CODEWITHSUNDEEP
cloudflarecloudflare-workers
stevehart808
stevehart808

Reputation: 21

Move Fastly config to CloudFlare Workers

How can the following code be re-written to work with the CF Workers feature?

# Start 
if(req.url ~ "^/app" ) { 
set req.url = regsub(req.url, "^/app/", "/"); 
set req.http.X-DR-SUBDIR = "app"; 
} 
#end condition

Upvotes: 2

Views: 484

Answers (1)

Harris Hancock
Harris Hancock

Reputation: 31

Cloudflare Workers implements the Service Worker standard, so you will need to reimplement the VCL code snippet you posted in terms of a Service Worker.

Before I show you how to do that, consider what happens when a request for https://example.com/apple arrives at the proxy. I would expect the first regex for ^/app to match, but the second one for ^/app/ not to match -- i.e., the request would be passed through with no change to the URL, but with the addition of an X-DR-SUBDIR: app header.

I suspect that behavior is a bug, so I'll first implement a worker as if the first regex were ^/app/.

addEventListener("fetch", event => {
  let request = event.request

  // Unlike VCL's req.url, request.url is an absolute URL string,
  // so we need to parse it to find the start of the path. We'll
  // need it as a separate object in order to mutate it, as well.
  let url = new URL(request.url)

  if (url.pathname.startsWith("/app/")) {
    // Rewrite the URL and set the X-DR-SUBDIR header.

    url.pathname = url.pathname.slice("/app".length)

    // Copying the request with `new Request()` serves two purposes:
    //   1. It is the only way to actually change the request's URL.
    //   2. It makes `request.headers` mutable. (The headers property
    //      on the original `event.request` is always immutable, meaning
    //      our call to `request.headers.set()` below would throw.)
    request = new Request(url, request)

    request.headers.set("X-DR-SUBDIR", "app")
  }

  event.respondWith(fetch(request))
})

To revisit the https://example.com/apple case, if we really wanted a Cloudflare Worker which pedantically reproduces the VCL snippet's behavior, we could change these lines (comments elided):

  if (url.pathname.startsWith("/app/")) {
    url.pathname = url.pathname.slice("/app".length)
    // ...
  }

to these:

  if (url.pathname.startsWith("/app")) {
    if (url.pathname.startsWith("/app/")) {
      url.pathname = url.pathname.slice("/app".length)
    }
    // ...
  }

Upvotes: 3

Related Questions