inspector/scripts/lib/render-smoke.mjs

/**
 * Spawn a terminal app, wait for it to paint a marker, and then wait again to
 * see whether it is still running (#2147).
 *
 * Extracted from `scripts/smoke-tui.mjs` for the same reason
 * `announced-child.mjs` was extracted from `smoke-web-app.mjs` (#2000): a smoke
 * script only ever exercises its own happy path, so the branch that matters
 * most here — a child that paints the marker and *then* dies — is unreachable
 * from the real TUI once it is fixed. Driving this from a test against a stub
 * that paints and immediately exits 1 is what keeps the assertion honest.
 *
 * The defect it encodes against: `smoke:tui` used to resolve OK the instant the
 * marker appeared and never looked at the child again. The TUI was exiting 1
 * about 40ms later, every run, on every machine, and the smoke won that race
 * and printed OK. So it asserted "painted once", while its own header claimed
 * "boots and renders without crashing". Worse, the race cut both ways: had the
 * `exit` event been processed first, the same run would have failed, which
 * reads as flake rather than as the standing defect it was.
 *
 * Hence `surviveMs`. First paint is not survival, and nothing shorter than an
 * explicit "still alive N ms later" check can tell the two apart.
 */

import { spawn } from "node:child_process";

/**
 * Tail of a child's output, for quoting in a diagnostic. Slicing a terminal
 * stream can land mid-CSI-sequence, so drop through the first newline rather
 * than lead with an escape-code fragment that mangles the line after it.
 *
 * @param {string} output
 * @param {number} [limit]
 * @returns {string}
 */
export function outputTail(output, limit = 800) {
  const tail = output.slice(-limit);
  const nl = tail.indexOf("\n");
  return output.length > limit && nl !== -1 ? tail.slice(nl + 1) : tail;
}

/**
 * @param {object} opts
 * @param {string} opts.command             Executable to spawn.
 * @param {string[]} [opts.args]            Arguments for it.
 * @param {object} [opts.spawnOptions]      Merged into the `spawn` options
 *                                          (`stdio` is fixed — see below).
 * @param {string} opts.marker              Substring whose appearance in the
 *                                          child's output counts as first paint.
 * @param {number} [opts.timeoutMs]         Budget for first paint (default 15s).
 * @param {number} [opts.surviveMs]         How long after first paint the child
 *                                          must stay alive (default 2s).
 * @param {number} [opts.exitGraceMs]       SIGTERM → SIGKILL grace (default 5s).
 * @param {number} [opts.drainMs]           Post-exit pipe-drain cap (default 500ms).
 * @param {(child: import("node:child_process").ChildProcess) => void} [opts.onSpawn]
 *   Called synchronously with the child, before any waiting — the caller's
 *   teardown handle on every failure path.
 * @param {(message: string) => void} [opts.warn]
 * @returns {Promise<{ code: 0 | 1, message: string, output: string }>}
 *   Resolves only after the child's streams have closed, so `output` is
 *   complete and the caller may safely remove a directory the child was using.
 */
export function runRenderSmoke({
  command,
  args = [],
  spawnOptions = {},
  marker,
  timeoutMs = 15_000,
  surviveMs = 2_000,
  exitGraceMs = 5_000,
  drainMs = 500,
  onSpawn = () => {},
  warn = (m) => console.warn(m),
}) {
  return new Promise((resolve) => {
    const child = spawn(command, args, {
      ...spawnOptions,
      // stdin is `ignore` (i.e. /dev/null) deliberately, even under a PTY: BSD
      // `script` refuses to start when its own stdin is a pipe
      // ("tcgetattr/ioctl: Operation not supported on socket"). It reads the
      // immediate EOF and forwards one ^D into the pty before the app mounts,
      // which is harmless — verified against the real TUI, which survives it.
      stdio: ["ignore", "pipe", "pipe"],
    });
    // Publish before waiting, so every path below leaves the caller holding a
    // stoppable handle rather than an orphan (the #2000 rule).
    onSpawn(child);

    let output = "";
    let settled = false;
    let finished = false;
    let childExited = false;
    let childClosed = false;
    let markerAt = null;
    /** @type {ReturnType<typeof setTimeout> | undefined} */
    let surviveTimer;

    const t0 = Date.now();
    const since = () => Date.now() - t0;

    const finish = (code, message) => {
      if (finished) return;
      finished = true;
      resolve({
        code,
        message: typeof message === "function" ? message() : message,
        output,
      });
    };

    // Settle the verdict, then wait for the child to actually close before
    // resolving (#1801). The caller's work dir doubles as the app's HOME, so it
    // is still being written to when we signal; removing it while those writes
    // land fails with ENOTEMPTY. Waiting on `close` rather than `exit` also
    // covers a *spawn failure*, which emits `error` + `close` and never `exit`
    // — and guarantees the pipes are drained, which is what makes the thunked
    // messages below complete rather than truncated at the interesting line.
    //
    // Deliberately not `lib/child-cleanup.mjs`'s `stopChild()`: that resolves
    // on the FIRST of exit/close, whereas this wait must keep going for `close`
    // after `exit`, on a shorter re-armed deadline, for the drain.
    const done = (code, message) => {
      if (settled) return;
      settled = true;
      clearTimeout(renderTimer);
      clearTimeout(surviveTimer);
      if (childClosed) {
        finish(code, message);
        return;
      }
      const forceKill = setTimeout(() => child.kill("SIGKILL"), exitGraceMs);

      let deadline;
      const armDeadline = (ms, warning) => {
        clearTimeout(deadline);
        deadline = setTimeout(() => {
          warn(`render-smoke — ${warning}`);
          finish(code, message);
        }, ms);
      };
      armDeadline(
        exitGraceMs * 2,
        `child did not close its output streams within ${exitGraceMs * 2}ms; giving up on the drain`,
      );

      // Once the child itself is gone only the pipe drain remains, so the wait
      // drops to `drainMs`. `close` is bounded by whoever holds the stdio
      // pipes, which can outlive the direct child: any descendant that
      // inherited them keeps it pending.
      const drainOnly = () => {
        clearTimeout(forceKill);
        armDeadline(
          drainMs,
          `child exited but held its output streams open for ${drainMs}ms (a descendant may have inherited them); giving up on the drain`,
        );
      };
      if (childExited) drainOnly();
      else child.once("exit", drainOnly);

      child.once("close", () => {
        clearTimeout(forceKill);
        clearTimeout(deadline);
        finish(code, message);
      });

      // Only signal a child that is still running: on the crash and
      // spawn-failure paths there is nothing left to signal, and we are here
      // purely to wait out the remaining `close`.
      if (
        child.exitCode === null &&
        child.signalCode === null &&
        !child.killed
      ) {
        child.kill("SIGTERM");
      }
    };

    const onData = (chunk) => {
      output += chunk.toString();
      if (markerAt !== null || !output.includes(marker)) return;
      markerAt = since();
      // First paint is not the verdict — it only starts the clock on the
      // question this smoke actually asks.
      surviveTimer = setTimeout(() => {
        done(
          0,
          `rendered "${marker}" at ${markerAt}ms and was still running ${surviveMs}ms later`,
        );
      }, surviveMs);
    };

    child.stdout.on("data", onData);
    child.stderr.on("data", onData);

    // Registered before done()'s own one-shot listener, so this always runs
    // first — done() can trust `childClosed` even when called from a handler.
    child.on("close", () => {
      childClosed = true;
    });

    child.on("exit", (code, signal) => {
      childExited = true;
      if (settled) return;
      const how = signal ? `signal ${signal}` : `code ${code}`;
      done(1, () =>
        markerAt === null
          ? `child exited (${how}) before rendering "${marker}"\n${outputTail(output)}`
          : `child rendered "${marker}" at ${markerAt}ms and then exited (${how}) ` +
            `${since() - markerAt}ms later, inside the ${surviveMs}ms survival window — ` +
            `it painted one frame, it did not run\n${outputTail(output)}`,
      );
    });

    child.on("error", (err) => {
      done(1, `failed to spawn ${command}: ${err.message}`);
    });

    const renderTimer = setTimeout(() => {
      done(
        1,
        () =>
          `child did not render "${marker}" within ${timeoutMs}ms\n${outputTail(output)}`,
      );
    }, timeoutMs);
  });
}