Notes from a 2 AM On-Call: Why Harper's WASM Module Silently Failed in Our Self-Hosted VSCode Server

Description and use

Adding worker‑src and script‑src CSP directives to Traefik/Nginx restored Harper extension functionality in a self‑hosted VSCode Server, fixing a silent Web Worker creation error.

Problem

Harper grammar checking stopped silently in a self-hosted VSCode Server after a reverse‑proxy CSP change.

Outcome

Adding worker‑src and script‑src CSP directives restored Harper functionality in a self‑hosted VSCode Server.

Workflow

• 1. Observe silent failure of Harper suggestions.
• 2. Verify extension activation, file associations, and language server process.
• 3. Check browser console for CSP errors – see "Refused to create a worker from 'blob:' (CSP violation)".
• 4. Update Traefik dynamic config to include worker‑src and script‑src directives.
• 5. Reload Traefik with SIGHUP and reload code‑server in browser.
• 6. Confirm "[Harper] WASM module loaded successfully" in console and suggestions appear.
• 7. Document CSP changes in runbook for future deployments.

Evidence

Refused to create a worker from 'blob:' (CSP violation)

Source

worker-src 'self' blob:

Source

script-src 'unsafe-eval'

Source