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perf(market): paginate Nostr offer discovery, infinite scroll, memory cap

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Bound market memory and let large areas page instead of loading everything:
- DiscoveryQuery gains an until cursor; OfferTransport gains discoverPage()
  (one-shot, EOSE-bounded, newest-first) alongside the existing live discover()
  stream, which now accepts since so it only carries NEW offers going forward.
- NostrOfferTransport.discoverPage sorts by created_at desc and derives the
  next cursor from the oldest event seen (not the oldest type-matched one, so
  filtering never skips a page).
- OffersCubit: discover() fetches the first page + opens a since=now live sub;
  loadNextPage() pages further back; the in-memory list is capped at 400
  offers (each can carry a ~40KB inline photo thumbnail, so unbounded growth in
  a busy area was a real OOM risk).
- market_screen: infinite scroll via a scroll-position trigger + footer
  spinner, instead of a single unbounded ListView.
- Added discoverPage unit tests (commons_core) and cubit pagination tests
  (first page/cursor, accumulation, cap, cross-page dedup).
This commit is contained in:
vjrj 2026-07-20 22:47:12 +02:00
parent 3de01bd948
commit f17ae7751c
9 changed files with 513 additions and 43 deletions
Download patch file Download diff file Expand all files Collapse all files

144
apps/app_seeds/lib/state/offers_cubit.dart
View file

@ -24,12 +24,16 @@ class OffersState extends Equatable {
this.blockedAuthors = const {},
this.hiddenOfferKeys = const {},
this.searching = false,
this.loadingMore = false,
this.nextPageCursor,
this.publishing = false,
this.hasSearched = false,
this.error,
});
/// Offers discovered so far for [areaGeohash], newest appended as they arrive.
/// Offers discovered so far for [areaGeohash], newest first. Bounded in size
/// (see [OffersCubit.maxOffersKept]) so a busy area can't grow the list — and
/// the inline photo thumbnails it carries — without limit.
final List<Offer> offers;
/// The coarse area currently being browsed.
@ -57,8 +61,21 @@ class OffersState extends Equatable {
final Set<String> hiddenOfferKeys;
final bool searching;
/// True while a "load more" page is in flight, so the UI shows a footer
/// spinner and doesn't fire overlapping page requests.
final bool loadingMore;
/// Cursor (Unix seconds) for the next older page, or null when the newest
/// page was short (nothing older) or the in-memory cap was reached — in both
/// cases there is no more to load.
final int? nextPageCursor;
final bool publishing;
/// Whether more offers can be paged in (drives the infinite-scroll trigger).
bool get canLoadMore => nextPageCursor != null;
/// True once a discovery has been started, so the UI can tell "no search yet"
/// from "searched, found nothing".
final bool hasSearched;
@ -115,6 +132,8 @@ class OffersState extends Equatable {
Set<String>? blockedAuthors,
Set<String>? hiddenOfferKeys,
bool? searching,
bool? loadingMore,
int? Function()? nextPageCursor,
bool? publishing,
bool? hasSearched,
String? Function()? error,
@ -129,6 +148,9 @@ class OffersState extends Equatable {
blockedAuthors: blockedAuthors ?? this.blockedAuthors,
hiddenOfferKeys: hiddenOfferKeys ?? this.hiddenOfferKeys,
searching: searching ?? this.searching,
loadingMore: loadingMore ?? this.loadingMore,
nextPageCursor:
nextPageCursor != null ? nextPageCursor() : this.nextPageCursor,
publishing: publishing ?? this.publishing,
hasSearched: hasSearched ?? this.hasSearched,
error: error != null ? error() : this.error,
@ -146,6 +168,8 @@ class OffersState extends Equatable {
blockedAuthors,
hiddenOfferKeys,
searching,
loadingMore,
nextPageCursor,
publishing,
hasSearched,
error,
@ -183,10 +207,23 @@ class OffersCubit extends Cubit<OffersState> {
StreamSubscription<Offer>? _sub;
Timer? _searchTimeout;
/// Upper bound on offers held in memory. Each offer can carry an inline
/// (~40 KB) photo thumbnail, so an unbounded list in a busy area is a real
/// out-of-memory risk on mobile. Paging stops once the list reaches this, and
/// live offers beyond it evict the oldest — the newest stay visible.
static const int maxOffersKept = 400;
/// Whether a live transport is available (relay configured and reachable).
bool get isOnline => _transport != null;
/// Starts (or restarts) discovery for [geohashPrefix]. Results stream in.
/// Current time in Unix seconds — the granularity Nostr filters use for
/// `since`/`until`.
int _now() => DateTime.now().millisecondsSinceEpoch ~/ 1000;
/// Starts (or restarts) discovery for [geohashPrefix]. Fetches the newest page
/// up front (bounded), then keeps a live subscription for offers published
/// from now on — older results arrive via [loadNextPage], not by draining the
/// whole area into memory.
Future<void> discover(String geohashPrefix) async {
final transport = _transport;
if (transport == null) {
@ -207,15 +244,38 @@ class OffersCubit extends Cubit<OffersState> {
searching: true,
hasSearched: true,
));
_sub = transport.discover(DiscoveryQuery(geohashPrefix: geohashPrefix)).listen(
(offer) =>
emit(state.copyWith(offers: _merge(state.offers, offer), searching: false)),
onError: (Object e) =>
emit(state.copyWith(searching: false, error: () => '$e')),
final query = DiscoveryQuery(
geohashPrefix: geohashPrefix,
types: state.typeFilter,
);
// The discover stream stays open for live offers and never signals "done",
// so stop the spinner after a beat: no results → show the empty state, not
// an endless "searching".
// Live subscription first, bounded to offers published from now on, so a new
// listing shows up immediately without re-dumping the whole area.
final since = _now();
_sub = transport.discover(query, since: since).listen(
(offer) => emit(state.copyWith(
offers: _capped(_prepend(state.offers, offer)),
searching: false,
)),
onError: (Object e) =>
emit(state.copyWith(searching: false, error: () => '$e')),
);
try {
final page = await transport.discoverPage(query);
if (!isClosed) {
emit(state.copyWith(
offers: _capped(_mergePage(state.offers, page.offers)),
nextPageCursor: () => page.nextCursor,
searching: false,
));
}
} catch (e) {
if (!isClosed) emit(state.copyWith(searching: false, error: () => '$e'));
}
// Safety net: if the first page hangs and no live offer arrives, still stop
// the spinner so the screen shows the empty state, not an endless search.
_searchTimeout = Timer(const Duration(seconds: 6), () {
if (!isClosed && state.searching) {
emit(state.copyWith(searching: false));
@ -223,18 +283,64 @@ class OffersCubit extends Cubit<OffersState> {
});
}
/// Appends [incoming] to [current], replacing any existing offer with the same
/// author + id. Relays legitimately resend addressable events (a stored copy
/// plus a live echo after publishing), so a plain append would double the
/// listing; keeping one entry per (author, id) is the NIP-99 semantics.
static List<Offer> _merge(List<Offer> current, Offer incoming) => [
for (final o in current)
if (!(o.id == incoming.id &&
o.authorPubkeyHex == incoming.authorPubkeyHex))
o,
/// Loads the next (older) page of offers for the current area. Called by the
/// list as it nears the end. No-op when offline, already loading, or there is
/// nothing older to fetch.
Future<void> loadNextPage() async {
final transport = _transport;
final cursor = state.nextPageCursor;
if (transport == null || cursor == null || state.loadingMore) return;
emit(state.copyWith(loadingMore: true));
try {
final page = await transport.discoverPage(DiscoveryQuery(
geohashPrefix: state.areaGeohash,
types: state.typeFilter,
until: cursor,
));
final merged = _mergePage(state.offers, page.offers);
// Stop paging once the cap is reached — the list is already as large as we
// keep — otherwise carry the transport's cursor onward.
final reachedCap = merged.length >= maxOffersKept;
emit(state.copyWith(
offers: _capped(merged),
nextPageCursor: () => reachedCap ? null : page.nextCursor,
loadingMore: false,
));
} catch (e) {
emit(state.copyWith(loadingMore: false, error: () => '$e'));
}
}
/// The offer's identity for de-duplication: NIP-99 addressable events are keyed
/// by (author, `d`-tag id), so the same listing from two relays — or a stored
/// copy plus a live echo — collapses to one entry.
static String _key(Offer o) => '${o.authorPubkeyHex}:${o.id}';
/// Prepends a freshly-arrived (newer) [incoming] offer, dropping any existing
/// entry with the same identity so a live echo never doubles the listing.
static List<Offer> _prepend(List<Offer> current, Offer incoming) => [
incoming,
for (final o in current)
if (_key(o) != _key(incoming)) o,
];
/// Appends an older [page] after [current] (older offers sort below newer),
/// skipping any already present. Keeps the newest-first ordering.
static List<Offer> _mergePage(List<Offer> current, List<Offer> page) {
final seen = {for (final o in current) _key(o)};
return [
...current,
for (final o in page)
if (seen.add(_key(o))) o,
];
}
/// Caps the list to [maxOffersKept], keeping the newest (front) and dropping
/// the oldest (tail) — bounds memory in a busy area.
static List<Offer> _capped(List<Offer> offers) => offers.length <= maxOffersKept
? offers
: offers.sublist(0, maxOffersKept);
/// Narrows the visible offers to those whose summary matches [query]. Purely
/// local over the already-discovered list; does not re-hit the transport.
void search(String query) => emit(state.copyWith(query: query));

53
apps/app_seeds/lib/ui/market_screen.dart
View file

@ -414,23 +414,44 @@ class MarketBody extends StatelessWidget {
),
],
)
: ListView.separated(
physics: const AlwaysScrollableScrollPhysics(),
padding: const EdgeInsets.all(16),
itemCount: visible.length,
separatorBuilder: (_, _) => const SizedBox(height: 12),
itemBuilder: (context, i) {
final o = visible[i];
final mine = o.authorPubkeyHex == selfPubkey;
return _OfferCard(
offer: o,
mine: mine,
onTap: () async {
await context.push('/market/offer', extra: o);
await onOfferClosed?.call();
},
);
: NotificationListener<ScrollNotification>(
// Page in older offers as the list nears its end, so a
// large area streams in on demand rather than all at
// once. The cubit guards against overlapping loads.
onNotification: (n) {
if (state.canLoadMore &&
!state.loadingMore &&
n.metrics.axis == Axis.vertical &&
n.metrics.extentAfter < 500) {
cubit.loadNextPage();
}
return false;
},
child: ListView.separated(
physics: const AlwaysScrollableScrollPhysics(),
padding: const EdgeInsets.all(16),
// A trailing spinner row while the next page loads.
itemCount: visible.length + (state.loadingMore ? 1 : 0),
separatorBuilder: (_, _) => const SizedBox(height: 12),
itemBuilder: (context, i) {
if (i >= visible.length) {
return const Padding(
padding: EdgeInsets.symmetric(vertical: 16),
child: Center(child: CircularProgressIndicator()),
);
}
final o = visible[i];
final mine = o.authorPubkeyHex == selfPubkey;
return _OfferCard(
offer: o,
mine: mine,
onTap: () async {
await context.push('/market/offer', extra: o);
await onOfferClosed?.call();
},
);
},
),
),
),
),