Implementing ETag Support in ASP.NET MVC4 WebAPI

Question

In the latest ASP.NET MVC4 beta, how would you support conditional GET support via ETags? The ActionFilter would need to be able to complete the request to generate the ETag for the returned resource in order to compare to the If-None-Match header in the request. And then, regardless of whether the incoming ETag in the If-None-Match header was the same as the generated ETag, add the generated ETag to the ETag response header. But with ASP.NET MVC4, I have no idea where to begin. Any suggestions?

Answer 1

Personally, I'm not a fan of "framework magic" and prefer plain old code in the web methods, else we end up with something more akin to WCF, yuk.

So, within your Get web method, manually create the response like so:

var response = this.Request.CreateResponse(HttpStatusCode.OK, obj);
string hash = obj.ModifiedDate.GetHashCode().ToString();

response.Headers.ETag =
    new EntityTagHeaderValue(String.Concat("\"", hash, "\""), true);

return response;

Please note that the ETag produced from the hash code of the timestamp is purely illustrative of a weak entity tagging system. It also shows the additional quotes required.