webAPI获得链接客户端IP地址

 public static class HttpRequestMessageExtensions
    {
        private const string HttpContext = "MS_HttpContext";
        private const string RemoteEndpointMessage =
            "System.ServiceModel.Channels.RemoteEndpointMessageProperty";
        private const string OwinContext = "MS_OwinContext";

        public static string GetClientIpAddress(this HttpRequestMessage request)
        {
            // Web-hosting. Needs reference to System.Web.dll
            if (request.Properties.ContainsKey(HttpContext))
            {
                dynamic ctx = request.Properties[HttpContext];
                if (ctx != null)
                {
                    return ctx.Request.UserHostAddress;
                }
            }

            // Self-hosting. Needs reference to System.ServiceModel.dll.
            if (request.Properties.ContainsKey(RemoteEndpointMessage))
            {
                dynamic remoteEndpoint = request.Properties[RemoteEndpointMessage];
                if (remoteEndpoint != null)
                {
                    return remoteEndpoint.Address;
                }
            }

            // Self-hosting using Owin. Needs reference to Microsoft.Owin.dll.
            if (request.Properties.ContainsKey(OwinContext))
            {
                dynamic owinContext = request.Properties[OwinContext];
                if (owinContext != null)
                {
                    return owinContext.Request.RemoteIpAddress;
                }
            }

            return null;
        }
    }