Fix incorrect addition of the "Vary: Accept-Encoding" header#173
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theandrew168 wants to merge 4 commits intolukeed:mainfrom
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Fix incorrect addition of the "Vary: Accept-Encoding" header#173theandrew168 wants to merge 4 commits intolukeed:mainfrom
theandrew168 wants to merge 4 commits intolukeed:mainfrom
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theandrew168
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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) { |
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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.
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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.