Add filterPolicy to block events that don't match the filter

entrypoint.example.ts

@@ -2,6 +2,7 @@
 //bin/true; exec deno run -A "$0" "$@"
 import {
   antiDuplicationPolicy,
+  filterPolicy,
   hellthreadPolicy,
   keywordPolicy,
   noopPolicy,
@@ -16,6 +17,7 @@ import {
 for await (const msg of readStdin()) {
   const result = await pipeline(msg, [
     noopPolicy,
+    [filterPolicy, { kinds: [0, 1, 3, 5, 7, 1984, 9734, 9735, 10002] }],
     [keywordPolicy, ['https://t.me/']],
     [regexPolicy, /(🟠|🔥|😳)ChtaGPT/i],
     [pubkeyBanPolicy, ['e810fafa1e89cdf80cced8e013938e87e21b699b24c8570537be92aec4b12c18']],

mod.ts

@@ -1,4 +1,5 @@
 export { default as antiDuplicationPolicy } from './src/policies/anti-duplication-policy.ts';
+export { default as filterPolicy } from './src/policies/filter-policy.ts';
 export { default as hellthreadPolicy } from './src/policies/hellthread-policy.ts';
 export { default as keywordPolicy } from './src/policies/keyword-policy.ts';
 export { default as noopPolicy } from './src/policies/noop-policy.ts';

src/policies/filter-policy.test.ts

@@ -0,0 +1,13 @@
+import { assertEquals } from '../deps.ts';
+import { buildEvent, buildInputMessage } from '../test.ts';
+
+import filterPolicy from './filter-policy.ts';
+
+Deno.test('only allows events that match the filter', async () => {
+  const msg0 = buildInputMessage({ event: buildEvent({ kind: 0 }) });
+  const msg1 = buildInputMessage({ event: buildEvent({ kind: 1 }) });
+
+  assertEquals((await filterPolicy(msg0, { kinds: [1] })).action, 'reject');
+  assertEquals((await filterPolicy(msg1, { kinds: [1] })).action, 'accept');
+  assertEquals((await filterPolicy(msg1, { kinds: [1], authors: [] })).action, 'reject');
+});

src/policies/filter-policy.ts

@@ -0,0 +1,24 @@
+import { Policy } from '../types.ts';
+
+import { Filter, matchFilter } from 'npm:nostr-tools@^1.7.4';
+
+/** Reject all events which don't match the filter. */
+const filterPolicy: Policy<Filter> = ({ event }, filter = {}) => {
+  if (matchFilter(filter, event)) {
+    return {
+      id: event.id,
+      action: 'accept',
+      msg: '',
+    };
+  }
+
+  return {
+    id: event.id,
+    action: 'reject',
+    msg: 'blocked: the event doesn\'t match the allowed filters',
+  };
+};
+
+export default filterPolicy;
+
+export type { Filter };