implement trailing slash redirect via pedestal

Workaround for traefik/traefik#4247
Usually Traefik and other reverse proxies handle this.

src/cljdoc/server/pedestal.clj

@@ -249,6 +249,15 @@
            (fn [request opts]
              (etag/add-file-etag request false)))})
 
+(def redirect-trailing-slash-interceptor
+  {:name ::redirect-trailing-slash
+   :leave (fn [ctx]
+            (let [uri (-> ctx :request :uri)]
+              (cond-> ctx
+                (.endsWith uri "/")
+                (assoc :response {:status 301
+                                  :headers {"Location" (subs uri 0 (dec (.length uri)))}}))))})
+
 (def not-found-interceptor
   {:name ::not-found-interceptor
    :leave (fn [context]
@@ -346,7 +355,10 @@
        ::http/resource-path "public"
        ::http/not-found-interceptor not-found-interceptor}
       http/default-interceptors
-      (update ::http/interceptors #(into [sentry/interceptor etag-interceptor] %))
+      (update ::http/interceptors #(into [sentry/interceptor
+                                          etag-interceptor
+                                          redirect-trailing-slash-interceptor]
+                                         %))
       (http/create-server)
       (http/start)))