Is there any way to get request body in .NET Core FilterAttribute?

Following snippet worked for me, to log request only if there is any exception.(.Net Core 3.1)

{

public class ExceptionFilter : IActionFilter
{
    private ConcurrentDictionary<string, string> requests = new ConcurrentDictionary<string, string>();

    public void OnActionExecuted(ActionExecutedContext context)
    {
        if (context.Exception != null)

        {
            StringBuilder parameters = new StringBuilder();

            _logger.LogError("Error while executing action:" + context.ActionDescriptor.DisplayName);

            string errRequest;
            if(requests.TryGetValue(context.HttpContext.TraceIdentifier,out errRequest))
            {
                _logger.LogError(errRequest);
            }

            _logger.LogError(context.Exception);

            context.Result = new ObjectResult("Error!!!")
            {
                StatusCode = 500,
            };
            context.ExceptionHandled = true;
        }

        string req;
            requests.Remove(context.HttpContext.TraceIdentifier, out req);


    }

    public void OnActionExecuting(ActionExecutingContext context)
    {
        StringBuilder sb = new StringBuilder();
        foreach (var arg in context.ActionArguments)
        {

            sb.Append(arg.Key.ToString() + ":" + Newtonsoft.Json.JsonConvert.SerializeObject(arg.Value) + "\n");

        }
        requests.TryAdd(context.HttpContext.TraceIdentifier, sb.ToString());
    }


}

}

    in .net core 3.1, I usually use this approach to handle this scenario
    
    1- Create Async Filter Attribute
    
    public class MyFilter : IAsyncAuthorizationFilter
        {
            private string _errorMessage = UserAccessErrorMessages.NO_ACCESS;
            public async Task OnAuthorizationAsync(AuthorizationFilterContext context)
            {
                string requestBody = await ReadBodyAsString(context.HttpContext.Request);
                var reportFiltration = JsonConvert.DeserializeObject<YourModel>(requestBody);
                var _myService = (IMyService)context.HttpContext.RequestServices.GetService(typeof(IMyService));
                    if (!hasAccess)
                    {
                        context.Result = new UnauthorizedObjectResult(_errorMessage);
                    }
            }
    
            private async Task<string> ReadBodyAsString(Microsoft.AspNetCore.Http.HttpRequest request)
            {
                var initialBody = request.Body; // Workaround
    
                try
                {
                    //request.EnableRewind();
    
                    using (StreamReader reader = new StreamReader(request.Body))
                    {
                        string text = await reader.ReadToEndAsync();
                        return text;
                    }
                }
                finally
                {
                    // Workaround so MVC action will be able to read body as well
                    request.Body = initialBody;
                }
            }
        }
2- Create Your Custom Attribute
public class MyAttribute : TypeFilterAttribute, IAllowAnonymous
    {
        public MyAttribute () : base(typeof(MyFilter))
        {

        }
    }

3- use your filter

    [HttpPost]
    [ActionName("MyAction")]
    [MyAttribute]
    public async Task<IActionResult> PostData([FromBody]MyModel model)

Accordingly to this "Best way to log/read request body in a middleware" thread, the following should work:

// using Microsoft.AspNetCore.Http.Internal;

public class SampleActionFilterAttribute : TypeFilterAttribute
{
    ... 

    public void OnActionExecuting(ActionExecutedContext context)
    {
        // read body before MVC action execution
        string bodyData = ReadBodyAsString(context.HttpContext.Request);
    }

    private string ReadBodyAsString(HttpRequest request)
    {
        var initialBody = request.Body; // Workaround

        try
        {
            request.EnableRewind();

            using (StreamReader reader = new StreamReader(request.Body))
            {
                string text = reader.ReadToEnd();
                return text;
            }
        }
        finally
        {
            // Workaround so MVC action will be able to read body as well
            request.Body = initialBody; 
        }

        return string.Empty;
    }
 }

Also similar approach described in Read request body twice SO post

---

Update: above approach in ReadBodyAsString with will work if used in middleware, not in action filter. The difference is that when action filter is calling (even for OnActionExecuting), the body stream already has been read and [FromBody] model has been populated.

The good nesw is that so it is possible to get model directly in action filter by using context.ActionArguments["<model_name>"]. In your case:

public void OnActionExecuted(ActionExecutedContext context)
{
   var model = context.ActionArguments["model"] as NoteModel;
}