Change session middleware's default to off

When `:session` key is absent in the route data, the session middleware will not
be attached to the route. To enable the middleware, the user at least need to
use an empty map `{}` for the `:session`, which uses the default options.

modules/reitit-middleware/src/reitit/ring/middleware/session.clj

@@ -35,5 +35,6 @@
   {:name    :session
    :spec    ::spec
    :compile (fn [{session-opts :session} _]
-              (let [session-opts (merge {:store store} session-opts)]
-                {:wrap #(session/wrap-session % session-opts)}))})
+              (if session-opts
+                (let [session-opts (merge {:store store} session-opts)]
+                  {:wrap #(session/wrap-session % session-opts)})))})

test/clj/reitit/ring/middleware/session_test.clj

@@ -11,11 +11,11 @@
   [request]
   (let [pattern  #"ring-session=([-\w]+);Path=/;HttpOnly"
         parse-fn (partial re-find pattern)]
-    (-> request
-        (get-in [:headers "Set-Cookie"])
-        first
-        parse-fn
-        second)))
+    (some-> request
+            (get-in [:headers "Set-Cookie"])
+            first
+            parse-fn
+            second)))
 
 (defn handler
   "The handler that increments the counter."
@@ -52,7 +52,8 @@
     (let [app             (ring/ring-handler
                            (ring/router
                             ["/api"
-                             {:middleware [session/session-middleware]}
+                             {:middleware [session/session-middleware]
+                              :session    {}}
                              ["/ping" handler]
                              ["/pong" handler]]))
           first-response  (app {:request-method :get
@@ -65,6 +66,18 @@
         (is (= (inc (get-in first-response [:body :counter]))
                (get-in second-response [:body :counter])))))))
 
+(deftest default-session-off-test
+  (testing "Default session middleware"
+    (let [app  (ring/ring-handler
+                (ring/router
+                 ["/api"
+                  {:middleware [session/session-middleware]}
+                  ["/ping" handler]]))
+          resp (app {:request-method :get
+                     :uri            "/api/ping"})]
+      (testing "off by default"
+        (is (nil? (get-session-id resp)))))))
+
 (deftest session-spec-test
   (testing "Session spec"
     (testing "with invalid session store type"