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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.

2016/02/07
1
225
2/7/2016 10:42:22 PM

Accepted Answer

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);
}
2014/02/13
252
2/13/2014 9:13:55 AM

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.


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.

2012/07/04

In MVC 5, things got easier:

return new StatusCodeResult(HttpStatusCode.NotModified, this);
2015/04/01

I hate bumping old articles but this is the first result for this in google search and I had a heck of a time with this problem (even with the support of you guys). So here goes nothing...

Hopefully my solution will help those that also was confused.

namespace MyApplication.WebAPI.Controllers
{
    public class BaseController : ApiController
    {
        public T SendResponse<T>(T response, HttpStatusCode statusCode = HttpStatusCode.OK)
        {
            if (statusCode != HttpStatusCode.OK)
            {
                // leave it up to microsoft to make this way more complicated than it needs to be
                // seriously i used to be able to just set the status and leave it at that but nooo... now 
                // i need to throw an exception 
                var badResponse =
                    new HttpResponseMessage(statusCode)
                    {
                        Content =  new StringContent(JsonConvert.SerializeObject(response), Encoding.UTF8, "application/json")
                    };

                throw new HttpResponseException(badResponse);
            }
            return response;
        }
    }
}

and then just inherit from the BaseController

[RoutePrefix("api/devicemanagement")]
public class DeviceManagementController : BaseController
{...

and then using it

[HttpGet]
[Route("device/search/{property}/{value}")]
public SearchForDeviceResponse SearchForDevice(string property, string value)
{
    //todo: limit search property here?
    var response = new SearchForDeviceResponse();

    var results = _deviceManagementBusiness.SearchForDevices(property, value);

    response.Success = true;
    response.Data = results;

    var statusCode = results == null || !results.Any() ? HttpStatusCode.NoContent : HttpStatusCode.OK;

    return SendResponse(response, statusCode);
}
2017/08/15

.net core 2.2 returning 304 status code. This is using an ApiController.

    [HttpGet]
    public ActionResult<YOUROBJECT> Get()
    {
        return StatusCode(304);
    }

Optionally you can return an object with the response

    [HttpGet]
    public ActionResult<YOUROBJECT> Get()
    {
        return StatusCode(304, YOUROBJECT); 
    }
2019/01/02