How to set ASP.NET Web Api Route Constraint HTTP Status Return Code

Question

I am using ASP.NET Web Api 2 framework and using a basic route constraint as below.

    [Route("Number/{id:int:min(2):max(10)}")]
    public HttpResponseMessage GetNumber([FromUri] int id)
    {
        return (id > 0)
            ? Request.CreateResponse(HttpStatusCode.OK, id)
            : Request.CreateResponse(HttpStatusCode.PreconditionFailed);
    }

I would like to know when the id is conflict with the constraint above, .e.g. 1 or 11, how can I overrride the default HTTP Status Return code which is 404?

Thanks very much.

Answer 1

You can create a custom route constraint that will check the min, max values like you wish, and additionally allow you to specify the HttpStatusCode in case the constraint is not fulfilled correctly.

public class RangeWithStatusRouteConstraint : IHttpRouteConstraint
{
    private readonly int _from;
    private readonly int _to;
    private readonly HttpStatusCode _statusCode;

    public RangeWithStatusRouteConstraint(int from, int to, string statusCode)
    {
        _from = from;
        _to = to;
        if (!Enum.TryParse(statusCode, true, out _statusCode))
        {
            _statusCode = HttpStatusCode.NotFound;
        }
    }

    public bool Match(HttpRequestMessage request, IHttpRoute route, string parameterName, IDictionary<string, object> values,
        HttpRouteDirection routeDirection)
    {
        object value;
        if (values.TryGetValue(parameterName, out value) && value != null)
        {
            var stringValue = value as string;
            var intValue = 0;

            if (stringValue != null && int.TryParse(stringValue, out intValue))
            {
                if (intValue >= _from && intValue <= _to)
                {
                    return true;
                }

                //only throw if we had the expected type of value
                //but it fell out of range
                throw new HttpResponseException(_statusCode);
            }
        }

        return false;
    }
}

Now you need to register it in the attribute mapping:

        var constraintResolver = new DefaultInlineConstraintResolver();
        constraintResolver.ConstraintMap.Add("rangeWithStatus", typeof(RangeWithStatusRouteConstraint));
        config.MapHttpAttributeRoutes(constraintResolver);

And your route can now look like this:

public class MyController : ApiController
{
    [Route("Number/{id:int:rangeWithStatus(2, 10, PreconditionFailed)}")]
    public HttpResponseMessage GetNumber([FromUri] int id)
    {
        return Request.CreateResponse(HttpStatusCode.OK, id);
    }
}

in this case Conflict is a string representation of HttpStatusCode.Conflict enumeration, which is later cast to the enum value in the constraint.

With such setup, if the value falls out of the [2, 10] range, the Web API infrastructure will respond with 409 status code instead of the default 404.