astrid-runtime/astrid · error

detached FUSE service exceeded the startup response size

Error message

detached FUSE service exceeded the startup response size

What it means

read_service_startup reads a single JSON ServiceStartup line from the detached FUSE service's stdout, bounded by a 64 KiB take() limit. If the line read back exceeds 64*1024 bytes, the parent concludes the child wrote garbage or a runaway payload instead of the expected compact startup response and bails with this error. It is a protocol sanity check protecting the parent from unbounded/unexpected child output.

Source

Thrown at crates/astrid-storage-provider-fuse/src/main.rs:704

    stdin.write_all(b"\n").await?;
    drop(stdin);
    let stdout = child
        .stdout
        .take()
        .context("FUSE service stdout is unavailable")?;
    let mut line = String::new();
    let reader = tokio::io::BufReader::new(stdout);
    let read = tokio::time::timeout(SERVICE_STARTUP_TIMEOUT, async {
        let mut limited = reader.take(64 * 1024 + 1);
        limited.read_line(&mut line).await
    })
    .await
    .context("timed out waiting for the FUSE service")??;
    if read == 0 {
        bail!("detached FUSE service exited before readiness");
    }
    if line.len() > 64 * 1024 {
        bail!("detached FUSE service exceeded the startup response size");
    }
    match serde_json::from_str(&line)? {
        ServiceStartup::Ready {
            mount_id,
            pid,
            access,
        } => {
            if !control_path.exists() {
                bail!("detached FUSE service did not retain its control endpoint");
            }
            if pid == 0 {
                bail!("detached FUSE service returned an invalid process identity");
            }
            Ok(ControlReady {
                mount_id,
                pid,
                access,
            })

View on GitHub (pinned to affd8760f4)

Solutions

1. Rebuild/reinstall the FUSE provider service binary so both sides use the same startup protocol version
2. Check the service (and any wrapper command in ServiceLaunch) for code that logs to stdout; route logs to stderr
3. Capture the raw stdout line (e.g. run the service in the foreground) and inspect what it prints before readiness
4. Verify no shell wrapper or alias echoes the JSON launch config piped to stdin

Example fix

// before: service prints banner + JSON to stdout
println!("fuse service starting, launch={launch:?}");
println!("{}", serde_json::to_string(&startup)?);
// after: only the single JSON line on stdout, everything else on stderr
eprintln!("fuse service starting");
println!("{}", serde_json::to_string(&startup)?);

// Parent-side guard before parsing child output
let line = read_startup_line_limited(child_stdout, 64 * 1024).await?;
if line.len() > 64 * 1024 { return Err(anyhow!("startup line exceeds protocol limit")); }
if !line.starts_with('{') { return Err(anyhow!("startup output is not JSON: {:?}", &line[..line.len().min(80)])); }

fn looks_like_startup(line: &str) -> bool {
    line.len() <= 64 * 1024 && serde_json::from_str::<ServiceStartup>(line).is_ok()
}

match read_service_startup(&mut child, &launch, &control_path).await {
    Ok(ready) => proceed(ready),
    Err(e) if e.to_string().contains("exceeded the startup response size") => {
        // capture raw child stdout/stderr for diagnosis, then fail
        diagnose_protocol_mismatch(&child);
    }
    Err(e) => return Err(e),
}

When it happens

Trigger: The FUSE service child process writes a startup line longer than 64 KiB on stdout before the newline — e.g. a corrupted or incompatible binary that echoes debug/launch-config data, logs to stdout instead of stderr, or a build whose ServiceStartup serialization ballooned.

Common situations: Running a mismatched/older version of the service binary that doesn't speak the one-line-JSON startup protocol; a wrapper script or shell echoing the stdin launch config back; stdout redirected or multiplexed with verbose logging.

Related errors

• detached FUSE service did not retain its control endpoint
• detached FUSE service returned an invalid process identity
• FUSE service control request exceeds limit
• FUSE callback probe correlation mismatch
• opaque capsule assets cannot be symlinks: {}

AI-assisted analysis of astrid-runtime/astrid@affd8760f4 (2026-09-09). Data as JSON: /api/errors/c08ae02b981bca05. Report an issue: GitHub.