{"record":{"id":"c08ae02b981bca05","repo":"astrid-runtime/astrid","slug":"detached-fuse-service-exceeded-the-startup-respons","errorCode":null,"errorMessage":"detached FUSE service exceeded the startup response size","messagePattern":"detached FUSE service exceeded the startup response size","errorType":"exception","errorClass":null,"httpStatus":null,"severity":"error","filePath":"crates/astrid-storage-provider-fuse/src/main.rs","lineNumber":704,"sourceCode":"    stdin.write_all(b\"\\n\").await?;\n    drop(stdin);\n    let stdout = child\n        .stdout\n        .take()\n        .context(\"FUSE service stdout is unavailable\")?;\n    let mut line = String::new();\n    let reader = tokio::io::BufReader::new(stdout);\n    let read = tokio::time::timeout(SERVICE_STARTUP_TIMEOUT, async {\n        let mut limited = reader.take(64 * 1024 + 1);\n        limited.read_line(&mut line).await\n    })\n    .await\n    .context(\"timed out waiting for the FUSE service\")??;\n    if read == 0 {\n        bail!(\"detached FUSE service exited before readiness\");\n    }\n    if line.len() > 64 * 1024 {\n        bail!(\"detached FUSE service exceeded the startup response size\");\n    }\n    match serde_json::from_str(&line)? {\n        ServiceStartup::Ready {\n            mount_id,\n            pid,\n            access,\n        } => {\n            if !control_path.exists() {\n                bail!(\"detached FUSE service did not retain its control endpoint\");\n            }\n            if pid == 0 {\n                bail!(\"detached FUSE service returned an invalid process identity\");\n            }\n            Ok(ControlReady {\n                mount_id,\n                pid,\n                access,\n            })","sourceCodeStart":686,"sourceCodeEnd":722,"githubUrl":"https://github.com/astrid-runtime/astrid/blob/affd8760f44190dbdfbec23403f4c4b642c33112/crates/astrid-storage-provider-fuse/src/main.rs#L686-L722","documentation":"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.","triggerScenarios":"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.","commonSituations":"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.","solutions":["Rebuild/reinstall the FUSE provider service binary so both sides use the same startup protocol version","Check the service (and any wrapper command in ServiceLaunch) for code that logs to stdout; route logs to stderr","Capture the raw stdout line (e.g. run the service in the foreground) and inspect what it prints before readiness","Verify no shell wrapper or alias echoes the JSON launch config piped to stdin"],"exampleFix":"// before: service prints banner + JSON to stdout\nprintln!(\"fuse service starting, launch={launch:?}\");\nprintln!(\"{}\", serde_json::to_string(&startup)?);\n// after: only the single JSON line on stdout, everything else on stderr\neprintln!(\"fuse service starting\");\nprintln!(\"{}\", serde_json::to_string(&startup)?);","handlingStrategy":"validation","validationCode":"// Parent-side guard before parsing child output\nlet line = read_startup_line_limited(child_stdout, 64 * 1024).await?;\nif line.len() > 64 * 1024 { return Err(anyhow!(\"startup line exceeds protocol limit\")); }\nif !line.starts_with('{') { return Err(anyhow!(\"startup output is not JSON: {:?}\", &line[..line.len().min(80)])); }","typeGuard":"fn looks_like_startup(line: &str) -> bool {\n    line.len() <= 64 * 1024 && serde_json::from_str::<ServiceStartup>(line).is_ok()\n}","tryCatchPattern":"match read_service_startup(&mut child, &launch, &control_path).await {\n    Ok(ready) => proceed(ready),\n    Err(e) if e.to_string().contains(\"exceeded the startup response size\") => {\n        // capture raw child stdout/stderr for diagnosis, then fail\n        diagnose_protocol_mismatch(&child);\n    }\n    Err(e) => return Err(e),\n}","preventionTips":["Route all service logging to stderr; reserve stdout exclusively for the single JSON startup line","Keep parent and service binaries versioned and deployed together","Add a startup-protocol integration test that asserts the child emits exactly one <=64KiB JSON line","Never wrap the service in scripts that echo stdin back to stdout"],"tags":["fuse","ipc","protocol","process"],"backgroundTag":"unexpected-response-shape","analyzedSha":"affd8760f44190dbdfbec23403f4c4b642c33112","analyzedAt":"2026-09-09T21:28:12.402Z","contentChangedAt":"2026-09-09T21:28:12.402Z","schemaVersion":2},"datasetVersion":"2026-09-14T05:17:10.506Z"}