Trace correlation (client ↔ server)

Hakka can link the hops of one logical request — a browser fetch, the server route that handled it, and the upstream calls that route made — under a shared correlationId, so the overlay shows the full stack of one request in a single trace.

How it works

1. Client originates. With trace enabled, the browser generates a trace id and sends it on the x-hakka-trace header for same-origin requests (plus any origins you allow). The client record is tagged with that id.
2. Server inherits. hakka-node/next reads the incoming header into a Node AsyncLocalStorage context (by hooking http.Server’s request emit — the APM-standard technique). The route handler and every fetch/http call it makes during that request inherit the same id.
3. Forwarded onward. Server-side upstream calls re-send the header, so multi-hop traces (service → service) keep linking.

The shared correlationId flows over the dev bridge into the same store the overlay reads — no extra wiring, no proxy.

Enable it

Client — opt in when you start the overlay (off by default so the header never leaks):

import { start } from 'hakka-browser'

start({
  trace: true, // same-origin only
  // or: trace: { propagateOrigins: ['https://api.example.com'] }
})

Server — hakka-node/next turns it on automatically; the standard one-liner is all you need:

instrumentation.ts

export { register } from 'hakka-node/next'

See the trace

In the overlay’s Network panel, set Group by → Trace. Each trace becomes a group containing its client and server hops (server rows carry a SERVER/EDGE runtime badge); everything else falls under No trace. A request’s Detail → Overview shows its Trace id.

Scope

• Node runtime. Correlation uses Node AsyncLocalStorage + the http.Server hook. The Edge runtime has no node http server, so edge route work isn’t linked (the client and any Node hops still are).
• Opt-in header. The x-hakka-trace header is only sent when you enable trace, and only same-origin unless you allowlist an origin — it won’t leak the id to third parties.
• The id is a debug correlation token, not a security/auth identifier.