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Add missing autoreset in Packer.pack_ext_type#663
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methane merged 3 commits intoJun 1, 2026
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pack_ext_type writes to the internal buffer but never checks self._autoreset, unlike every other public pack method. This means it always returns None and the packed data leaks into the output of the next pack() call, corrupting the serialized stream. Add the same autoreset pattern used by pack(), pack_map_pairs(), pack_array_header(), and pack_map_header().
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Pull request overview
This PR addresses a long-standing behavior mismatch in Packer.pack_ext_type() where the pure-Python fallback implementation writes to the internal buffer but doesn’t honor self._autoreset, causing pack_ext_type() to return None and potentially corrupt subsequent packed output.
Changes:
- Add autoreset handling to
msgpack/fallback.py:Packer.pack_ext_type()so it returns bytes and clears the internal buffer whenself._autoresetis enabled.
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methane
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methane
merged commit 284782d
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msgpack:main
Jun 1, 2026
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Packer.pack_ext_type()writes to the internal buffer but never checksself._autoreset. Every other public pack method (pack,pack_map_pairs,pack_array_header,pack_map_header) has this pattern:Without it,
pack_ext_type()always returnsNone, and the packed ext data stays in the buffer. The next call topack()then returns both the extension data and the new value concatenated together, corrupting the serialized stream.