From 39650923ae446dfa5243301a9136a0cf43a0be82 Mon Sep 17 00:00:00 2001
From: Nathan Whitaker <nathan@deno.com>
Date: Tue, 28 Apr 2026 08:42:13 +0000
Subject: [PATCH] fix(ext/node): support `encoding` option in `fs.watch`

`fs.watch(path, { encoding })` previously emitted the filename as a plain
utf8 string regardless of the requested encoding. Match Node:
- `encoding: 'buffer'` returns a `Buffer`,
- any other named encoding (e.g. `'hex'`, `'base64'`) re-encodes the
  filename via `Buffer.from(filename).toString(encoding)`,
- the default (`'utf8'` or absent) leaves the string unchanged.

See https://github.com/nodejs/node/blob/main/lib/internal/fs/watchers.js

Enables `parallel/test-fs-watch-encoding.js`.
---
 ext/node/polyfills/fs.ts       | 26 ++++++++++++++++++++++++--
 tests/node_compat/config.jsonc |  1 +
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/ext/node/polyfills/fs.ts b/ext/node/polyfills/fs.ts
index 7d7c490126d04b..b683da164c0443 100644
--- a/ext/node/polyfills/fs.ts
+++ b/ext/node/polyfills/fs.ts
@@ -3135,7 +3135,28 @@ type watchOptions = {
   encoding?: string;
 };
 
-type watchListener = (eventType: string, filename: string) => void;
+type watchListener = (
+  eventType: string,
+  filename: string | Buffer,
+) => void;
+
+// Match Node: `encoding: 'buffer'` returns a Buffer, any other named encoding
+// returns the filename re-encoded from utf8. Default ('utf8' or absent) leaves
+// the string unchanged. https://github.com/nodejs/node/blob/main/lib/internal/fs/watchers.js
+function encodeWatchFilename(
+  filename: string,
+  encoding: string | undefined,
+): string | Buffer {
+  if (!encoding || encoding === "utf8" || encoding === "utf-8") {
+    return filename;
+  }
+  const asBuffer = Buffer.from(filename);
+  if (encoding === "buffer") {
+    return asBuffer;
+  }
+  // deno-lint-ignore prefer-primordials
+  return asBuffer.toString(encoding as BufferEncoding);
+}
 
 function watch(
   filename: string | URL,
@@ -3171,6 +3192,7 @@ function watch(
   const watchPath = getValidatedPath(filename).toString();
 
   const recursive = options?.recursive || false;
+  const encoding = options?.encoding;
   const iterator: Deno.FsWatcher = Deno.watchFs(watchPath, {
     recursive,
   });
@@ -3190,7 +3212,7 @@ function watch(
     fsWatcher.emit(
       "change",
       convertDenoFsEventToNodeFsEvent(val.kind),
-      filename,
+      encodeWatchFilename(filename, encoding),
     );
   }, (e) => {
     fsWatcher.emit("error", e);
diff --git a/tests/node_compat/config.jsonc b/tests/node_compat/config.jsonc
index 93a58f911a2cc9..ba670bda5e0030 100644
--- a/tests/node_compat/config.jsonc
+++ b/tests/node_compat/config.jsonc
@@ -1189,6 +1189,7 @@
     "parallel/test-fs-util-validateoffsetlength.js": {},
     "parallel/test-fs-utimes-y2K38.js": {},
     "parallel/test-fs-utimes.js": {},
+    "parallel/test-fs-watch-encoding.js": {},
     "parallel/test-fs-watch-file-enoent-after-deletion.js": {},
     "parallel/test-fs-watch-recursive-add-file-to-existing-subfolder.js": {},
     "parallel/test-fs-watch-recursive-add-folder.js": {},