Scott Hanselman

I got an email today where someone had built a REST(ful/ish) API with ASP.NET Web API that had a customer who was against the idea of using GET, POST, PUT, and DELETE, and insisted that they only use GET and POST.

Sometimes this is because of a browser or client limitaton, sometimes it's a really tense corporate firewall. They wanted to know what they could do.

One thing you can do is to "tunnel" HTTP Methods inside another HTTP Header. Basically you have a header that says "No, seriously, I know I got here via a POST, but use this one instead." You would still POST, but then you'd have "X-HTTP-Method-Override:PUT" as a header.

Here is a PUT in the Postman REST client:

So that's:

PUT /api/Person/4 HTTP/1.1
Host: localhost:10320
Content-Type: application/json
Cache-Control: no-cache

And here's the same PUT, except as a POST plus an X-HTTP-Method-Override header.

Raw, that's like this:

POST /api/Person/4 HTTP/1.1
Host: localhost:10320
Content-Type: application/json
X-HTTP-Method-Override: PUT
Cache-Control: no-cache

Now, how do you get ASP.NET Web API to respect this new way to route things? You may have a Web API Controller like this:

public IEnumerable<Person> Get() { }

// GET api/person/5
public Person Get(int id) { }

// POST api/person
public void Post([FromBody]Person value) { }

// PUT api/person/5
public void Put(int id, [FromBody]Person value) { }

// DELETE api/person/5
public void Delete(int id) { }

And you likely don't want to change it. Make a MethodOverrideHandler like this one. You can add the code yourself, get it from a NuGet package, or use one from the WebAPIContrib project. It's up to you.

public class MethodOverrideHandler : DelegatingHandler
{
    readonly string[] _methods = { "DELETE", "HEAD", "PUT" };
    const string _header = "X-HTTP-Method-Override";

    protected override Task<HttpResponseMessage> SendAsync(
        HttpRequestMessage request, CancellationToken cancellationToken)
    {
        // Check for HTTP POST with the X-HTTP-Method-Override header.
        if (request.Method == HttpMethod.Post && request.Headers.Contains(_header))
        {
            // Check if the header value is in our methods list.
            var method = request.Headers.GetValues(_header).FirstOrDefault();
            if (_methods.Contains(method, StringComparer.InvariantCultureIgnoreCase))
            {
                // Change the request method.
                request.Method = new HttpMethod(method);
            }
        }
        return base.SendAsync(request, cancellationToken);
    }
}

You see it checks if it's a post, looks for the extra header, then changes the request's Method property after the message has been received, but before it's been sent through the pipeline. It'll show up on the right method just as if a PUT had been sent, because from its perspective, a PUT was sent.

You need to register this new MethodOverrideHandler in your WebApiConfig like this, just by adding to the MessageHandlers collection, next to the rest of the configuration and routing code.

public static void Register(HttpConfiguration config)
{
    config.MessageHandlers.Add(new MethodOverrideHandler());

    //OTHER REGULAR STUFF HERE

    // Web API routes
    config.MapHttpAttributeRoutes();

    config.Routes.MapHttpRoute(
        name: "DefaultApi",
        routeTemplate: "api/{controller}/{id}",
        defaults: new { id = RouteParameter.Optional }
    );
}

On the client side, you can keep sending a post with your .ajax call in jQuery, for example, just make sure the override header in there.

$.ajax({
  url: "http://localhost:10320/api/Person/4",
  type: "POST",
  data: JSON.stringify(whatever),
  headers: { 
      "Content-Type": "application/json",
      "X-HTTP-Method-Override": "PUT" },
})

That's the general idea, enjoy!

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About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

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