Is it possible to implement X-HTTP-Method-Override in ASP.NET MVC?

Question

I'm implementing a prototype of a RESTful API using ASP.NET MVC and apart from the odd bug here and there I've achieve all the requirements I set out at the start, apart from callers being able to use the X-HTTP-Method-Override custom header to override the HTTP method.

What I'd like is that the following request...

GET /someresource/123 HTTP/1.1
X-HTTP-Method-Override: DELETE

...would be dispatched to my controller method that implements the DELETE functionality rather than the GET functionality for that action (assuming that there are multiple methods implementing the action, and that they are marked with different [AcceptVerbs] attributes). So, given the following two methods, I would like the above request to be dispatched to the second one:

[ActionName("someresource")]
[AcceptVerbs(HttpVerbs.Get)]
public ActionResult GetSomeResource(int id) { /* ... */ }

[ActionName("someresource")]
[AcceptVerbs(HttpVerbs.Delete)]
public ActionResult DeleteSomeResource(int id) { /* ... */ }

Does anybody know if this is possible? And how much work would it be to do so...?

Answer 1

You won't be able to use the [AcceptVerbs] attribute as-is since it's tied to the request's actual HTTP verb. Fortunately the [AcceptVerbs] attribute is very simple; you can see the source for yourself at http://www.codeplex.com/aspnet/SourceControl/changeset/view/21528#266431.

In short, subclass AcceptsVerbsAttribute and override the IsValidForRequest() method. The implementation would be something like the following:

string incomingVerb = controllerContext.HttpContext.Request.Headers["X-HTTP-Method-Override"] ?? controllerContext.HttpContext.Request.Method;
return Verbs.Contains(incomingVerb, StringComparer.OrdinalIgnoreCase);

Answer 2

Levi's answer is great. Additionally, I added a check in the custom AcceptsVerbsAttribute that also examines the FORM collection, so you can simply put a hidden input to trigger the DELETE (similar to MVC 2's Html.HttpMethodOverride(HttpVerbs.Delete)).

<input name="X-HTTP-Method-Override" type="hidden" value="DELETE" />

Change the incomingVerb assignment to:

string incomingVerb = controllerContext.HttpContext.Request.Headers["X-HTTP-Method-Override"] ?? controllerContext.HttpContext.Request.Form["X-HTTP-Method-Override"] ??controllerContext.HttpContext.Request.HttpMethod;

Be careful with this approach! See a related post by Stephen Walther.

Hopefully this helps someone.