Use the original URL when requests are forwarded

[jorgelbg]

When the request is forwarded to the edge worker instead of running as a transparent proxy (via the routes) the original URL gets lost. This PR defines a new custom header x-original-url for passing the original URL around. If the request is forwarded and the header is found it will be used to extract the domain, path, query for the logging of the visit.

Since the new request should be initialized using the original request, all headers should be passed down to the edge worker, so the referer parsing should still continue to work and not be lost in the process. The new header needs to be manually added to the outgoing request:

let req = new Request('https://dashflare.test.workers.dev', origReq);
req.headers.append('x-original-url', origReq.url)

This is especially relevant for integrations with Cloudflare's Worker Sites because it is not possible to set multiple workers on the same route.

FYI @mre

[mre]

wait a sec, so request.headers.get returns false if the header doesn't exist? If so, why not only use url = request.headers.get('x-original-url') || request.url and skip the if (request.headers.get('x-original-url') != null) { line altogether? Only in the case where x-original-url is set will it be overwritten. Or am I misunderstanding the logic here?

[jorgelbg]

request.headers.get('x-original-url') returns null|string but it can be used in this short or syntax. In any case I can definitively move the url initialization up like you mentioned:

let url = request.headers.get('x-original-url') || request.url

but we still need the conditional for creating the new Response instance. On the plus side it makes easier the code.