traceon-loadrunner

The local HTTP load generator for the traceOn Chrome extension's Load Test feature, run as a Chrome Native Messaging host.

The extension can't generate high-rate HTTP load itself without freezing the browser, and it can't reach a local process except through a registered native-messaging host. This package is that host.

Install

Requires Node.js ≥ 18.

npx traceon-loadrunner --extension-id <your-extension-id>

Get the full command — with your extension's ID already filled in — from the extension's Load Test panel (Performance Test tab). Then reload the extension and click Start TraceOn Load Test Engine.

If you run more than one traceOn install (e.g. an unpacked dev build alongside the Web Store one), pass --extension-id once per ID.

What it writes to your machine

• A ~10 KB host script at:
  • Linux: ~/.local/share/traceon-loadrunner/host.mjs
  • macOS: ~/Library/Application Support/traceon-loadrunner/host.mjs
  • Windows: %LOCALAPPDATA%\traceon-loadrunner\host.mjs (+ host.cmd)
• One native-messaging manifest (com.traceon.loadrunner.json) in Chrome's / Chromium's NativeMessagingHosts directory, listing your extension ID(s) in allowed_origins. On Windows, an HKCU registry key pointing at it.

The script's shebang is set to the absolute path of the Node that ran the install, so Chrome doesn't need node on its PATH. If you later remove or relocate that Node (e.g. an nvm switch), re-run the install command.

Uninstall

npx traceon-loadrunner --uninstall

Removes the data directory and the manifest(s) / registry key.

Platform support

Implemented and verified on Linux. macOS and Windows follow Chrome's documented native-messaging locations but haven't been exercised end-to-end — file an issue if registration fails.

For contributors

• src/protocol.ts is the source of truth for the wire types (LoadTestConfig, LoadMetrics, LoadTestResult, EngineRequest, EngineResponse, …). It's published as the traceon-loadrunner/protocol subpath, and the traceOn extension imports its types from there.
• src/engine.ts + rateScheduler.ts + concurrencyPool.ts + histogram.ts — the load engine (rate scheduling, concurrency cap, streaming latency histogram). Chrome-free, Node-free beyond fetch.
• src/host.ts — the native-messaging framing (4-byte length prefix + JSON).
• src/install.ts — this CLI.
• npm run build bundles dist/host.js (self-contained) + dist/install.js via esbuild and emits dist/protocol.d.ts via tsc.
• npm test — engine + install + host tests (no real Chrome involved).