Update cache headers to include max-age and immutable#12420
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sfc-gh-gwatters merged 3 commits intodevelopfrom Sep 4, 2025
Merged
Update cache headers to include max-age and immutable#12420sfc-gh-gwatters merged 3 commits intodevelopfrom
max-age and immutable#12420sfc-gh-gwatters merged 3 commits intodevelopfrom
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Pull Request Overview
This PR updates cache headers for static assets to include explicit max-age and immutable directives instead of relying on browser heuristic caching. The change addresses the issue where browsers use unpredictable heuristic caching (typically 10% of time since Last-Modified) for assets without explicit cache duration, which can result in very short cache times for recently deployed files.
- Updates cache control headers to use explicit one-year max-age for hashed static assets
- Adds
immutabledirective to indicate cached assets won't change - Maintains no-cache behavior for HTML files and manifest.json files
Reviewed Changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| lib/streamlit/web/server/routes.py | Updates StaticFileHandler to set explicit cache headers with max-age and immutable for hashed assets |
| lib/tests/streamlit/web/server/routes_test.py | Adds comprehensive test coverage for the new cache control header behavior |
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Describe your changes
Without
max-agedefined in the cache header, browsers fallback to use a heuristic caching strategy which is typically (Chrome)10% of the time since the "Last Modified" header (see https://datatracker.ietf.org/doc/html/rfc7234#section-4.2.2). Firefox caps this at a week. Since the files being served all contain a hash, the actual cache duration can be much much longer.For environments where the static files get written at deployment or startup time, the heuristic cache can be on the order of minutes/hours.
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By submitting this pull request you agree that all contributions to this project are made under the Apache 2.0 license.