From 5bffffe07b6d268f7cb7f6336b869b1382bf519c Mon Sep 17 00:00:00 2001
From: Alex Gleason <alex@alexgleason.me>
Date: Wed, 3 Jan 2024 16:35:40 -0600
Subject: [PATCH] Add a function to calculate the intrinsic limit of a filter

---
 src/filter.test.ts        | 12 +++++++++++-
 src/filter.ts             | 24 ++++++++++++++++++++++++
 src/storages/memorelay.ts |  6 ++++--
 3 files changed, 39 insertions(+), 3 deletions(-)

diff --git a/src/filter.test.ts b/src/filter.test.ts
index efc00d7..b1ea872 100644
--- a/src/filter.test.ts
+++ b/src/filter.test.ts
@@ -4,7 +4,7 @@ import { assertEquals } from '@/deps-test.ts';
 import event0 from '~/fixtures/events/event-0.json' assert { type: 'json' };
 import event1 from '~/fixtures/events/event-1.json' assert { type: 'json' };
 
-import { eventToMicroFilter, getFilterId, getMicroFilters, isMicrofilter } from './filter.ts';
+import { eventToMicroFilter, getFilterId, getFilterLimit, getMicroFilters, isMicrofilter } from './filter.ts';
 
 Deno.test('getMicroFilters', () => {
   const event = event0 as Event<0>;
@@ -35,3 +35,13 @@ Deno.test('getFilterId', () => {
     '{"authors":["79c2cae114ea28a981e7559b4fe7854a473521a8d22a66bbab9fa248eb820ff6"],"kinds":[0]}',
   );
 });
+
+Deno.test('getFilterLimit', () => {
+  assertEquals(getFilterLimit({ ids: [event0.id] }), 1);
+  assertEquals(getFilterLimit({ ids: [event0.id], limit: 2 }), 1);
+  assertEquals(getFilterLimit({ ids: [event0.id], limit: 0 }), 0);
+  assertEquals(getFilterLimit({ ids: [event0.id], limit: -1 }), 0);
+  assertEquals(getFilterLimit({ kinds: [0], authors: [event0.pubkey] }), 1);
+  assertEquals(getFilterLimit({ kinds: [1], authors: [event0.pubkey] }), Infinity);
+  assertEquals(getFilterLimit({}), Infinity);
+});
diff --git a/src/filter.ts b/src/filter.ts
index 430a8d3..b98d44e 100644
--- a/src/filter.ts
+++ b/src/filter.ts
@@ -2,6 +2,7 @@ import { Conf } from '@/config.ts';
 import { type Event, type Filter, matchFilters, stringifyStable, z } from '@/deps.ts';
 import { nostrIdSchema } from '@/schemas/nostr.ts';
 import { type EventData } from '@/types.ts';
+import { isReplaceableKind } from '@/kinds.ts';
 
 /** Additional properties that may be added by Ditto to events. */
 type Relation = 'author' | 'author_stats' | 'event_stats';
@@ -82,11 +83,34 @@ function isMicrofilter(filter: Filter): filter is MicroFilter {
   return microFilterSchema.safeParse(filter).success;
 }
 
+/** Calculate the intrinsic limit of a filter. */
+function getFilterLimit(filter: Filter): number {
+  if (filter.ids && !filter.ids.length) return 0;
+  if (filter.kinds && !filter.kinds.length) return 0;
+  if (filter.authors && !filter.authors.length) return 0;
+
+  return Math.min(
+    Math.max(0, filter.limit ?? Infinity),
+    filter.ids?.length ?? Infinity,
+    filter.authors?.length &&
+      filter.kinds?.every((kind) => isReplaceableKind(kind))
+      ? filter.authors.length * filter.kinds.length
+      : Infinity,
+  );
+}
+
+/** Returns true if the filter could potentially return any stored events at all. */
+function canFilter(filter: Filter): boolean {
+  return getFilterLimit(filter) > 0;
+}
+
 export {
   type AuthorMicrofilter,
+  canFilter,
   type DittoFilter,
   eventToMicroFilter,
   getFilterId,
+  getFilterLimit,
   getMicroFilters,
   type IdMicrofilter,
   isMicrofilter,
diff --git a/src/storages/memorelay.ts b/src/storages/memorelay.ts
index 71c68c6..66c2c17 100644
--- a/src/storages/memorelay.ts
+++ b/src/storages/memorelay.ts
@@ -1,4 +1,5 @@
 import { Debug, type Event, type Filter, LRUCache, matchFilter, matchFilters } from '@/deps.ts';
+import { canFilter, getFilterLimit } from '@/filter.ts';
 import { type EventStore, type GetEventsOpts } from '@/store.ts';
 
 /** In-memory data store for events. */
@@ -27,6 +28,7 @@ class Memorelay implements EventStore {
   /** Get events from memory. */
   getEvents<K extends number>(filters: Filter<K>[], opts: GetEventsOpts = {}): Promise<Event<K>[]> {
     if (opts.signal?.aborted) return Promise.resolve([]);
+    filters = filters.filter(canFilter);
     if (!filters.length) return Promise.resolve([]);
     this.#debug('REQ', JSON.stringify(filters));
 
@@ -37,7 +39,7 @@ class Memorelay implements EventStore {
       let index = 0;
 
       for (const filter of filters) {
-        const limit = filter.limit ?? Infinity;
+        const limit = getFilterLimit(filter);
         const usage = usages[index] ?? 0;
 
         if (usage >= limit) {
@@ -50,7 +52,7 @@ class Memorelay implements EventStore {
         index++;
       }
 
-      if (filters.every((filter, index) => usages[index] >= (filter.limit ?? Infinity))) {
+      if (filters.every((filter, index) => usages[index] >= getFilterLimit(filter))) {
         break;
       }
     }