1 files changed, 470 insertions, 0 deletions
diff --git a/devtools/shared/event-emitter.js b/devtools/shared/event-emitter.js
new file mode 100644
index 0000000000..2ba4ae927b
--- /dev/null
+++ b/devtools/shared/event-emitter.js
@@ -0,0 +1,470 @@
+/* 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 BAD_LISTENER =
+  "The event listener must be a function, or an object that has " +
+  "`EventEmitter.handler` Symbol.";
+
+const eventListeners = Symbol("EventEmitter/listeners");
+const onceOriginalListener = Symbol("EventEmitter/once-original-listener");
+const handler = Symbol("EventEmitter/event-handler");
+loader.lazyRequireGetter(this, "flags", "resource://devtools/shared/flags.js");
+
+class EventEmitter {
+  /**
+   * Registers an event `listener` that is called every time events of
+   * specified `type` is emitted on the given event `target`.
+   *
+   * @param {Object} target
+   *    Event target object.
+   * @param {String} type
+   *    The type of event.
+   * @param {Function|Object} listener
+   *    The listener that processes the event.
+   * @param {Object} options
+   * @param {AbortSignal} options.signal
+   *     The listener will be removed when linked AbortController’s abort() method is called
+   * @returns {Function}
+   *    A function that removes the listener when called.
+   */
+  static on(target, type, listener, { signal } = {}) {
+    if (typeof listener !== "function" && !isEventHandler(listener)) {
+      throw new Error(BAD_LISTENER);
+    }
+
+    if (signal?.aborted === true) {
+      // The signal is already aborted so don't setup the listener.
+      // We return an empty function as it's the expected returned value.
+      return () => {};
+    }
+
+    if (!(eventListeners in target)) {
+      target[eventListeners] = new Map();
+    }
+
+    const events = target[eventListeners];
+
+    if (events.has(type)) {
+      events.get(type).add(listener);
+    } else {
+      events.set(type, new Set([listener]));
+    }
+
+    const offFn = () => EventEmitter.off(target, type, listener);
+
+    if (signal) {
+      signal.addEventListener("abort", offFn, { once: true });
+    }
+
+    return offFn;
+  }
+
+  /**
+   * Removes an event `listener` for the given event `type` on the given event
+   * `target`. If no `listener` is passed removes all listeners of the given
+   * `type`. If `type` is not passed removes all the listeners of the given
+   * event `target`.
+   * @param {Object} target
+   *    The event target object.
+   * @param {String} [type]
+   *    The type of event.
+   * @param {Function|Object} [listener]
+   *    The listener that processes the event.
+   */
+  static off(target, type, listener) {
+    const length = arguments.length;
+    const events = target[eventListeners];
+
+    if (!events) {
+      return;
+    }
+
+    if (length >= 3) {
+      // Trying to remove from the `target` the `listener` specified for the
+      // event's `type` given.
+      const listenersForType = events.get(type);
+
+      // If we don't have listeners for the event's type, we bail out.
+      if (!listenersForType) {
+        return;
+      }
+
+      // If the listeners list contains the listener given, we just remove it.
+      if (listenersForType.has(listener)) {
+        listenersForType.delete(listener);
+      } else {
+        // If it's not present, there is still the possibility that the listener
+        // have been added using `once`, since the method wraps the original listener
+        // in another function.
+        // So we iterate all the listeners to check if any of them is a wrapper to
+        // the `listener` given.
+        for (const value of listenersForType.values()) {
+          if (
+            onceOriginalListener in value &&
+            value[onceOriginalListener] === listener
+          ) {
+            listenersForType.delete(value);
+            break;
+          }
+        }
+      }
+    } else if (length === 2) {
+      // No listener was given, it means we're removing all the listeners from
+      // the given event's `type`.
+      if (events.has(type)) {
+        events.delete(type);
+      }
+    } else if (length === 1) {
+      // With only the `target` given, we're removing all the listeners from the object.
+      events.clear();
+    }
+  }
+
+  static clearEvents(target) {
+    const events = target[eventListeners];
+    if (!events) {
+      return;
+    }
+    events.clear();
+  }
+
+  /**
+   * Registers an event `listener` that is called only the next time an event
+   * of the specified `type` is emitted on the given event `target`.
+   * It returns a Promise resolved once the specified event `type` is emitted.
+   *
+   * @param {Object} target
+   *    Event target object.
+   * @param {String} type
+   *    The type of the event.
+   * @param {Function|Object} [listener]
+   *    The listener that processes the event.
+   * @param {Object} options
+   * @param {AbortSignal} options.signal
+   *     The listener will be removed when linked AbortController’s abort() method is called
+   * @return {Promise}
+   *    The promise resolved once the event `type` is emitted.
+   */
+  static once(target, type, listener, options) {
+    return new Promise(resolve => {
+      // This is the actual listener that will be added to the target's listener, it wraps
+      // the call to the original `listener` given.
+      const newListener = (first, ...rest) => {
+        // To prevent side effects we're removing the listener upfront.
+        EventEmitter.off(target, type, newListener);
+
+        let rv;
+        if (listener) {
+          if (isEventHandler(listener)) {
+            // if the `listener` given is actually an object that handles the events
+            // using `EventEmitter.handler`, we want to call that function, passing also
+            // the event's type as first argument, and the `listener` (the object) as
+            // contextual object.
+            rv = listener[handler](type, first, ...rest);
+          } else {
+            // Otherwise we'll just call it
+            rv = listener.call(target, first, ...rest);
+          }
+        }
+
+        // We resolve the promise once the listener is called.
+        resolve(first);
+
+        // Listeners may return a promise, so pass it along
+        return rv;
+      };
+
+      newListener[onceOriginalListener] = listener;
+      EventEmitter.on(target, type, newListener, options);
+    });
+  }
+
+  static emit(target, type, ...rest) {
+    EventEmitter._emit(target, type, false, rest);
+  }
+
+  static emitAsync(target, type, ...rest) {
+    return EventEmitter._emit(target, type, true, rest);
+  }
+
+  /**
+   * Emit an event of a given `type` on a given `target` object.
+   *
+   * @param {Object} target
+   *    Event target object.
+   * @param {String} type
+   *    The type of the event.
+   * @param {Boolean} async
+   *    If true, this function will wait for each listener completion.
+   *    Each listener has to return a promise, which will be awaited for.
+   * @param {Array} args
+   *    The arguments to pass to each listener function.
+   * @return {Promise|undefined}
+   *    If `async` argument is true, returns the promise resolved once all listeners have resolved.
+   *    Otherwise, this function returns undefined;
+   */
+  static _emit(target, type, async, args) {
+    if (loggingEnabled) {
+      logEvent(type, args);
+    }
+
+    const targetEventListeners = target[eventListeners];
+    if (!targetEventListeners) {
+      return undefined;
+    }
+
+    const listeners = targetEventListeners.get(type);
+    if (!listeners?.size) {
+      return undefined;
+    }
+
+    const promises = async ? [] : null;
+
+    // Creating a temporary Set with the original listeners, to avoiding side effects
+    // in emit.
+    for (const listener of new Set(listeners)) {
+      // If the object was destroyed during event emission, stop emitting.
+      if (!(eventListeners in target)) {
+        break;
+      }
+
+      // If listeners were removed during emission, make sure the
+      // event handler we're going to fire wasn't removed.
+      if (listeners && listeners.has(listener)) {
+        try {
+          let promise;
+          if (isEventHandler(listener)) {
+            promise = listener[handler](type, ...args);
+          } else {
+            promise = listener.apply(target, args);
+          }
+          if (async) {
+            // Assert the name instead of `constructor != Promise` in order
+            // to avoid cross compartment issues where Promise can be multiple.
+            if (!promise || promise.constructor.name != "Promise") {
+              console.warn(
+                `Listener for event '${type}' did not return a promise.`
+              );
+            } else {
+              promises.push(promise);
+            }
+          }
+        } catch (ex) {
+          // Prevent a bad listener from interfering with the others.
+          console.error(ex);
+          const msg = ex + ": " + ex.stack;
+          dump(msg + "\n");
+        }
+      }
+    }
+
+    if (async) {
+      return Promise.all(promises);
+    }
+
+    return undefined;
+  }
+
+  /**
+   * Returns a number of event listeners registered for the given event `type`
+   * on the given event `target`.
+   *
+   * @param {Object} target
+   *    Event target object.
+   * @param {String} type
+   *    The type of event.
+   * @return {Number}
+   *    The number of event listeners.
+   */
+  static count(target, type) {
+    if (eventListeners in target) {
+      const listenersForType = target[eventListeners].get(type);
+
+      if (listenersForType) {
+        return listenersForType.size;
+      }
+    }
+
+    return 0;
+  }
+
+  /**
+   * Decorate an object with event emitter functionality; basically using the
+   * class' prototype as mixin.
+   *
+   * @param Object target
+   *    The object to decorate.
+   * @return Object
+   *    The object given, mixed.
+   */
+  static decorate(target) {
+    const descriptors = Object.getOwnPropertyDescriptors(this.prototype);
+    delete descriptors.constructor;
+    return Object.defineProperties(target, descriptors);
+  }
+
+  static get handler() {
+    return handler;
+  }
+
+  on(...args) {
+    return EventEmitter.on(this, ...args);
+  }
+
+  off(...args) {
+    EventEmitter.off(this, ...args);
+  }
+
+  clearEvents() {
+    EventEmitter.clearEvents(this);
+  }
+
+  once(...args) {
+    return EventEmitter.once(this, ...args);
+  }
+
+  emit(...args) {
+    EventEmitter.emit(this, ...args);
+  }
+
+  emitAsync(...args) {
+    return EventEmitter.emitAsync(this, ...args);
+  }
+
+  emitForTests(...args) {
+    if (flags.testing) {
+      EventEmitter.emit(this, ...args);
+    }
+  }
+
+  count(...args) {
+    return EventEmitter.count(this, ...args);
+  }
+}
+
+module.exports = EventEmitter;
+
+const isEventHandler = listener =>
+  listener && handler in listener && typeof listener[handler] === "function";
+
+const {
+  getNthPathExcluding,
+} = require("resource://devtools/shared/platform/stack.js");
+let loggingEnabled = false;
+
+if (!isWorker) {
+  loggingEnabled = Services.prefs.getBoolPref("devtools.dump.emit", false);
+  const observer = {
+    observe: () => {
+      loggingEnabled = Services.prefs.getBoolPref("devtools.dump.emit");
+    },
+  };
+  Services.prefs.addObserver("devtools.dump.emit", observer);
+
+  // Also listen for Loader unload to unregister the pref observer and
+  // prevent leaking
+  const unloadObserver = function (subject) {
+    if (subject.wrappedJSObject == require("@loader/unload")) {
+      Services.prefs.removeObserver("devtools.dump.emit", observer);
+      Services.obs.removeObserver(unloadObserver, "devtools:loader:destroy");
+    }
+  };
+  Services.obs.addObserver(unloadObserver, "devtools:loader:destroy");
+}
+
+function serialize(target) {
+  const MAXLEN = 60;
+
+  // Undefined
+  if (typeof target === "undefined") {
+    return "undefined";
+  }
+
+  if (target === null) {
+    return "null";
+  }
+
+  // Number / String
+  if (typeof target === "string" || typeof target === "number") {
+    return truncate(target, MAXLEN);
+  }
+
+  // HTML Node
+  if (target.nodeName) {
+    let out = target.nodeName;
+
+    if (target.id) {
+      out += "#" + target.id;
+    }
+    if (target.className) {
+      out += "." + target.className;
+    }
+
+    return out;
+  }
+
+  // Array
+  if (Array.isArray(target)) {
+    return truncate(target.toSource(), MAXLEN);
+  }
+
+  // Function
+  if (typeof target === "function") {
+    return `function ${target.name ? target.name : "anonymous"}()`;
+  }
+
+  // Window
+  if (target?.constructor?.name === "Window") {
+    return `window (${target.location.origin})`;
+  }
+
+  // Object
+  if (typeof target === "object") {
+    let out = "{";
+
+    const entries = Object.entries(target);
+    for (let i = 0; i < Math.min(10, entries.length); i++) {
+      const [name, value] = entries[i];
+
+      if (i > 0) {
+        out += ", ";
+      }
+
+      out += `${name}: ${truncate(value, MAXLEN)}`;
+    }
+
+    return out + "}";
+  }
+
+  // Other
+  return truncate(target.toSource(), MAXLEN);
+}
+
+function truncate(value, maxLen) {
+  // We don't use value.toString() because it can throw.
+  const str = String(value);
+  return str.length > maxLen ? str.substring(0, maxLen) + "..." : str;
+}
+
+function logEvent(type, args) {
+  let argsOut = "";
+
+  // We need this try / catch to prevent any dead object errors.
+  try {
+    argsOut = `${args.map(serialize).join(", ")}`;
+  } catch (e) {
+    // Object is dead so the toolbox is most likely shutting down,
+    // do nothing.
+  }
+
+  const path = getNthPathExcluding(0, "devtools/shared/event-emitter.js");
+
+  if (args.length) {
+    dump(`EMITTING: emit(${type}, ${argsOut}) from ${path}\n`);
+  } else {
+    dump(`EMITTING: emit(${type}) from ${path}\n`);
+  }
+}