vjrj
49b872b405
Throwaway research spike (spike/ branch, outside pub workspace, no prod deps touched). Validates the open Block 2 decisions before committing a funded round: 1. Deterministic one-way secp256k1 (Nostr) key derived from the Ğ1 root seed via HKDF — user still backs up ONE thing. Reproducible + signs (BIP340). 2. OfferTransport abstraction over Nostr NIP-99 (kind 30402); Offer stays inventory/location-agnostic, geohash coarsened on the wire (tested). 3. publish->discover-by-geohash proven end-to-end against an in-process hermetic mini-relay (~34ms round-trip). Findings + risks + recommendation in docs/design/spike-block2-findings.md. Block 1 suite untouched. 14 tests green, analyzer clean.
118 lines
4.1 KiB
Dart
118 lines
4.1 KiB
Dart
import 'nostr_event.dart';
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import 'offer.dart';
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/// Maps [Offer] ↔ Nostr NIP-99 "Classified Listing" events (kind 30402), the
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/// first concrete `OfferTransport` backend (sharing-model.md §2).
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///
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/// This codec is where the privacy contract is *enforced on the wire*: the only
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/// location that ever leaves the device is a coarse geohash, truncated here to
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/// [maxGeohashChars]. There is no field that could carry the inventory or an
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/// exact address, because [Offer] itself has none — the seam does the work.
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class Nip99Codec {
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/// NIP-99 addressable classified listing.
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static const kindActive = 30402;
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/// A geohash of 5 chars ≈ ±2.4 km cell — the coarse "near you" of the mocks.
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/// Anything finer is refused so a slip in the caller can't leak a precise fix.
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static const maxGeohashChars = 5;
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/// Builds an UNSIGNED event from [offer]. Caller signs with the derived key.
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NostrEvent encode(Offer offer, {required int createdAt}) {
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final coarse = _coarsen(offer.approxGeohash);
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final tags = <List<String>>[
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['d', offer.id],
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['title', offer.summary],
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['status', offer.status == OfferStatus.active ? 'active' : 'sold'],
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// Reciprocity mode is a Tanemaki concept NIP-99 lacks; carry it explicitly.
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['offer_type', offer.type.name],
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];
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// NIP-52 geohash ladder: one `g` tag per prefix length so an area query
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// matches by *exact* tag (how Nostr relays filter) yet still finds coarser
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// searches. Coarse only — NO "location"/address/exact-fix tag ever.
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for (var i = 1; i <= coarse.length; i++) {
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tags.add(['g', coarse.substring(0, i)]);
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}
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if (offer.category != null) tags.add(['t', offer.category!]);
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if (offer.radiusKm != null) {
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tags.add(['radius_km', '${offer.radiusKm}']);
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}
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if (offer.type == OfferType.sale && offer.priceAmount != null) {
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tags.add([
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'price',
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'${offer.priceAmount}',
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offer.priceCurrency ?? 'EUR',
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]);
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}
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if (offer.type == OfferType.exchange && offer.exchangeTerms != null) {
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tags.add(['exchange_terms', offer.exchangeTerms!]);
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}
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if (offer.imageUrl != null) tags.add(['image', offer.imageUrl!]);
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if (offer.expiresAt != null) {
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tags.add([
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'expiration',
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'${offer.expiresAt!.millisecondsSinceEpoch ~/ 1000}',
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]);
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}
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return NostrEvent(
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pubkey: offer.authorPubkeyHex,
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createdAt: createdAt,
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kind: kindActive,
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tags: tags,
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content: offer.summary,
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);
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}
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/// Reconstructs an [Offer] from a received event.
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Offer decode(NostrEvent event) {
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final priceTag = _fullTag(event, 'price');
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return Offer(
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id: event.tag('d') ?? event.id,
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authorPubkeyHex: event.pubkey,
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summary: event.tag('title') ?? event.content,
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type: _parseType(event.tag('offer_type')),
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status: event.tag('status') == 'sold'
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? OfferStatus.closed
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: OfferStatus.active,
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category: event.tag('t'),
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approxGeohash: _longestGeohash(event),
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radiusKm: int.tryParse(event.tag('radius_km') ?? ''),
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priceAmount: priceTag != null && priceTag.length > 1
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? num.tryParse(priceTag[1])
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: null,
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priceCurrency: priceTag != null && priceTag.length > 2
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? priceTag[2]
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: null,
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exchangeTerms: event.tag('exchange_terms'),
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imageUrl: event.tag('image'),
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);
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}
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String _coarsen(String geohash) => geohash.length > maxGeohashChars
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? geohash.substring(0, maxGeohashChars)
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: geohash;
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/// The finest `g` tag present (top of the prefix ladder).
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String _longestGeohash(NostrEvent event) {
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var best = '';
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for (final t in event.tags) {
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if (t.isNotEmpty && t[0] == 'g' && t.length > 1 && t[1].length > best.length) {
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best = t[1];
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}
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}
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return best;
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}
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List<String>? _fullTag(NostrEvent event, String name) {
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for (final t in event.tags) {
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if (t.isNotEmpty && t[0] == name) return t;
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}
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return null;
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}
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OfferType _parseType(String? name) => OfferType.values.firstWhere(
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(t) => t.name == name,
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orElse: () => OfferType.gift,
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);
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}
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