WI-144: in-flight PAR2 slice verifier core (nzb-decode) - #144
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Add the computational core of in-flight PAR2 verification: a slice verifier that turns article writes into a per-slice Verified / Damaged / Unknown map, so a clean job can skip the post-download verify pass (WI-147) and damage can be weighed against recovery blocks during the download (WI-145). Articles land out of order at arbitrary offsets, and MD5 is not associative, so a slice cannot be hashed incrementally. Instead each slice tracks how many of its bytes are filled; once its range is complete the caller reads it back (page-cache-hot) and calls verify(), which zero-pads the final partial slice to the slice size — matching PAR2 IFSC — and compares MD5 and CRC32. The verifier holds only plain PAR2 geometry (SliceLayout), so nzb-decode gains no PAR2-parser dependency; the download engine will build the layout from a parsed rust-par2 file set and the NZB-file mapping when it is wired in (follow-up). Adds md-5 alongside the existing crc32fast. Six-path unit coverage: in-order writes, an article spanning two slices with out-of-order fill, corruption -> Damaged, partial fill stays Unknown, and direct mark_damaged. Full nzb-decode suite 35 passed; fmt and clippy -D warnings clean. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01TpoFnScdkRq7qxQLQZe1we
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The computational core of in-flight PAR2 verification (Vogt WI-144). Rebased onto main after the WI-143 ledger (#140) landed — this diff is only the slice verifier. (Supersedes #141, which GitHub auto-closed when its stacked base branch was deleted on #140's merge.)
What
SliceVerifierincrates/nzb-decode/src/slice_map.rsturns article writes into a per-sliceVerified/Damaged/Unknownmap, so a clean job can skip the post-download verify pass (WI-147) and damage can be weighed against recovery blocks during the download (WI-145).Articles land out of order at arbitrary offsets, and MD5 is not associative, so a slice can't be hashed from fragments. The verifier tracks per-slice filled bytes; once a slice's range is complete the caller reads it back (page-cache-hot) and calls
verify(), which zero-pads the final partial slice toslice_size(matching PAR2 IFSC) and compares MD5 + CRC32.Dependency-light: holds only plain geometry (
SliceLayout), so nzb-decode gains no PAR2-parser dependency — onlymd-5. The download engine builds the layout from a parsed rust-par2 file set when wired in (follow-up).Tests
5 deterministic unit tests (in-order, article spanning two slices out-of-order, corruption → Damaged, partial fill stays Unknown, mark_damaged). Full nzb-decode suite 35 passed; fmt + clippy -D warnings clean; additive public surface.
Its fixture counterpart (IFSC slice checksums) is #143.
🤖 Generated with Claude Code
https://claude.ai/code/session_01TpoFnScdkRq7qxQLQZe1we