# all files / lib/ _stream_duplex.js

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     // 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) {
      Iif (!(this instanceof Duplex)) return new Duplex(options);

      Readable.call(this, options);
      Writable.call(this, options);

      Iif (options && options.readable === false) this.readable = false;

      Iif (options && options.writable === false) this.writable = false;

      this.allowHalfOpen = true;
      Iif (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.
      Eif (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);
      }
    }