X-HTTP-Method-Override gives NotFound (404) on ASP.NET Web API

Question

I am trying to implement HTTP method override following the steps described here. Basically, I am creating a DelegatingHandler, similar to the following, and adding it as a

Answer 1

I have tried to reproduce your error but I wasn't able to. Here, you can download my simple project with your message handler: https://dl.dropbox.com/u/20568014/WebApplication6.zip

I would like to point out that message handlers run before the action selection logic is performed. So, in your case, probably something else causes the problem and I think you should look at your other message handlers, your message handler's registration code, etc because the problem occurs due to the fact that your message handler never runs.

Also, I think your IRouteConstraint implementation, GetHttpMethodConstraint, looks suspicious to me.

Here is my registration code for the message handler:

protected void Application_Start(object sender, EventArgs e) {

    var config = GlobalConfiguration.Configuration;
    config.Routes.MapHttpRoute(
        "DefaultHttpRoute",
        "api/{controller}/{id}",
        new { id = RouteParameter.Optional }
    );

    config.MessageHandlers.Add(new MethodOverrideHandler());
}

Answer 2

I think I'm having the same problem. It does look like the route constraints are checked before any message handlers.

So I created a custom constraint that knows to check for an overridden HTTP method:

class OverrideableHttpMethodConstraint : HttpMethodConstraint
{
    public OverrideableHttpMethodConstraint(HttpMethod httpMethod) : base(httpMethod)
    {
    }

    protected override bool Match(HttpRequestMessage request, IHttpRoute route, string parameterName, IDictionary<string, object> values, HttpRouteDirection routeDirection)
    {
        IEnumerable<string> headerValues;
        if (request.Method.Method.Equals("POST", StringComparison.OrdinalIgnoreCase) && 
            request.Headers.TryGetValues("X-HTTP-Method-Override", out headerValues))
        {
            var method = headerValues.FirstOrDefault();
            if (method != null)
            {
                request.Method = new HttpMethod(method);
            }
        }

        return base.Match(request, route, parameterName, values, routeDirection);
    }
}