Why do the `cf-ray` headers differ between requests and responses?

Developers Workers
#1

Why do the cf-ray headers differ between the incoming request and outgoing response? ie i have a simple worker:

addEventListener("fetch", event => {
  event.respondWith(new Response(event.request.headers.get('cf-ray')))
})

The body of this response is 6c1e75538d86f009 but its cf-ray header is 6c1e75538d86f009-EWR … ie, the outgoing header has the colo but the incoming header does not… is this a bug? FWIW the preview window in the worker edit console does not have this discrepancy (they both have the colo).

You can see it here: https://cf-ray.jed.workers.dev/

#2

That is the data centre location at the end. In this case near Newark, NJ, US.

#3

The question is why do the headers differ? Why does only the outbound one have the colo?

#4

You can get the colo with another value from the request.
https://developers.cloudflare.com/workers/examples/geolocation-hello-world

Not sure why they do it this way. Personally, I like not having it as I can put it in the logs or pass it along in subrequests without trimming the colo off. :man_shrugging: