overleaf/overleaf · info

Not Found (connected client not found res.sendStatus(404))

Error message

Not Found (connected client not found res.sendStatus(404))

What it means

GET /api/:project_id/client/:client_id returns HTTP 404 when no socket with the given client_id exists in io.sockets.sockets on this instance. It reports that the connected client view cannot be found — the client is disconnected, the id is wrong, or the socket is homed on another instance.

Source

Thrown at services/real-time/app/js/HttpController.js:49

      // room names are composed as '<NAMESPACE>/<ROOM>' and the default
      //  namespace is empty (see comments in RoomManager), just drop the '/'
      .map(fullRoomPath => fullRoomPath.slice(1))
    return client
  },

  getConnectedClients(req, res) {
    const io = req.app.get('io')
    const ioClients = io.sockets.clients()

    res.json(ioClients.map(HttpController._getConnectedClientView))
  },

  getConnectedClient(req, res) {
    const { client_id: clientId } = req.params
    const io = req.app.get('io')
    const ioClient = io.sockets.sockets[clientId]
    if (!ioClient) {
      res.sendStatus(404)
      return
    }
    res.json(HttpController._getConnectedClientView(ioClient))
  },
}

View on GitHub (pinned to 28ad3b03b7)

Solutions

1. Re-obtain the current client id from the client (it changes on every reconnect)
2. Treat 404 as 'not currently connected' and query the right instance or a shared registry
3. Enable sticky sessions so lookups reach the instance owning the socket
4. Validate the client_id format before the call to rule out typos

Example fix

// before
const view = await getConnectedClient(projectId, staleClientId)
// after
const res = await getConnectedClient(projectId, clientId)
if (res.status === 404) {
  return handleClientOffline(clientId) // refetch id or mark offline
}
const view = await res.json()

if (!/^[A-Za-z0-9_-]+$/.test(clientId)) throw new Error('malformed client id')

const res = await fetch(clientUrl)
if (res.status === 404) {
  return handleClientOffline(clientId) // refetch id / mark offline
}
const view = await res.json()

When it happens

Trigger: Querying a client id that has since disconnected, a typo'd/old id, or a socket connected to a different real-time server (multi-instance without sticky routing).

Common situations: Debug tooling querying a live client after it refreshed the page; scripts caching client ids across reconnects; load-balanced clusters where the lookup instance is not the owning instance.

Related errors

• Not Found (client already disconnected res.sendStatus(404))
• ProjectNotFound
• no git access
• NotFoundError
• NotFoundError

AI-assisted analysis of overleaf/overleaf@28ad3b03b7 (2026-09-03). Data as JSON: /api/errors/2142e71935a0920d. Report an issue: GitHub.