Add additional Link header - nancy

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);`
}

Answer 2

According to the RFC the Link Header admits multiple values separated by comma(",").
Link: </TheBook/chapter2>; rel="previous"; title*=UTF-8'de'letztes%20Kapitel,
</TheBook/chapter4>; rel="next"; title*=UTF-8'de'n%c3%a4chstes%20Kapitel
So maybe you should add your multiple links manually and then create the header.
String link1 = #"</TheBook/chapter2>; rel="previous"; title*=UTF-8'de'letztes%20Kapitel";
String link2 = #"</TheBook/chapter4>; rel="next"; title*=UTF-8'de'n%c3%a4chstes%20Kapitel";
String linkHeader = link1+","+link2;
context.Response.Headers.Add("Link", linkHeader);