compress: add Vary to cached client responses - #13580
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Pull request overview
This PR updates the compress plugin to avoid attempting to mutate cached response headers (which can be read-only in some upgrade/cached-object scenarios) and instead ensures Vary: Accept-Encoding is present on the client response when serving a cached, compressible object. It also adds a gold test to exercise the cached-object path and assert the plugin no longer logs errors while producing the expected headers/body.
Changes:
- Adjust
compressplugin flow soVary: Accept-Encodingis added to origin responses before caching, and (for cached hits) added atTS_HTTP_SEND_RESPONSE_HDR_HOOKto the client response. - Add a new gold test that seeds cache without the plugin, then verifies cached delivery through the plugin adds
Vary: Accept-EncodingwithoutContent-Encodingwhen the client omitsAccept-Encoding.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
plugins/compress/compress.cc |
Adds a client-response Vary update path for cached hits via TS_HTTP_SEND_RESPONSE_HDR_HOOK, while keeping origin-response Vary insertion for cacheable origin responses. |
tests/gold_tests/pluginTest/compress/compress-vary-cached-response.test.py |
New regression test covering cached-hit behavior and verifying both headers and body while asserting no mutation-error logs occur. |
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serrislew
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Aug 25, 2026
serrislew
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Aug 25, 2026
serrislew
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Aug 25, 2026
cmcfarlen
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Aug 25, 2026
* compress: add Vary to cached client responses * rename function to add_vary_header_to_server_response (cherry picked from commit 4676308)
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Related to Vary header for compressible content (#12741).
If a compressible cached object did not have the vary header (like after an ATS upgrade from 10.0.x to 10.1.x), the plugin gets read only access to the cached header and tries to add the Vary header. This triggers errors in the logs for every matching request and doesn't add the Vary header to a client response.
With this fix the Vary header is added at the client response header hook if it does not already exist in the client response.