facebook/flow · error

failed to write spinner status

Error message

failed to write spinner status

What it means

In eprintf_with_spinner's terminal branch, after clearing the spinner line the CLI writes '<message>: <spinner-frame>' to stderr (spinner(false) returns the next ASCII spinner frame). If the terminal's pts master has closed, this write returns EIO and the .expect() panics mid-status-line, typically during server connect/retry messages.

Source

Thrown at rust_port/crates/flow_cli/src/command_utils.rs:3007

                &command,
                stream,
                bincode::config::legacy()
                    .with_limit::<{ flow_commands_connect::command_connect_simple::MAX_FRAME_BYTES }>(),
            )
        })?;
        Ok(())
    }

    fn eprintf_with_spinner(msg: &str) {
        let stderr = std::io::stderr();
        let mut stderr = stderr.lock();
        if stderr.is_terminal() {
            if flow_utils_tty::spinner_used() {
                flow_utils_tty::print_clear_line(&mut stderr)
                    .expect("failed to clear spinner line");
            }
            write!(stderr, "{}: {}", msg, flow_utils_tty::spinner(false))
                .expect("failed to write spinner status");
            stderr.flush().expect("failed to flush spinner status");
        } else {
            writeln!(stderr, "{}", msg).expect("failed to write spinner status");
            stderr.flush().expect("failed to flush spinner status");
        }
    }

    // Waits for a response over the socket. If the connection dies, this will throw an exception
    fn wait_for_response(
        stream: &mut flow_common_socket::socket::SocketStream,
        quiet: bool,
        emoji: bool,
        _root: &std::path::Path,
    ) -> Result<server_prot::response::Response, ()> {
        let use_emoji = flow_utils_tty::supports_emoji() && emoji;
        stream.set_read_timeout(None).map_err(|_| ())?;
        loop {
            let response: Result<MonitorToClientMessage, _> =

View on GitHub (pinned to f88ac94bcf)

Solutions

1. Redirect stderr to a file for detached runs: `flow ... 2>flow.log &`
2. Run the command inside a session that stays alive (tmux attach kept open, ssh kept connected)
3. Maintainer: treat status-line writes as best-effort (ignore or log-and-continue on Err) instead of expect

Example fix

// before
write!(stderr, "{}: {}", msg, flow_utils_tty::spinner(false))
    .expect("failed to write spinner status");

// after
let _ = write!(stderr, "{}: {}", msg, flow_utils_tty::spinner(false));

// Progress output is best-effort; skip silently when stderr is dead
let _ = write!(stderr, "{}: {}", msg, flow_utils_tty::spinner(false));

When it happens

Trigger: The controlling terminal/ssh session dies (with SIGHUP ignored or under nohup) while the CLI is printing connect progress such as 'Please hold' or retry notices; a tmux pane holding the process is killed; stderr redirected to a pts that has been recycled.

Common situations: Disconnecting from long-running remote checks; automation that detaches sessions mid-run; pty-based harnesses torn down early.

Related errors

• failed to clear spinner line
• failed to flush spinner status
• failed to write cli errors
• failed to flush cli errors
• failed to get current directory

AI-assisted analysis of facebook/flow@f88ac94bcf (2026-08-20). Data as JSON: /api/errors/d0ddc81f90e727d0. Report an issue: GitHub.