implement auto-checkpoint logic

www/common/outer/roster.js

@@ -2,6 +2,11 @@
 var factory = function (Util, Hash, CPNetflux, Sortify, nThen, Crypto) {
     var Roster = {};
 
+    // this constant is somewhat arbitrary.
+    // Adjust it as you like to suit performance expectations
+    var CHECKPOINT_INTERVAL = 25;
+    var TIMEOUT_INTERVAL = 30000; // TIMEOUT after 30s
+
     /*
         roster: {
             state: {
@@ -42,6 +47,7 @@ var factory = function (Util, Hash, CPNetflux, Sortify, nThen, Crypto) {
 
         // find the author's role from your knoweldge of the state
         var role = Util.find(members, [author, 'role']);
+
         // and check if it is 'OWNER' or 'ADMIN'
         return ['OWNER', 'ADMIN'].indexOf(role) !== -1;
     };
@@ -109,10 +115,22 @@ var factory = function (Util, Hash, CPNetflux, Sortify, nThen, Crypto) {
         return Boolean(authorRole && ['OWNER', 'ADMIN'].indexOf(authorRole) !== -1);
     };
 
-    var shouldCheckpoint = function (ref) {
-        ref = ref;
+    var shouldCheckpoint = function (me, ref) {
+        // if you can't send valid checkpoints, don't try
+        if (!canCheckpoint(me, ref.state.members)) { return false; }
+
+        // avoid sending checkpoints too often
+        // it's a balance between network constraints
+        // and the size of the roster's log
+        var since = ref.internal.sinceLastCheckpoint;
+
+        if (!since || typeof(since) !== 'number' || since < CHECKPOINT_INTERVAL) {
+            return false;
+        }
+
+        // if you can't think of any other reason not to...
+        return true;
     };
-    shouldCheckpoint = shouldCheckpoint; // XXX lint
 
     var commands = Roster.commands = {};
     /*  Commands are functions with the signature
@@ -342,6 +360,7 @@ var factory = function (Util, Hash, CPNetflux, Sortify, nThen, Crypto) {
             },
             internal: {
                 initialized: false,
+                sinceLastCheckpoint: 0,
             },
         };
         var roster = {};
@@ -377,10 +396,21 @@ var factory = function (Util, Hash, CPNetflux, Sortify, nThen, Crypto) {
             return Util.clone(ref.state);
         };
 
+        var clearPendingCheckpoints = function () {
+            // clear any pending checkpoints you might have...
+            if (ref.internal.pendingCheckpointId) {
+                response.clear(ref.internal.pendingCheckpointId);
+                delete ref.internal.pendingCheckpointId;
+            }
+            clearTimeout(ref.internal.checkpointTimeout);
+            delete ref.internal.checkpointTimeout;
+        };
+
         var webChannel;
         roster.stop = function () {
             if (webChannel && typeof(webChannel.leave) === 'function') {
                 webChannel.leave();
+                clearPendingCheckpoints();
             } else {
                 console.log("FAILED TO LEAVE");
             }
@@ -415,6 +445,10 @@ var factory = function (Util, Hash, CPNetflux, Sortify, nThen, Crypto) {
         };
 
         var onMessage = function (msg, user, vKey, isCp , hash, author) {
+            // count messages received since the last checkpoint
+            // even if they fail to parse
+            ref.internal.sinceLastCheckpoint++;
+
             var parsed = Util.tryParse(msg);
 
             if (!parsed) { return void console.error("could not parse"); }
@@ -446,9 +480,27 @@ var factory = function (Util, Hash, CPNetflux, Sortify, nThen, Crypto) {
             // if a checkpoint was successfully applied, emit an event
             if (parsed[0] === 'CHECKPOINT' && changed) {
                 events.checkpoint.fire(hash);
+                // reset the counter for messages since the last checkpoint
+                ref.internal.sinceLastCheckpoint = 0;
             } else if (changed) {
                 events.change.fire();
             }
+
+            // CHECKPOINT logic...
+            clearPendingCheckpoints();
+            if (!isReady() || !shouldCheckpoint(me, ref)) { return; }
+            // a random number of seconds between 5 and 25
+            var delay = (1000 * Math.floor(Math.random() * 20)) + 5000;
+
+            // if you're here then you can and should send a checkpoint
+            // but since multiple users who can and should might be online at once
+            // and since they'll all trigger this process at the same time...
+            // we want to stagger attempts at random intervals
+            setTimeout(function () {
+                ref.internal.pendingCheckpointId = roster.checkpoint(function (err) {
+                    if (err) { console.error(err); }
+                });
+            }, delay);
         };
 
         var metadata, crypto;
@@ -471,13 +523,14 @@ var factory = function (Util, Hash, CPNetflux, Sortify, nThen, Crypto) {
             //console.log("Sending with id [%s]", id, msg);
             //console.log();
 
-            response.expect(id, cb, 3000);
+            response.expect(id, cb, TIMEOUT_INTERVAL);
             anon_rpc.send('WRITE_PRIVATE_MESSAGE', [
                 channel,
                 ciphertext
             ], function (err) {
                 if (err) { return response.handle(id, [err]); }
             });
+            return id;
         };
 
         roster.init = function (_data, _cb) {