nodejs/lib/events.js

// 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.

'use strict';

var spliceOne;

const {
  ERR_INVALID_ARG_TYPE,
  ERR_OUT_OF_RANGE,
  ERR_UNHANDLED_ERROR
} = require('internal/errors').codes;

function EventEmitter() {
  EventEmitter.init.call(this);
}
module.exports = EventEmitter;
module.exports.once = once;

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

EventEmitter.usingDomains = false;

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.
var defaultMaxListeners = 10;

function checkListener(listener) {
  if (typeof listener !== 'function') {
    throw new ERR_INVALID_ARG_TYPE('listener', 'Function', 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 ERR_OUT_OF_RANGE('defaultMaxListeners',
                                 'a non-negative number',
                                 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 ERR_OUT_OF_RANGE('n', 'a non-negative number', 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);
};

// Returns the length and line number of the first sequence of `a` that fully
// appears in `b` with a length of at least 4.
function identicalSequenceRange(a, b) {
  for (var i = 0; i < a.length - 3; i++) {
    // Find the first entry of b that matches the current entry of a.
    const pos = b.indexOf(a[i]);
    if (pos !== -1) {
      const rest = b.length - pos;
      if (rest > 3) {
        let len = 1;
        const maxLen = Math.min(a.length - i, rest);
        // Count the number of consecutive entries.
        while (maxLen > len && a[i + len] === b[pos + len]) {
          len++;
        }
        if (len > 3) {
          return [len, i];
        }
      }
    }
  }

  return [0, 0];
}

function enhanceStackTrace(err, own) {
  const sep = '\nEmitted \'error\' event at:\n';

  const errStack = err.stack.split('\n').slice(1);
  const ownStack = own.stack.split('\n').slice(1);

  const [ len, off ] = identicalSequenceRange(ownStack, errStack);
  if (len > 0) {
    ownStack.splice(off + 1, len - 2,
                    '    [... lines matching original stack trace ...]');
  }
  // Do this last, because it is the only operation with side effects.
  err.stack = err.stack + sep + ownStack.join('\n');
}

EventEmitter.prototype.emit = function emit(type, ...args) {
  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) {
      try {
        const { kExpandStackSymbol } = require('internal/util');
        const capture = {};
        // eslint-disable-next-line no-restricted-syntax
        Error.captureStackTrace(capture, EventEmitter.prototype.emit);
        Object.defineProperty(er, kExpandStackSymbol, {
          value: enhanceStackTrace.bind(null, er, capture),
          configurable: true
        });
      } catch {}

      // 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
    }

    let stringifiedEr;
    const { inspect } = require('internal/util/inspect');
    try {
      stringifiedEr = inspect(er);
    } catch {
      stringifiedEr = er;
    }

    // At least give some kind of context to the user
    const err = new ERR_UNHANDLED_ERROR(stringifiedEr);
    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 (var i = 0; i < len; ++i)
      Reflect.apply(listeners[i], this, args);
  }

  return true;
};

function _addListener(target, type, listener, prepend) {
  var m;
  var events;
  var existing;

  checkListener(listener);

  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.
    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
    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;
      process.emitWarning(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(...args) {
  if (!this.fired) {
    this.target.removeListener(this.type, this.wrapFn);
    this.fired = true;
    return Reflect.apply(this.listener, this.target, args);
  }
}

function _onceWrap(target, type, listener) {
  var state = { fired: false, wrapFn: undefined, target, type, listener };
  var 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) {
      var list, events, position, i, originalListener;

      checkListener(listener);

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

      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') {
        position = -1;

        for (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 {
          if (spliceOne === undefined)
            spliceOne = require('internal/util').spliceOne;
          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) {
      var listeners, events, i;

      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) {
        for (const key of Object.keys(events)) {
          if (key === 'removeListener') continue;
          this.removeAllListeners(key);
        }
        this.removeAllListeners('removeListener');
        this._events = Object.create(null);
        this._eventsCount = 0;
        return this;
      }

      listeners = events[type];

      if (typeof listeners === 'function') {
        this.removeListener(type, listeners);
      } else if (listeners !== undefined) {
        // LIFO order
        for (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) {
  var copy = new Array(n);
  for (var i = 0; i < n; ++i)
    copy[i] = arr[i];
  return copy;
}

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

function once(emitter, name) {
  return new Promise((resolve, reject) => {
    const eventListener = (...args) => {
      if (errorListener !== undefined) {
        emitter.removeListener('error', errorListener);
      }
      resolve(args);
    };
    let errorListener;

    // Adding an error listener is not optional because
    // if an error is thrown on an event emitter we cannot
    // guarantee that the actual event we are waiting will
    // be fired. The result could be a silent way to create
    // memory or file descriptor leaks, which is something
    // we should avoid.
    if (name !== 'error') {
      errorListener = (err) => {
        emitter.removeListener(name, eventListener);
        reject(err);
      };

      emitter.once('error', errorListener);
    }

    emitter.once(name, eventListener);
  });
}