@wdio/devtools-backend

@wdio/devtools-backend

The server that the three adapter packages connect to and the dashboard UI talks to. Internal to the monorepo — not published.

Responsibilities

• Fastify HTTP server — REST endpoints for preserve/clear/run/stop and the dashboard's baseline pair lookups.
• WebSocket gateway — one connection per adapter worker, one per dashboard client. Adapter events fan out to every connected dashboard.
• Baseline store (in-memory) — captures a snapshot of a failing test attempt, plus per-uid metadata, so the "Preserve & Rerun" flow can show a side-by-side diff.
• Rerun spawner (runner.ts) — spawns the user's wdio / nightwatch / selenium binary with rerun filters built from the dashboard's payload.
• Worker-message handler — dispatches messages from spawned workers (config path, session id, video path, ...).

Framework awareness

Lives only in runner.ts and framework-filters.ts. Both branch on a typed TestRunnerId from @wdio/devtools-shared (never a magic string). framework-filters.ts uses an explicit switch over the runner id rather than a Map/object lookup so CodeQL's unvalidated-dynamic-method-call query trusts the dispatch.

Public API

The backend is consumed only by other workspace packages. Adapter launchers call start({ port, hostname }) and receive the bound port. The dashboard accesses it via the documented HTTP routes (packages/shared/src/baseline.ts, packages/shared/src/runner.ts) and WS scopes (packages/shared/src/ws.ts, packages/shared/src/routes.ts).

For the full picture of how events flow adapter → backend → dashboard, see ARCHITECTURE.md.