Expose read-only channel membership for invitation UI

tools/chatgui/db/db_manager.cpp

@@ -144,6 +144,17 @@ QList<ChannelRow> DbManager::getChannels(ChannelSortMode sort) const {
     return list;
 }
 
+bool DbManager::isChannelMember(const QString& chId, quint64 nodeId) const {
+    const QByteArray sql = QStringLiteral("SELECT 1 FROM \"%1\" WHERE node_id=?").arg(peersTableName(chId)).toUtf8();
+    sqlite3_stmt* statement = prepareOrNull(sql.constData());
+    if (!statement) return false;
+    sqlite3_bind_int64(statement, 1, (sqlite3_int64)nodeId);
+    const int result = sqlite3_step(statement);
+    if (result != SQLITE_ROW && result != SQLITE_DONE) GUI_ERROR("channel membership read failed ch=%s rc=%d", qPrintable(chId), result);
+    sqlite3_finalize(statement);
+    return result == SQLITE_ROW;
+}
+
 /* Формирует человекочитаемое тело превью последнего сообщения по content_type и "d"-полю. */
 static QString mediaPreviewBody(const QString& ct, const QByteArray& d) {
     bool isText = ct.isEmpty() || ct == QStringLiteral("text/plain") ||