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decompress: ZSTD_getDictID_fromFrame() returns 0 for skippable frames #4894

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decompress: ZSTD_getDictID_fromFrame() returns 0 for skippable frames #4894

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2 changes: 2 additions & 0 deletions lib/decompress/zstd_decompress.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1645,6 +1645,8 @@ unsigned ZSTD_getDictID_fromFrame(const void* src, size_t srcSize)
ZSTD_FrameHeader zfp = { 0, 0, 0, ZSTD_frame, 0, 0, 0, 0, 0 };
size_t const hError = ZSTD_getFrameHeader(&zfp, src, srcSize);
if (ZSTD_isError(hError)) return 0;
/* for skippable frames, dictID holds the magic variant : no dictionary is required */
if (zfp.frameType == ZSTD_skippableFrame) return 0;
return zfp.dictID;
}

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12 changes: 12 additions & 0 deletions tests/fuzzer.c
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Expand Up @@ -2814,6 +2814,18 @@ static int basicUnitTests(U32 const seed, double compressibility)
}
DISPLAYLEVEL(3, "OK \n");

DISPLAYLEVEL(3, "test%3i : skippable frames don't require a dictionary : ", testNb++);
{ unsigned magicVariant;
for (magicVariant = 0; magicVariant < 16; magicVariant++) {
size_t const skippableSize = ZSTD_writeSkippableFrame(
compressedBuffer, compressedBufferSize,
CNBuffer, 10, magicVariant);
CHECK_Z(skippableSize);
CHECK_EQ(0, ZSTD_getDictID_fromFrame(compressedBuffer, skippableSize));
}
}
DISPLAYLEVEL(3, "OK \n");

/* Dictionary and CCtx Duplication tests */
{ ZSTD_CCtx* const ctxOrig = ZSTD_createCCtx();
ZSTD_CCtx* const ctxDuplicated = ZSTD_createCCtx();
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