What is the best way to return errors from a WCF service in a RESTful way?

Question

Using WCF in a RESTful way seems great. I’m a big fan of the big guns like simplicity and flexibility, but I also love the way the Urls end up looking. What can I say, I’m a programmer.

The simple API for retrieving and editing resources is matched by an almost equally simple set of possible error responses, and I can’t help feeling that to keep to a “pure” RESTful approach I may be cutting my nose off to spite by face, or more specifically, the nose of my web service consumers. I could be wrong, but there doesn’t seem to be very many Http error codes that I can use, and no ways to pass back a custom error message.

To clarify, I am talking about proper exceptional errors and not expected errors. I want to actually communicate a problem to the user to help them identify what they need to do to correct it.

Possible options I am considering...

1. Just use the Http error codes – This seem like it would be too restrictive in what I am able to express, and won’t allow me to supply a custom message. Please(!) correct me if I am wrong.

2. Always return Http Success but return custom error objects – Obviously the most flexible but certainly not the most RESTful.

I would really appreciate it if anyone could share some real world experience of this particular problem.

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Update

Thanks for the suggestion of using the StatusDescription property of the OutgoingWebResponseContext object. It seemed at first to be something that I could use.

I have come to the conclusion that my second option above is not for me. I want to stick to the what Http can give me.

I am having problems getting it to work, however. Regardless of the value I supply for this property, it doesn’t get returned in the response.

My service method looks like this

public MyType GetMyTypes(string criteria)
{
    try
    {
        return GetMyTypes();
    }
    catch (Exception ex)
    {
        OutgoingWebResponseContext response = WebOperationContext.Current.OutgoingResponse;
        response.StatusCode = HttpStatusCode.Forbidden;
        response.StatusDescription = "A Big fat error occurred";
        return null;
    }
}

And here is the raw response message. There is no mention of the custom message...

HTTP/1.1 403 Forbidden
Server: ASP.NET Development Server/9.0.0.0
Date: Wed, 07 Jan 2009 14:01:20 GMT
X-AspNet-Version: 2.0.50727
Cache-Control: private
Content-Length: 0
Connection: Close

It's not as if I just need to access the correct property on the client. The information is simply not being sent across the link.

What does this StatusDescription property actually do?

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Update

I never did find out how to set the StatusDescription property. I ended up not including any error message at all, and going solely with the Http status codes. I have chosen to expose both Soap and Restful endpoints for my services, and so clients can choose which they prefer to use – the simple Restful messages or the relatively richer Soap messages.

Answer 1

Send the proper response code and you can supply the custom error message in the body of the response.

Answer 2

See this thread for a similar question.

In a nutshell I believe you can set the HTTP status code (to one of the error codes), and provide your custom message in the StatusDescription property:

OutgoingWebResponseContext response = WebOperationContext.Current.OutgoingResponse;
response.StatusCode = System.Net.HttpStatusCode.Forbidden;
response.StatusDescription = "Custom";

I don't know much about the prevalence of this technique in the real world unfortunately.

Answer 3

I add the error code both as above (in the status description) and in the body of the returned page in my REST services as:

OutgoingWebResponseContext response = WebOperationContext.Current.OutgoingResponse; response.StatusCode = HttpStatusCode.Unauthorized; response.StatusDescription = "You are not authorized."; HttpContext.Current.Response.Write("You are not authorized."); return null;

Answer 4

I am having the same complaint about the wcf service. Marshalling custom errors or exceptions from the server back is almost impossible, if you are using non-MS AJAX client. It seems that OutgoingWebResponseContext is an extended class from the generic response and the StatusDescription never gets packed. Only MS AJAX client can get StatusDescription.

BTW, I am using restful wcf services + either dojo or flex.