Home/ Questions/Q 3843784
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-19T15:59:14+00:00

I’ve just finished my first WCF 4.0 Rest service and don’t understand why the

  • 0

I’ve just finished my first WCF 4.0 Rest service and don’t understand why the Content-Type of the data being returned changes between calling the service via Fiddler and Firefox. Here’s my service contract:

[ServiceContract]
public interface IProjectService
{
    [OperationContract]
    [WebGet(UriTemplate = "project/{id}/json", BodyStyle = WebMessageBodyStyle.Bare, ResponseFormat = WebMessageFormat.Json)]
    ProjectDataContract GetProjectJson(string id);

    [OperationContract]
    [WebGet(UriTemplate = "project/{id}/xml", BodyStyle = WebMessageBodyStyle.Bare, ResponseFormat = WebMessageFormat.Xml)]
    ProjectDataContract GetProjectXml(string id);

    [OperationContract]
    [WebGet(UriTemplate = "userprojects/{userKey}/json", BodyStyle = WebMessageBodyStyle.Bare, ResponseFormat = WebMessageFormat.Json)]
    List<ProjectDataContract> GetProjectsByUserJson(string userKey);

    [OperationContract]
    [WebGet(UriTemplate = "userprojects/{userKey}/xml", BodyStyle = WebMessageBodyStyle.Bare, ResponseFormat = WebMessageFormat.Xml)]
    List<ProjectDataContract> GetProjectsByUserXml(string userKey);
}

As you can see, I’m setting the response format for each operation. If the request ends with “/json” then I’m returning json data. If the request ends with “/xml”, then xml data is returned. At least that is what my intentions are.

When I make a call to http://localhost:5050/ProjectServiceLibrary/project/27/xml in Firefox, I can see the content-type is set to “text/html” whereas the same request invoked in fiddler shows the correct content type of “application/xml”. Same thing happens for a call to a “/json” suffixed request – “text/html” in firefox and “application/json” in fiddler.

So, why is this happening? Which one do I trust? I downloaded JSONView Firefox add-on, but that makes everything look like json. It treats the XML as JSON.

I’m sure I’m missing something obvious. Any help would be greatly appreciated.

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    This is related to the Accept header in the request sent by the client. The Accept header contains a prioritized list of MIME types. Accept headers are defined by the client (Firefox, Fiddler), and tell the server which content-types it is capable of receiving. The server will use the best match based on priority and compatibility.

    Accept headers generated by FireFox give text/html a higher priority – telling the server to send text/html if it is possible. You will probably find that Fiddler does the opposite, giving application/xml the higher priority – this explains what you are seeing.

    There’s more detailed information about request headers on Kris Jordans blog.

    • 0