Working on the D2R Parser

The parser lives in plugins/d2r/d2s/. It's a WASM plugin that reads .d2s binary save files and emits ndjson to stdout. See docs/plugins.md for the plugin contract and working-on-plugins skill for section design guidance.

Verification

cd plugins/d2r && just test      # D2R-specific tests
just test-go                      # Full Go test suite
just lint-go                      # Includes D2R with relaxed lint rules

D2R v105 (Reign of the Warlock) Specifics

This parser targets v105 only (version byte 0x69). Classic LoD saves are not supported.

Expansion detection: v105+ saves do NOT set the LoD status bit (0x20) in the header. You must check header.Realm >= RealmLoD to gate mercenary and golem parsing. This is a common trap — the LoD bit check works for older saves but silently misparses v105.

Warlock class: Class index 7. Skill offset is 373 (not 281 — those are monster skills). Skills.txt extracted via CASC.

Item codes: Huffman-encoded in D2R (not ASCII like LoD). The Huffman tree is in d2s/huffman.go.

ISC (ItemStatCost): RotW ISC is IDENTICAL to vanilla D2R — zero property bit width changes. RotW added properties 365 (sB=6) and 366 (sB=8), plus items not in vanilla tables.

Lint Exceptions

golangci-lint config has exclusions for plugins/d2r/:

• govet/shadow (binary parsing has lots of shadowed err)
• globals (lookup tables are package-level)
• complexity (binary parsing functions are inherently complex)
• magic numbers (byte offsets, bit widths)

These exclusions are intentional. Don't try to "fix" them.

Test Data

• Primary test save: reference/Diablo II Resurrected/Atmus.d2s — Level 74 Warlock, 45 items + 3 merc items.
• Reference implementation: reference/olegbl-d2rmm/.../d2s/d2/items.ts — readItem() function.

CASC Data

Game data tables are extracted from the D2R CASC archive:

• Archive: reference/d2r-casc/ (gitignored, must copy locally)
• Extracted tables: reference/d2r-rotw-excel/ (gitignored — Blizzard IP, NEVER check in)
• Extract tool: plugins/d2r/tools/casc-extract/ (uses CascLib, cloned at build time)
• Plugin devenv.nix adds cmake/gcc/zlib for building the extract tool

cd plugins/d2r
just build-casc-extract
just casc-extract "data/global/excel/Skills.txt"

Shared Stash

.d2i files (e.g. ModernSharedStashSoftCoreV2.d2i) — multi-section format with 64-byte headers per tab, same item format as d2s. Not yet implemented.

Architecture

One plugin per game. The plugin detects save version internally. Only v105 for now.

plugins/d2r/
├── d2s/           # Parser source (header, attributes, skills, items, merc, corpse, golem)
├── parser/        # WASM entrypoint (main.go → stdin bytes → ndjson stdout)
├── data/          # Shared lookup tables (items, runewords, treasure classes)
├── tools/         # casc-extract tool
└── plugin.toml    # Plugin metadata