Add primitive record/replay features

These currently need to be accessed in the JS console and record things
into localStorage.

Towards #8: add record (screencast) feature

raft.js

@@ -72,7 +72,7 @@ var stepDown = function(model, server, term) {
   server.term = term;
   server.state = 'follower';
   server.votedFor = null;
-  if (server.electionAlarm < model.time || server.electionAlarm == Infinity) {
+  if (server.electionAlarm < model.time || server.electionAlarm == util.Inf) {
     server.electionAlarm = makeElectionAlarm(model.time);
   }
 };
@@ -112,9 +112,9 @@ rules.becomeLeader = function(model, server) {
     //console.log('server ' + server.id + ' is leader in term ' + server.term);
     server.state = 'leader';
     server.nextIndex    = util.makeMap(server.peers, server.log.length + 1);
-    server.rpcDue       = util.makeMap(server.peers, Infinity);
+    server.rpcDue       = util.makeMap(server.peers, util.Inf);
     server.heartbeatDue = util.makeMap(server.peers, 0);
-    server.electionAlarm = Infinity;
+    server.electionAlarm = util.Inf;
   }
 };
 
@@ -177,7 +177,7 @@ var handleRequestVoteReply = function(model, server, reply) {
     stepDown(model, server, reply.term);
   if (server.state == 'candidate' &&
       server.term == reply.term) {
-    server.rpcDue[reply.from] = Infinity;
+    server.rpcDue[reply.from] = util.Inf;
     server.voteGranted[reply.from] = reply.granted;
   }
 };
@@ -263,7 +263,7 @@ raft.update = function(model) {
   model.messages.forEach(function(message) {
     if (message.recvTime <= model.time)
       deliver.push(message);
-    else if (message.recvTime < Infinity)
+    else if (message.recvTime < util.Inf)
       keep.push(message);
   });
   model.messages = keep;
@@ -320,7 +320,7 @@ raft.spreadTimers = function(model) {
   var timers = [];
   model.servers.forEach(function(server) {
     if (server.electionAlarm > model.time &&
-        server.electionAlarm < Infinity) {
+        server.electionAlarm < util.Inf) {
       timers.push(server.electionAlarm);
     }
   });
@@ -351,7 +351,7 @@ raft.alignTimers = function(model) {
   var timers = [];
   model.servers.forEach(function(server) {
     if (server.electionAlarm > model.time &&
-        server.electionAlarm < Infinity) {
+        server.electionAlarm < util.Inf) {
       timers.push(server.electionAlarm);
     }
   });

script.js

@@ -12,11 +12,23 @@
 var playback;
 var render = {};
 var state;
+var record;
+var replay;
 
 $(function() {
 
 var ARC_WIDTH = 5;
 
+var onReplayDone = undefined;
+record = function(name) {
+  localStorage.setItem(name, state.exportToString());
+};
+replay = function(name, done) {
+  state.importFromString(localStorage.getItem(name));
+  render.update();
+  onReplayDone = done;
+};
+
 state = makeState({
   servers: [],
   messages: [],
@@ -460,7 +472,7 @@ render.messages = function(messagesSame) {
 };
 
 var relTime = function(time, now) {
-  if (time == Infinity)
+  if (time == util.Inf)
     return 'infinity';
   var sign = time > now ? '+' : '';
   return sign + ((time - now) / 1e3).toFixed(3) + 'ms';
@@ -615,6 +627,11 @@ render.update = function() {
       var modelMicrosElapsed = wallMicrosElapsed / speed;
       var modelMicros = state.current.time + modelMicrosElapsed;
       state.seek(modelMicros);
+      if (modelMicros >= state.getMaxTime() && onReplayDone !== undefined) {
+        var f = onReplayDone;
+        onReplayDone = undefined;
+        f();
+      }
       render.update();
     }
     last = timestamp;

state.js

@@ -14,7 +14,6 @@ var makeState = function(initial) {
   };
   var self = {
     current: initial,
-    _checkpoints: checkpoints,
     getMaxTime: function() {
       return maxTime;
     },
@@ -51,6 +50,25 @@ var makeState = function(initial) {
       }
     },
     updater: function() { return false; },
+    exportToString: function() {
+      return JSON.stringify({
+        checkpoints: checkpoints,
+        maxTime: maxTime,
+      });
+    },
+    importFromString: function(s) {
+      var o = JSON.parse(s);
+      checkpoints = o.checkpoints
+      maxTime = o.maxTime;
+      self.current = util.clone(checkpoints[0]);
+      self.current.time = 0;
+    },
+    clear: function() {
+      checkpoints = [];
+      self.current = initial;
+      self.current.time = 0;
+      maxTime = 0;
+    },
   };
   self.current.time = 0;
   return self;

util.js

@@ -6,6 +6,10 @@
 
 var util = {};
 
+// Really big number. Infinity is problematic because
+// JSON.stringify(Infinity) returns 'null'.
+util.Inf = 1e300;
+
 util.value = function(v) {
   return function() { return v; };
 };