fix(route/telegram): fall back to the web preview on MTProto flood waits

The MTProto path cached the resolved input entity for the default 5
minutes, so every process that started later or missed the cache called
contacts.ResolveUsername again for each channel. That method is heavily
rate limited, and once the account hit a flood wait the route failed
with "A wait of N seconds is required" even for channels that the public
web preview serves fine.

Keep the channel ID and access hash for 30 days, since they do not
change, and fall back to the web preview when MTProto raises a
FloodWaitError. Other MTProto errors are still reported.

Closes #20454

lib/routes/telegram/channel.ts

@@ -3,11 +3,13 @@ import querystring from 'node:querystring';
 import { load } from 'cheerio';
 import { FetchError } from 'ofetch';
 import pMap from 'p-map';
+import { errors } from 'teleproto';
 
 import { config } from '@/config';
 import type { DataItem, Route } from '@/types';
 import { ViewType } from '@/types';
 import cache from '@/utils/cache';
+import logger from '@/utils/logger';
 import ofetch from '@/utils/ofetch';
 import { parseDate } from '@/utils/parse-date';
 import { fallback, queryToBoolean } from '@/utils/readable-social';
@@ -159,7 +161,15 @@ When a reverse proxy removes a public URL prefix (for example, \`/rss\`), set it
 async function handler(ctx) {
     const useWeb = ctx.req.param('routeParams') || !config.telegram.session;
     if (!useWeb) {
-        return tglibchannel(ctx);
+        try {
+            return await tglibchannel(ctx);
+        } catch (error) {
+            // A flood wait blocks the account for minutes to hours, while the public web preview still works
+            if (!(error instanceof errors.FloodWaitError)) {
+                throw error;
+            }
+            logger.warn(`Telegram MTProto requires a wait of ${error.seconds} seconds, falling back to the web preview`);
+        }
     }
 
     const username = ctx.req.param('username');

lib/routes/telegram/tglib/channel.ts

@@ -148,7 +148,8 @@ export default async function handler(ctx: Context) {
     if (!peerCache) {
         const p = await client.getInputEntity(username!);
         peerCache = JSON.stringify(p.toJSON());
-        await cache.set(`telegram:inputEntity:${username}`, peerCache);
+        // The channel ID and access hash do not change, and contacts.ResolveUsername is heavily rate limited
+        await cache.set(`telegram:inputEntity:${username}`, peerCache, 30 * 24 * 60 * 60);
     }
     const peerData = JSON.parse(peerCache, (k, v) => (k === 'channelId' || k === 'accessHash' ? returnBigInt(v) : v));
     const peer = new Api.InputPeerChannel(peerData);