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[plugin/cache] create a copy of a response to ensure original res.Msg is never modified#7357

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yongtang merged 1 commit into
coredns:masterfrom
veshij:copy
Jun 6, 2025
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[plugin/cache] create a copy of a response to ensure original res.Msg is never modified#7357
yongtang merged 1 commit into
coredns:masterfrom
veshij:copy

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@veshij

@veshij veshij commented Jun 5, 2025

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1. Why is this pull request needed and what does it do?

cache plugin mutates responses of other plugins:
https://github.com/coredns/coredns/blob/master/plugin/cache/cache.go#L216-L228
The behavior seems to be against the plugin guideline:

Using a custom ResponseWriter, a plugin can mutate a response when another plugin further down the chain writes the response to the client. If a plugin mutates a response it MUST make a copy of the entire response before doing so. A response is a pointer to a dns.Msg and as such you will be manipulating the original response, which could have been generated from a data store.

2. Which issues (if any) are related?

Fixes #7335

3. Which documentation changes (if any) need to be made?

None

4. Does this introduce a backward incompatible change or deprecation?

No

@veshij veshij marked this pull request as ready for review June 5, 2025 21:19
@veshij veshij requested review from chrisohaver and miekg as code owners June 5, 2025 21:19
… never modified

Signed-off-by: Oleg Guba <oleg.guba@gmail.com>
@codecov

codecov Bot commented Jun 6, 2025

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 59.91%. Comparing base (93c57b6) to head (87a41cf).
Report is 1492 commits behind head on master.

Additional details and impacted files
@@            Coverage Diff             @@
##           master    #7357      +/-   ##
==========================================
+ Coverage   55.70%   59.91%   +4.21%     
==========================================
  Files         224      273      +49     
  Lines       10016    17919    +7903     
==========================================
+ Hits         5579    10737    +5158     
- Misses       3978     6559    +2581     
- Partials      459      623     +164     

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@yongtang yongtang merged commit 27273a3 into coredns:master Jun 6, 2025
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Cache plugin mutates state of other plugins

2 participants