openclaw - 💡(How to fix) Fix [Bug] EPERM fsync on Windows — image_generate + Feishu picture receive both broken in 2026.5.2 [1 comments, 2 participants]

Bug type

Regression (worked before 2026.5.2, now fails on Windows)

Beta release blocker

Yes — affects core media functionality

Summary

Two distinct features fail with the same root cause on Windows after upgrading to 2026.5.2:

1. image_generate tool — generated images cannot be saved, throwing EPERM: operation not permitted, fsync
2. Feishu picture receive — inbound images via Feishu channel are not downloaded, also throwing EPERM: operation not permitted, fsync

Both trace back to writeSavedMediaBuffer in the media store opening the temp file with read-only mode "r" before calling handle.sync(), which Windows rejects with EPERM.

Error Message

Error: EPERM: operation not permitted, fsync
  at async fsync (node:internal/fs/promises:842)
  at async fsCall (node:internal/fs/promises:468)
  at async writeSavedMediaBuffer (store-*.js:236)

Environment

• OS: Windows 11 (Windows_NT 10.0.19045 x64)
• OpenClaw version: 2026.5.2 (8b2a6e5)
• Node.js: v24.15.0
• Gateway mode: local

Steps to reproduce

image_generate:

1. Run image_generate prompt="test" on Windows
2. Image generation request succeeds but saving to disk fails with EPERM

Feishu picture receive:

1. Send a picture via Feishu direct message
2. Message received as <media:image> placeholder, media/inbound stays empty
3. Gateway log shows EPERM during media offload

Expected behavior

• Generated images saved successfully to media/tool-image-generation/
• Feishu inbound pictures saved to media/inbound/ and parseable by AI

Actual behavior

Both fail with EPERM: operation not permitted, fsync

Root Cause

In src/media/store.ts, writeSavedMediaBuffer opens the staged temp file with read-only mode "r" before calling handle.sync():

// current code (line ~351)
const handle = await fs.open(tempDest, "r");  // read-only fails sync on Windows
try {
    await handle.sync();
} finally {
    await handle.close();
}

On Windows, calling fsync() on a read-only file handle returns EPERM (operation not permitted). Linux/macOS allow this, so the bug is Windows-specific and hidden in dev/testing.

Fix

Change the open mode from "r" to "r+" (read-write):

// fixed code
const handle = await fs.open(tempDest, "r+");  // read-write allows sync
try {
    await handle.sync();
} finally {
    await handle.close();
}

This matches the fix proposed in PR #76593 (fix(media): use r+ instead of r for fs.open to fix EPERM on fsync on Windows).

Related Issues

• #76844 — Windows: EPERM fsync error when uploading .docx files via WebChat (same root cause)
• #76977 — MediaOffloadError: EPERM operation not permitted, fsync (closed as duplicate of #76844)

Impact and Severity

• Affected: All Windows users (all OpenClaw versions 2026.5.x)
• Severity: High — blocks image generation and inbound media parsing, two core features
• Workaround: None for image_generate; manual file placement for Feishu inbound
• Fix diff: one character ("r" to "r+") — minimal risk