stream: add writableFinished

add a new getter to duplex stream to replace the property `this
.writableState.finished` of the object that inherited duplex.

Refs: https://github.com/nodejs/node/issues/445

PR-URL: https://github.com/nodejs/node/pull/28007
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Rich Trott <rtrott@gmail.com>

1 files changed, 30 insertions, 0 deletions

diff --git a/test/parallel/test-stream-duplex-writable-finished.js b/test/parallel/test-stream-duplex-writable-finished.js
new file mode 100644
index 0000000000..6d9e860b61
--- /dev/null
+++ b/test/parallel/test-stream-duplex-writable-finished.js
@@ -0,0 +1,30 @@
+'use strict';
+
+const common = require('../common');
+const { Duplex } = require('stream');
+const assert = require('assert');
+
+// basic
+{
+  // Find it on Duplex.prototype
+  assert(Duplex.prototype.hasOwnProperty('writableFinished'));
+}
+
+// event
+{
+  const duplex = new Duplex();
+
+  duplex._write = (chunk, encoding, cb) => {
+    // The state finished should start in false.
+    assert.strictEqual(duplex.writableFinished, false);
+    cb();
+  };
+
+  duplex.on('finish', common.mustCall(() => {
+    assert.strictEqual(duplex.writableFinished, true);
+  }));
+
+  duplex.end('testing finished state', common.mustCall(() => {
+    assert.strictEqual(duplex.writableFinished, true);
+  }));
+}