etagresponse.cs

/// <summary>
/// Gets response with ETag. Returns empty body if ETag matches (no data changes)
/// </summary>
/// <param name="data">Data to match with ETag</param>
/// <param name="model">Model to return</param>
/// <returns>Response</returns>
protected Response GetResponseWithEtag(object data, object model)
{
    string etag = Utils.ComputeHash(data);

    if (CacheHelpers.ReturnNotModified(etag, null, this.Context))
    {
        return HttpStatusCode.NotModified;
    }

    return Response.AsJson(model).WithHeader("ETag", etag);
}

usage.cs

Get["/startlist/{id}"] = parameters =>
{
    var startList = _competitionService.GetStartList((int)parameters.id);
    var model = new StartListModel() { StartList = startList };

    return GetResponseWithEtag(startList, model);
};