CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

What this is

A collection of Matter commissioning QR decoders (the MT: URI format used by Matter/CHIP devices), plus a standalone bash decoder for Apple HomeKit setup codes (the X-HM:// payload — a different on-wire format, in homekit-decode.sh). For Matter, a user runs matter-decode.sh with an MT: URI (as a positional argument or on stdin); it decodes the 84-bit payload and prints the fields — version, vendor/product IDs, commissioning flow, discovery capabilities, discriminator, passcode, and the derived manual pairing code. Key files:

matter-decode.sh — the pure-bash CLI Matter decoder. Takes an MT: URI as an argument or on stdin and prints the decoded fields. It has no camera/QR-scanning (that was the only feature the former browser app added, and it is gone).
homekit-decode.sh — a standalone pure-bash decoder for Apple HomeKit setup codes (the X-HM:// payload an accessory shows on first setup — a different format from Matter's MT:). No companion TSV (the accessory-category table is inlined). See the HomeKit setup-code decode section below.
manufacturers.tsv — vendor ID → name table (~900 rows), consumed by matter-decode.sh; optional (a missing file only drops the vendor-name lookup).
gen-manufacturers.py — Python 3 stdlib script that regenerates manufacturers.tsv. Default source is the upstream manufacturers.xml fetched over the network (via curl; a GitHub blob/ URL is auto-rewritten to its raw.githubusercontent.com form). A positional arg overrides with another URL or a local XML file. Reproduces the committed TSV byte-for-byte.
products.tsv — 3-column vendor ID → product ID → name table, consumed by matter-decode.sh's get_product_name(): when the decoded vendor ID (or an equivalent, see vendor-equivalents.tsv) is present, the product ID is resolved to a name and printed on the Product ID line. LIFX's rows are keyed under 4870. Optional — a missing file only drops the product-name lookup.
vendor-equivalents.tsv — 2-column alias vendor ID → canonical vendor ID table, hand-edited, recording companies that are the same after a merger/acquisition (e.g. Feit 5155 → LIFX 4870). Used by matter-decode.sh so a product resolves under either ID and the vendor name is annotated (a.k.a. ...). #-comment lines are ignored. Optional.
gen-lifx-products.py — Python 3 stdlib script that regenerates LIFX's rows (vendor 4870) in products.tsv. Default source is LIFX's upstream products.json fetched over the network (via curl, falling back to urllib); a positional arg overrides with another URL or a local .json file. It merges LIFX's rows into products.tsv (dropping LIFX's old rows, preserving every other vendor's), so re-running it is safe alongside other vendors' generators. Caveat: products.json carries only a pid per product (no separate Matter/CHIP product-id field), so the lookup assumes LIFX's Matter product ID equals their pid.
README.md — user-facing docs; this file documents the internals.

Commands

There is no build, test, lint, or package step — this is not a build project. The two decoders are standalone bash scripts and the two gen-*.py are Python 3 stdlib regenerators; nothing is compiled or bundled.

Run the Matter decoder: ./matter-decode.sh "MT:...", or pipe it: echo "MT:..." | ./matter-decode.sh.
Run the HomeKit decoder: ./homekit-decode.sh [code] (with no argument it decodes the demo payload 005KEOUCE).
Regenerate manufacturers.tsv: python3 gen-manufacturers.py pulls the pinned upstream manufacturers.xml over the network; pass a URL or a local .xml file to use a different source.
Regenerate LIFX's products.tsv rows: python3 gen-lifx-products.py (network by default; a positional URL or local .json overrides).
The decoders read their companion TSVs (manufacturers.tsv, products.tsv, vendor-equivalents.tsv) from their own directory; a missing TSV drops that extra lookup — it is never an error.
Pure bash (3.x+); the gen-*.py scripts need only the Python 3 standard library.

Architecture

The decode logic lives directly in the bash scripts — there is no shared library, no embedded data map, and no build output. There are two decoders, and they decode two different on-wire formats, so they are independent and should not be unified.

matter-decode.sh — the Matter `MT:` pipeline

main() decodes a URI given as an argument or read from stdin, in order:

Validate the MT: prefix, then take the base38 payload after it.
Base38-decode it to bytes. The charset is 0-9A-Z-. (38 chars). Chunking is greedy: 5 chars→3 bytes, 4→2, 2→1; a length that doesn't fit those groupings errors. Bytes are extracted little-endian (value & 0xFF, then >>= 8).
Read the 84-bit field layout LSB-first. Fixed field order/widths (see the "Data Encoding Format" table in README.md for the source of truth): version(3), vendor ID(16), product ID(16), custom flow(2), discovery caps(8), discriminator(12), passcode(27).
Display helpers translate the raw numbers: a custom-flow name, discovery capabilities (bit flags: SoftAP / BLE / On IP Network), and decimal + 0x-hex (padded to 4) for the vendor/product IDs.

Vendor / product / equivalence lookups (matter-decode.sh only)

Three optional companion TSVs add names on top of the raw decode; each degrades silently (a missing file drops its extra, never an error):

manufacturers.tsv (vendor ID \t name) — resolves the decoded vendor ID to a name, printed on the Vendor ID line.
products.tsv (vendor ID \t product ID \t name) — resolved via get_product_name VENDOR PRODUCT, which checks the exact vendor first, then every equivalent; first match wins.
vendor-equivalents.tsv (alias \t canonical, # lines ignored, canonical-form: the canonical id never appears in col 1) — resolved via equivalent_vendor_ids VENDOR, which returns the whole equivalence class (the vendor plus every alias sharing its canonical id, sorted). The other class members' names are joined and appended to the Vendor ID line as (a.k.a. X, ...), so a Feit (5155) device reads Feit Electric Company, Inc. (a.k.a. Lifi Labs INC. dba LIFX) and a LIFX (4870) device reads the mirror image.

get_product_name must return 0 on a miss: under set -e, a non-zero status in the pname=$(...) substitution would abort the script before anything prints.

gen-lifx-products.py regenerates LIFX's rows into products.tsv by merging (dropping only vendor 4870's rows, preserving others). To add another vendor, write a sibling gen-<vendor>-products.py that parses that vendor's catalog and merges its rows — keyed under its own vendor ID — into the same products.tsv; then add that vendor's equivalences (if any) to vendor-equivalents.tsv.

Manual pairing code (matter-decode.sh only)

matter-decode.sh also prints a Pairing Code: line: the Matter manual pairing code — the PIN a commissioning app (Apple Home, Google Home, the Matter app) asks you to type. It is not a raw payload field; it is derived from the passcode and discriminator and, for non-standard commissioning flows, the vendor/product IDs, then guarded by a Verhoeff check digit. This is a port of generateManualPairingCode() from the standalone "Matter QR Code Tool" (chill-uk/matter-qr-app, web/app.js).

Two helpers, defined just above main():

verhoeff_check_digit DIGITS — the Verhoeff check digit over a decimal string (the three standard Verhoeff tables are inlined; digits are processed right-to-left, as the reference does).
compute_pairing_code VENDOR PRODUCT FLOW DISCRIMINATOR PASSCODE — assembles the code. The 12-bit discriminator contributes its top 4 bits; the 27-bit passcode is split into its low 14 and high 13 bits; non-standard flows (user-intent 1, custom 2) append 5-digit vendor and product groups. Result: 11 digits for the standard flow, 21 otherwise, plus the check digit.

HomeKit setup-code decode (homekit-decode.sh)

homekit-decode.sh is a second, independent decoder — for Apple HomeKit setup codes, the X-HM:// payload an accessory (or its packaging) shows on first setup. That is a different on-wire format from Matter's MT:, so this is not a port of matter-decode.sh's pipeline; it is standalone, with no companion TSV (the accessory-category table is inlined). It sits alongside matter-decode.sh as the repo's other CLI decoder.

Input is an optional positional argument, defaulting to the demo payload 005KEOUCE. A leading X-HM:// is stripped if present. The first 9 characters are the fixed parameter block; anything after them is a variable-length setup id, carried through verbatim (it is not part of the numeric block).

Unlike Matter's base38 payload (charset 0-9 A-Z - ., 38 symbols), the HomeKit block is base36 (0-9 A-Z, 36 symbols): each char does val = val*36 + digit, and an out-of-range character is a hard error (to stderr, exit 1). val is then sliced LSB-first into the HomeKit layout:

pin(27) | flag(4) | categoryId(8) | reserved(4) | version(3)

flag is a 4-bit sub-flag set — 1=NFC, 2=IP, 4=BLE, 8=WAC/MFi — printed as True/False lines.
categoryId is resolved to its HAP homekit_accessory_category_* name (e.g. 5 → "Lightbulb", 8 → "Switch") via an inlined case; an id not in the table prints "unknown" (id 25 is reserved by HomeKit, so it is unknown by design, and "Heater" corrects a "Header" typo in the source table). A case rather than an associative array is used on purpose so the script runs on the stock macOS bash 3.2 that #!/usr/bin/env bash resolves to.
The decoded fields are packed back into a 9-char block (mirroring composeSetupUri's stepwise packing) and printed as a reconstructed X-HM://… payload, so the output is a complete record the barcode can be rebuilt from.

This is the corrected bit layout — the one composeSetupUri in the homekit-code package actually encodes — rather than a misaligned earlier one. The header comments in homekit-decode.sh record each fix (the categoryId / flag / version positions, and the dropped "Thread" misread of categoryId bits).

Gotchas

matter-decode.sh (Matter MT:, base38) and homekit-decode.sh (HomeKit X-HM://, base36) decode different on-wire formats. Don't try to unify the two decoders; when editing homekit-decode.sh, keep the corrected bit layout (pin / flag / categoryId / reserved / version) as the source of truth.
manufacturers.tsv is the only copy of the vendor map now. Regenerate it with gen-manufacturers.py: the default source is the upstream manufacturers.xml fetched over the network (via curl; a GitHub blob/ URL is auto-rewritten to its raw.githubusercontent.com form), pinned to the same commit the committed TSV was generated from, so it reproduces the TSV byte-for-byte. A positional arg overrides with another URL or a local XML file.
The product-name lookup and vendor equivalences live only in matter-decode.sh — products.tsv and vendor-equivalents.tsv are optional and degrade silently (a missing file means no name / no equivalent, never an error). vendor-equivalents.tsv is canonical-form, one hop: the canonical id must not itself appear in col 1. get_product_name must return 0 on a miss or set -e aborts the decode.

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