How to add headers to a clojure.java.io/resource response

[Jonathon McKitrick]

I have a GET route returning the result of this:

(io/resource "public/html/confirm.html")

but I need to add Cache-Control headers.  Since the `resource` function returns a java.net.URL object, how can I add headers?  The normal Ring way with ring.util.response/header only operates on a Ring response.

[James Reeves]

Compojure uses the compojure.response/render protocol method to turn values like URLs into Ring responses. So you could write:

    (-> (io/resource "public/html/confirm.html")

        (compojure.response/render)

        (response/header "X-Foo" "Bar"))

Or you could use some middleware, if the header is standard across your application. Or since you know that you're delivering a HTML file, you could also write:

    (-> (response/resource-response "public/html/confirm.html")

        (response/content-type "text/html; charset=utf-8")

        (response/header "X-Foo" "Bar"))

That should result in the same thing, as the only thing Compojure does that Ring doesn't is try to make an educated guess about the content type.

- James

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[Jonathon McKitrick]

Hmm.  I tried this:

(-> (io/resource "public/html/confirm.html")
             (cr/render)
             (resp/header "Cache-Control" "no-cache, no-store"))

and got this:

Exception in thread "main" java.lang.IllegalArgumentException: No single method: render of interface: compojure.response.Renderable found for function: render of protocol: Renderable, compiling:(pts/server.clj:483:14)

[James Reeves]

Oh, my apologies. You also need to pass the request map to the render method.

    (-> (io/resource "public/html/confirm.html")

        (cr/render request)

        (resp/header "Cache-Control" "no-cache, no-store"))

You could also write it as:

    (-> (resp/resource-response "public/html/confirm.html)

        (resp/content-type "text/html; charset=utf-8")

        (resp/header "Cache-Control" "no-cache, no-store"))

Or write some middleware:

    (defn wrap-cache-control [handler cache-control]

      (fn [request]

        (some-> (handler request)

                (resp/header "Cache-Control" cache-control))))

- James

[Jonathon McKitrick]

I'll give that a shot, thanks!