Prevent 256-bytes compression windows, unsupported by zlib. - #1768
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🟡 Changes recommended
Tests must verify that valid 8-bit decompressor negotiation remains accepted.
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What changed in this PR
Prevents unsupported 8-bit zlib compression windows while retaining 8-bit decompression support.
Changes:
- Validates local compression windows as 9–15.
- Rejects negotiated 8-bit local compressor windows.
- Adds regression tests and a changelog entry.
| File | Description |
|---|---|
src/websockets/extensions/permessage_deflate.py |
Adds validation and negotiation guards. |
tests/extensions/test_permessage_deflate.py |
Tests 8-bit rejection paths. |
docs/project/changelog.rst |
Documents the improvement. |
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* When initializing the extension, reject window bits = 8 for the local compressor. * When negotiating the extension, reject if the other side attempts to limit the local compressor to window bits = 8. * Confirm that a remote compressor limited to window bits = 8 is still supported. This avoids zlib.compressobj(wbits=-8), which raises ValueError due to madler/zlib#171. Fix #1757.
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for the local compressor.
sets a limit to window bits = 8
This avoids zlib.compressobj(wbits=-8), which raises ValueError
due to madler/zlib#171.
Fix #1757.