libfreemkv/CLAUDE.md

libfreemkv — Rules

No English in library code

The library contains ZERO user-facing English text. All errors use numeric codes from error.rs. Applications (CLI, GUI, server) handle i18n.

• io::Error::new(kind, "english string") — NEVER. Use Error::VariantName.into().
• If you need a new error, add a variant to error.rs with a code, not a string.
• Acceptable strings: debug/trace logging, test assertions, comments, data format strings (paths, codec IDs).
• Error implements From<Error> for io::Error — use ? or .into() anywhere an io::Error is expected.

Architecture

• Streams are PES. Every stream reads its format → PES frames out, or PES frames in → writes its format. One type per format.
• Disc::copy() for sector dumps. disc→ISO is NOT a stream. It's Disc::copy().
• DiscStream = any disc. Physical drive or ISO file. Same type, different SectorReader.
• No IOStream. Deleted. No byte-level Read/Write on streams.
• Streams don't know their size. Progress/file_size is a CLI concern.
• One method per action. No foo_with_X variants. Use Option<T> params.
• Streams impl Read only (conceptually). No Seek, no File backing.
• Functions return errors, only main() exits. No process::exit in library code.

Device rules

• Always use /dev/sg* not /dev/sr* for SCSI.
• --raw only skips decryption. Init/probe/speed still run.
• Each function does one thing. One runner orchestrates the sequence.

macOS IOKit transport

The macOS SCSI transport uses exclusive IOKit access, not hybrid MMC+pread.

• C shim (src/scsi/macos_shim.c): diskutil unmountDisk force → find IOBDServices via IOServiceMatching → MMCDeviceInterface → SCSITaskDeviceInterface → ObtainExclusiveAccess → raw CDB dispatch via CreateSCSITask + ExecuteTaskSync.
• Build (build.rs): compiles shim via cc into static lib, linked by Cargo. NOT the cc crate (produces object code that breaks IOKit exclusive access).
• Rust (src/scsi/macos.rs): three FFI calls (shim_open_exclusive, shim_close, shim_execute). All CDBs go through single path — 1:1 with Linux SG_IO.
• Key: must find IOBDServices directly (not walk up from IOMedia). Must unmount before exclusive access. Must release service immediately after creating plugin.
• IOBDServices parent chain: IOMedia → IOBDBlockStorageDriver → IOBDServices → IOSCSIPeripheralDeviceType05. The block storage driver holds exclusive unless unmounted.
• Test disc: DUNE_PART_TWO UHD, /dev/disk6, 41288704 sectors.

Bad-sector handling (BU40N + Initio INIC-1618L)

Three failure modes on this USB bridge:

1. NOT READY (sense_key=2, ASC=0x04, ASCQ=0x3E) — most common on BU40N for bad sectors. Pause 3s, retry up to 3x, then mark NonTrimmed.
2. Transport failure (status=0xFF) — bridge crash, auto-recovers ~15s. Aborts copy.
3. INCOMPATIBLE FORMAT (ASC=0x30) wedge — ALL sectors fail, requires power cycle.

Damage-jump algorithm (Pass 1 sweep)

When skip_on_error=true (multipass mode):

• Read each ECC block sequentially. Track a sliding window of the last 50 ECC block results.
• On error: zero-fill, mark NonTrimmed, push false to window.
• On success: write data, mark Finished, push true to window. Track consecutive good count.
• When ≥25% of the 50-block window are failures → jump ahead by 256×batch×multiplier sectors (8 MB base). Zero-fill the gap as NonTrimmed. Double the multiplier (8→16→32→64 MB...).
• When 50 consecutive good reads → reset multiplier to 1.
• Only transport failures (bridge crash) abort the pass.

Two tuning knobs: DAMAGE_WINDOW (50 ECC blocks) and DAMAGE_THRESHOLD_PCT (25%). If the jump is too aggressive or too timid, adjust these.

Public repo rules

• No internal docs. Audit reports, test plans, roadmaps, TODOs go in freemkv-private, never here.
• No Co-Authored-By in commit messages. One contributor: MattJackson.
• No private references. No Gitea URLs, no /data/code paths, no internal IPs in code.