fix: use base64url encoding to prevent esbuild ?source= corruption#1648
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askoufis merged 4 commits intovanilla-extract-css:masterfrom Dec 7, 2025
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Base64-encoded CSS data in virtual file paths as the source query parameter can contain `/` and `//` characters, which are susceptible to path normalization in bundler plugin systems. While the source parameter should be opaque it is not URL safe and esbuild configurations can collapse `//` → `/`, which corrupts the base64 data preventing compressed source data from being read. Switching to base64url encoding replaces `/` with `_` and `+` with `-`, making the encoded data safe for use in file paths and resilient to this class of error.
🦋 Changeset detectedLatest commit: c461e2b The changes in this PR will be included in the next version bump. This PR includes changesets to release 9 packages
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We encountered this in production using @vanilla-extract/esbuild-plugin with a CSS file where gzip+base64 produced
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askoufis
approved these changes
Dec 7, 2025
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@sallustfire Thanks for the PR! |
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@sallustfire This fix is now available in the latest version of all the bundler plugins. |
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Base64-encoded CSS data in virtual file paths as the source query parameter can contain
/and//characters, which are susceptible to path normalization in bundler plugin systems. While the source parameter should be opaque it is not URL safe and esbuild configurations can collapse//→/, which corrupts the base64 data preventing compressed source data from being read.Switching to base64url encoding replaces
/with_and+with-, making the encoded data safe for use in file paths and resilient to this class of error.