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fix(webhook): return 500 on handler failure to enable Telegram retries #86

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fix(webhook): return 500 on handler failure to enable Telegram retries #86

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34 changes: 16 additions & 18 deletions app/bot/webhook.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -3,15 +3,13 @@
*
* Flow:
* - User sends a message in Telegram → Telegram POSTs that update here.
* - We return 200 OK immediately so Telegram does not retry or hide the user's message.
* - We process the update in the background (waitUntil).
* - We process the update and return 200 on success (or 500 on failure so Telegram retries).
*
* Per-chat serialization: we process one update per chat at a time. When a new update arrives
* for a chat, we wait for the previous handler for that chat to finish, then run the new one.
* So Reply A is always sent before we start processing Prompt B — no reorder flash.
*/

import { waitUntil } from '@vercel/functions';
import { createBot } from './grammy.js';

interface TelegramUpdate {
Expand Down Expand Up @@ -126,8 +124,7 @@ export async function handleRequest(request: Request): Promise<Response> {
return jsonResponse({ ok: false, error: 'BOT_TOKEN not set' }, 500);
}

// Read body before returning 200. Once we return, the request may be closed and body
// unavailable, so reading it inside waitUntil can fail and the message is lost.
// Read body before processing the update.
let update: TelegramUpdate;
try {
const body =
Expand All @@ -147,27 +144,28 @@ export async function handleRequest(request: Request): Promise<Response> {
return jsonResponse({ ok: false, error: 'invalid_update' }, 400);
}

// Return 200 OK immediately so Telegram applies the message to the chat. Process update
// in waitUntil so we don't block the response on AI/DB.
// Process update and return 200 on success (or 500 on failure so Telegram retries).
// Serialize per chat so Reply A is always sent before we start processing Prompt B.
const updateId = update.update_id;
const chatId = getChatIdFromUpdate(update);
const prev = chatId !== undefined ? chatQueue.get(chatId) : undefined;
const work = (prev ?? Promise.resolve())
.then(() => ensureBotInit())
.then(() => bot!.handleUpdate(update as Parameters<typeof bot.handleUpdate>[0]))
.then(() => {
console.log('[webhook] handled update', updateId);
})
.catch((err) => {
console.error('[bot]', err);
});
const work = (prev ?? Promise.resolve()).then(async () => {
await ensureBotInit();
await bot!.handleUpdate(update as Parameters<typeof bot.handleUpdate>[0]);
console.log('[webhook] handled update', updateId);
});
const tail = work.then(() => {}, () => {});
if (chatId !== undefined) {
chatQueue.set(chatId, tail);
}
waitUntil(work);
return jsonResponse({ ok: true });

try {
await work;
return jsonResponse({ ok: true });
} catch (err) {
console.error('[webhook] handleUpdate failed', { updateId, chatId, err });
return jsonResponse({ ok: false, error: 'handler_error' }, 500);
}
}

/** Legacy (req, res) handler; also used when Vercel passes (request, context). */
Expand Down