Fall back to level-1 compressor for unsupported compression levels - #255
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rootkiller6788 wants to merge 1 commit into
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Fall back to level-1 compressor for unsupported compression levels#255rootkiller6788 wants to merge 1 commit into
rootkiller6788 wants to merge 1 commit into
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CompressionOptions accepts any compression level, but InternalCompress only handles levels 1 and 2. For any other level the `end` pointer was left nullptr, so `end - dest` was undefined behaviour and the resulting write length was garbage, which crashed or corrupted the compressed output. Treat every unsupported level as level 1 instead, and add a regression test that verifies unsupported levels produce the level-1 output and round-trip correctly.
rootkiller6788
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August 26, 2026 15:10
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What
CompressionOptionsis constructible with anyintcompression level, andsnappy.ccdocuments levels 3+ as "currently not supported" rather than rejecting them. InInternalCompress, the level dispatch only setendfor levels 1 and 2; for any other levelendstayednullptr, andwriter->Append(dest, end - dest)then computed a garbage length from undefined behaviour. The string-basedCompress()path would throwstd::out_of_rangefromstd::string::erase, and the raw path wrote through a wild pointer.This only manifests with levels outside
[1, 2], so the fuzzers (which iterate levels 1..2) never hit it.Fix
Treat every level other than 2 as the default (level 1) compressor instead of leaving
enduninitialized. The existingassert(options.level == 1 || options.level == 2)was relaxed toassert(options.level >= 1)to match the new tolerant dispatch.Test
Added
Snappy.UnsupportedCompressionLevels, which compresses with levels 3..9, asserts the output matches the level-1 baseline, and round-trips throughUncompress. Full suite passes in Debug and Release (25/25).