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 f

Answer 1

I'm surprised that this hasn't been mentioned yet, but ASP.NET MVC natively supports X-HTTP-Method-Override and has been doing so from at least version 2. There's no need to write custom code to handle this.

It work in the following way:

Inside AcceptVerbsAttribute (also proxied by [HttpPut], [HttpPost], etc), there's an IsValidForRequest method. Inside that method, it checks with Request.GetHttpMethodOverride(), which returns the proper overriden HTTP method with the following conditions:

• Overriding is only supported in POST requests. All others are ignored.
• If the X-HTTP-Method-Override value is GET or POST, it's ignored. This makes sense, as you'd never need to override with these values.
• It looks for X-HTTP-Method-Override in the following places in this priority: 1) HTTP Header 2) Form Body 3) Query String

If you're really curious, here's how GetHttpMethodOverride() looks (from MVC 3's source code):

public static class HttpRequestExtensions {
    internal const string XHttpMethodOverrideKey = "X-HTTP-Method-Override";

    public static string GetHttpMethodOverride(this HttpRequestBase request) {
        if (request == null) {
            throw new ArgumentNullException("request");
        }

        string incomingVerb = request.HttpMethod;

        if (!String.Equals(incomingVerb, "POST", StringComparison.OrdinalIgnoreCase)) {
            return incomingVerb;
        }

        string verbOverride = null;
        string headerOverrideValue = request.Headers[XHttpMethodOverrideKey];
        if (!String.IsNullOrEmpty(headerOverrideValue)) {
            verbOverride = headerOverrideValue;
        }
        else {
            string formOverrideValue = request.Form[XHttpMethodOverrideKey];
            if (!String.IsNullOrEmpty(formOverrideValue)) {
                verbOverride = formOverrideValue;
            }
            else {
                string queryStringOverrideValue = request.QueryString[XHttpMethodOverrideKey];
                if (!String.IsNullOrEmpty(queryStringOverrideValue)) {
                    verbOverride = queryStringOverrideValue;
                }
            }
        }
        if (verbOverride != null) {
            if (!String.Equals(verbOverride, "GET", StringComparison.OrdinalIgnoreCase) &&
                !String.Equals(verbOverride, "POST", StringComparison.OrdinalIgnoreCase)) {
                incomingVerb = verbOverride;
            }
        }
        return incomingVerb;
    }
}