Add additional Link header

Question

This may be a stupid question, but how is it possible to add an extra Link header to a response in Nancy?

I can't do that

context.Response.Headers.Add("Link", "value");

because that fails if there is already a header set. I also cannot use the extension

context.Response.WithHeader("Link", "value");

because it replaces any preexisting headers.

So isn't there a convenient way to work with multiple headers?

Answer 1

This is what I do with an extension method. Notice the check to see if the Link header already exists

    public static Response AsCreatedResourceWithLinks(this IResponseFormatter formatter, Resource resource)
    {
        return CreateResponse(formatter, resource.Id.ToString(), resource.Links);
    }

    private static Response CreateResponse(IResponseFormatter formatter, string id, IEnumerable<ResourceLink> links = null)
    {
        string url = formatter.Context.Request.Url.ToString();
        var response = new Response { StatusCode = HttpStatusCode.Created, Headers = { { "Location", url + "/" + id } } };

        if (links != null && links.Any())
        {
            foreach (var resourceLink in links)
            {
                var link = "<" + url + "/" + resourceLink.Link + ">; anchor=\"" + url + "/" + resourceLink.Anchor + "\"; rel=\"" + resourceLink.Rel + "\"";
                if (response.Headers.ContainsKey("Link"))
                {
                    response.Headers["Link"] += "," + link;
                }
                else
                {
                    response.Headers.Add("Link", link);
                }
            }
        }

        return response;
    }

The Resource & ResourceLink classes look like so:

public class Resource
{
    public int Id { get; set; }
    public List<ResourceLink> Links { get; set; }
}

public class ResourceLink
{
    public string Link { get; set; }
    public string Anchor { get; set; }
    public string Rel { get; set; }
}

The usage is then like so:

Post["/"] = _ => 
{ 
  //Returns Id and Links for Location/Links headers 
  var resource = something.SaveResource(); 

  return Response.AsCreatedResourceWithLinks(resource);`
}