Question

Is it possible to change the data of incoming HTTP request in WCF?

I’ve already found out how to change HTTP method (using IDispatchOperationSelector and HttpRequestMessageProperty of the incoming message).

I’m writing behavior that would enable to make “POST” requests using GET requests (with method and data stored in query string). I can override the HTTP method, but I can’t find the solution to override the data. I need to load the data stored in query string and use them as HTTP body.

Any thoughts?

Answer 1

You’ll need to recreate the incoming message so that the message body contains the information you want to pass. The body will likely be in either XML or JSON format (supported out-of-the-box). The code below shows one example of how this can be done.

public class StackOverflow_10391354
{
    [ServiceContract]
    public class Service
    {
        [WebInvoke(BodyStyle = WebMessageBodyStyle.WrappedRequest)]
        public int Add(int x, int y)
        {
            return x + y;
        }
    }
    class MyWebHttpBehavior : WebHttpBehavior
    {
        protected override WebHttpDispatchOperationSelector GetOperationSelector(ServiceEndpoint endpoint)
        {
            return new MyOperationSelector();
        }
        public override void ApplyDispatchBehavior(ServiceEndpoint endpoint, EndpointDispatcher endpointDispatcher)
        {
            base.ApplyDispatchBehavior(endpoint, endpointDispatcher);
        }
    }
    class MyOperationSelector : WebHttpDispatchOperationSelector
    {
        protected override string SelectOperation(ref Message message, out bool uriMatched)
        {
            HttpRequestMessageProperty prop = (HttpRequestMessageProperty)message.Properties[HttpRequestMessageProperty.Name];
            if (message.Headers.To.LocalPath.EndsWith("/Add") && prop.Method == "GET")
            {
                prop.Method = "POST";
                uriMatched = true;
                message = CreateBodyMessage(message);
                return "Add";
            }
            else
            {
                return base.SelectOperation(ref message, out uriMatched);
            }
        }

        private Message CreateBodyMessage(Message message)
        {
            HttpRequestMessageProperty prop = message.Properties[HttpRequestMessageProperty.Name] as HttpRequestMessageProperty;
            string queryString = prop.QueryString;
            NameValueCollection nvc = HttpUtility.ParseQueryString(queryString);
            StringBuilder sb = new StringBuilder();
            sb.Append('{');
            bool first = true;
            foreach (string key in nvc.Keys)
            {
                if (first)
                {
                    first = false;
                }
                else
                {
                    sb.Append(',');
                }

                sb.Append('\"');
                sb.Append(key);
                sb.Append("\":\"");
                sb.Append(nvc[key]);
                sb.Append('\"');
            }
            sb.Append('}');
            string json = sb.ToString();
            XmlDictionaryReader jsonReader = JsonReaderWriterFactory.CreateJsonReader(Encoding.UTF8.GetBytes(json), XmlDictionaryReaderQuotas.Max);
            Message result = Message.CreateMessage(MessageVersion.None, null, jsonReader);
            result.Properties.Add(HttpRequestMessageProperty.Name, prop);
            result.Properties.Add(WebBodyFormatMessageProperty.Name, new WebBodyFormatMessageProperty(WebContentFormat.Json));
            result.Headers.To = message.Headers.To;
            return result;
        }
    }
    public static void Test()
    {
        string baseAddress = "http://" + Environment.MachineName + ":8000/Service";
        ServiceHost host = new ServiceHost(typeof(Service), new Uri(baseAddress));
        ServiceEndpoint endpoint = host.AddServiceEndpoint(typeof(Service), new WebHttpBinding(), "");
        endpoint.Behaviors.Add(new MyWebHttpBehavior());
        host.Open();
        Console.WriteLine("Host opened");

        WebClient c = new WebClient();
        Console.WriteLine(c.DownloadString(baseAddress + "/Add?x=66&y=88"));

        Console.Write("Press ENTER to close the host");
        Console.ReadLine();
        host.Close();
    }
}