HttpRequestMessageHelper.cs

// Original idea: http://stackoverflow.com/questions/9565889/get-the-ip-address-of-the-remote-host

using System.Net.Http;
using System.ServiceModel.Channels;
using System.Web;

namespace CrowSoftware.Api
{
    public static class HttpRequestMessageHelper
    {
        public static string GetClientIpAddress(this HttpRequestMessage request)
        {
            if (request.Properties.ContainsKey("MS_HttpContext"))
            {
                return ((HttpContextWrapper)request.Properties["MS_HttpContext"]).Request.UserHostAddress;
            }
            else if (request.Properties.ContainsKey(RemoteEndpointMessageProperty.Name))
            {
                RemoteEndpointMessageProperty prop;
                prop = (RemoteEndpointMessageProperty)request.Properties[RemoteEndpointMessageProperty.Name];
                return prop.Address;
            }
            else
            {
                return null;
            }
        }
    }
}