How to return error pages with body using HttpListener/HttpListenerResponse

Question

I'm in the process of creating a REST API using HttpListener in .NET (C#). This all works out great, except for one slight issue.

I'm trying to return responses with Status Codes other than OK (200), for instance ResourceNotFound (404).

When I set the StatusCode of the HttpListenerResponse to something other than 200, and create a response body (using HttpListenerResponse.OutputStream), it seems to be resetting the status code to 200. I'm not able to send a response with StatusCode 404 and a message body. However, this should be possible according to the HTTP specs. I'm checking the requests and responses with Fiddler, but I'm not able to get what I'm looking for.

Answer 1

I've had the same problem and found the source of the problem :

If you write the body in the OutputStream before set the StatusCode (or any other property), the response will be sent before the modification is applied !

So, you have to proceed in this order :

public void Send(HttpListenerContext context, byte[] body)
{
    // First, set a random status code and other stuffs
    context.Response.StatusCode = (int)HttpStatusCode.Unauthorized;
    context.Response.ContentType = "text/plain";

    // Write to the stream IN LAST (will send request)
    context.Response.OutputStream.Write(body, 0, body.Length);
}