Minor fix + code refactoring.

server/lib/database/channel.ts

@@ -18,9 +18,34 @@ async function getChannelNameById (options: RegisterServerOptions, channelId: nu
     options.peertubeHelpers.logger.debug(`getChannelNameById: channel ${channelId} not found.`)
     return null
   }
-  return (results[0].preferredUsername ?? null) as string
+  return results[0].preferredUsername ?? null
+}
+
+async function getUserNameByChannelId (options: RegisterServerOptions, channelId: number): Promise<string | null> {
+  if (!channelId) {
+    throw new Error('Missing channelId')
+  }
+  if (!Number.isInteger(channelId)) {
+    throw new Error('Invalid channelId: not an integer')
+  }
+  const [results] = await options.peertubeHelpers.database.query(
+    'SELECT "user"."username"' +
+    ' FROM "videoChannel"' +
+    ' JOIN "account" ON "account"."id" = "videoChannel"."accountId"' +
+    ' JOIN "user" ON "account"."userId" = "user"."id" ' +
+    ' WHERE "videoChannel"."id" = ' + channelId.toString()
+  )
+  if (!Array.isArray(results)) {
+    throw new Error('getUserNameByChannelId: query result is not an array.')
+  }
+  if (!results[0]) {
+    options.peertubeHelpers.logger.debug(`getUserNameByChannelId: channel ${channelId} not found.`)
+    return null
+  }
+  return results[0].username ?? null
 }
 
 export {
-  getChannelNameById
+  getChannelNameById,
+  getUserNameByChannelId
 }