windmill-labs/windmill · error

Could not find a free recording file name

Error message

Could not find a free recording file name

What it means

Exhaustion guard in writeRecording (app dev session recorder): it tried 100 candidate recording filenames — recordingFileName(now, attempt) for attempt 0..99 — and every one hit an existing file (the 'wx' exclusive-create flag fails when the name is taken). With per-attempt distinct names, hitting all 100 means something pathological: a directory pre-filled with recordings sharing the same timestamp base, or repeated write failures being misread as existence collisions. The input at fault is the recordings directory's existing contents.

Solutions

1. Clean or archive old recording files in the app's recordings directory so fresh names are available
2. Check for the real failure mode: if the directory is unwritable, fix permissions on recordingsDir instead of relying on retries
3. If caused by an external process creating files with identical naming, change the recording directory for the dev session

When it happens

Trigger: Thrown at cli/src/commands/app/dev.ts:778 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of windmill-labs/windmill@e474e8803c (2026-09-03). Data as JSON: /api/errors/f7b3944f6a9ba081. Report an issue: GitHub.

Appendix: source

Thrown at cli/src/commands/app/dev.ts:778

  }

  /** Write the recording under a name nothing else holds. `wx` is what makes
   * this safe: two tabs stopping in the same millisecond both create, and the
   * loser retries rather than overwriting the winner. */
  async function writeRecording(body: string): Promise<string> {
    const now = new Date();
    for (let attempt = 0; attempt < 100; attempt++) {
      const file = recordingFileName(now, attempt);
      try {
        await fs.promises.writeFile(path.join(recordingsDir, file), body, {
          flag: "wx",
        });
        return file;
      } catch (error: any) {
        if (error?.code !== "EEXIST") throw error;
      }
    }
    throw new Error("Could not find a free recording file name");
  }

  function saveRecording(req: http.IncomingMessage, res: http.ServerResponse) {
    if (!isOwnOrigin(req.headers.origin, req.headers.host)) {
      sendJson(res, 403, { error: "Cross-origin recording upload refused" });
      return;
    }
    const chunks: Buffer[] = [];
    let size = 0;
    let refused = false;
    // An upload cut short (by the refusal below, or by the browser) raises
    // 'error' on the request, which unhandled takes the dev server down.
    req.on("error", (error: Error) => {
      if (!refused) {
        log.warn(colors.yellow(`Recording upload failed: ${error.message}`));
      }
    });
    req.on("data", (chunk: Buffer) => {

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