build: support decoding legacy zstd formats v0.4-v0.7#73
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Add -DZSTD_LEGACY_SUPPORT=4 and the four legacy decoders it pulls in
(zstd_v04.c-zstd_v07.c), matching what zstd-jni ships by default.
v0.1-v0.3 stay off — those predate zstd's 1.0 stabilization and are
essentially never seen in the wild.
Verified with real legacy-format data, not just "still links": the
vendored third_party/zstd/tests/legacy.c embeds a 917-byte fixture of
five concatenated frames (magic numbers 0xFD2FB524-0xFD2FB528 - v0.4
through v0.7 plus a current-format frame), each encoding the same
haiku text. Extracted it and round-tripped through a small harness
linked against the built library:
- built without this change: "Unknown frame descriptor" (fails, as
expected - this is the control)
- built with this change: decompresses all five frames correctly,
byte-for-byte matching the expected text
deprecated/ (the old ZBUFF_* streaming wrapper) stays excluded -
unrelated to legacy decoding, superseded by ZSTD_CCtx streaming.
All six classifiers cross-compile cleanly; local unit + integration
tests pass on osx-aarch64.
Ref #70
This was referenced Jul 17, 2026
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Jul 18, 2026
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Summary
Last unchecked item from #70's checklist:
DZSTD_LEGACY_SUPPORT=4 like zstd-jni.-DZSTD_LEGACY_SUPPORT=4plus the four legacy decoders it requires (zstd_v04.c-zstd_v07.c), matching zstd-jni's default. v0.1-v0.3 stay off — those predate zstd's 1.0 stabilization and are essentially never encountered in practice.deprecated/(the oldZBUFF_*streaming wrapper) stays excluded — unrelated to legacy decoding, superseded byZSTD_CCtxstreaming.Verified with real legacy-format data, not just "still links":
third_party/zstd/tests/legacy.c(vendored, part of zstd's own test suite) embeds a 917-byte fixture — five concatenated frames with magic numbers0xFD2FB524-0xFD2FB528(v0.4 through v0.7, plus a current-format frame), each encoding the same haiku text. I extracted it and round-tripped it through a small harness linked against the built library:ZSTD_decompressfails withUnknown frame descriptor(control case, confirms the fixture actually exercises legacy decoding)Test plan
./mvnw -q validate(checkstyle) clean./mvnw -q -pl zstd,integration-tests -am testpasses on osx-aarch64 (no regression to current-format decode)osx-aarch64,osx-x86_64,linux-x86_64,linux-aarch64,windows-x86_64,windows-aarch64) cross-compile cleanly🤖 Generated with Claude Code