Is it possible to enable CORS using NancyFX?

Question

I have an API service made with NancyFX, and a couple of front-end developers creating an SPA JS client against this API.

We would like to test the client side code

Answer 1

If your HTTP request is simple then Phill's answer will suffice, but if the request is not so simple, the browser will send a preflight check. The preflight check is an OPTIONS HTTP request and this has to be handled too.

Here is an extension method to configure CORS:

public static class MyNancyExtension
{
    public static void EnableCORS(this Nancy.Bootstrapper.IPipelines pipelines)
    {
        pipelines.AfterRequest.AddItemToEndOfPipeline(ctx =>
        {
            if (ctx.Request.Headers.Keys.Contains("Origin"))
            {
                var origins = "" + string.Join(" ", ctx.Request.Headers["Origin"]);
                ctx.Response.Headers["Access-Control-Allow-Origin"] = origins;

                if (ctx.Request.Method == "OPTIONS")
                {
                    // handle CORS preflight request

                    ctx.Response.Headers["Access-Control-Allow-Methods"] =
                        "GET, POST, PUT, DELETE, OPTIONS";

                    if (ctx.Request.Headers.Keys.Contains("Access-Control-Request-Headers"))
                    {
                        var allowedHeaders = "" + string.Join(
                            ", ", ctx.Request.Headers["Access-Control-Request-Headers"]);
                        ctx.Response.Headers["Access-Control-Allow-Headers"] = allowedHeaders;
                    }
                }
            }
        });
    }
}

To enable CORS call this extension method in the bootstrapper:

protected override void ApplicationStartup(Nancy.TinyIoc.TinyIoCContainer container, Nancy.Bootstrapper.IPipelines pipelines)
{
    base.ApplicationStartup(container, pipelines);

    pipelines.EnableCORS();
}

Please note it is not extending NancyModule because OPTIONS is handled outside of module (also here).