Function handleRenderChunk

packages/aws-lambda/src/handler.ts:302–365

(
  event: RenderChunkEvent,
  deps?: HandlerDeps,
)

// ── RenderChunk ─────────────────────────────────────────────────────────────

async function handleRenderChunk(
  event: RenderChunkEvent,
  deps?: HandlerDeps,
): Promise<RenderChunkLambdaResult> {
  const started = Date.now();
  const s3 = deps?.s3 ?? getS3Client();
  const primitive = deps?.primitives?.renderChunk ?? renderChunk;

  // Sparticuz decompresses Chromium into /tmp on first call; warm starts
  // skip the work (path already cached). Guard the env-var mutation too so
  // a caller-supplied PRODUCER_HEADLESS_SHELL_PATH (e.g. the SAM-local
  // RIE smoke) wins over the auto-resolution.
  if (!deps?.skipChromeResolution && !process.env.PRODUCER_HEADLESS_SHELL_PATH) {
    const chromePath = await resolveChromeExecutablePath();
    // The OSS engine resolves Chrome via `PRODUCER_HEADLESS_SHELL_PATH`
    // first (see `browserManager.resolveHeadlessShellPath`); set it before
    // invoking the primitive so launch picks up the bundled binary.
    process.env.PRODUCER_HEADLESS_SHELL_PATH = chromePath;
  }

  const work = mkdtempSync(join(deps?.tmpRoot ?? tmpdir(), "hf-lambda-chunk-"));
  const planTar = join(work, "plan.tar.gz");
  const planDir = join(work, "plan");

  try {
    await downloadS3ObjectToFile(s3, event.PlanS3Uri, planTar);
    await untarDirectory(planTar, planDir);

    // Verify the plan's hash matches what Step Functions told us to render.
    // The producer's renderChunk re-checks internally (defense-in-depth),
    // but doing it here at the handler boundary lets us fail before paying
    // the Chrome-launch + render cost on a misrouted chunk. Throws a
    // typed PLAN_HASH_MISMATCH that Step Functions can route as
    // non-retryable.
    verifyPlanHash(planDir, event.PlanHash);

    const chunkOutputBase = join(
      work,
      event.Format === "png-sequence"
        ? `chunk-${pad(event.ChunkIndex)}`
        : `chunk-${pad(event.ChunkIndex)}${formatExtension(event.Format)}`,
    );

    const result: ChunkResult = await primitive(planDir, event.ChunkIndex, chunkOutputBase);

    const chunkUri = await uploadChunkOutput(
      s3,
      result,
      event.ChunkOutputS3Prefix,
      event.ChunkIndex,
    );

    return {
      Action: "renderChunk",
      ChunkS3Uri: chunkUri,
      ChunkIndex: event.ChunkIndex,
      Sha256: result.sha256,
      FramesEncoded: result.framesEncoded,