Replace the stub scanner with the real incremental algorithm:
- discover: page get_unspent_outputs (with proofs) from the cursor to
the tip, rewind each new output against caught-up accounts, store
matches with their derivation path + a derived lock_height (coinbase
maturity = 1440)
- spend reconcile: mark any stored-unspent commit the node no longer
lists (grin has no per-block inputs; spends = absence from the set)
- reorg: detect via header-hash mismatch at the checkpoint height,
roll back a bounded depth, reseek from the fork
- backfill: bring a newly-registered account up from its birthday index
- cursor only advances after discover AND reconcile succeed
DB: chain_cursor gains output_mmr_index (tip height/hash become the
reorg checkpoint); new helpers (list_accounts, all_unspent_commits,
mark_unspent, account_unlocked_totals, scan-height advance/clamp).
Read path: get_balance adds `unlocked` (spendable-now) and
get_unspent_outs flags per-output `spendable`, so immature coinbase /
locked outputs are never presented as spendable.
Grin scans by PMMR output index, not block-by-block, so replace the
block-based stubs with the actual Foreign-API-v2 surface:
- get_unspent_outputs(start,end,max, include_proof=true): page the UTXO
set WITH rangeproofs (the discovery call the scanner rewinds)
- get_outputs(commits): spend detection by absence from the unspent set
- get_pmmr_indices(height): birthday height -> start index for backfill
- get_header(height) + get_tip(): reorg detection + tip hash
- push_transaction: fix the {"Ok":null} success case (the generic rpc
helper mis-read null as an error) via a null-tolerant rpc_ok_unit
- delete get_block/BlockView (grin's get_block returns no proofs)
- reshape ChainOutput to the UTXO-listing fields; permissive,
version-tolerant deserialization; per-output decode failures skip.
Tests for the node JSON parsing + spent/proofless filtering.
Replace the rewind_output stub with a real, view-only implementation:
- src/rewind.rs: derive the v3 rewind nonce (keyed BLAKE2b over the
commitment) and rewind the Bulletproof via upstream grin_secp256k1zkp,
then parse the 20-byte proof message into the authoritative key_id +
value. Faithful minimal port of grin-ext's cross-validated crypto; no
private key is ever involved. v3-only (legacy needs the master secret,
same limit as grin-wallet's view-only scan); paths are advisory.
- src/grin.rs: wire rewind_output with hostile-input-safe hex decoding.
- Cargo.toml: depend on upstream grin_secp256k1zkp + blake2 (not the
vendored fork — the server target needs no wasm patch).
- Golden-vector tests generated by grin's OWN reference ProofBuilder
(depth-3 Grim + depth-4 Smirk [0,0,n,0]); proves byte-compatibility
with the published secp crate. Passed an adversarial money-safety
review (no false-positive/negative, panic-safe).
Make the scaffold standalone and publish-ready:
- Rewrite code + README references to the originating backend as a generic
"wallet backend" so the service reads as a reusable, run-anywhere LWS.
- Add the MIT LICENSE file (matches Cargo.toml) and a short provenance note.
- Add repository/readme/keywords/categories metadata to Cargo.toml.
A standalone, self-hostable Grin light-wallet-server mirroring the Monero LWS:
register a view/rewind credential, run a background chain scanner, rewind outputs
against registered keys, store per-account matches in a DB, and serve balance /
outputs / broadcast / height fast (vs the current on-demand stateless scan proxy).
This is the scaffold — README (architecture + HTTP surface + DB schema + how a
wallet backend proxies to it), Cargo skeleton, migrations sketch, and route/scanner
stubs. Public-clean: no operator-specific infra, hosts, or secrets.
jwinterm