

@nhwilly It would help if you could open a new issue and explain what you're trying to do from the beginning.

[nhwilly]

Thanks again for responding. I've done that, here. #6225

[rynowak]

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