From 0a4cd53fecf0d328b94cf31a7028f9fd9f22ab0a Mon Sep 17 00:00:00 2001
From: Renegade334 <contact.9a5d6388@renegade334.me.uk>
Date: Fri, 1 May 2026 15:13:17 +0200
Subject: [PATCH] stream: disallow writing string chunk with 'buffer' encoding

Signed-off-by: Renegade334 <contact.9a5d6388@renegade334.me.uk>
---
 lib/internal/streams/writable.js              |  3 +++
 .../parallel/test-stream-base-typechecking.js | 18 ---------------
 .../test-stream-writable-write-error.js       | 22 +++++++++++++------
 3 files changed, 18 insertions(+), 25 deletions(-)
 delete mode 100644 test/parallel/test-stream-base-typechecking.js

diff --git a/lib/internal/streams/writable.js b/lib/internal/streams/writable.js
index 89d384e9f2fb8f..94913461cb6044 100644
--- a/lib/internal/streams/writable.js
+++ b/lib/internal/streams/writable.js
@@ -466,6 +466,9 @@ function _write(stream, chunk, encoding, cb) {
     }
 
     if (typeof chunk === 'string') {
+      if (encoding === 'buffer') {
+        throw new ERR_UNKNOWN_ENCODING(encoding);
+      }
       if ((state[kState] & kDecodeStrings) !== 0) {
         chunk = Buffer.from(chunk, encoding);
         encoding = 'buffer';
diff --git a/test/parallel/test-stream-base-typechecking.js b/test/parallel/test-stream-base-typechecking.js
deleted file mode 100644
index ae8582642344ee..00000000000000
--- a/test/parallel/test-stream-base-typechecking.js
+++ /dev/null
@@ -1,18 +0,0 @@
-'use strict';
-const common = require('../common');
-const assert = require('assert');
-const net = require('net');
-
-const server = net.createServer().listen(0, common.mustCall(() => {
-  const client = net.connect(server.address().port, common.mustCall(() => {
-    assert.throws(() => {
-      client.write('broken', 'buffer');
-    }, {
-      name: 'TypeError',
-      code: 'ERR_INVALID_ARG_TYPE',
-      message: 'Second argument must be a buffer'
-    });
-    client.destroy();
-    server.close();
-  }));
-}));
diff --git a/test/parallel/test-stream-writable-write-error.js b/test/parallel/test-stream-writable-write-error.js
index 069e32e1be8e3e..76f797fb1bd583 100644
--- a/test/parallel/test-stream-writable-write-error.js
+++ b/test/parallel/test-stream-writable-write-error.js
@@ -31,7 +31,7 @@ function test(autoDestroy) {
   {
     const w = new Writable({
       autoDestroy,
-      _write() {}
+      write() {}
     });
     w.end();
     expectError(w, ['asd'], 'ERR_STREAM_WRITE_AFTER_END');
@@ -40,7 +40,7 @@ function test(autoDestroy) {
   {
     const w = new Writable({
       autoDestroy,
-      _write() {}
+      write() {}
     });
     w.destroy();
   }
@@ -48,7 +48,7 @@ function test(autoDestroy) {
   {
     const w = new Writable({
       autoDestroy,
-      _write() {}
+      write() {}
     });
     expectError(w, [null], 'ERR_STREAM_NULL_VALUES', true);
   }
@@ -56,18 +56,26 @@ function test(autoDestroy) {
   {
     const w = new Writable({
       autoDestroy,
-      _write() {}
+      write() {}
     });
     expectError(w, [{}], 'ERR_INVALID_ARG_TYPE', true);
   }
 
   {
     const w = new Writable({
-      decodeStrings: false,
       autoDestroy,
-      _write() {}
+      write() {}
+    });
+    expectError(w, ['asd', 'buffer'], 'ERR_UNKNOWN_ENCODING', true);
+  }
+
+  {
+    const w = new Writable({
+      autoDestroy,
+      decodeStrings: false,
+      write() {}
     });
-    expectError(w, ['asd', 'noencoding'], 'ERR_UNKNOWN_ENCODING', true);
+    expectError(w, ['asd', 'buffer'], 'ERR_UNKNOWN_ENCODING', true);
   }
 }