net,stream: remove DuplexBase

`DuplexBase` was added to prevent the "no-half-open enforcer" from
being inherited by `net.Socket`. The main reason to use it instead
of `Duplex` was that it allowed to not copy the options object but
since commit 5e3f516 the options object is copyed anyway so it is
no longer useful.

PR-URL: https://github.com/nodejs/node/pull/19779
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/_stream_duplex.js

@@ -29,15 +29,33 @@
 module.exports = Duplex;
 
 const util = require('util');
-const DuplexBase = require('internal/streams/duplex_base');
+const Readable = require('_stream_readable');
+const Writable = require('_stream_writable');
 
-util.inherits(Duplex, DuplexBase);
+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);
 
-  DuplexBase.call(this, 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) {

lib/internal/streams/duplex_base.js

@@ -1,30 +0,0 @@
-'use strict';
-
-const util = require('util');
-const Readable = require('_stream_readable');
-const Writable = require('_stream_writable');
-
-function DuplexBase(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;
-}
-
-util.inherits(DuplexBase, Readable);
-
-{
-  // Avoid scope creep, the keys array can then be collected.
-  const keys = Object.keys(Writable.prototype);
-  for (var v = 0; v < keys.length; v++) {
-    const method = keys[v];
-    if (!DuplexBase.prototype[method])
-      DuplexBase.prototype[method] = Writable.prototype[method];
-  }
-}
-
-module.exports = DuplexBase;

lib/net.js

@@ -75,7 +75,6 @@ const {
   ERR_SOCKET_BAD_PORT,
   ERR_SOCKET_CLOSED
 } = errors.codes;
-const DuplexBase = require('internal/streams/duplex_base');
 const dns = require('dns');
 
 const kLastWriteQueueSize = Symbol('lastWriteQueueSize');
@@ -242,19 +241,19 @@ function Socket(options) {
 
   if (typeof options === 'number')
     options = { fd: options }; // Legacy interface.
-  else if (options === undefined)
-    options = {};
   else
     options = util._extend({}, options);
 
+  const allowHalfOpen = options.allowHalfOpen;
+
+  // Prevent the "no-half-open enforcer" from being inherited from `Duplex`.
+  options.allowHalfOpen = true;
   // For backwards compat do not emit close on destroy.
   options.emitClose = false;
+  stream.Duplex.call(this, options);
 
-  // `DuplexBase` is just a slimmed down constructor for `Duplex` which allow
-  // us to not inherit the "no-half-open enforcer" as there is already one in
-  // place. Instances of `Socket` are still instances of `Duplex`, that is,
-  // `socket instanceof Duplex === true`.
-  DuplexBase.call(this, options);
+  // Default to *not* allowing half open sockets.
+  this.allowHalfOpen = Boolean(allowHalfOpen);
 
   if (options.handle) {
     this._handle = options.handle; // private
@@ -300,9 +299,6 @@ function Socket(options) {
   // handle strings directly
   this._writableState.decodeStrings = false;
 
-  // default to *not* allowing half open sockets
-  this.allowHalfOpen = options.allowHalfOpen || false;
-
   // if we have a handle, then start the flow of data into the
   // buffer.  if not, then this will happen when we connect
   if (this._handle && options.readable !== false) {

node.gyp

@@ -150,7 +150,6 @@
       'lib/internal/streams/lazy_transform.js',
       'lib/internal/streams/async_iterator.js',
       'lib/internal/streams/buffer_list.js',
-      'lib/internal/streams/duplex_base.js',
       'lib/internal/streams/duplexpair.js',
       'lib/internal/streams/legacy.js',
       'lib/internal/streams/destroy.js',