Limit requestPlaylist to once per 60 seconds

If clients call it quickly in succession with large playlists, it can
cause node to get stuck stringifying socket.io frames and cause an out
of memory crash.

src/channel/playlist.js

@@ -11,6 +11,13 @@ var CustomEmbedFilter = require("../customembed").filter;
 var XSS = require("../xss");
 
 const MAX_ITEMS = Config.get("playlist.max-items");
+// Limit requestPlaylist to once per 60 seconds
+const REQ_PLAYLIST_THROTTLE = {
+    burst: 1,
+    sustained: 0,
+    cooldown: 60
+};
+
 
 const TYPE_QUEUE = {
     id: "string,boolean",
@@ -216,9 +223,7 @@ PlaylistModule.prototype.onUserPostJoin = function (user) {
     user.socket.on("playerReady", function () {
         self.sendChangeMedia([user]);
     });
-    user.socket.on("requestPlaylist", function () {
-        self.sendPlaylist([user]);
-    });
+    user.socket.on("requestPlaylist", this.handleRequestPlaylist.bind(this, user));
     user.on("login", function () {
         self.sendPlaylist([user]);
     });
@@ -1323,4 +1328,16 @@ PlaylistModule.prototype.handleQueuePlaylist = function (user, data) {
     });
 };
 
+PlaylistModule.prototype.handleRequestPlaylist = function (user) {
+    if (user.reqPlaylistLimiter.throttle(REQ_PLAYLIST_THROTTLE)) {
+        user.socket.emit("errorMsg", {
+            msg: "Get Playlist URLs is limited to 1 usage every 60 seconds.  " +
+                    "Please try again later.",
+            code: "REQ_PLAYLIST_LIMIT_REACHED"
+        });
+    } else {
+        this.sendPlaylist([user]);
+    }
+};
+
 module.exports = PlaylistModule;

src/user.js

@@ -21,6 +21,7 @@ function User(socket) {
     self.channel = null;
     self.queueLimiter = util.newRateLimiter();
     self.chatLimiter = util.newRateLimiter();
+    self.reqPlaylistLimiter = util.newRateLimiter();
     self.awaytimer = false;
 
     var announcement = Server.getServer().announcement;