[Webkit-unassigned] [Bug 242910] New: A stopped service worker fails to pass header and referrer on fetch request

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=242910

            Bug ID: 242910
           Summary: A stopped service worker fails to pass header and
                    referrer on fetch request
           Product: WebKit
           Version: Safari 15
          Hardware: All
                OS: All
            Status: NEW
          Severity: Blocker
          Priority: P2
         Component: Service Workers
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: boguinn at etsy.com

As of Safari 15.5/Webkit 613.2.7, when a service worker has just moved from "idle" to "active", any fetch requests it makes will lack custom headers and referrer.

I am able to reproduce this problem consistently via installing this sandbox service worker:

```
self.addEventListener("fetch", (event) => {
    const newRequest = new Request(event.request, {
        headers: { "X-My-Custom-Header": "1" },
    });
    event.respondWith(fetch(newRequest));
});

```

And then checking the contents of the "$_SERVER" variable on my my PHP server (or whatever equivalent you use):

```
    [HTTP_HOST] => <my test server url>
    [HTTP_ACCEPT] => text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
    [HTTP_COOKIE] => <omitted, but looks good>
    [HTTP_USER_AGENT] => Mozilla/5.0 (iPhone; CPU iPhone OS 15_5 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/15.5 Mobile/15E148 Safari/604.1
    [HTTP_ACCEPT_LANGUAGE] => en-US,en;q=0.9
    [HTTP_ACCEPT_ENCODING] => gzip, deflate, br
    [HTTP_CONNECTION] => keep-alive
    [HTTP_REFERER] =>  
```

And you can see that `HTTP_X_MY_CUSTOM_HEADER` is missing.

To reproduce:

1. Install the sandbox service worker I posted above.
2. Load a page and see that the custom header and referrer are sent correctly in a network request.
3. Allow the service worker to go to the idle state. Practically, this looks like closing the test domain's tab and visiting another site for roughly 10 seconds. You can check the `Develop > Service Workers` drop-down menu to see if the service worker has been idled; if it has, it will be missing from this list.
4. Re-visit your test domain and see that the new request is now missing the custom header and referrer.
5. Re-load the page and see that a page request from an active and started service worker always contains the custom header and referrer.

Thanks for your help, and let me know whatever other info you need to debug. This is a blocking bug for Etsy's use of service workers.

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