gistfile1.cs

    /// <summary>
    /// Based on code from:
    /// http://pedroreys.com/2012/02/17/extending-asp-net-web-api-content-negotiation/
    /// </summary>
    public class NotAcceptableConnegHandler : DelegatingHandler {
        
        private readonly HttpConfiguration _configuration;

        public NotAcceptableConnegHandler(HttpConfiguration configuration) {
            if (configuration == null) {
                throw new ArgumentNullException("configuration");
            }
            _configuration = configuration;
        }

        protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) {
            var acceptHeader = request.Headers.Accept;
            
            // from RFC:
            // If no Accept header field is present, then it is assumed that the client accepts all media types. 
            if (!acceptHeader.Any()) {
                return base.SendAsync(request, cancellationToken);
            }
            
            // if client explicitly accepts all media types (*/*)
            if (acceptHeader.Any(a => a.MediaType == "*/*" && a.Quality != 0.0)) {
                return base.SendAsync(request, cancellationToken);
            }
            
            var hasFormatterForRequestedMediaType = _configuration
                .Formatters
                .Any(formatter => acceptHeader.Any(mediaType => formatter.SupportedMediaTypes.Contains(mediaType)));

            if (!hasFormatterForRequestedMediaType) {
                return Task<HttpResponseMessage>.Factory.StartNew(() => new HttpResponseMessage(HttpStatusCode.NotAcceptable));
            }
            return base.SendAsync(request, cancellationToken);
        }
    }