1 files changed, 113 insertions, 0 deletions
diff --git a/toolkit/jetpack/sdk/input/system.js b/toolkit/jetpack/sdk/input/system.js
new file mode 100644
index 000000000..66bc6daec
--- /dev/null
+++ b/toolkit/jetpack/sdk/input/system.js
@@ -0,0 +1,113 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+"use strict";
+
+const { Cc, Ci, Cr, Cu } = require("chrome");
+const { Input, start, stop, end, receive, outputs } = require("../event/utils");
+const { once, off } = require("../event/core");
+const { id: addonID } = require("../self");
+
+const unloadMessage = require("@loader/unload");
+const observerService = Cc['@mozilla.org/observer-service;1'].
+                          getService(Ci.nsIObserverService);
+const { ShimWaiver } = Cu.import("resource://gre/modules/ShimWaiver.jsm");
+const addObserver = ShimWaiver.getProperty(observerService, "addObserver");
+const removeObserver = ShimWaiver.getProperty(observerService, "removeObserver");
+
+
+const addonUnloadTopic = "sdk:loader:destroy";
+
+const isXrayWrapper = Cu.isXrayWrapper;
+// In the past SDK used to double-wrap notifications dispatched, which
+// made them awkward to use outside of SDK. At present they no longer
+// do that, although we still supported for legacy reasons.
+const isLegacyWrapper = x =>
+    x && x.wrappedJSObject &&
+    "observersModuleSubjectWrapper" in x.wrappedJSObject;
+
+const unwrapLegacy = x => x.wrappedJSObject.object;
+
+// `InputPort` provides a way to create a signal out of the observer
+// notification subject's for the given `topic`. If `options.initial`
+// is provided it is used as initial value otherwise `null` is used.
+// Constructor can be given `options.id` that will be used to create
+// a `topic` which is namespaced to an add-on (this avoids conflicts
+// when multiple add-on are used, although in a future host probably
+// should just be shared across add-ons). It is also possible to
+// specify a specific `topic` via `options.topic` which is used as
+// without namespacing. Created signal ends whenever add-on is
+// unloaded.
+const InputPort = function InputPort({id, topic, initial}) {
+  this.id = id || topic;
+  this.topic = topic || "sdk:" + addonID + ":" + id;
+  this.value = initial === void(0) ? null : initial;
+  this.observing = false;
+  this[outputs] = [];
+};
+
+// InputPort type implements `Input` signal interface.
+InputPort.prototype = new Input();
+InputPort.prototype.constructor = InputPort;
+
+// When port is started (which is when it's subgraph get's
+// first subscriber) actual observer is registered.
+InputPort.start = input => {
+  input.addListener(input);
+  // Also register add-on unload observer to end this signal
+  // when that happens.
+  addObserver(input, addonUnloadTopic, false);
+};
+InputPort.prototype[start] = InputPort.start;
+
+InputPort.addListener = input => addObserver(input, input.topic, false);
+InputPort.prototype.addListener = InputPort.addListener;
+
+// When port is stopped (which is when it's subgraph has no
+// no subcribers left) an actual observer unregistered.
+// Note that port stopped once it ends as well (which is when
+// add-on is unloaded).
+InputPort.stop = input => {
+  input.removeListener(input);
+  removeObserver(input, addonUnloadTopic);
+};
+InputPort.prototype[stop] = InputPort.stop;
+
+InputPort.removeListener = input => removeObserver(input, input.topic);
+InputPort.prototype.removeListener = InputPort.removeListener;
+
+// `InputPort` also implements `nsIObserver` interface and
+// `nsISupportsWeakReference` interfaces as it's going to be used as such.
+InputPort.prototype.QueryInterface = function(iid) {
+  if (!iid.equals(Ci.nsIObserver) && !iid.equals(Ci.nsISupportsWeakReference))
+    throw Cr.NS_ERROR_NO_INTERFACE;
+
+  return this;
+};
+
+// `InputPort` instances implement `observe` method, which is invoked when
+// observer notifications are dispatched. The `subject` of that notification
+// are received on this signal.
+InputPort.prototype.observe = function(subject, topic, data) {
+  // Unwrap message from the subject. SDK used to have it's own version of
+  // wrappedJSObjects which take precedence, if subject has `wrappedJSObject`
+  // and it's not an XrayWrapper use it as message. Otherwise use subject as
+  // is.
+  const message = subject === null ? null :
+        isLegacyWrapper(subject) ? unwrapLegacy(subject) :
+        isXrayWrapper(subject) ? subject :
+        subject.wrappedJSObject ? subject.wrappedJSObject :
+        subject;
+
+  // If observer topic matches topic of the input port receive a message.
+  if (topic === this.topic) {
+    receive(this, message);
+  }
+
+  // If observe topic is add-on unload topic we create an end message.
+  if (topic === addonUnloadTopic && message === unloadMessage) {
+    end(this);
+  }
+};
+
+exports.InputPort = InputPort;