nodejs/lib/_stream_duplex.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.

// 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';

module.exports = Duplex;

const util = require('util');
const Readable = require('_stream_readable');
const Writable = require('_stream_writable');

util.inherits(Duplex, Readable);

{
  // Allow the keys array to be GC'ed.
  const keys = Object.keys(Writable.prototype);
  for (var v = 0; v < keys.length; v++) {
    const 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);
  this.allowHalfOpen = true;

  if (options) {
    if (options.readable === false)
      this.readable = false;

    if (options.writable === false)
      this.writable = false;

    if (options.allowHalfOpen === false) {
      this.allowHalfOpen = false;
      this.once('end', onend);
    }
  }
}

Object.defineProperty(Duplex.prototype, 'writableHighWaterMark', {
  // making it explicit this property is not enumerable
  // because otherwise some prototype manipulation in
  // userland will fail
  enumerable: false,
  get() {
    return this._writableState.highWaterMark;
  }
});

Object.defineProperty(Duplex.prototype, 'writableBuffer', {
  // making it explicit this property is not enumerable
  // because otherwise some prototype manipulation in
  // userland will fail
  enumerable: false,
  get: function() {
    return this._writableState && this._writableState.getBuffer();
  }
});

Object.defineProperty(Duplex.prototype, 'writableLength', {
  // making it explicit this property is not enumerable
  // because otherwise some prototype manipulation in
  // userland will fail
  enumerable: false,
  get() {
    return this._writableState.length;
  }
});

// the no-half-open enforcer
function onend() {
  // If the writable side ended, then we're ok.
  if (this._writableState.ended)
    return;

  // no more data can be written.
  // But allow more writes to happen in this tick.
  process.nextTick(onEndNT, this);
}

function onEndNT(self) {
  self.end();
}

Object.defineProperty(Duplex.prototype, 'destroyed', {
  // making it explicit this property is not enumerable
  // because otherwise some prototype manipulation in
  // userland will fail
  enumerable: false,
  get() {
    if (this._readableState === undefined ||
        this._writableState === undefined) {
      return false;
    }
    return this._readableState.destroyed && this._writableState.destroyed;
  },
  set(value) {
    // we ignore the value if the stream
    // has not been initialized yet
    if (this._readableState === undefined ||
        this._writableState === undefined) {
      return;
    }

    // backward compatibility, the user is explicitly
    // managing destroyed
    this._readableState.destroyed = value;
    this._writableState.destroyed = value;
  }
});