Introduce Syndicate.Ack() to reliably detect lack of demand in DOMFragment.

js/src/ack.js

@@ -0,0 +1,41 @@
+// Utility protocol for measuring when a stateChange takes effect.
+
+var RandomID = require('./randomid.js');
+var Syndicate = require('./syndicate.js');
+var Route = require('./route.js');
+var Patch = require('./patch.js');
+
+var $Ack = new Route.$Special('ack');
+
+function Ack(metaLevel, id) {
+  this.metaLevel = metaLevel || 0;
+  this.id = id || RandomID.randomId(16);
+  this.done = false;
+}
+
+Ack.prototype.arm = function () {
+  Syndicate.Network.stateChange(Patch.sub([$Ack, this.id], this.metaLevel));
+  Syndicate.Network.send([$Ack, this.id], this.metaLevel);
+};
+
+Ack.prototype.disarm = function () {
+  Syndicate.Network.stateChange(Patch.unsub([$Ack, this.id], this.metaLevel));
+};
+
+Ack.prototype.check = function (e) {
+  if (!this.done) {
+    if (e.type === 'message') {
+      var m = Patch.stripAtMeta(e.message, this.metaLevel);
+      if (m && m[0] === $Ack && m[1] === this.id) {
+	this.disarm();
+	this.done = true;
+      }
+    }
+  }
+  return this.done;
+};
+
+///////////////////////////////////////////////////////////////////////////
+
+module.exports.$Ack = $Ack;
+module.exports.Ack = Ack;

js/src/dom-driver.js

@@ -33,6 +33,8 @@ function DOMFragment(selector, fragmentClass, fragmentSpec, domWrapFunction, jQu
   this.fragmentSpec = fragmentSpec;
   this.domWrapFunction = domWrapFunction;
   this.jQueryWrapFunction = jQueryWrapFunction;
+  this.demandExists = false;
+  this.subscriptionEstablished = new Syndicate.Ack();
   this.nodes = this.buildNodes();
 }
 
@@ -45,22 +47,36 @@ DOMFragment.prototype.boot = function () {
 				       1,
 				       self.jQueryWrapFunction);
     Network.spawn({
+      demandExists: false,
+      subscriptionEstablished: new Syndicate.Ack(1),
       boot: function () {
+	this.subscriptionEstablished.arm();
 	return Patch.sub(Patch.advertise(specification), 1);
       },
       handleEvent: function (e) {
-	if (e.type === "stateChange" && e.patch.hasRemoved()) {
+	this.subscriptionEstablished.check(e);
+	if (e.type === "stateChange") {
+	  if (e.patch.hasAdded()) this.demandExists = true;
+	  if (e.patch.hasRemoved()) this.demandExists = false;
+	}
+	if (this.subscriptionEstablished.done && !this.demandExists) {
 	  Network.exitNetwork();
 	}
       }
     });
   }));
 
+  this.subscriptionEstablished.arm();
   return Patch.sub(specification).andThen(Patch.pub(specification));
 };
 
 DOMFragment.prototype.handleEvent = function (e) {
-  if (e.type === "stateChange" && e.patch.hasRemoved()) {
+  this.subscriptionEstablished.check(e);
+  if (e.type === "stateChange") {
+    if (e.patch.hasAdded()) this.demandExists = true;
+    if (e.patch.hasRemoved()) this.demandExists = false;
+  }
+  if (this.subscriptionEstablished.done && !this.demandExists) {
     for (var i = 0; i < this.nodes.length; i++) {
       var n = this.nodes[i];
       n.parentNode.removeChild(n);

js/src/main.js

@@ -19,7 +19,9 @@ copyKeys(['__', '_$', '$Capture', '$Special',
 
 module.exports.DemandMatcher = require('./demand-matcher.js').DemandMatcher;
 module.exports.Seal = require('./seal.js').Seal;
+module.exports.Ack = require('./ack.js').Ack;
 
+module.exports.RandomID = require('./randomid.js');
 module.exports.DOM = require("./dom-driver.js");
 module.exports.JQuery = require("./jquery-driver.js");
 // module.exports.RoutingTableWidget = require("./routing-table-widget.js");

js/src/patch.js

@@ -33,6 +33,17 @@ function prependAtMeta(p, level) {
   return p;
 }
 
+function stripAtMeta(p, level) {
+  while (level--) {
+    if (p.length === 2 && p[0] === $AtMeta) {
+      p = p[1];
+    } else {
+      return null;
+    }
+  }
+  return p;
+}
+
 function observeAtMeta(p, level) {
   if (level === 0) {
     return Route.compilePattern(true, observe(p));
@@ -240,6 +251,7 @@ module.exports.isAtMeta = isAtMeta;
 module.exports.isAdvertise = isAdvertise;
 
 module.exports.prependAtMeta = prependAtMeta;
+module.exports.stripAtMeta = stripAtMeta;
 module.exports.observeAtMeta = observeAtMeta;
 module.exports.assert = assert;
 module.exports.retract = retract;

js/src/randomid.js

@@ -0,0 +1,20 @@
+var randomId;
+
+if ((typeof window !== 'undefined') &&
+    (typeof window.crypto !== 'undefined') &&
+    (typeof window.crypto.getRandomValues !== 'undefined')) {
+  randomId = function (byteCount) {
+    var buf = new Uint8Array(byteCount);
+    window.crypto.getRandomValues(buf);
+    return btoa(String.fromCharCode.apply(null, buf)).replace(/=/g,'');
+  };
+} else if ((typeof crypto !== 'undefined') &&
+	   (typeof crypto.randomBytes !== 'undefined')) {
+  randomId = function (byteCount) {
+    return crypto.randomBytes(byteCount).base64Slice().replace(/=/g,'');
+  };
+} else {
+  console.warn('No suitable implementation for RandomID.randomId available.');
+}
+
+module.exports.randomId = randomId;