@frida/events/events.js

Node.js's events module for Frida

// Copyright Joyent, Inc. and other Node contributors.
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to permit
// persons to whom the Software is furnished to do so, subject to the
// following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
// USE OR OTHER DEALINGS IN THE SOFTWARE.

export default EventEmitter;
export { EventEmitter, once };

function ProcessEmitWarning(warning) {
  console.warn(warning);
}

function EventEmitter() {
  EventEmitter.init.call(this);
}

// Backwards-compat with node 0.10.x
EventEmitter.EventEmitter = EventEmitter;

EventEmitter.prototype._events = undefined;
EventEmitter.prototype._eventsCount = 0;
EventEmitter.prototype._maxListeners = undefined;

// By default EventEmitters will print a warning if more than 10 listeners are
// added to it. This is a useful default which helps finding memory leaks.
let defaultMaxListeners = 10;

function checkListener(listener) {
  if (typeof listener !== 'function') {
    throw new TypeError('The "listener" argument must be of type Function. Received type ' + typeof listener);
  }
}

Object.defineProperty(EventEmitter, 'defaultMaxListeners', {
  enumerable: true,
  get: function() {
    return defaultMaxListeners;
  },
  set: function(arg) {
    if (typeof arg !== 'number' || arg < 0 || Number.isNaN(arg)) {
      throw new RangeError('The value of "defaultMaxListeners" is out of range. It must be a non-negative number. Received ' + arg + '.');
    }
    defaultMaxListeners = arg;
  }
});

EventEmitter.init = function() {

  if (this._events === undefined ||
      this._events === Object.getPrototypeOf(this)._events) {
    this._events = Object.create(null);
    this._eventsCount = 0;
  }

  this._maxListeners = this._maxListeners || undefined;
};

// Obviously not all Emitters should be limited to 10. This function allows
// that to be increased. Set to zero for unlimited.
EventEmitter.prototype.setMaxListeners = function setMaxListeners(n) {
  if (typeof n !== 'number' || n < 0 || Number.isNaN(n)) {
    throw new RangeError('The value of "n" is out of range. It must be a non-negative number. Received ' + n + '.');
  }
  this._maxListeners = n;
  return this;
};

function _getMaxListeners(that) {
  if (that._maxListeners === undefined)
    return EventEmitter.defaultMaxListeners;
  return that._maxListeners;
}

EventEmitter.prototype.getMaxListeners = function getMaxListeners() {
  return _getMaxListeners(this);
};

EventEmitter.prototype.emit = function emit(type) {
  const args = [];
  for (let i = 1; i < arguments.length; i++) args.push(arguments[i]);
  let doError = (type === 'error');

  const events = this._events;
  if (events !== undefined)
    doError = (doError && events.error === undefined);
  else if (!doError)
    return false;

  // If there is no 'error' event listener then throw.
  if (doError) {
    let er;
    if (args.length > 0)
      er = args[0];
    if (er instanceof Error) {
      // Note: The comments on the `throw` lines are intentional, they show
      // up in Node's output if this results in an unhandled exception.
      throw er; // Unhandled 'error' event
    }
    // At least give some kind of context to the user
    const err = new Error('Unhandled error.' + (er ? ' (' + er.message + ')' : ''));
    err.context = er;
    throw err; // Unhandled 'error' event
  }

  const handler = events[type];

  if (handler === undefined)
    return false;

  if (typeof handler === 'function') {
    Reflect.apply(handler, this, args);
  } else {
    const len = handler.length;
    const listeners = arrayClone(handler, len);
    for (let i = 0; i < len; ++i)
      Reflect.apply(listeners[i], this, args);
  }

  return true;
};

function _addListener(target, type, listener, prepend) {
  let existing;

  checkListener(listener);

  let events = target._events;
  if (events === undefined) {
    events = target._events = Object.create(null);
    target._eventsCount = 0;
  } else {
    // To avoid recursion in the case that type === "newListener"! Before
    // adding it to the listeners, first emit "newListener".
    if (events.newListener !== undefined) {
      target.emit('newListener', type,
                  listener.listener ? listener.listener : listener);

      // Re-assign `events` because a newListener handler could have caused the
      // this._events to be assigned to a new object
      events = target._events;
    }
    existing = events[type];
  }

  if (existing === undefined) {
    // Optimize the case of one listener. Don't need the extra array object.
    existing = events[type] = listener;
    ++target._eventsCount;
  } else {
    if (typeof existing === 'function') {
      // Adding the second element, need to change to array.
      existing = events[type] =
        prepend ? [listener, existing] : [existing, listener];
      // If we've already got an array, just append.
    } else if (prepend) {
      existing.unshift(listener);
    } else {
      existing.push(listener);
    }

    // Check for listener leak
    const m = _getMaxListeners(target);
    if (m > 0 && existing.length > m && !existing.warned) {
      existing.warned = true;
      // No error code for this since it is a Warning
      // eslint-disable-next-line no-restricted-syntax
      const w = new Error('Possible EventEmitter memory leak detected. ' +
                          existing.length + ' ' + String(type) + ' listeners ' +
                          'added. Use emitter.setMaxListeners() to ' +
                          'increase limit');
      w.name = 'MaxListenersExceededWarning';
      w.emitter = target;
      w.type = type;
      w.count = existing.length;
      ProcessEmitWarning(w);
    }
  }

  return target;
}

EventEmitter.prototype.addListener = function addListener(type, listener) {
  return _addListener(this, type, listener, false);
};

EventEmitter.prototype.on = EventEmitter.prototype.addListener;

EventEmitter.prototype.prependListener =
    function prependListener(type, listener) {
      return _addListener(this, type, listener, true);
    };

function onceWrapper() {
  if (!this.fired) {
    this.target.removeListener(this.type, this.wrapFn);
    this.fired = true;
    if (arguments.length === 0)
      return this.listener.call(this.target);
    return this.listener.apply(this.target, arguments);
  }
}

function _onceWrap(target, type, listener) {
  const state = { fired: false, wrapFn: undefined, target: target, type: type, listener: listener };
  const wrapped = onceWrapper.bind(state);
  wrapped.listener = listener;
  state.wrapFn = wrapped;
  return wrapped;
}

EventEmitter.prototype.once = function once(type, listener) {
  checkListener(listener);
  this.on(type, _onceWrap(this, type, listener));
  return this;
};

EventEmitter.prototype.prependOnceListener =
    function prependOnceListener(type, listener) {
      checkListener(listener);
      this.prependListener(type, _onceWrap(this, type, listener));
      return this;
    };

// Emits a 'removeListener' event if and only if the listener was removed.
EventEmitter.prototype.removeListener =
    function removeListener(type, listener) {
      checkListener(listener);

      const events = this._events;
      if (events === undefined)
        return this;

      const list = events[type];
      if (list === undefined)
        return this;

      if (list === listener || list.listener === listener) {
        if (--this._eventsCount === 0)
          this._events = Object.create(null);
        else {
          delete events[type];
          if (events.removeListener)
            this.emit('removeListener', type, list.listener || listener);
        }
      } else if (typeof list !== 'function') {
        let originalListener;
        let position = -1;

        for (let i = list.length - 1; i >= 0; i--) {
          if (list[i] === listener || list[i].listener === listener) {
            originalListener = list[i].listener;
            position = i;
            break;
          }
        }

        if (position < 0)
          return this;

        if (position === 0)
          list.shift();
        else {
          spliceOne(list, position);
        }

        if (list.length === 1)
          events[type] = list[0];

        if (events.removeListener !== undefined)
          this.emit('removeListener', type, originalListener || listener);
      }

      return this;
    };

EventEmitter.prototype.off = EventEmitter.prototype.removeListener;

EventEmitter.prototype.removeAllListeners =
    function removeAllListeners(type) {
      const events = this._events;
      if (events === undefined)
        return this;

      // not listening for removeListener, no need to emit
      if (events.removeListener === undefined) {
        if (arguments.length === 0) {
          this._events = Object.create(null);
          this._eventsCount = 0;
        } else if (events[type] !== undefined) {
          if (--this._eventsCount === 0)
            this._events = Object.create(null);
          else
            delete events[type];
        }
        return this;
      }

      // emit removeListener for all listeners on all events
      if (arguments.length === 0) {
        const keys = Object.keys(events);
        for (let i = 0; i < keys.length; ++i) {
          const key = keys[i];
          if (key === 'removeListener') continue;
          this.removeAllListeners(key);
        }
        this.removeAllListeners('removeListener');
        this._events = Object.create(null);
        this._eventsCount = 0;
        return this;
      }

      const listeners = events[type];

      if (typeof listeners === 'function') {
        this.removeListener(type, listeners);
      } else if (listeners !== undefined) {
        // LIFO order
        for (let i = listeners.length - 1; i >= 0; i--) {
          this.removeListener(type, listeners[i]);
        }
      }

      return this;
    };

function _listeners(target, type, unwrap) {
  const events = target._events;

  if (events === undefined)
    return [];

  const evlistener = events[type];
  if (evlistener === undefined)
    return [];

  if (typeof evlistener === 'function')
    return unwrap ? [evlistener.listener || evlistener] : [evlistener];

  return unwrap ?
    unwrapListeners(evlistener) : arrayClone(evlistener, evlistener.length);
}

EventEmitter.prototype.listeners = function listeners(type) {
  return _listeners(this, type, true);
};

EventEmitter.prototype.rawListeners = function rawListeners(type) {
  return _listeners(this, type, false);
};

EventEmitter.listenerCount = function(emitter, type) {
  if (typeof emitter.listenerCount === 'function') {
    return emitter.listenerCount(type);
  } else {
    return listenerCount.call(emitter, type);
  }
};

EventEmitter.prototype.listenerCount = listenerCount;
function listenerCount(type) {
  const events = this._events;

  if (events !== undefined) {
    const evlistener = events[type];

    if (typeof evlistener === 'function') {
      return 1;
    } else if (evlistener !== undefined) {
      return evlistener.length;
    }
  }

  return 0;
}

EventEmitter.prototype.eventNames = function eventNames() {
  return this._eventsCount > 0 ? Reflect.ownKeys(this._events) : [];
};

function arrayClone(arr, n) {
  const copy = new Array(n);
  for (let i = 0; i < n; ++i)
    copy[i] = arr[i];
  return copy;
}

function spliceOne(list, index) {
  for (; index + 1 < list.length; index++)
    list[index] = list[index + 1];
  list.pop();
}

function unwrapListeners(arr) {
  const ret = new Array(arr.length);
  for (let i = 0; i < ret.length; ++i) {
    ret[i] = arr[i].listener || arr[i];
  }
  return ret;
}

function once(emitter, name) {
  return new Promise(function (resolve, reject) {
    function errorListener(err) {
      emitter.removeListener(name, resolver);
      reject(err);
    }

    function resolver() {
      if (typeof emitter.removeListener === 'function') {
        emitter.removeListener('error', errorListener);
      }
      resolve([].slice.call(arguments));
    };

    eventTargetAgnosticAddListener(emitter, name, resolver, { once: true });
    if (name !== 'error') {
      addErrorHandlerIfEventEmitter(emitter, errorListener, { once: true });
    }
  });
}

function addErrorHandlerIfEventEmitter(emitter, handler, flags) {
  if (typeof emitter.on === 'function') {
    eventTargetAgnosticAddListener(emitter, 'error', handler, flags);
  }
}

function eventTargetAgnosticAddListener(emitter, name, listener, flags) {
  if (typeof emitter.on === 'function') {
    if (flags.once) {
      emitter.once(name, listener);
    } else {
      emitter.on(name, listener);
    }
  } else if (typeof emitter.addEventListener === 'function') {
    // EventTarget does not have `error` event semantics like Node
    // EventEmitters, we do not listen for `error` events here.
    emitter.addEventListener(name, function wrapListener(arg) {
      // IE does not have builtin `{ once: true }` support so we
      // have to do it manually.
      if (flags.once) {
        emitter.removeEventListener(name, wrapListener);
      }
      listener(arg);
    });
  } else {
    throw new TypeError('The "emitter" argument must be of type EventEmitter. Received type ' + typeof emitter);
  }
}