From 794a27cd0b342e6c523aefc18caeb5716f9d2fb2 Mon Sep 17 00:00:00 2001
From: scui73414-bot <301006987+scui73414-bot@users.noreply.github.com>
Date: Tue, 22 Sep 2026 10:55:24 +0800
Subject: [PATCH] fix(lock): open owner file writable before fdatasync

---
 src/canonicalIdentityLock.js       |  3 ++-
 test/canonicalIdentityLock.test.js | 22 ++++++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/src/canonicalIdentityLock.js b/src/canonicalIdentityLock.js
index 236b9f2c..d0867fa0 100644
--- a/src/canonicalIdentityLock.js
+++ b/src/canonicalIdentityLock.js
@@ -298,7 +298,8 @@ function prepareOwnerFile(lockDir, token) {
       mode: PRIVATE_FILE_MODE,
       flag: 'wx',
     });
-    descriptor = fs.openSync(preparedOwnerFile, 'r');
+    // Windows requires a writable handle for FlushFileBuffers/fdatasync.
+    descriptor = fs.openSync(preparedOwnerFile, 'r+');
     fs.fdatasyncSync(descriptor);
     fs.closeSync(descriptor);
     descriptor = null;
diff --git a/test/canonicalIdentityLock.test.js b/test/canonicalIdentityLock.test.js
index a39835c0..4d566576 100644
--- a/test/canonicalIdentityLock.test.js
+++ b/test/canonicalIdentityLock.test.js
@@ -177,6 +177,28 @@ test('partial owner preparation failure never exposes a canonical lock', () => {
   }
 });
 
+test('prepares owner files with a writable descriptor for fdatasync', () => {
+  const root = fs.mkdtempSync(path.join(os.tmpdir(), 'canonical-lock-fdatasync-'));
+  const nodeIdFile = path.join(root, 'node_id');
+  const lock = require('../src/canonicalIdentityLock');
+  const originalOpenSync = fs.openSync;
+  let stagedOwnerFlags = null;
+
+  try {
+    fs.openSync = function captureStagedOwnerFlags(file, flags, ...args) {
+      if (String(file).endsWith('.tmp')) stagedOwnerFlags = flags;
+      return originalOpenSync.call(fs, file, flags, ...args);
+    };
+
+    const release = lock.acquireCanonicalIdentityLock(nodeIdFile);
+    release();
+    assert.equal(stagedOwnerFlags, 'r+');
+  } finally {
+    fs.openSync = originalOpenSync;
+    fs.rmSync(root, { recursive: true, force: true });
+  }
+});
+
 test('release cleanup failure leaves canonical path available to a successor', () => {
   const root = fs.mkdtempSync(path.join(os.tmpdir(), 'canonical-lock-release-'));
   const nodeIdFile = path.join(root, 'node_id');