Add support for "local" subjects, which don't get pushed to the serve and get destroyed on unsubscribe.

static/cosmopolite.js

@@ -290,6 +290,12 @@ Cosmopolite.prototype.subscribe = function(subjects, opt_messages, opt_lastID) {
     var subject = subjects[i];
 
     ret.push(this.newPromise_(function(resolve, reject) {
+      if (subject['local'] && (subject['readable_only_by'] || subject['writable_only_by'])) {
+        console.log(this.loggingPrefix_(), 'local subjects can\'t have ACLs:', subject);
+        reject();
+        return;
+      }
+
       /** @type {Cosmopolite.typeSubject} */
       var canonicalSubject = this.canonicalSubject_(subject);
       /** @type {string} */
@@ -303,6 +309,13 @@ Cosmopolite.prototype.subscribe = function(subjects, opt_messages, opt_lastID) {
         };
       }
 
+      if (subject['local']) {
+        this.subscriptions_[subjectString].state =
+            Cosmopolite.SubscriptionState_.ACTIVE;
+        resolve();
+        return;
+      }
+
       var args = {
         'subject': canonicalSubject
       };
@@ -374,6 +387,10 @@ Cosmopolite.prototype.unsubscribe = function(subject) {
     /** @type {string} */
     var subjectString = this.subjectString_(canonicalSubject);
     delete this.subscriptions_[subjectString];
+    if (subject['local']) {
+      resolve();
+      return;
+    }
     var args = {
       'subject': canonicalSubject
     };
@@ -390,12 +407,25 @@ Cosmopolite.prototype.unsubscribe = function(subject) {
  */
 Cosmopolite.prototype.sendMessage = function(subject, message) {
   return this.newPromise_(function(resolve, reject) {
+    if (subject['local'] && (subject['readable_only_by'] || subject['writable_only_by'])) {
+      console.log(this.loggingPrefix_(), 'local subjects can\'t have ACLs:', subject);
+      reject();
+      return;
+    }
+
     var args = /** @type {Cosmopolite.typeMessage} */ ({
       'subject': this.canonicalSubject_(subject),
       'message': JSON.stringify(message),
       'sender_message_id': this.uuid()
     });
 
+    if (subject['local']) {
+      resolve(message);
+      args['id'] = this.uuid();
+      this.onMessage_(args);
+      return;
+    }
+
     // No message left behind.
     var messageQueue = JSON.parse(localStorage[this.messageQueueKey_]);
     messageQueue.push(args);
@@ -496,11 +526,20 @@ Cosmopolite.prototype.pin = function(subject, message) {
       'sender_message_id': id
     };
 
-
-    this.sendRPC_('pin', args, function() {
+    var onSuccess = function() {
       this.pins_[id] = args;
       resolve(id);
-    });
+    }
+
+    if (subject['local']) {
+      onSuccess.bind(this)();
+      // Ugly hack, but we need this to promise to resolve before the callback fires.
+      // This is the equivalent of sched_yield(), and probably about as reliable.
+      window.setTimeout(this.onPin_.bind(this, Object.create(args)), 0);
+      return;
+    }
+
+    this.sendRPC_('pin', args, onSuccess);
   }.bind(this));
 };
 
@@ -520,6 +559,12 @@ Cosmopolite.prototype.unpin = function(id) {
 
     delete this.pins_[id];
 
+    if (pin['subject']['local']) {
+      resolve();
+      window.setTimeout(this.onUnpin_.bind(this, Object.create(pin)), 0);
+      return;
+    }
+
     this.sendRPC_('unpin', args, resolve);
   }.bind(this));
 };
@@ -682,6 +727,9 @@ Cosmopolite.prototype.canonicalSubject_ = function(subject) {
   if (subject['writable_only_by'] === null) {
     delete subject['writable_only_by'];
   }
+  if (!subject['local']) {
+    delete subject['local'];
+  }
   return subject;
 };
 
@@ -698,7 +746,8 @@ Cosmopolite.prototype.subjectString_ = function(subject) {
   return [
     subject['name'],
     subject['readable_only_by'],
-    subject['writable_only_by']
+    subject['writable_only_by'],
+    subject['local']
   ].toString();
 };
 
@@ -970,6 +1019,9 @@ Cosmopolite.prototype.onReconnect_ = function() {
     if (subscription.state != Cosmopolite.SubscriptionState_.ACTIVE) {
       continue;
     }
+    if (subject['local']) {
+      continue;
+    }
     /** @type {number} */
     var lastID = 0;
     if (subscription.messages.length > 0) {
@@ -986,6 +1038,9 @@ Cosmopolite.prototype.onReconnect_ = function() {
   for (var id in this.pins_) {
     /** @type {Cosmopolite.typeMessage} */
     var pin = this.pins_[id];
+    if (pin.subject['local']) {
+      continue;
+    }
     rpcs.push({
       'command': 'pin',
       'arguments': pin