Thanks to a suggestion by @seancorfield to use a middleware function for this I came up with the following which works. Excuse the beginner-level Clojure 😅
;; middleware.clj
(def api-subdomain-to-path
{:name ::api-subdomain-to-path
:compile (fn [_ _]
(fn [handler _]
(fn [req]
(if (str/starts-with? (:server-name req) "api.")
(handler (assoc req :uri (str "/api" (:uri req))))
(handler req)))))})
;; core.clj
(ring/ring-handler
(ring/router routes
{:exception pretty/exception
:data {:middleware [...]})
(ring/routes ...)
{:middleware [[middleware/api-subdomain-to-path :api-subdomain-to-path]]}))
At first I had this new middleware function as first in the middleware
vector in the ring/router
data
map, and while this did update the uri
in the request the routing wasn't working. I then realised there was a different place for top-level middleware, which is given to the ring-handler
.that's cool