feat: add mime_type column in nostr_events, add the following NIP 50 search extensions:

exact_mime_type, example: 'exact_mime_type:image/png' (uses hash index)
partial_mime_type, example 'partial_mime_type:image' (uses b-tree index)
only_media, example 'only_media:true' (sometimes uses index)

src/db/DittoTables.ts

@@ -14,6 +14,7 @@ export interface DittoTables extends NPostgresSchema {
 
 type NostrEventsRow = NPostgresSchema['nostr_events'] & {
   language: string | null;
+  mime_type: string | null;
 };
 
 interface AuthorStatsRow {

src/db/migrations/042_add_mime_type.ts

@@ -0,0 +1,40 @@
+import { Kysely, sql } from 'kysely';
+
+export async function up(db: Kysely<any>): Promise<void> {
+  await db.schema
+    .alterTable('nostr_events')
+    .addColumn('mime_type', 'text').execute();
+
+  await db.schema
+    .createIndex('nostr_events_mime_type_prefix_idx')
+    .on('nostr_events')
+    .expression(sql`split_part(mime_type, '/', 1)`)
+    .column('mime_type')
+    .ifNotExists()
+    .execute();
+
+  await db.schema
+    .createIndex('nostr_events_mime_type_hash_idx')
+    .on('nostr_events')
+    .column('mime_type')
+    .using('hash')
+    .ifNotExists()
+    .execute();
+}
+
+export async function down(db: Kysely<any>): Promise<void> {
+  await db.schema
+    .alterTable('nostr_events')
+    .dropColumn('mime_type')
+    .execute();
+
+  await db.schema
+    .dropIndex('nostr_events_mime_type_prefix_idx')
+    .on('nostr_events')
+    .execute();
+
+  await db.schema
+    .dropIndex('nostr_events_mime_type_hash_idx')
+    .on('nostr_events')
+    .execute();
+}

src/pipeline.ts

@@ -103,6 +103,7 @@ async function handleEvent(event: DittoEvent, signal: AbortSignal): Promise<void
       handleZaps(kysely, event),
       parseMetadata(event, signal),
       setLanguage(event),
+      setMimeType(event),
       generateSetEvents(event),
     ])
       .then(() =>
@@ -248,6 +249,25 @@ async function setLanguage(event: NostrEvent): Promise<void> {
   }
 }
 
+/** Update the event in the database and set its MIME type. */
+async function setMimeType(event: NostrEvent): Promise<void> {
+  const imeta = event.tags.find(([value]) => value === 'imeta');
+  if (!imeta) return;
+
+  const mime_type = imeta.find((value) => value?.split(' ')[0] === 'm')?.split(' ')[1];
+  if (!mime_type) return;
+
+  const kysely = await Storages.kysely();
+  try {
+    await kysely.updateTable('nostr_events')
+      .set('mime_type', mime_type)
+      .where('id', '=', event.id)
+      .execute();
+  } catch {
+    // do nothing
+  }
+}
+
 /** Determine if the event is being received in a timely manner. */
 function isFresh(event: NostrEvent): boolean {
   return eventAge(event) < Time.minutes(1);

src/storages/EventsDB.ts

@@ -158,16 +158,41 @@ class EventsDB extends NPostgres {
       }) as SelectQueryBuilder<DittoTables, 'nostr_events', DittoTables['nostr_events']>;
 
       const languages = new Set<string>();
+      let exact_mime_type: string | undefined;
+      let partial_mime_type: string | undefined;
+      let only_media: boolean | undefined;
 
       for (const token of tokens) {
         if (typeof token === 'object' && token.key === 'language') {
           languages.add(token.value);
         }
+        if (typeof token === 'object' && token.key === 'exact_mime_type') {
+          exact_mime_type = token.value;
+        }
+        if (typeof token === 'object' && token.key === 'partial_mime_type') {
+          partial_mime_type = token.value;
+        }
+        if (typeof token === 'object' && token.key === 'only_media') {
+          if (token.value === 'true') only_media = true;
+          if (token.value === 'false') only_media = false;
+        }
       }
 
       if (languages.size) {
         query = query.where('language', 'in', [...languages]);
       }
+      if (exact_mime_type) {
+        query = query.where('mime_type', '=', exact_mime_type);
+      }
+      if (partial_mime_type) {
+        query = query.where(
+          (eb) => eb.fn('split_part', [eb.ref('mime_type'), eb.val('/'), eb.val(1)]),
+          '=',
+          partial_mime_type,
+        );
+      }
+      if (only_media) query = query.where('mime_type', 'is not', null);
+      if (only_media === false) query = query.where('mime_type', 'is', null);
 
       return query;
     }