How to set custom headers when using IHttpActionResult?

Question

In ASP.NET Web API 2, the IHttpActionResult offers a lot of value in simplifying controller code and I\'m reluctant to stop using it, but I\'ve hit a problem.

Answer 1

public static class HttpExtentions
{
    public static IHttpActionResult AddHeader(this IHttpActionResult action,
        string headerName, IEnumerable headerValues)
    {
        return new HeaderActionResult(action, headerName, headerValues);
    }

    public static IHttpActionResult AddHeader(this IHttpActionResult action,
        string headerName, string header)
    {
        return AddHeader(action, headerName, new[] {header});
    }

    private class HeaderActionResult : IHttpActionResult
    {
        private readonly IHttpActionResult action;

        private readonly Tuple> header;

        public HeaderActionResult(IHttpActionResult action, string headerName,
            IEnumerable headerValues)
        {
            this.action = action;

            header = Tuple.Create(headerName, headerValues);
        }

        public async Task ExecuteAsync(CancellationToken cancellationToken)
        {
            var response = await action.ExecuteAsync(cancellationToken);

            response.Headers.Add(header.Item1, header.Item2);

            return response;
        }
    }
}