Project: Native Node Permit Gateway

Build contract

• Count actual request bytes and validate a complete typed command before mutation.
• Stop CSV production on response backpressure and release its cursor on disconnect.
• Bound worker count and queue length; reject overload without blocking the event loop.
• Carry one total deadline through outbound headers, body read, and retries.
• Reconcile an ambiguous upstream mutation under one stable identity.

Implementation checkpoint

function routeBudget(kind) {
  return { intake: 37 * 1024, export: 7, timetable: 64 * 1024 }[kind] ?? null;
}
console.log(routeBudget("intake"), routeBudget("timetable"));

Cost and boundaries

Reading B admitted body bytes uses O(B) time and retained memory. A streamed export over N rows uses O(N) total work and a bounded O(K) batch buffer when upstream fetching pauses with the response. A worker pool adds W worker heaps and at most Q queued task payloads; worker count is a capacity decision, not a function of connection count. Outbound fanout costs up to F concurrent upstream connections per request. Record the queue and byte budgets beside p95 request latency so a load test can show where the first limit is reached.

Failure drill

Run an absent or false Content-Length, a truncated JSON body, and a limit-plus-one request. Slow the CSV reader and abort after row 19. Flood the score route past its queue cap, then kill a worker mid-task. Delay the timetable after headers and make a reservation commit before its connection drops. The system must not duplicate the reservation or turn its unknown state into a clean failure. Repeat with twenty ordinary detail requests in flight and verify they retain the agreed latency budget. Inspect resource cleanup, not only returned status codes.

Acceptance checks

• Count actual request bytes and validate a complete typed command before mutation.
• Stop CSV production on response backpressure and release its cursor on disconnect.
• Bound worker count and queue length; reject overload without blocking the event loop.
• Carry one total deadline through outbound headers, body read, and retries.
• Reconcile an ambiguous upstream mutation under one stable identity.

Common Mistakes

• Checking only successful responses instead of failed intermediate states.
• Conflating a local cancellation with rollback of an external effect.
• Leaving resource ownership implicit after client disconnect.

Related lessons

Native Node HTTP and Runtime Boundaries; Node Incoming Body Limits and Abort State; Node Response Backpressure and Export Aborts; Node CPU Work, Worker Pools, and Event Loop Delay; Node Outbound Fetch Deadlines and Response Ownership.