send filler packets to keep latency low

node_app/server.js

@@ -34,6 +34,42 @@ var io = require('socket.io')(server);
 
 
 io.on('connection', function (socket) {
+    var done = false;
+    var fillerTimeout = null;
+
+    socket.on("disconnect", function () {
+        done = true;
+        if (fillerTimeout) {
+            clearTimeout(fillerTimeout);
+        }
+    });
+
+    function sendFiller() {
+        if (!done) {
+            socket.send("filler");
+            if (Date.now() - socket.conn.lastMidi < 1000) {
+                fillerTimeout = setTimeout(sendFiller, 50);
+            }
+        }
+    }
+
+    socket.conn.startFiller = function () {
+        socket.conn.lastMidi = Date.now();
+        if (!fillerTimeout) {
+            fillerTimeout = setTimeout(sendFiller, 50);
+        }
+    };
+
+    socket.conn.on('packetCreate', function (d) {
+        if (d.data !== '2["message","filler"]') {
+            // we're already sending a packet, so cancel next filler
+            if (fillerTimeout) {
+                clearTimeout(fillerTimeout);
+                fillerTimeout = setTimeout(sendFiller, 50);
+            }
+        }
+    });
+
     socket.on('message', function (data) {
         midi.sendMidi([240, 247]);
         zmq.request(data).then(
@@ -53,9 +89,10 @@ var iomidi = io.of("/midi");
 
 iomidi.on('connection', function (socket) {
     socket.on('message', function (data) {
+        socket.conn.startFiller();
         socket.send("ack"); // this trick should prevent nagle's algorithm. Some serious profiling is needed to be sure http://stackoverflow.com/a/13406438/34871
         if (!data.notes && data.constructor !== Array) { // tried to send filler packets to force flushing, so data.notes will be not present for them
-            return ;
+            return;
         }
 
         var notes;

src/io.js

@@ -1,8 +1,7 @@
 import io from 'socket.io-client';
 
 var url = window.location.protocol + "//" + window.location.host + "/";
-var opts = {transports: ["websocket"]};
 
-export var iorequest = io(url, opts);
-export var ioevents = io(url + 'events', opts);
-export var iomidi = io(url + 'midi', {transports: ["websocket"], forceNew: true});
+export var iorequest = io(url);
+export var ioevents = io(url + 'events');
+export var iomidi = io(url + 'midi');