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 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 values, HttpRouteDirection routeDirection)
    {
        IEnumerable 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);
    }
}