C#: webApi cache, Etag and 304(NotModified) StatusCode [2/2]

part 2: The Demo

We have two ways (at least) to intercept requests on webapi before they arrive to controllers:

- MessageHandler: as CacheCow do.

- ActionFilterAttribute: I will use this.


ActionFilterAttribute expose the method OnActionExecuting(), it occurs before the controller's action method is invoked.

All we need to do is create a class derived from ActionAttributeFilter and override method OnActionExecuting().

   public class ETagAttribute : ActionFilterAttribute  
   {  
     public override void OnActionExecuting(HttpActionContext actionContext)  
     {  
         // we will put our ode here
     }  
   }  

Now add the attribute to our test controller's action:

     [ETag]  
     [HttpGet]  
     [Route("api/values/{id}")]  
     public string Get(int id)  
     {  
       var r = new Random();  
       var data = $"{r.Next(0, 10)} {r.Next(0, 10)} {r.Next(0, 10)} {r.Next(0, 10)}";  
       return $"value request: {id}. {data}";  
     }  

Put a breakpoint on Etag attribute method, start on Debug mode (F5) and do a GET request to the test resource "api/values/5"
We are now stopped inside our attribute class and all request information is available there.

I'm requesting the same resource this time but populating the If-None-Match header,

Run with F5 again and lets check the actionContext param:

Our header is populated, now we can do whatever we want before let request pass to controller.