Repository navigation
Node adapter sends Vary: Accept-Encoding even when not applicable #10343
Description
Activity
We don't set that header anywhere, which makes me think this is either from
polkaor sth else.We don't set that header anywhere, which makes me think this is either from polka or sth else
Ah okay, then yeah I guess probably. Either way I'd say this should be considered a bug.
It looks like this header is actually being added by sirv (behavior added in this PR). SvelteKit utilizes sirv with both
gzipandbrotliunconditionally enabled here. Looking at sirv's code, it looks like this header is added whengzipand / orbrotlicompression is generally enabled without also checking if a corresponding compressed file actually exists.I see two potential solutions (though I'm unsure which would be better / more correct):
- Only pass
gzip: trueandbrotli: trueto sirv whenprecompress: trueis set- This might cast too wide of a net and unintentionally impact other aspects of
adapter-nodethat utilize asset compression
- This might cast too wide of a net and unintentionally impact other aspects of
- Fix sirv to only add
Vary: Accept-Encodingwhen a compressed version of the requested file is present- This seems like the "more correct" approach to me (it'd also solve this for any other users of sirv)
If a best approach can be agreed upon, I have the capacity to make either fix.
- Only pass
Hi Andrew. I think both are correct based on the docs https://github.com/lukeed/sirv/tree/main/packages/sirv#optsgzip it says that the options should only be enabled for precompressed assets. So we should disable these if precompress is false.
It also says that it looks for .gzip files but I don’t think it’s doing that at the moment.
Feel free to submit a PR for both options! The Kit one might be easier to get done first
Reacted by Andrew Dailey- added a commit that references this issue
on Jul 30, 2026
Describe the bug
The Node adapter currently sends back the
Vary: Accept-Encodingheader as part of the response (when files under/_applike.jsand.cssfiles are requested) even when theprecompressconfiguration option isfalse; meaning even when the response won't vary based on theAccept-Encodingheader of the request, which is whatVary: Accept-Encodingis supposed to indicate.In summary,
adapter-nodeshould not includeVary: Accept-Encodingin the response ifprecompress: false.Reproduction
Just build a SvelteKit Demo App with
adapter-nodeand send a request usingcurl -ito some CSS/JS file, and examine the response headers.Logs
No response
System Info
Severity
annoyance
Additional Information
No response