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-rw-r--r--src/liblzma/common/stream_decoder_mt.c26
1 files changed, 24 insertions, 2 deletions
diff --git a/src/liblzma/common/stream_decoder_mt.c b/src/liblzma/common/stream_decoder_mt.c
index 47433de8..7f445982 100644
--- a/src/liblzma/common/stream_decoder_mt.c
+++ b/src/liblzma/common/stream_decoder_mt.c
@@ -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)