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liblzma: Threaded decoder: Always wait for output if LZMA_FINISH is used.

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This makes the behavior consistent with the single-threaded
decoder when handling truncated .xz files.

Thanks to Jia Tan for finding this issue.
This commit is contained in:
Lasse Collin 2022-04-05 12:24:57 +03:00
parent e671bc8828
commit 64b6d496dc
1 changed files with 24 additions and 2 deletions
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26
src/liblzma/common/stream_decoder_mt.c
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@ -1000,8 +1000,30 @@ stream_decode_mt(void *coder_ptr, const lzma_allocator *allocator,
// if they assume that output-not-full implies that all input has
// been consumed. If and only if timeout is enabled, we may return
// when output isn't full *and* not all input has been consumed.
const bool waiting_allowed = *in_pos == in_size
&& !coder->out_was_filled;
//
// However, if LZMA_FINISH is used, the above is ignored and we always
// wait (timeout can still cause us to return) because we know that
// we won't get any more input. This matters if the input file is
// truncated and we are doing single-shot decoding, that is,
// timeout = 0 and LZMA_FINISH is used on the first call to
// lzma_code() and the output buffer is known to be big enough
// to hold all uncompressed data:
//
// - If LZMA_FINISH wasn't handled specially, we could return
// LZMA_OK before providing all output that is possible with the
// truncated input. The rest would be available if lzma_code() was
// called again but then it's not single-shot decoding anymore.
//
// - By handling LZMA_FINISH specially here, the first call will
// produce all the output, matching the behavior of the
// single-threaded decoder.
//
// So it's a very specific corner case but also easy to avoid. Note
// that this special handling of LZMA_FINISH has no effect for
// single-shot decoding when the input file is valid (not truncated);
// premature LZMA_OK wouldn't be possible as long as timeout = 0.
const bool waiting_allowed = action == LZMA_FINISH
|| (*in_pos == in_size && !coder->out_was_filled);
coder->out_was_filled = false;
while (true)