[issue21872] LZMA library sometimes fails to decompress a file

[Ma Lin]

Ma Lin <malincns at 163.com> added the comment:

Some memos:

1, In liblzma, these missing bytes were copied inside `dict_repeat` function:

 788         case SEQ_COPY:
 789                 // Repeat len bytes from distance of rep0.
 790                 if (unlikely(dict_repeat(&dict, rep0, &len))) {

See liblzma's source code (xz-5.2 branch):
https://git.tukaani.org/?p=xz.git;a=blob;f=src/liblzma/lzma/lzma_decoder.c

2, Above replies said xz's command line tools can extract the problematic files successfully.

This is because xz checks `if (avail_out == 0)` first, then checks `if (avail_in == 0)`
See `uncompress` function in this source code (xz-5.2 branch):
https://git.tukaani.org/?p=xz.git;a=blob;f=src/xzdec/xzdec.c;hb=refs/heads/v5.2

This check order just avoids the problem.

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue21872>
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