text: // a duplex stream is just a stream that is both readable and writable.
  // Since JS doesn't have multiple prototypal inheritance, this class
  // prototypally inherits from Readable, and then parasitically from
  // Writable.
  
  'use strict';
  
  /*<replacement>*/
  
  var objectKeys = Object.keys || function (obj) {
    var keys = [];
    for (var key in obj) {
      keys.push(key);
    }return keys;
  };
  /*</replacement>*/
  
  module.exports = Duplex;
  
  /*<replacement>*/
  var processNextTick = require('process-nextick-args');
  /*</replacement>*/
  
  /*<replacement>*/
  var util = require('core-util-is');
  util.inherits = require('inherits');
  /*</replacement>*/
  
  var Readable = require('./_stream_readable');
  var Writable = require('./_stream_writable');
  
  util.inherits(Duplex, Readable);
  
  var keys = objectKeys(Writable.prototype);
  for (var v = 0; v < keys.length; v++) {
    var method = keys[v];
    if (!Duplex.prototype[method]) Duplex.prototype[method] = Writable.prototype[method];
  }
  
  function Duplex(options) {
    if (!(this instanceof Duplex)) return new Duplex(options);
  
    Readable.call(this, options);
    Writable.call(this, options);
  
    if (options && options.readable === false) this.readable = false;
  
    if (options && options.writable === false) this.writable = false;
  
    this.allowHalfOpen = true;
    if (options && options.allowHalfOpen === false) this.allowHalfOpen = false;
  
    this.once('end', onend);
  }
  
  // the no-half-open enforcer
  function onend() {
    // if we allow half-open state, or if the writable side ended,
    // then we're ok.
    if (this.allowHalfOpen || this._writableState.ended) return;
  
    // no more data can be written.
    // But allow more writes to happen in this tick.
    processNextTick(onEndNT, this);
  }
  
  function onEndNT(self) {
    self.end();
  }
  
  function forEach(xs, f) {
    for (var i = 0, l = xs.length; i < l; i++) {
      f(xs[i], i);
    }
  }