net: do not inherit the no-half-open enforcer

`Socket.prototype.destroySoon()` is called as soon as `UV_EOF` is read
if the `allowHalfOpen` option is disabled. This already works as a
"no-half-open enforcer" so there is no need to inherit another from
`stream.Duplex`.

PR-URL: nodejs#18974
Reviewed-By: Benjamin Gruenbaum <[email protected]>
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Matteo Collina <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Chen Gang <[email protected]>
Reviewed-By: Ruben Bridgewater <[email protected]>

lib/net.js

@@ -64,6 +64,7 @@ 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');
@@ -238,7 +239,11 @@ function Socket(options) {
  // 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);
 
  if (options.handle) {
  this._handle = options.handle; // private
@@ -263,8 +268,6 @@ function Socket(options) {
  this._writev = null;
  this._write = makeSyncWrite(fd);
  }
- this.readable = options.readable !== false;
- this.writable = options.writable !== false;
  } else {
  // these will be set once there is a connection
  this.readable = this.writable = false;
@@ -282,7 +285,7 @@ function Socket(options) {
  this._writableState.decodeStrings = false;
 
  // default to *not* allowing half open sockets
- this.allowHalfOpen = options && options.allowHalfOpen || false;
+ 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

test/parallel/test-http-connect.js

@@ -75,12 +75,7 @@ server.listen(0, common.mustCall(() => {
  assert.strictEqual(socket.listeners('connect').length, 0);
  assert.strictEqual(socket.listeners('data').length, 0);
  assert.strictEqual(socket.listeners('drain').length, 0);
-
- // the stream.Duplex onend listener
- // allow 0 here, so that i can run the same test on streams1 impl
- assert(socket.listenerCount('end') <= 2,
- `Found ${socket.listenerCount('end')} end listeners`);
-
+ assert.strictEqual(socket.listeners('end').length, 1);
  assert.strictEqual(socket.listeners('free').length, 0);
  assert.strictEqual(socket.listeners('close').length, 0);
  assert.strictEqual(socket.listeners('error').length, 0);

test/parallel/test-net-socket-no-halfopen-enforcer.js

@@ -0,0 +1,11 @@
+'use strict';
+require('../common');
+
+// This test ensures that `net.Socket` does not inherit the no-half-open
+// enforcer from `stream.Duplex`.
+
+const { Socket } = require('net');
+const { strictEqual } = require('assert');
+
+const socket = new Socket({ allowHalfOpen: false });
+strictEqual(socket.listenerCount('end'), 1);