How to communicate WCF exceptions to WebClient

Question

I have a WCF web service which throws exceptions when invalid data is submitted. The data is submitted via an HTTP Post using the WebClient object.

Here is the code for the web service:

[WebInvoke(UriTemplate = "update", Method = "POST")]
public JsonValue Update(HttpRequestMessage message)
{
    var context = new Entities();
    dynamic response = new JsonObject();

    // in order to retrieve the submitted data easily, reference the data as a dynamic object
    dynamic data = message.Content.ReadAs(typeof(JsonObject), new[] { new FormUrlEncodedMediaTypeFormatter() });

    // retrieve the submitted data
    int requestId = data.requestId;
    int statusId = data.statusId;
    string user = data.user;
    string encryptedToken = data.token;
    string notes = data.notes;

    // retrieve the request with a matching Id
    var request = context.Requests.Find(requestId);

    // make sure the request exists
    if (request == null)
        throw new FaultException("The supplied requestId does not exist.");

    // make sure the submitted encrypted token is valid
    var token = DecryptToken(encryptedToken);
    if (token == null)
        throw new FaultException("Invalid security token.");

    // TODO: Validate other token properties (e.g. email)?
    if (!request.User.UserName.Equals(token.UserName))
        throw new FaultException("Invalid security token.");

    // additional logic removed ...
}

And here is the code that submits data to the web service:

            // use the WebClient object to submit data to the WCF web service
            using (var client = new WebClient())
            {
                client.Encoding = Encoding.UTF8;

                // the data will be submitted in the format of a form submission
                client.Headers[HttpRequestHeader.ContentType] = "application/x-www-form-urlencoded";

                var data = new NameValueCollection();

                // prepare the data to be submitted
                data.Add("requestId", requestId.ToString());
                data.Add("statusId", this.StatusId);
                data.Add("token", token.ToString());
                data.Add("user", this.User);
                data.Add("notes", this.Notes);

                // submit the data to the web service
                var response = client.UploadValues(this.Address, data);
           }

I keep getting an exception with message: "The remote server returned an error: (500) Internal Server Error" at client.UploadValues(this.Address, data);.

Is there a way I can make sure that more detailed information is returned to the WebClient?

Also, how can I make sure that these exceptions (in the WCF service) are logged to the EventLog? (Basically I just need to know what happened).

Answer 1

Take a look at HttpResponseException (namespace Microsoft.ApplicationServer.Http.Dispatcher) - they're the way where you can control the response for error cases. You can specify the status code, and you have control over the HttpResponseMessage, in which you can control the message body.

On the client side, when you call WebClient.UploadValues, wrap that call and catch a WebException. If the service returns a response with a non-successful status code (e.g., 500, 400), the Response property of the WebException will have the body, in which you can read in your client.

Another option is to use HttpClient instead of the WebClient, in which case you can simply look at the HttpResponseMessage directly.