Add :keep-empty option to Lack.Middleware.Session for preventing from…

… sending Set-Cookie header until the session is used.

src/middleware/session.lisp

@@ -20,20 +20,27 @@
 (defparameter *lack-middleware-session*
   (lambda (app &key
             (store (make-memory-store))
-            (state (make-cookie-state)))
+            (state (make-cookie-state))
+            (keep-empty t))
     (lambda (env)
       (let* ((sid (extract-sid state env))
              (session (and sid
                            (fetch-session store sid)))
              (sid (or sid
-                      (generate-sid state env))))
-        (setf (getf env :lack.session)
-              (or session (make-hash-table :test 'equal)))
+                      (generate-sid state env)))
+             (new-session-p (not session))
+             (session (or session (make-hash-table :test 'equal))))
+        (setf (getf env :lack.session) session)
         (setf (getf env :lack.session.options)
-              (if session
-                  (list :id sid)
-                  (list :id sid :new-session t)))
-        (finalize store state env (funcall app env)))))
+              (if new-session-p
+                  (list :id sid :new-session t)
+                  (list :id sid)))
+        (let ((res (funcall app env)))
+          (if (and (not keep-empty)
+                   new-session-p
+                   (zerop (hash-table-count session)))
+              res
+              (finalize store state env res))))))
   "Middleware for session management")
 
 (defun finalize (store state env res)

t/middleware/session.lisp

@@ -6,7 +6,7 @@
         :lack.test))
 (in-package :t.lack.middleware.session)
 
-(plan 4)
+(plan 5)
 
 (ok (lack.session.state:make-state)
     "Base class of session state")
@@ -103,4 +103,20 @@
           "Set-Cookie header exists")
       (is body '("hi") "body"))))
 
+(subtest ":keep-empty nil"
+  (let ((app (builder
+              (:session :keep-empty nil)
+              (lambda (env)
+                (when (string= (getf env :path-info) "/session")
+                  (setf (gethash "user" (getf env :lack.session)) "Eitaro"))
+                '(200 () ("hi"))))))
+    (destructuring-bind (status headers body)
+        (funcall app (generate-env "/"))
+      (declare (ignore status body))
+      (is headers nil))
+    (destructuring-bind (status headers body)
+        (funcall app (generate-env "/session"))
+      (declare (ignore status body))
+      (is-type (getf headers :set-cookie) 'string))))
+
 (finalize)