Ignore Cloudflare Priority header

[gusdleon]

Refine handling of HTTP Priority header

Part of: #351, #353, #461, ...

This PR improves the handling of the new HTTP Priority header (RFC 9218) commonly affecting ntfy instances running behind Cloudflare.

Changes:

• Now if the received PUT/POST request contains the mentioned header simply ignores it and continues searching for another header or query parameter
• This PR reverts some changes in 95bd876

A working instance with this fix can be tested Here
😀

[danricho]

+1 for this as it would enable me to use NTFY with Uptime Kuma behind cloudflare. It inherently sets the priority of alerts which don’t come through on iOS properly.

[binwiederhier]

This function is used not just by the priority, but also by other headers. So one could not use a notification title u=hello anymore. Why not keep this logic only in the parsePrio function like it was before?

[gusdleon]

Sorry sorry sorry 🤯
Sorry for the error, I was so focussed trying to solve specifically the problem with the CF priority header that I didn't think about the possibility of another header having a value starting with u=, even knowing this function is used with with all headers.

Why not keep this logic only in the parsePrio function like it was before?

You mean this?

ntfy/util/util.go

Lines 163 to 170 in 2305ebc

	default:
	// Ignore new HTTP Priority header (see https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-priority)
	// Cloudflare adds this to requests when forwarding to the backend (ntfy), so we just ignore it.
	if strings.HasPrefix(p, "u=") {
	return 3, nil
	}
	return 0, errInvalidPriority
	}

Well, if you're referring to that part of the code, it's because at that point of execution, we have already parsed the headers and query parameters. If we find any priority header (priority, x-priority, prio, p), the others will not even be read, including the query parameters.

For instance, if a user is using the web interface to send a notification with priority 5, the request will include a query string like this:
?title=titulodeprueba&priority=5

If we send the request directly to the server, all will be ok, it will work, but if the server is behind CF, it will (in the majority of cases) have the priority:"u=*" header, causing the priority set in the query parameter to be ignored.

Nevertheless, I am fixing this issue in my next commit.
Thank you for all your comments.
😉

[binwiederhier]

Refined and merged in #895 - Sorry it took so long. Thank you for fixing this!