[Worker runtime]

Worker runtime

Abstract

frontend/worker/src/runtime.ts implements handleRun for POST /api/run. Execution preference is documented in-file:

1. PYODIDE_IN_WORKER=enabled → tryRunInWorker (pyodide_runtime.ts)
2. Else EXTERNAL_BACKEND set → HTTP proxy to ${EXTERNAL_BACKEND}/run
3. Else 503 NO_BACKEND with a pointer at env vars and RUNTIME.md

Production reality: ships as a proxy to Flask (or another Python host). In-worker Pyodide is a scaffold, not a complete wheel-upload pipeline.

Conceptual model

Interface surface

Request body

{
  script: string;           // required non-empty
  data: Bar[];              // required non-empty OHLCV array
  mode?: 'interpret' | 'compile';
}

Invalid bodies → 400 { status: 'error', code: 'BAD_REQUEST', message }.

Success / upstream

Proxy returns upstream status and body verbatim (JSON content-type, CORS origin header). Flask Pro API is the usual upstream.

Error codes (Worker-originated)

Usage metering

If Authorization: Bearer … and USAGE KV bound:

usage:{key} → count++, TTL 30 days

Internals

pyodide_runtime scaffold

When enabled:

• Lazy-loads Pyodide from jsDelivr v0.26.2 (dev fallback).
• Production intent: R2 wheels + module-level cache (RUNTIME.md).
• Calls run_script(script, bars) via runPythonAsync — requires runtime bootstrap that is not fully wired like the browser engine’s pynescript_runtime.py + micropip install.

Do not enable in production without completing the wheel pipeline and load testing CPU/memory limits.

Constraints (from RUNTIME.md)

Roll-out flag

RUNTIME.md also mentions RUNTIME_MODE=in-worker as product language; code checks PYODIDE_IN_WORKER === 'enabled'. Prefer the code flag when configuring.

Invariants & edge cases

1. Body stream — request body is consumed once; proxy re-serializes the already-parsed object.
2. CORS — run responses set Access-Control-Allow-Origin from pickOrigin (see CORS).
3. PWA path mismatch — browser server engine posts to {endpoint}/run; Worker route is /api/run. Align via gateway rewrite or endpoint base path convention.
4. No response caching yet — README lists cache for identical (script, data_hash) as deferred.

Worked examples

Local proxy to Flask

# wrangler.toml [vars]
EXTERNAL_BACKEND = "http://127.0.0.1:5002"
PYODIDE_IN_WORKER = "disabled"

curl -sS -X POST http://127.0.0.1:8787/api/run \
  -H 'content-type: application/json' \
  -d '{"script":"//@version=5\nindicator(\"t\")\nplot(close)","data":[{"time":1,"open":1,"high":1,"low":1,"close":1}]}'

Force 503 for missing backend

Unset EXTERNAL_BACKEND, keep Pyodide disabled → expect NO_BACKEND message referencing RUNTIME.md.

Failure modes

See also

• Bindings
• Engines
• Auth (Bearer on run for metering)