Question

I am using the new MVC4 ASP.Net Web API system.

I am calling my API in a test project using WebClient. If I use GET or POST, it works fine. If I use anything else, I get Method Not Allowed. I am actually “faking” the method by injecting the following header. I am doing this because my end users will also have to do this due to the limitations of some firewalls.

I am calling the URL via IIS (i.e. not cassini) – e.g. http://localhost/MyAPI/api/Test

wc.Headers.Add("X-HTTP-Method", "PUT");

I tried adjusting the script mappings in IIS, but as there is no extension, I don’t know what I am meant to be adjusting!

Any ideas?
Regards
Nick

Answer 1

The X-HTTP-Method (or X-HTTP-Method-Override) header is not supported out of the box by Web API. You will need to create a custom DelegatingHandler (below implementation assumes that you are making your request with POST method as it should be):

public class XHttpMethodDelegatingHandler : DelegatingHandler
{
    private static readonly string[] _allowedHttpMethods = { "PUT", "DELETE" };
    private static readonly string _httpMethodHeader = "X-HTTP-Method";

    protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        if (request.Method == HttpMethod.Post && request.Headers.Contains(_httpMethodHeader))
        {
            string httpMethod = request.Headers.GetValues(_httpMethodHeader).FirstOrDefault();
            if (_allowedHttpMethods.Contains(httpMethod, StringComparer.InvariantCultureIgnoreCase))
            request.Method = new HttpMethod(httpMethod);
        }
        return base.SendAsync(request, cancellationToken);
    }
}

Now you just need to register your DelegatingHandler in Global.asax:

protected void Application_Start(object sender, EventArgs e)
{
    GlobalConfiguration.Configuration.MessageHandlers.Add(new XHttpMethodDelegatingHandler());
    ...
}

This should do the trick.