Returning http status code from Web Api controller

Question

I'm trying to return a status code of 304 not modified for a GET method in a web api controller.

The only way I succeeded was something like this:

public class TryController : ApiController
{
    public User GetUser(int userId, DateTime lastModifiedAtClient)
    {
        var user = new DataEntities().Users.First(p => p.Id == userId);
        if (user.LastModified <= lastModifiedAtClient)
        {
             throw new HttpResponseException(HttpStatusCode.NotModified);
        }
        return user;
    }
}

The problem here is that it's not an exception, It's just not modified so the client cache is OK. I also want the return type to be a User (as all the web api examples shows with GET) not return HttpResponseMessage or something like this.

Answer 1

You can also do the following if you want to preserve the action signature as returning User:

public User GetUser(int userId, DateTime lastModifiedAtClient) 

If you want to return something other than 200 then you throw an HttpResponseException in your action and pass in the HttpResponseMessage you want to send to the client.

Answer 2

I did not know the answer so asked the ASP.NET team here.

So the trick is to change the signature to HttpResponseMessage and use Request.CreateResponse.

[ResponseType(typeof(User))]
public HttpResponseMessage GetUser(HttpRequestMessage request, int userId, DateTime lastModifiedAtClient)
{
    var user = new DataEntities().Users.First(p => p.Id == userId);
    if (user.LastModified <= lastModifiedAtClient)
    {
         return new HttpResponseMessage(HttpStatusCode.NotModified);
    }
    return request.CreateResponse(HttpStatusCode.OK, user);
}

Answer 3

Change the GetXxx API method to return HttpResponseMessage and then return a typed version for the full response and the untyped version for the NotModified response.

    public HttpResponseMessage GetComputingDevice(string id)
    {
        ComputingDevice computingDevice =
            _db.Devices.OfType<ComputingDevice>()
                .SingleOrDefault(c => c.AssetId == id);

        if (computingDevice == null)
        {
            return this.Request.CreateResponse(HttpStatusCode.NotFound);
        }

        if (this.Request.ClientHasStaleData(computingDevice.ModifiedDate))
        {
            return this.Request.CreateResponse<ComputingDevice>(
                HttpStatusCode.OK, computingDevice);
        }
        else
        {
            return this.Request.CreateResponse(HttpStatusCode.NotModified);
        }
    }

*The ClientHasStale data is my extension for checking ETag and IfModifiedSince headers.

The MVC framework should still serialize and return your object.

NOTE

I think the generic version is being removed in some future version of the Web API.

Answer 4

Another option:

return new NotModified();

---

public class NotModified : IHttpActionResult
{
    public Task<HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken)
    {
        var response = new HttpResponseMessage(HttpStatusCode.NotModified);
        return Task.FromResult(response);
    }
}

Answer 5

I don't like having to change my signature to use the HttpCreateResponse type, so I came up with a little bit of an extended solution to hide that.

public class HttpActionResult : IHttpActionResult
{
    public HttpActionResult(HttpRequestMessage request) : this(request, HttpStatusCode.OK)
    {
    }

    public HttpActionResult(HttpRequestMessage request, HttpStatusCode code) : this(request, code, null)
    {
    }

    public HttpActionResult(HttpRequestMessage request, HttpStatusCode code, object result)
    {
        Request = request;
        Code = code;
        Result = result;
    }

    public HttpRequestMessage Request { get; }
    public HttpStatusCode Code { get; }
    public object Result { get; }

    public Task<HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken)
    {
        return Task.FromResult(Request.CreateResponse(Code, Result));
    }
}

You can then add a method to your ApiController (or better your base controller) like this:

protected IHttpActionResult CustomResult(HttpStatusCode code, object data) 
{
    // Request here is the property on the controller.
    return new HttpActionResult(Request, code, data);
}

Then you can return it just like any of the built in methods:

[HttpPost]
public IHttpActionResult Post(Model model)
{
    return model.Id == 1 ?
                Ok() :
                CustomResult(HttpStatusCode.NotAcceptable, new { 
                    data = model, 
                    error = "The ID needs to be 1." 
                });
}

Answer 6

public HttpResponseMessage Post(Article article)
{
    HttpResponseMessage response = Request.CreateResponse<Article>(HttpStatusCode.Created, article);

    string uriToTheCreatedItem = Url.Route(null, new { id = article.Id });
    response.Headers.Location = new Uri(Request.RequestUri, uriToTheCreatedItem);

    return response;
}