Support returning promises on Session prototype methods

.eslintrc.yml

@@ -1,4 +1,6 @@
 root: true
+parserOptions:
+  ecmaVersion: 2017
 rules:
   eol-last: error
   eqeqeq: ["error", "always", { "null": "ignore" }]

README.md

@@ -314,7 +314,7 @@ app.get('/', function(req, res, next) {
 })
 ```
 
-#### Session.regenerate(callback)
+#### Session.regenerate(callback) => Promise
 
 To regenerate the session simply invoke the method. Once complete,
 a new SID and `Session` instance will be initialized at `req.session`
@@ -324,9 +324,26 @@ and the `callback` will be invoked.
 req.session.regenerate(function(err) {
   // will have a new session here
 })
+
+// or promises
+req.session.regenerate().then(function() {
+  // will have a new session here
+}).catch(function(err) {
+  // a problem...
+})
+
+// or async/await
+(async function() {
+  try {
+    await req.session.regenerate()
+    // will have a new session here
+  } catch(err) {
+    // a problem...
+  }
+})()
 ```
 
-#### Session.destroy(callback)
+#### Session.destroy(callback) => Promise
 
 Destroys the session and will unset the `req.session` property.
 Once complete, the `callback` will be invoked.
@@ -335,9 +352,26 @@ Once complete, the `callback` will be invoked.
 req.session.destroy(function(err) {
   // cannot access session here
 })
+
+// or promises
+req.session.destroy().then(function() {
+  // cannot access session here
+}).catch(function(err) {
+  // a problem...
+})
+
+// or async/await
+(async function() {
+  try {
+    await req.session.destroy()
+    // cannot access session here
+  } catch(err) {
+    // a problem...
+  }
+})()
 ```
 
-#### Session.reload(callback)
+#### Session.reload(callback) => Promise
 
 Reloads the session data from the store and re-populates the
 `req.session` object. Once complete, the `callback` will be invoked.
@@ -346,9 +380,26 @@ Reloads the session data from the store and re-populates the
 req.session.reload(function(err) {
   // session updated
 })
+
+// or promises
+req.session.reload().then(function() {
+  // session updated
+}).catch(function(err) {
+  // a problem...
+})
+
+// or async/await
+(async function() {
+  try {
+    await req.session.reload()
+    // session updated
+  } catch(err) {
+    // a problem...
+  }
+})()
 ```
 
-#### Session.save(callback)
+#### Session.save(callback) => Promise
 
 Save the session back to the store, replacing the contents on the store with the
 contents in memory (though a store may do something else--consult the store's
@@ -366,6 +417,23 @@ redirects, long-lived requests or in WebSockets.
 req.session.save(function(err) {
   // session saved
 })
+
+// or promises
+req.session.save().then(function() {
+  // session saved
+}).catch(function(err) {
+  // a problem...
+})
+
+// or async/await
+(async function() {
+  try {
+    await req.session.save()
+    // session saved
+  } catch(err) {
+    // a problem...
+  }
+})()
 ```
 
 #### Session.touch()

index.js

@@ -383,16 +383,25 @@ function session(options) {
 
       function reload(callback) {
         debug('reloading %s', this.id)
-        _reload.call(this, function () {
+        if (typeof callback === 'function') {
+          return _reload.call(this, function() {
+            wrapmethods(req.session)
+            callback.apply(this, arguments)
+          });
+        }
+
+        return _reload.call(this).then(function() {
+          wrapmethods(req.session)
+        }).catch(function(err) {
           wrapmethods(req.session)
-          callback.apply(this, arguments)
+          throw err
         })
       }
 
       function save() {
         debug('saving %s', this.id);
         savedHash = hash(this);
-        _save.apply(this, arguments);
+        return _save.apply(this, arguments);
       }
 
       Object.defineProperty(sess, 'reload', {

package.json

@@ -10,6 +10,7 @@
   "repository": "expressjs/session",
   "license": "MIT",
   "dependencies": {
+    "bluebird": "3.7.2",
     "cookie": "0.4.0",
     "cookie-signature": "1.0.6",
     "debug": "2.6.9",

session/session.js

@@ -7,6 +7,12 @@
 
 'use strict';
 
+/**
+ * Module dependencies.
+ * @private
+ */
+var Promise = typeof Promise === 'undefined' ? require('bluebird') : Promise;
+
 /**
  * Expose Session.
  */
@@ -69,8 +75,12 @@ defineMethod(Session.prototype, 'resetMaxAge', function resetMaxAge() {
  */
 
 defineMethod(Session.prototype, 'save', function save(fn) {
-  this.req.sessionStore.set(this.id, this, fn || function(){});
-  return this;
+  return stdCallbackOrPromiseWrapper.call(
+    this,
+    this.req.sessionStore,
+    'set',
+    [ this.id, this ],
+    fn);
 });
 
 /**
@@ -86,16 +96,28 @@ defineMethod(Session.prototype, 'save', function save(fn) {
  */
 
 defineMethod(Session.prototype, 'reload', function reload(fn) {
-  var req = this.req
-  var store = this.req.sessionStore
-
-  store.get(this.id, function(err, sess){
-    if (err) return fn(err);
-    if (!sess) return fn(new Error('failed to load session'));
-    store.createSession(req, sess);
-    fn();
+  var self = this;
+  var req = this.req;
+  var store = this.req.sessionStore;
+
+  if (typeof fn === 'function') {
+    store.get(self.id, function(err, sess){
+      if (err) return fn(err);
+      if (!sess) return fn(new Error('failed to load session'));
+      store.createSession(req, sess);
+      fn();
+    });
+    return this;
+  }
+
+  return new Promise(function(resolve, reject){
+    store.get(self.id, function(err, sess){
+      if (err) return reject(err);
+      if (!sess) return reject(new Error('failed to load session'));
+      store.createSession(req, sess);
+      resolve();
+    });
   });
-  return this;
 });
 
 /**
@@ -108,8 +130,12 @@ defineMethod(Session.prototype, 'reload', function reload(fn) {
 
 defineMethod(Session.prototype, 'destroy', function destroy(fn) {
   delete this.req.session;
-  this.req.sessionStore.destroy(this.id, fn);
-  return this;
+  return stdCallbackOrPromiseWrapper.call(
+    this,
+    this.req.sessionStore,
+    'destroy',
+    [ this.id ],
+    fn);
 });
 
 /**
@@ -121,8 +147,12 @@ defineMethod(Session.prototype, 'destroy', function destroy(fn) {
  */
 
 defineMethod(Session.prototype, 'regenerate', function regenerate(fn) {
-  this.req.sessionStore.regenerate(this.req, fn);
-  return this;
+  return stdCallbackOrPromiseWrapper.call(
+    this,
+    this.req.sessionStore,
+    'regenerate',
+    [ this.req ],
+    fn);
 });
 
 /**
@@ -141,3 +171,17 @@ function defineMethod(obj, name, fn) {
     writable: true
   });
 };
+
+function stdCallbackOrPromiseWrapper(thisArg, method, args, callback) {
+  if (typeof callback === 'function') {
+    thisArg[method].apply(thisArg, args.concat([ callback ]))
+    return this
+  }
+
+  return new Promise(function(resolve, reject) {
+    thisArg[method].apply(thisArg, args.concat([function(err) {
+      if (err) return reject(err)
+      resolve()
+    }]))
+  })
+}