Add rolling function as options

README.md

@@ -247,6 +247,24 @@ set to `false`, the cookie will not be set on a response with an uninitialized
 session. This option only modifies the behavior when an existing session was
 loaded for the request.
 
+**Note** If this is set to true, option `rollingFunction` is ignored and every request will roll the session.
+
+##### rollingFunction
+
+Similar to [`rolling`](#rolling) option, but can conditionally roll the session. Only if the provided function returns true, the response will contain the cookie with the reset expiration to the original [`maxAge`](#cookiemaxage).
+
+```js
+/**
+ * @param {Object} req - Request object from the middleware.
+ * @returns {Boolean} - Whether the session will be rolled or not.
+ * Use req.session to access the session object.
+ */
+...
+rollingFunction: function([req]): Boolean {...}
+```
+
+**Note** In order for this function to be called, [`rolling`](#rolling) must be `false`.
+
 ##### saveUninitialized
 
 Forces a session that is "uninitialized" to be saved to the store. A session is

index.js

@@ -76,6 +76,7 @@ var defer = typeof setImmediate === 'function'
  * @param {Boolean} [options.proxy]
  * @param {Boolean} [options.resave] Resave unmodified sessions back to the store
  * @param {Boolean} [options.rolling] Enable/disable rolling session expiration
+ * @param {Function} [options.rollingFunction] Function for enabling/disabling rolling session expiration
  * @param {Boolean} [options.saveUninitialized] Save uninitialized sessions to the store
  * @param {String|Array} [options.secret] Secret for signing session ID
  * @param {Object} [options.store=MemoryStore] Session store
@@ -108,6 +109,9 @@ function session(options) {
   // get the rolling session option
   var rollingSessions = Boolean(opts.rolling)
 
+  // get the rolling function option
+  var rollingFunction = opts.rollingFunction;
+
   // get the save uninitialized session option
   var saveUninitializedSession = opts.saveUninitialized
 
@@ -456,6 +460,14 @@ function session(options) {
         return false;
       }
 
+      if (
+        !rollingSessions &&
+        cookieId === req.sessionID &&
+        typeof rollingFunction === "function"
+      ) {
+        return rollingFunction(req);
+      }
+
       return cookieId !== req.sessionID
         ? saveUninitializedSession || isModified(req.session)
         : rollingSessions || req.session.cookie.expires != null && isModified(req.session);

test/session.js

@@ -962,6 +962,112 @@ describe('session()', function(){
       });
     });
 
+    it('should not force cookie if rolling function returns false', function(done){
+      var server = createServer(
+        {
+          rollingFunction: function() {
+            return false;
+          }
+        },
+        function(req, res) {
+          req.session.user = "bob";
+          res.end();
+        }
+      );
+
+      request(server)
+      .get('/')
+      .expect(shouldSetCookie('connect.sid'))
+      .expect(200, function(err, res){
+        if (err) return done(err);
+        request(server)
+        .get('/')
+        .set('Cookie', cookie(res))
+        .expect(shouldNotHaveHeader('Set-Cookie'))
+        .expect(200, done)
+      });
+    });
+
+    it('should force cookie if rolling function returns false and rolling option is set', function(done){
+      var server = createServer(
+        {
+          rollingFunction: function() {
+            return false;
+          },
+          rolling: true
+        },
+        function(req, res) {
+          req.session.user = "bob";
+          res.end();
+        }
+      );
+
+      request(server)
+      .get('/')
+      .expect(shouldSetCookie('connect.sid'))
+      .expect(200, function(err, res){
+        if (err) return done(err);
+        request(server)
+        .get('/')
+        .set('Cookie', cookie(res))
+        .expect(shouldSetCookie('connect.sid'))
+        .expect(200, done)
+      });
+    });
+
+    it('should force cookie if rolling function returns true and rolling option is set', function(done){
+      var server = createServer(
+        {
+          rollingFunction: function() {
+            return true;
+          },
+          rolling: true
+        },
+        function(req, res) {
+          req.session.user = "bob";
+          res.end();
+        }
+      );
+
+      request(server)
+      .get('/')
+      .expect(shouldSetCookie('connect.sid'))
+      .expect(200, function(err, res){
+        if (err) return done(err);
+        request(server)
+        .get('/')
+        .set('Cookie', cookie(res))
+        .expect(shouldSetCookie('connect.sid'))
+        .expect(200, done)
+      });
+    });
+
+    it('should force cookie if rolling function returns true', function(done){
+      var server = createServer(
+        {
+          rollingFunction: function() {
+            return true;
+          }
+        },
+        function(req, res) {
+          req.session.user = "bob";
+          res.end();
+        }
+      );
+
+      request(server)
+      .get('/')
+      .expect(shouldSetCookie('connect.sid'))
+      .expect(200, function(err, res){
+        if (err) return done(err);
+        request(server)
+        .get('/')
+        .set('Cookie', cookie(res))
+        .expect(shouldSetCookie('connect.sid'))
+        .expect(200, done)
+      });
+    });
+
     it('should not force cookie on uninitialized session if saveUninitialized option is set to false', function(done){
       var store = new session.MemoryStore()
       var server = createServer({ store: store, rolling: true, saveUninitialized: false })