Fix incorrect addition of the "Vary: Accept-Encoding" header #173
+98
−1
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
theandrew168
commented
Jan 17, 2026
| // and was chosen instead of the requested file. | ||
| const isChosenFileCompressed = !!data.headers['Content-Encoding']; | ||
| const doesChosenFileMatchRequestedFile = data.abs.endsWith(pathname); | ||
| if (isChosenFileCompressed && !doesChosenFileMatchRequestedFile) { |
Author
There was a problem hiding this comment.
After a second look, !doesChosenFileMatchRequestedFile might alone suffice for this check since choosing a compressed version of a requested file is the only reason they'd differ.
6 tasks
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
1 participant
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Hello there! This PR relates to a downstream bug in SvelteKit. While an in-project fix was found, I think the logic used here in
sirvfor adding the "Vary: Accept-Encoding" header could be improved.Today, the header is always added to the response if either
opts.gziporopts.brotliare enabled. However, for files that don't have an alternative, compressed version to serve, adding this header means that CDNs and Web Caches are unable to safely cache the file.The fix applied by this PR updates the logic to instead ensure that both:
This way, the "Vary: Accept-Encoding" header will not be added for files without compressed version OR for compressed files that are requested directly.