WI-144: in-flight PAR2 slice verifier core (nzb-decode) - #141
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WI-144: in-flight PAR2 slice verifier core (nzb-decode)#141thedancingdeveloper wants to merge 1 commit into
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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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Second code payload of the parity-in-flight initiative (Vogt WI-144). Stacked on #140 (WI-143) — base is
feat/wi-143-damage-ledger, so this diff is only the slice verifier. Retarget tomainonce #140 merges.What
The computational core of in-flight PAR2 verification:
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).Why not incremental hashing: articles land out of order at arbitrary offsets, and MD5 is not associative — 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: the verifier holds only plain geometry (
SliceLayout= slice_size + per-file size + IFSC digests), so nzb-decode gains no PAR2-parser dependency — onlymd-5(crc32fast was already present). The download engine will build the layout from a parsed rust-par2 file set when it's wired in (follow-up).API:
new/mark_written(→ completed global indices) /slice_range/verify/mark_damaged/states/damaged_count/total_slices/is_complete.Tests
5 deterministic unit tests: in-order writes, an article spanning two slices with out-of-order fill, corruption → Damaged, partial fill stays Unknown, direct mark_damaged. Full nzb-decode suite 35 passed.
cargo fmt --check+cargo clippy -D warningsclean. Additive public surface.Notable finding
rust-par2 0.1.3 (the pinned version) already exposes what WI-144 needs —
parse_par2_reader,Par2FileSet.slice_size/file_order/recovery_block_count, and per-filePar2File.slices: Vec<SliceChecksum{md5,crc32}>. So WI-144 does not need the unpublished rust-par2 0.2 (WI-152/153) first.Follow-up (WI-144 integration, not in this PR)
Download-engine PAR2-index parse + layout build, the 16 KiB MD5 file-matcher move (nzbdav-pipeline → nzb-core), the assembler hook (
mark_written/verify), emitting the slice map to WI-145/147, and benchnzb. Needs WI-151 generated PAR2 fixtures for the end-to-end "agrees with rust-par2 verify" acceptance.🤖 Generated with Claude Code
https://claude.ai/code/session_01TpoFnScdkRq7qxQLQZe1we