423 Locked

Meaning & Description

Common Causes

• Another user or process holds an active lock on the requested resource.
• The client application failed to include the necessary lock token in the 'If' request header.
• A background synchronization process has temporarily locked the file.

How to fix a 423 error

1. Check the response body for WebDAV-specific XML error details indicating the nature of the lock.
2. Verify if your client application is correctly parsing and sending the 'If' header with a valid lock token.
3. Use a PROPFIND request to inspect the active locks on the resource.
4. Wait for the existing lock to expire or contact the user holding the lock.

Browser & SEO Behaviour

Code Examples

PUT /workspace/document.txt HTTP/1.1
Host: api.example.com
Content-Type: text/plain

[Updated content here]

app.put('/api/documents/:id', (req, res) => {
  const doc = getDocument(req.params.id);
  if (doc.isLocked && doc.lockToken !== req.headers['if']) {
    return res.status(423).json({ error: "Resource is locked." });
  }
  // Proceed with update
});

@app.put("/api/documents/{doc_id}")
def update_document(doc_id: str, if_header: str = Header(None, alias="If")):
    if is_locked(doc_id) and if_header != get_lock_token(doc_id):
        raise HTTPException(status_code=423, detail="Resource is locked")
    return {"message": "Updated successfully"}

func updateHandler(w http.ResponseWriter, r *http.Request) {
    ifHeader := r.Header.Get("If")
    if resourceIsLocked("doc1") && ifHeader == "" {
        http.Error(w, "Resource is locked", 423)
        return
    }
    w.WriteHeader(http.StatusOK)
}

[HttpPut("{id}")]
public IActionResult UpdateDocument(string id, [FromHeader(Name = "If")] string lockToken) {
    if (DocumentService.IsLocked(id) && lockToken == null) {
        return StatusCode(423, "The resource is locked.");
    }
    return Ok();
}

curl -X PUT https://api.example.com/docs/file.txt \
  -H "Content-Type: text/plain" \
  -d "New content" \
  -i

Raw HTTP Response Example

HTTP/1.1 423 Locked
Content-Type: application/xml; charset=utf-8
Content-Length: 185

<?xml version="1.0" encoding="utf-8" ?>
<d:error xmlns:d="DAV:">
  <d:lock-token-submitted/>
</d:error>

Real-world Examples

Frequently Asked Questions

Developer Tips

• When designing APIs that require concurrency control, consider using ETags and 412 Precondition Failed instead of WebDAV locks for simpler HTTP compliance.
• Always include a meaningful error message in the response body when returning 423, so the client knows who holds the lock or when it expires.
• Implement administrative endpoints to forcefully release stale locks that might block users indefinitely.
• Ensure your WebDAV implementation properly cleans up expired locks via a background job or during subsequent access attempts.

Interview Questions

These are questions you might face in a backend or API design interview that touch on HTTP 423.