Function connectEvents

static/js/job.js:276–336

(jobId)

// terminal, accept its final state; otherwise reconnect with backoff.
// Falls back to REST polling only after SSE exhausts its retry budget.
function connectEvents(jobId) {
  let attempt = 0;
  let stopped = false;

  const open = () => {
    const es = new EventSource(`/api/jobs/${jobId}/events`);
    setEventSource(es);

    es.onmessage = (ev) => {
      attempt = 0; // any successful frame resets backoff
      let s;
      try { s = JSON.parse(ev.data); } catch { return; }
      // Defer by one tick so synchronous user event handlers (clicks,
      // input events) always complete before SSE state is applied.
      setTimeout(() => {
        applyState(s);
        if (TERMINAL_STATUSES.has(s.status)) {
          stopped = true;
          es.close();
          setEventSource(null);
        }
      }, 0);
    };

    es.onerror = async () => {
      if (stopped) return;
      es.close();
      setEventSource(null);

      // Probe REST once before declaring failure -- handles dev-server
      // reloads and brief network blips where the job is actually fine.
      try {
        const s = await probeJob(jobId);
        if (TERMINAL_STATUSES.has(s.status)) {
          stopped = true;
          return;
        }
      } catch (err) {
        if (err.message === "Job no longer exists on the server") {
          stopped = true;
          showError(err.message);
          setSubmitProcessing(false);
          return;
        }
        // Network down -- fall through to backoff.
      }

      attempt += 1;
      if (attempt > 6) {
        // SSE gave up — activate REST polling as the fallback.
        startJobPolling(jobId);
        return;
      }
      // 0.5s, 1s, 2s, 4s, 8s, 16s
      const delay = 500 * Math.pow(2, attempt - 1);
      setTimeout(() => { if (!stopped) open(); }, delay);
    };
  };