net: handle allowHalfOpen before calling super ctor

If the `allowHalfOpen` option is not provided, use its default value
before calling the `Duplex` constructor. This allows the no-half-open
enforcer to be properly added.

Fixes: nodejs#19764

lib/net.js

@@ -207,10 +207,11 @@ function Socket(options) {
   this[kLastWriteQueueSize] = 0;
 
   if (typeof options === 'number')
-    options = { fd: options }; // Legacy interface.
-  else if (options === undefined)
-    options = {};
+    options = { allowHalfOpen: false, fd: options }; // Legacy interface.
+  else
+    options = util._extend({}, options);
 
+  options.allowHalfOpen = Boolean(options.allowHalfOpen);
   stream.Duplex.call(this, options);
 
   if (options.handle) {
@@ -236,8 +237,6 @@ 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;
@@ -255,9 +254,6 @@ function Socket(options) {
   // handle strings directly
   this._writableState.decodeStrings = false;
 
-  // default to *not* allowing half open sockets
-  this.allowHalfOpen = options && 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) {

test/parallel/test-child-process-stdout-stderr-finish.js

@@ -0,0 +1,19 @@
+'use strict';
+const { mustCall } = require('../common');
+const { path } = require('../common/fixtures');
+
+// This test ensures that the `'finish'` event is emitted on the child process's
+// `stdout` and `stderr` when using `child_process.spawn()`.
+// This is a regression test for https://github.com/nodejs/node/issues/19764.
+
+const { spawn } = require('child_process');
+
+const child = spawn(process.argv[0], [path('print-chars.js'), 10]);
+
+child.stdout.on('finish', mustCall());
+child.stdout.on('end', mustCall());
+child.stdout.resume();
+
+child.stderr.on('finish', mustCall());
+child.stderr.on('end', mustCall());
+child.stderr.resume();